Advanced Higher Chemistry Course Specification

Advanced Higher Chemistry

Course code:

C813 77

Course assessment code:

X813 77

SCQF:

level 7 (32 SCQF credit points)

Valid from:

session 2019–20

This document provides detailed information about the course and course assessment to

ensure consistent and transparent assessment year on year. It describes the structure of

the course and the course assessment in terms of the skills, knowledge and understanding

that are assessed.

This document is for teachers and lecturers and contains all the mandatory information

required to deliver the course.

The information in this document may be reproduced in support of SQA qualifications only on

a non-commercial basis. If it is reproduced, SQA must be clearly acknowledged as the

source. If it is to be reproduced for any other purpose, written permission must be obtained

from permissions@sqa.org.uk

This edition: April 2021 (version 3.1)

Contents

Course overview 1

Course rationale 2

Purpose and aims 2

Who is this course for? 3

Course content 4

Skills, knowledge and understanding 5

Skills for learning, skills for life and skills for work 38

Course assessment 39

Course assessment structure: question paper 39

Course assessment structure: project 40

Grading 46

Equality and inclusion 47

Further information 48

Appendix: course support notes 49

Introduction 49

Approaches to learning and teaching 49

Preparing for course assessment 126

Developing skills for learning, skills for life and skills for work 126

Version 3.1 1

Course overview

This course consists of 32 SCQF credit points, which includes time for preparation for course

assessment. The notional length of time for candidates to complete the course is 160 hours.

The course assessment has two components.

Component Marks Scaled mark Duration

Question paper

110

120

3 hours

Project

see ‘Course

assessment’ section

Recommended entry Progression

Entry to this course is at the discretion of the

centre.

Candidates should have achieved the Higher

Chemistry course or equivalent qualifications

and/or experience prior to starting this course.

♦ an Higher National Diploma (HND), or

degree in Chemistry or a related area,

such as medicine, law, dentistry, veterinary

medicine, engineering, environmental and

health sciences

♦ a career in a Chemistry-based discipline or

related area such as renewable energy

development, engineering, technology,

pharmaceuticals, environmental

monitoring, forensics, research and

development, oil and gas exploration,

management, civil service and education,

or in a wide range of other areas

♦ further study, employment and/or training

Conditions of award

The grade awarded is based on the total marks achieved across both course assessment

components.

Version 3.1 2

Course rationale

National Courses reflect Curriculum for Excellence values, purposes and principles. They offer

flexibility, provide time for learning, focus on skills and applying learning, and provide scope for

personalisation and choice.

Every course provides opportunities for candidates to develop breadth, challenge and application.

The focus and balance of assessment is tailored to each subject area.

Chemistry, the study of matter and its interactions, plays an increasingly important role in most

aspects of modern life. This course allows candidates to develop a deep understanding of the

nature of matter, from its most fundamental level to the macroscopic interactions driving chemical

change.

Candidates develop their abilities to think analytically, creatively, and independently to make

reasoned evaluations, and to apply critical thinking in new and unfamiliar contexts to solve

problems. The course offers candidates’ flexibility and personalisation as they decide the choice of

topic for their project.

Purpose and aims

The course builds on the knowledge and skills developed by candidates in the Higher Chemistry

course and continues to develop their curiosity, interest and enthusiasm for chemistry in a range of

contexts. Skills of scientific inquiry and investigation are developed throughout the course.

The course offers opportunities for collaborative and independent learning set within familiar and

unfamiliar contexts, and seeks to illustrate and emphasise situations where the principles of

chemistry are used and applied in everyday life.

Candidates develop important skills relating to chemistry, including developing scientific and

analytical thinking skills and making reasoned evaluations.

The course aims to:

♦ develop a critical understanding of the role of chemistry in scientific issues and relevant

applications, including the impact these could make in society and the environment

♦ extend and apply skills, knowledge and understanding of chemistry

♦ develop and apply the skills to carry out complex practical scientific activities, including the use

of risk assessments, technology, equipment and materials

♦ develop and apply scientific inquiry and investigative skills, including planning and experimental

design

♦ develop and apply analytical thinking skills, including critical evaluation of experimental

procedures in a chemistry context

♦ extend and apply problem-solving skills in a chemistry context

♦ further develop an understanding of scientific literacy, using a wide range of resources, in order to

communicate complex ideas and issues and to make scientifically informed choices

♦ extend and apply skills of autonomous working in chemistry

Version 3.1 3

Who is this course for?

The course is suitable for candidates who are secure in their attainment of Higher Chemistry or

equivalent qualifications. It is designed for candidates who can respond to a level of challenge,

especially those considering further study or a career in chemistry and related disciplines.

The course emphasises practical and experiential learning opportunities, with a strong skills-based

approach to learning. It takes account of the needs of all candidates, and provides sufficient

flexibility to enable candidates to achieve in different ways.

Version 3.1 4

Course content

The course content includes the following areas of chemistry:

Inorganic chemistry

The topics covered are:

♦ electromagnetic radiation and atomic spectra

♦ atomic orbitals, electronic configurations and the periodic table

♦ transition metals

Physical chemistry

The topics covered are:

♦ chemical equilibrium

♦ reaction feasibility

♦ kinetics

Organic chemistry and instrumental analysis

The topics covered are:

♦ molecular orbitals

♦ synthesis

♦ stereo chemistry

♦ experimental determination of structure

♦ pharmaceutical chemistry

Researching chemistry

The topics covered are:

♦ common chemical apparatus

♦ skills involved in experimental work

♦ stoichiometric calculations

♦ gravimetric analysis

♦ volumetric analysis

♦ practical skills and techniques

Version 3.1 5

Skills, knowledge and understanding

Skills, knowledge and understanding for the course

The following provides a broad overview of the subject skills, knowledge and understanding

developed in the course:

♦ extending and applying knowledge of chemistry to new situations, interpreting and analysing

information to solve complex problems

♦ planning and designing chemical experiments/investigations, including risk assessments, to

make a discovery, demonstrate a known fact, illustrate particular effects or test a hypothesis

♦ carrying out complex experiments in chemistry safely, recording systematic detailed

observations and collecting data

♦ selecting information from a variety of sources and presenting detailed information

appropriately, in a variety of forms

♦ processing and analysing chemical information and data (using calculations, significant figures

and units, where appropriate)

♦ making reasoned predictions and generalisations from a range of evidence and/or information

♦ drawing valid conclusions and giving explanations supported by evidence and/or justification

♦ critically evaluating experimental procedures by identifying sources of uncertainty and

suggesting and implementing improvements

♦ drawing on knowledge and understanding of chemistry to make accurate statements, describe

complex information, provide detailed explanations and integrate knowledge

♦ communicating chemical findings and information fully and effectively

♦ analysing and evaluating scientific publications and media reports

Version 3.1 6

Skills, knowledge and understanding for the course assessment

The following provides details of skills, knowledge and understanding sampled in the course

assessment:

Inorganic chemistry

(a) Electromagnetic radiation and atomic spectra

Electromagnetic radiation can be described in terms of waves and characterised in terms

of wavelength and/or frequency.

The relationship between these quantities is given by

The different types of radiation arranged in order of wavelength is known as the

electromagnetic spectrum.

Wavelengths of visible light are normally expressed in nanometres (nm).

Electromagnetic radiation can be described as a wave (has a wavelength and frequency),

and as a particle, and is said to have a dual nature.

When electromagnetic radiation is absorbed or emitted by matter it behaves like a stream

of particles. These particles are known as photons.

A photon carries quantised energy proportional to the frequency of radiation.

When a photon is absorbed or emitted, energy is gained or lost by electrons within the

substance.

The photons in high frequency radiation can transfer greater amounts of energy than

photons in low frequency radiation.

The energy associated with a single photon is given by:

E hf E

= =

The energy associated with one mole of photons is given by:

Lhc

E Lhf E

= =

Energy is often in units of kJ mol

-1

When energy is transferred to atoms, electrons within the atoms may be promoted to

higher energy levels.

An atom emits a photon of light energy when an excited electron moves from a higher

energy level to a lower energy level.

The light energy emitted by an atom produces a spectrum that is made up of a series of

lines at discrete (quantised) energy levels. This provides direct evidence for the existence

of these energy levels.

Version 3.1 7

Inorganic chemistry (continued)

(a) Electromagnetic radiation and atomic spectra (continued)

Each element in a sample produces characteristic absorption and emission spectra. These

spectra can be used to identify and quantify the element.

In absorption spectroscopy, electromagnetic radiation is directed at an atomised sample.

Radiation is absorbed as electrons are promoted to higher energy levels.

An absorption spectrum is produced by measuring how the intensity of absorbed light

varies with wavelength.

In emission spectroscopy, high temperatures are used to excite the electrons within atoms.

As the electrons drop to lower energy levels, photons are emitted.

An emission spectrum of a sample is produced by measuring the intensity of light emitted

at different wavelengths.

In atomic spectroscopy, the concentration of an element within a sample is related to the

intensity of light emitted or absorbed.

(b) Atomic orbitals, electronic configurations and the periodic table

The discrete lines observed in atomic spectra can be explained if electrons, like photons,

also display the properties of both particles and waves.

Electrons behave as standing (stationary) waves in an atom. These are waves that vibrate

in time but do not move in space. There are different sizes and shapes of standing wave

possible around the nucleus, known as orbitals. Orbitals can hold a maximum of two

electrons.

The different shapes of orbitals are identified as s, p, d and f (knowledge of the shape of f

orbitals is not required).

Electrons within atoms have fixed amounts of energy called quanta.

It is possible to describe any electron in an atom using four quantum numbers:

♦ the principal quantum number

indicates the main energy level for an electron and is

related to the size of the orbital

♦ the angular momentum quantum number

determines the shape of the subshell and

can have values from zero to

1n −

♦ the magnetic quantum number

determines the orientation of the orbital and can

have values between

and ll−+

♦ the spin magnetic quantum number

determines the direction of spin and can have

values of

+−

Version 3.1 8

Inorganic chemistry (continued)

(b) Atomic orbitals, electronic configurations and the periodic table (continued)

Electrons within atoms are arranged according to:

♦ the aufbau principle — electrons fill orbitals in order of increasing energy (‘aufbau’

means ‘building up’ in German)

♦ Hund’s rule — when degenerate orbitals are available, electrons fill each singly,

keeping their spins parallel before spin pairing starts

♦ the Pauli exclusion principle — no two electrons in one atom can have the same set of

four quantum numbers, therefore, no orbital can hold more than two electrons and

these two electrons must have opposite spins

In an isolated atom the orbitals within each subshell are degenerate.

The relative energies corresponding to each orbital can be represented diagrammatically

using orbital box notation for the first four shells of a multi-electron atom.

Electronic configurations using spectroscopic notation and orbital box notation can be

written for elements of atomic numbers 1 to 36.

The periodic table is subdivided into four blocks (s, p, d and f) corresponding to the outer

electronic configurations of the elements within these blocks.

The variation in first, second and subsequent ionisation energies with increasing atomic

number for the first 36 elements can be explained in terms of the relative stability of

different subshell electronic configurations. This provides evidence for these electronic

configurations. Anomalies in the trends of ionisation energies can be explained by

considering the electronic configurations.

There is a special stability associated with half-filled and full subshells. The more stable

the electronic configuration, the higher the ionisation energy.

VSEPR (valence shell electron pair repulsion) theory can be used to predict the shapes of

molecules and polyatomic ions.

The number of electron pairs surrounding a central atom can be found by:

♦ taking the total number of valence (outer) electrons on the central atom and adding

one for each atom attached

♦ adding an electron for every negative charge

♦ removing an electron for every positive charge

♦ dividing the total number of electrons by two to give the number of electron pairs

Electron pairs are negatively charged and repel each other. They are arranged to minimise

repulsion and maximise separation.

Version 3.1 9

Inorganic chemistry (continued)

(b) Atomic orbitals, electronic configurations and the periodic table (continued)

The arrangement of electron pairs around a central atom is:

♦ linear for two electron pairs

♦ trigonal planar for three electron pairs

♦ tetrahedral for four electron pairs

♦ trigonal bipyramidal for five electron pairs

♦ octahedral for six electron pairs

Shapes of molecules or polyatomic ions are determined by the shapes adopted by the

atoms present based on the arrangement of electron pairs. Electron dot diagrams can be

used to show these arrangements.

Electron pair repulsions decrease in strength in the order:

non-bonding pair/non-bonding pair

non-bonding pair/bonding pair

bonding

pair/bonding pair

The d-block transition metals are metals with an incomplete d subshell in at least one of

their ions.

The filling of the d orbitals follows the aufbau principle, with the exception of chromium and

copper atoms.

These exceptions are due to the special stability associated with the d subshell being half-

filled or completely filled.

When atoms from the first row of the transition elements form ions, it is the 4s electrons

that are lost first rather than the 3d electrons.

An element is said to be in a particular oxidation state when it has a specific oxidation

number.

The oxidation number can be determined by the following:

♦ uncombined elements have an oxidation number of 0

♦ ions containing single atoms have an oxidation number that is the same as the charge

on the ion

♦ in most of its compounds, oxygen has an oxidation number of

2−

♦ in most of its compounds, hydrogen has an oxidation number of

♦ the sum of all the oxidation numbers of all the atoms in a neutral compound must add

up to zero

♦ the sum of all the oxidation numbers of all the atoms in a polyatomic ion must be equal

to the charge on the ion

Version 3.1 10

Inorganic chemistry (continued)

A transition metal can have different oxidation states in its compounds

Compounds of the same transition metal in different oxidation states may have different

colours.

Oxidation can be defined as an increase in oxidation number. Reduction can be

considered as a decrease in oxidation number.

Changes in oxidation number of transition metal ions can be used to determine whether

oxidation or reduction has occurred.

Compounds containing metals in high oxidation states are often oxidising agents, whereas

compounds with metals in low oxidation states are often reducing agents.

Ligands may be negative ions or molecules with non-bonding pairs of electrons that they

donate to the central metal atom or ion, forming dative covalent bonds.

Ligands can be classified as monodentate, bidentate, up to hexadentate.

It is possible to deduce the ligand classification from a formula or structure of the ligand or

complex.

The total number of bonds from the ligands to the central transition metal is known as the

coordination number.

Names and formulae can be written according to IUPAC rules for complexes containing:

♦ central metals that obey the normal IUPAC rules

♦ copper (cuprate) and iron (ferrate)

♦ ligands, including water, ammonia, halogens, cyanide, hydroxide, and oxalate

In a complex of a transition metal, the d orbitals are no longer degenerate.

Splitting of d orbitals to higher and lower energies occurs when the electrons present in

approaching ligands cause the electrons in the orbitals lying along the axes to be repelled.

Ligands that cause a large difference in energy between subsets of d orbitals are strong

field ligands. Weak field ligands cause a small energy difference.

Ligands can be placed in an order of their ability to split d orbitals. This is called the

spectrochemical series.

Colours of many transition metal complexes can be explained in terms of d-d transitions.

Light is absorbed when electrons in a lower energy d orbital are promoted to a d orbital of

higher energy.

Version 3.1 11

Inorganic chemistry (continued)

If light of one colour is absorbed, then the complementary colour will be observed.

Electrons transition to higher energy levels when energy corresponding to the ultraviolet or

visible regions of the electromagnetic spectrum is absorbed.

Transition metals and their compounds can act as catalysts.

Heterogeneous catalysts are in a different state to the reactants.

Heterogeneous catalysis can be explained in terms of the formation of activated

complexes and the adsorption of reactive molecules onto active sites. The presence of

unpaired d electrons or unfilled d orbitals is thought to allow activated complexes to form.

This can provide reaction pathways with lower activation energies compared to the

uncatalysed reaction.

Homogeneous catalysts are in the same state as the reactants.

Homogeneous catalysis can be explained in terms of changing oxidation states with the

formation of intermediate complexes.

Version 3.1 12

Physical chemistry

(a) Chemical equilibrium

A chemical reaction is in equilibrium when the composition of the reactants and products

remains constant indefinitely.

The equilibrium constant (

) characterises the equilibrium composition of the reaction

mixture.

For the general reaction

aA bB cC dD



the equilibrium expression is:

[ ] [ ]

[

] [

]

[ ]

[

]

, , and ABC D

are the equilibrium concentrations of

, , and

ABC D

and

, , and

abc d

are the stoichiometric coefficients in the balanced reaction equation.

The value of equilibrium constants can be calculated.

The value of an equilibrium constant indicates the position of equilibrium.

Equilibrium constants have no units.

The concentrations of pure solids and pure liquids at equilibrium are taken as constant and

given a value of 1 in the equilibrium expression.

The numerical value of the equilibrium constant depends on the reaction temperature and

is independent of concentration and/or pressure.

For endothermic reactions, a rise in temperature causes an increase in

and the yield of

the product is increased.

For exothermic reactions, a rise in temperature causes a decrease in

and the yield of

the product is decreased.

The presence of a catalyst does not affect the value of the equilibrium constant.

In water and aqueous solutions there is an equilibrium between the water molecules and

hydronium (hydrogen) and hydroxide ions.

This ionisation of water can be represented by:

( ) ( )

() ()

22 3

HO HO HO aq OH aq

−

++ 

()

H O aq

represents a hydronium ion, a hydrated proton. A shorthand representation of

()

H O aq

)

H (aq

Version 3.1 13

Physical chemistry (continued)

(a) Chemical equilibrium (continued)

Water is amphoteric (can react as an acid and a base).

The dissociation constant for the ionisation of water is known as the ionic product and is

represented by

–

H O OH

  

  

The value of the ionic product varies with temperature.

At 25°C the value of

is approximately

-14

1 × 10

The relationship between pH and the hydrogen ion concentration is given by:

log

10 3 3

pH H O and H O 10

+ +−

 

=−=

 

In water and aqueous solutions with a pH value of 7 the concentrations of

()

H O aq

and

OH (aq)

−

are both

-7

mol l

-1

at 25°C.

If the concentration of

()

H O aq

or the concentration of

OH (aq)

−

is known, the

concentration of the other ion can be calculated using

or by using

pH pOH 14+=

The Brønsted-Lowry definitions of acids and bases state that an acid is a proton donor and

a base is a proton acceptor.

For every acid there is a conjugate base, formed by the loss of a proton.

For every base there is a conjugate acid, formed by the gain of a proton.

Strong acids and strong bases are completely dissociated into ions in aqueous solution.

Weak acids and weak bases are only partially dissociated into ions in aqueous solution.

Examples of strong acids include hydrochloric acid, sulfuric acid and nitric acid.

Ethanoic acid, carbonic acid and sulfurous acid are examples of weak acids.

Solutions of metal hydroxides are strong bases.

Ammonia and amines are examples of weak bases.

The weakly acidic nature of solutions of carboxylic acids, sulfur dioxide and carbon dioxide

can be explained by reference to equations showing the equilibria.

The weakly alkaline nature of a solution of ammonia or amines can be explained by

reference to an equation showing the equilibrium.

Version 3.1 14

Physical chemistry (continued)

(a) Chemical equilibrium (continued)

Equimolar solutions of weak and strong acids (or bases) have different pH values,

conductivity, and reaction rates, but the stoichiometry of reactions are the same.

The acid dissociation constant is represented by

[ ]

HO A

+−

  

  

or by:

log

p where p

a aa

KKK= −

The approximate pH of a weak acid can be calculated using:

log

pH p c

K= −

A soluble salt of a strong acid and a strong base dissolves in water to produce a neutral

solution.

A soluble salt of a weak acid and a strong base dissolves in water to produce an alkaline

solution.

A soluble salt of a strong acid and a weak base dissolves in water to produce an acidic

solution.

The name of the salt produced depends on the acid and base used.

Using the appropriate equilibria, the changes in concentrations of

and

−

ions of

salt solutions can be explained.

A buffer solution is one in which the pH remains approximately constant when small

amounts of acid, base or water are added.

An acid buffer consists of a solution of a weak acid and one of its salts made from a strong

base.

In an acid buffer solution the weak acid provides hydrogen ions when these are removed

by the addition of a small amount of base. The salt of the weak acid provides the conjugate

base, which can absorb excess hydrogen ions produced by the addition of a small amount

of acid.

A basic buffer consists of a solution of a weak base and one of its salts.

In a basic buffer solution the weak base removes excess hydrogen ions, and the conjugate

acid provided by the salt supplies hydrogen ions when these are removed.

Version 3.1 15

Physical chemistry (continued)

(a) Chemical equilibrium (continued)

An approximate pH of an acid buffer solution can be calculated from its composition and

from the acid dissociation constant:

[ ]

[

]

log

acid

pH p

salt

K= −

Indicators are weak acids for which the dissociation can be represented as:

In ( ) In ( )

H (aq) H O H O (aq) aq

+−

++

The acid indicator dissociation constant is represented as

and is given by the following

expression:

[ ]

−

  

  

In aqueous solution the colour of an acid indicator is distinctly different from that of its

conjugate base.

The colour of the indicator is determined by the ratio of

[ ]

In In

H to

−





The theoretical point at which colour change occurs is when

In3

HO K





The colour change is assumed to be distinguishable when

[ ]

In InH and

−





differ by a

factor of 10.

The pH range over which a colour change occurs can be estimated by the expression:

pH p 1K= ±

Suitable indicators can be selected from pH data, including titration curves.

(b) Reaction feasibility

The standard enthalpy of formation,

H∆°

, is the enthalpy change when one mole of a

substance is formed from its elements in their standard states.

The standard state of a substance is its most stable state at a pressure of 1 atmosphere

and at a specified temperature, usually taken as 298 K.

The standard enthalpy of a reaction can be calculated from the standard enthalpies of

formation of the reactants and products:

()

(products) reactantsHH H

∆°=Σ∆° −Σ∆°

Version 3.1 16

Physical chemistry (continued)

(b) Reaction feasibility (continued)

The entropy (S) of a system is a measure of the degree of disorder of the system.

The greater the degree of disorder, the greater the entropy.

Solids have low disorder and gases have high disorder.

Entropy increases as temperature increases.

There is a rapid increase in entropy at the melting point of a substance and an even more

rapid and larger change in entropy at the boiling point.

The second law of thermodynamics states that the total entropy of a reaction system and

its surroundings always increases for a spontaneous process.

Heat energy released by the reaction system into the surroundings increases the entropy

of the surroundings.

Heat energy absorbed by the reaction system from the surroundings decreases the

entropy of the surroundings.

The third law of thermodynamics states that the entropy of a perfect crystal at 0 K is zero.

The standard entropy of a substance is the entropy value for the substance in its standard

state.

The change in standard entropy for a reaction system can be calculated from the standard

entropies of the reactants and products:

()SS S∆°=Σ° −Σ°(products) reactants

The change in free energy for a reaction is related to the enthalpy and entropy changes:

G H TS∆ °=∆ °− ∆ °

If the change in free energy (

G∆°

) between reactants and products is negative, a reaction

may occur and the reaction is said to be feasible. A feasible reaction is one that tends

towards the products rather than the reactants. This does not give any indication of the

rate of the reaction.

The standard free energy change for a reaction can be calculated from the standard free

energies of formation of the reactants and products using the relationship:

()(products) reactantsGG G∆°=Σ∆° −Σ∆°

The feasibility of a chemical reaction under standard conditions can be predicted from the

calculated value of the change in standard free energy (

G∆°

The temperatures at which a reaction may be feasible can be estimated by considering the

range of values of

for which

0G∆ °<

Version 3.1 17

Physical chemistry (continued)

(b) Reaction feasibility (continued)

Under non-standard conditions any reaction is feasible if

G∆

is negative.

At equilibrium,

0G∆=

A reversible reaction will proceed spontaneously until the composition is reached where

0G∆=

The rate of a chemical reaction normally depends on the concentrations of the reactants.

Orders of reaction are used to relate the rate of a reaction to the reacting species.

If changing the concentration of a reactant

has no effect on the rate of the reaction, then

the reaction is zero order with respect to

If doubling the concentration of a reactant

doubles the rate of the reaction, then the

reaction is first order with respect to

. The rate can be expressed as:

[ ]

rate kA=

where

is the rate constant and

[ ]

is the concentration of reactant

mol

-1

If doubling the concentration of a reactant

increases the rate of the reaction fourfold,

then the reaction is second order with respect to

. The rate can be expressed as:

[ ]

rate kA=

The order of a reaction with respect to any one reactant is the power to which the

concentration of that reactant is raised in the rate equation.

The overall order of a reaction is the sum of the powers to which the concentrations of the

reactants are raised in the rate equation.

The order of a reaction can only be determined from experimental data.

The rate equation and the rate constant, including units, can be determined from initial rate

data for a series of reactions in which the initial concentrations of reactants are varied.

These can be zero, first, second or third order.

Reactions usually occur by a series of steps called a reaction mechanism.

The rate of reaction is dependent on the slowest step, which is called the ‘rate determining

step’.

Experimentally determined rate equations can be used to determine possible reaction

mechanisms.

Version 3.1 18

Organic chemistry and instrumental analysis

(a) Molecular orbitals

VSEPR cannot explain the bonding in all compounds. Molecular orbital theory can provide

an explanation for more complex molecules.

Molecular orbitals form when atomic orbitals combine. The number of molecular orbitals

formed is equal to the number of atomic orbitals that combine. The combination of two

atomic orbitals results in the formation of a bonding molecular orbital and an antibonding

orbital. The bonding molecular orbital encompasses both nuclei. The attraction of the

positively charged nuclei and the negatively charged electrons in the bonding molecular

orbital is the basis of bonding between atoms. Each molecular orbital can hold a maximum

of two electrons.

In a non-polar covalent bond, the bonding molecular orbital is symmetrical about the

midpoint between two atoms. Polar covalent bonds result from bonding molecular orbitals

that are asymmetric about the midpoint between two atoms. The atom with the greater

value for electronegativity has the greater share of the bonding electrons. Ionic compounds

are an extreme case of asymmetry, with the bonding molecular orbitals being almost

entirely located around just one atom, resulting in the formation of ions.

Molecular orbitals that form by end-on overlap of atomic orbitals along the axis of the

covalent bond are called sigma (

) molecular orbitals or sigma bonds.

Molecular orbitals that form by side-on overlap of parallel atomic orbitals that lie

perpendicular to the axis of the covalent bond are called pi (

) molecular orbitals or

pi bonds.

The electronic configuration of an isolated carbon atom cannot explain the number of

bonds formed by carbon atoms in molecules. The bonding and shape of molecules of

carbon can be explained by hybridisation.

Hybridisation is the process of mixing atomic orbitals within an atom to generate a set of

new atomic orbitals called hybrid orbitals. These hybrid orbitals are degenerate.

In alkanes, the 2s orbital and the three 2p orbitals of carbon hybridise to form four

degenerate sp

hybrid orbitals. These adopt a tetrahedral arrangement. The sp

hybrid

orbitals overlap end-on with other atomic orbitals to form

bonds.

The bonding in alkenes can be described in terms of sp

hybridisation. The 2s orbital and

two of the 2p orbitals hybridise to form three degenerate sp

hybrid orbitals. These adopt a

trigonal planar arrangement. The hybrid sp

orbitals overlap end-on to form

bonds. The

remaining 2p orbital on each carbon atom of the double bond is unhybridised and lies

perpendicular to the axis of the

bond. The unhybridised p orbitals overlap side-on to

form

bonds.

Version 3.1 19

Organic chemistry and instrumental analysis (continued)

(a) Molecular orbitals (continued)

The bonding in benzene and other aromatic systems can be described in terms of sp

hybridisation. The six carbon atoms in benzene are arranged in a cyclic structure with

bonds between the carbon atoms. The unhybridised p orbitals on each carbon atom

overlap side-on to form a

molecular system, perpendicular to the plane of the

bonds.

This

molecular system extends across all six carbon atoms. The electrons in this

system are delocalised.

The bonding in alkynes can be described in terms of sp hybridisation. The 2s orbital and

one 2p orbital of carbon hybridise to form two degenerate hybrid orbitals. These adopt a

linear arrangement. The hybrid sp orbitals overlap end-on to form

bonds. The remaining

two 2p orbitals on each carbon atom lie perpendicular to each other and to the axis of the

bond. The unhybridised p orbitals overlap side-on to form two

bonds.

Molecular orbital theory can be used to explain why organic molecules are colourless or

coloured. Electrons fill bonding molecular orbitals, leaving higher energy antibonding

orbitals unfilled. The highest bonding molecular orbital containing electrons is called the

highest occupied molecular orbital (HOMO). The lowest antibonding molecular orbital is

called the lowest unoccupied molecular orbital (LUMO).

Absorption of electromagnetic energy can cause electrons to be promoted from HOMO to

LUMO.

Most organic molecules appear colourless because the energy difference between HOMO

and LUMO is relatively large. This results in absorption of light from the ultraviolet region of

the spectrum.

Some organic molecules contain chromophores. A chromophore is a group of atoms within

a molecule that is responsible for absorption of light in the visible region of the spectrum.

Light can be absorbed when electrons in a chromophore are promoted from the HOMO to

the LUMO.

Chromophores exist in molecules containing a conjugated system — a system of adjacent

unhybridised p orbitals that overlap side-on to form a molecular orbital across a number of

carbon atoms. Electrons within this conjugated system are delocalised. Molecules with

alternating single and double bonds, and aromatic molecules have conjugated systems.

The more atoms in the conjugated system the smaller the energy gap between HOMO and

LUMO. A lower frequency of light (longer wavelength, lower energy) is absorbed by the

compound. When the wavelength of light absorbed is in the visible region, the compound

will exhibit the complementary colour.

Version 3.1 20

Organic chemistry and instrumental analysis (continued)

(b) Synthesis

When an organic reaction takes place, bonds in the reactant molecules are broken and

bonds in the product molecules are made. The process of bond breaking is known as bond

fission.

There are two types of bond fission, homolytic and heterolytic.

Homolytic fission:

♦ results in the formation of two neutral radicals

♦ occurs when each atom retains one electron from the

covalent bond and the bond

breaks evenly

♦ normally occurs when non-polar covalent bonds are broken

Reactions involving homolytic fission tend to result in the formation of very complex

mixtures of products, making them unsuitable for organic synthesis.

Heterolytic fission:

♦ results in the formation of two oppositely charged ions

♦ occurs when one atom retains both electrons from the

covalent bond and the bond

breaks unevenly

♦ normally occurs when polar covalent bonds are broken

Reactions involving heterolytic fission tend to result in far fewer products than reactions

involving homolytic fission, and so are better suited for organic synthesis.

The movement of electrons during bond fission and bond making can be represented

using curly arrow notation where:

♦ a single-headed arrow indicates the movement of a single electron

♦ a double-headed arrow indicates the movement of an electron pair

♦ the tail of the arrow shows the source of the electron(s)

♦ the head of the arrow indicates the destination of the electron(s)

♦ two single-headed arrows starting at the middle of a covalent bond indicate homolytic

bond fission is occurring

♦ a double-headed arrow starting at the middle of a covalent bond indicates heterolytic

bond fission is occurring

♦ an arrow drawn with the head pointing to the space between two atoms indicates that a

covalent bond will be formed between those two atoms

Version 3.1 21

Organic chemistry and instrumental analysis (continued)

(b) Synthesis (continued)

In reactions involving heterolytic bond fission, attacking groups are classified as

nucleophiles or electrophiles.

Nucleophiles are:

♦ negatively charged ions or neutral molecules that are electron rich, such as

Cl , Br , OH , CN

−− − −

NH and H O

♦ attracted towards atoms bearing a partial

()

or full positive charge

♦ capable of donating an electron pair to form a new covalent bond

Electrophiles are:

♦ positively charged ions or neutral molecules that are electron deficient, such as

and SO

♦ attracted towards atoms bearing a partial

()

−

or full negative charge

♦ capable of accepting an electron pair to form a new covalent bond

The following reaction types can be identified from a chemical equation:

♦ substitution

♦ addition

♦ elimination

♦ condensation

♦ hydrolysis

♦ oxidation

♦ reduction

♦ neutralisation

Synthetic routes can be devised, with no more than three steps, from a given reactant to a

final product.

The possible reactions of a particular molecule can be deduced by looking at the structural

formula.

The structure of any molecule can be drawn as a full, shortened or skeletal structural

formula.

In a skeletal structural formula, neither the carbon atoms, nor any hydrogens attached to

the carbon atoms, are shown. The presence of a carbon atom is implied by a ‘kink’ in the

carbon backbone, and at the end of a line.

Given a full or shortened structural formula for a compound, the skeletal structural formula

can be drawn.

Given a skeletal structural formula for a compound, the full or shortened structural formula

can be drawn.

Molecular formulae can be written from a full, shortened or skeletal structural formula.

Version 3.1 22

Organic chemistry and instrumental analysis (continued)

(b) Synthesis (continued)

Straight and branched chain alkanes; alkenes; alcohols; carboxylic acids; aldehydes and

ketones; haloalkanes; and ethers can be systematically named, indicating the position of

the functional group where appropriate, from structural formulae containing no more than

eight carbon atoms in their longest chain. Straight chain esters can be systematically

named from the names of their parent alcohol and carboxylic acid or their structural

formula.

Molecular formulae can be written and structural formulae drawn from systematic names of

straight and branched chain alkanes; alkenes; alcohols; carboxylic acids; aldehydes and

ketones; haloalkanes; and ethers containing no more than eight carbon atoms in their

longest chain. Molecular formulae can be written and structural formulae drawn for esters

from the systematic name or the structural formulae of their parent alcohol and carboxylic

acid.

Haloalkanes (alkyl halides) are substituted alkanes in which one or more of the hydrogen

atoms is replaced with a halogen atom.

Monohaloalkanes:

♦ contain only one halogen atom

♦ can be classified as primary, secondary or tertiary according to the number of alkyl

groups attached to the carbon atom containing the halogen atom

♦ take part in elimination reactions to form alkenes using a strong base, such as

potassium or sodium hydroxide in ethanol

♦ take part in nucleophilic substitution reactions with:

— aqueous alkalis to form alcohols

— alcoholic alkoxides to form ethers

— ethanolic cyanide to form nitriles (chain length increased by one carbon atom)

that can be hydrolysed to carboxylic acids

A monohaloalkane can take part in nucleophilic substitution reactions by one of two

different mechanisms.

1 is a nucleophilic substitution reaction with one species in the rate determining step

and occurs in a minimum of two steps via a trigonal planar carbocation intermediate.

2 is a nucleophilic substitution reaction with two species in the rate determining step and

occurs in a single step via a single five-centred, trigonal bipyramidal transition state.

The reaction mechanisms for S

1 and S

2 reactions can be represented using curly

arrows. Steric hindrance and the inductive stabilisation of the carbocation intermediate can

be used to explain which mechanism will be preferred for a given haloalkane.

Version 3.1 23

Organic chemistry and instrumental analysis (continued)

(b) Synthesis (continued)

Alcohols are substituted alkanes in which one or more of the hydrogen atoms is replaced

with a hydroxyl functional group, –OH group.

Alcohols can be prepared from:

♦ haloalkanes by substitution

♦ alkenes by acid-catalysed hydration (addition)

♦ aldehydes and ketones by reduction using a reducing agent such as lithium aluminium

hydride

Reactions of alcohols include:

♦ dehydration to form alkenes using aluminium oxide, concentrated sulfuric acid or

concentrated phosphoric acid

♦ oxidation of primary alcohols to form aldehydes and then carboxylic acids and

secondary alcohols to form ketones, using acidified permanganate, acidified

dichromate or hot copper(II) oxide

♦ formation of alcoholic alkoxides by reaction with some reactive metals such as

potassium or sodium, which can then be reacted with monohaloalkanes to form ethers

♦ formation of esters by reaction with carboxylic acids using concentrated sulfuric acid or

concentrated phosphoric acid as a catalyst

♦ formation of esters by reaction with acid chlorides ( ) — this gives a faster

reaction than reaction with carboxylic acids, and no catalyst is needed

Hydroxyl groups make alcohols polar, which gives rise to hydrogen bonding. Hydrogen

bonding can be used to explain the properties of alcohols including boiling points, melting

points, viscosity and solubility or miscibility in water.

Ethers can be regarded as substituted alkanes in which a hydrogen atom is replaced with

an alkoxy functional group, –OR, and have the general structure R' – O – R'', where R' and

R'' are alkyl groups.

Ethers are named as substituted alkanes. The alkoxy group is named by adding the

ending ‘oxy’ to the alkyl substituent, and this prefixes the name of the longest carbon

chain.

Ethers can be prepared in a nucleophilic substitution reaction by reacting a

monohaloalkane with an alkoxide.

Due to the lack of hydrogen bonding between ether molecules, they have lower boiling

points than the corresponding isomeric alcohols.

Version 3.1 24

Organic chemistry and instrumental analysis (continued)

(b) Synthesis (continued)

Methoxymethane and methoxyethane are soluble in water. Larger ethers are insoluble in

water due to their increased molecular size.

Ethers are commonly used as solvents since they are relatively inert chemically and will

dissolve many organic compounds.

Alkenes can be prepared by:

♦ dehydration of alcohols using aluminium oxide, concentrated sulfuric acid or

concentrated phosphoric acid

♦ base-induced elimination of hydrogen halides from monohaloalkanes

Alkenes take part in electrophilic addition reactions with:

♦ hydrogen to form alkanes in the presence of a catalyst

♦ halogens to form dihaloalkanes

♦ hydrogen halides to form monohaloalkanes

♦ water using an acid catalyst to form alcohols

Markovnikov’s rule states that when a hydrogen halide or water is added to an

unsymmetrical alkene, the hydrogen atom becomes attached to the carbon with the most

hydrogen atoms attached to it already. Markovnikov’s rule can be used to predict major

and minor products formed during the reaction of a hydrogen halide or water with alkenes.

The reaction mechanisms for the addition of a hydrogen halide and the acid-catalysed

addition of water can be represented using curly arrows and showing the intermediate

carbocation. The inductive stabilisation of intermediate carbocations formed during these

reactions can be used to explain the products formed.

The reaction mechanism for the addition of a halogen can be represented using curly

arrows and showing the cyclic ion intermediate.

Carboxylic acids can be prepared by:

♦ oxidising primary alcohols using acidified permanganate, acidified dichromate and hot

copper(II) oxide

♦ oxidising aldehydes using acidified permanganate, acidified dichromate, Fehling’s

solution and Tollens’ reagent

♦ hydrolysing nitriles, esters or amides

Version 3.1 25

Organic chemistry and instrumental analysis (continued)

(b) Synthesis (continued)

Reactions of carboxylic acids include:

♦ formation of salts by reactions with metals or bases

♦ condensation reactions with alcohols to form esters in the presence of concentrated

sulfuric or concentrated phosphoric acid

♦ reaction with amines to form alkylammonium salts that form amides when heated

♦ reduction with lithium aluminium hydride to form primary alcohols

Amines are organic derivatives of ammonia in which one or more hydrogen atoms of

ammonia has been replaced by an alkyl group.

Amines can be classified as primary, secondary or tertiary according to the number of alkyl

groups attached to the nitrogen atom.

Amines react with acids to form salts.

Primary and secondary amines, but not tertiary amines, display hydrogen bonding. As a

result, primary and secondary amines have higher boiling points than isomeric tertiary

amines.

Primary, secondary and tertiary amine molecules can hydrogen-bond with water molecules,

thus explaining the appreciable solubility of the shorter chain length amines in water.

Amines like ammonia are weak bases and dissociate to a slight extent in aqueous solution.

The nitrogen atom has a lone pair of electrons which can accept a proton from water,

producing hydroxide ions.

Benzene (C

) is the simplest member of the class of aromatic hydrocarbons.

The benzene ring has a distinctive structural formula. The stability of the benzene ring is due

to the delocalisation of electrons in the conjugated system. The presence of delocalised

electrons explains why the benzene ring does not take part in addition reactions.

Bonding in benzene can be described in terms of sp

hybridisation, sigma and pi bonds, and

electron delocalisation.

A benzene ring in which one hydrogen atom has been substituted by another group is

known as the phenyl group. The phenyl group has the formula –C

Benzene rings can take part in electrophilic substitution reactions. Reactions at benzene

rings include:

♦ halogenation by reaction of a halogen using aluminium chloride or iron(III) chloride for

chlorination and aluminium bromide or iron(III) bromide for bromination

♦ alkylation by reaction of a haloalkane using aluminium chloride

♦ nitration using concentrated sulfuric acid and concentrated nitric acid

♦ sulfonation using concentrated sulfuric acid

Version 3.1 26

Organic chemistry and instrumental analysis (continued)

Molecules that have the same molecular formula but different structural formulae are

called isomers.

Structural isomers occur when the atoms are bonded together in a different order in each

isomer.

Stereoisomers occur when the order of the bonding in the atoms is the same but the

spatial arrangement of the atoms is different in each isomer. There are two types of

stereoisomer, geometric and optical.

Geometric isomers:

♦ can occur when there is restricted rotation around a carbon-carbon double bond or a

carbon-carbon single bond in a cyclic compound

♦ must have two different groups attached to each of the carbon atoms that make up the

bond with restricted rotation

♦ can be labelled cis or trans according to whether the substituent groups are on the

same side (cis) or on different sides (trans) of the bond with restricted rotation

♦ have differences in physical properties, such as melting point and boiling point

♦ can have differences in chemical properties

Optical isomers:

♦ occur in compounds in which four different groups are arranged tetrahedrally around a

central carbon atom (chiral carbon or chiral centre)

♦ are asymmetric

♦ are non-superimposable mirror images of each other

♦ can be described as enantiomers

♦ have identical physical properties, except for their effect on plane-polarised light

♦ have identical chemical properties, except when in a chiral environment such as that

found in biological systems (only one optical isomer is usually present)

♦ rotate plane-polarised light by the same amount but in opposite directions and so are

optically active

♦ when mixed in equal amounts are optically inactive because the rotational effect of the

plane-polarised light cancels out — this is called a racemic mixture

Version 3.1 27

Organic chemistry and instrumental analysis (continued)

(d) Experimental determination of structure

In organic chemistry a number of experimental techniques are carried out to verify the

chemical structure of a substance.

Elemental microanalysis is used to determine the masses of C, H, O, S and N in a sample

of an organic compound in order to determine its empirical formula.

An empirical formula shows the simplest ratio of the elements in a molecule.

Elemental microanalysis can be determined from:

♦ combustion product masses

♦ percentage product by mass

Mass spectrometry can be used to determine the accurate gram formula mass (GFM) and

structural features of an organic compound.

In mass spectrometry, a small sample of an organic compound is bombarded by

high-energy electrons. This removes electrons from the organic molecule generating

positively charged molecular ions known as parent ions. These molecular ions then break

into smaller positively charged ion fragments. A mass spectrum is obtained showing a plot

of the relative abundance of the ions detected against the mass-to-charge (m/z) ratio.

The mass-to-charge ratio of the parent ion can be used to determine the GFM of the

molecular ion, and so a molecular formula can be determined using the empirical formula.

The fragmentation data can be interpreted to gain structural information.

Infrared spectroscopy is used to identify certain functional groups in an organic compound.

When infrared radiation is absorbed by organic compounds, bonds within the molecule

vibrate (stretch and bend). The wavelengths of infrared radiation that are absorbed depend

on the type of atoms that make up the bond and the strength of the bond.

In infrared spectroscopy, infrared radiation is passed through a sample of the organic

compound and then into a detector that measures the intensity of the transmitted radiation

at different wavelengths. The absorbance of infrared radiation is measured in

wavenumbers, the reciprocal of wavelength, in units of cm

-1

Characteristic absorptions by particular vibrations are given in the data booklet.

Version 3.1 28

Organic chemistry and instrumental analysis (continued)

(d) Experimental determination of structure (continued)

Proton nuclear magnetic resonance spectroscopy (proton NMR or

H NMR) can give

information about the different chemical environments of hydrogen atoms (protons or

in an organic molecule, and about how many hydrogen atoms there are in each of these

environments.

H nuclei behave like tiny magnets and in a strong magnetic field some align with the field

(lower energy), whilst the rest align against it (higher energy). Absorption of radiation in the

radio frequency region of the electromagnetic spectrum causes the

H nuclei to ‘flip’ from

the lower to the higher energy alignment. As they fall back from the higher to the lower

energy alignment the emitted radiation is detected and plotted on a spectrum.

In a

H NMR spectrum the chemical shift,

, (peak position) is related to the environment

of the

H atom and is measured in parts per million (ppm).

Chemical shift values for

H in different chemical environments are given in the data

booklet.

The area under the peak is related to the number of

H atoms in that environment and is

often given by an integration curve on a spectrum. The height of an integration curve is

proportional to the number of

H atoms in that environment, and so a ratio of

H atoms in

each environment can be determined.

The standard reference substance used in

H NMR spectroscopy is tetramethylsilane

(TMS), which is assigned a chemical shift value equal to zero.

H NMR spectra can be obtained using low-resolution or high-resolution NMR.

High-resolution

H NMR uses higher radio frequencies than those used in low-resolution

H NMR and provides more detailed spectra.

In a high-resolution

H NMR an interaction with

H atoms on neighbouring carbon atoms

can result in the splitting of peaks into multiplets. The number of

H atoms on neighbouring

carbon atoms will determine the number of peaks within a multiplet and can be determined

using the n+1 rule, where n is the number of

H atoms on the neighbouring carbon atom.

Low- and high-resolution

H NMR spectra can be analysed, and low-resolution

H NMR

spectra can be sketched for any given compound.

Version 3.1 29

Organic chemistry and instrumental analysis (continued)

(e) Pharmaceutical chemistry

Drugs are substances that alter the biochemical processes in the body.

Drugs that have beneficial effects are used in medicines.

A medicine usually contains the drug plus other ingredients such as fillers to add bulk or

sweeteners to improve the taste.

Drugs generally work by binding to specific protein molecules. These protein molecules

can be found on the surface of a cell (receptor) or can be specific enzyme molecules within

a cell.

Drugs that act on receptors can be classified as agonists or antagonists.

♦ An agonist mimics the natural compound and binds to the receptor molecules to

produce a response similar to the natural active compound.

♦ An antagonist prevents the natural compound from binding to the receptor, and so

blocks the natural response from occurring.

Many drugs that act on enzymes are classified as enzyme inhibitors and act by binding to

the active site of the enzyme and blocking the reaction normally catalysed there.

The overall shape and size of a drug is such that it interacts with a receptor binding site or

to the active site of an enzyme. The types of interactions formed can include van der

Waals forces and/or ionic bonds.

The structural fragment of a drug molecule that allows it to form interactions with a

receptor binding site or to an enzyme active site normally consists of different functional

groups correctly orientated with respect to each other.

By comparing the structures of drugs that have similar effects on the body, the structural

fragment that is involved in the drug action can be identified.

Version 3.1 30

Researching chemistry

(a) Common chemical apparatus

Candidates must be familiar with the use(s) of the following types of apparatus:

♦ conical flask

♦ digital balance

♦ pipette with safety filler

♦ burette

♦ volumetric (standard) flask

♦ distillation (round-bottomed) flask

♦ condenser

♦ thermometer

♦ Buchner or Hirsch or sintered glass funnel

♦ glassware with ground glass joints (‘Quickfit’ or similar)

♦ thin-layer chromatography apparatus

♦ colorimeter

♦ melting point

♦ separating funnel

(b) Skills involved in experimental work

Candidates must be able to:

♦ tabulate data using appropriate headings and units of measurement

♦ represent data as a scatter graph with suitable scales and labels

♦ sketch a line of best fit (straight or curved) to represent the trend observed in the data

♦ calculate average (mean) values

♦ identify and eliminate rogue points

♦ qualitatively appreciate the relative accuracy of apparatus used to measure the volume

of liquids

♦ comment on the reproducibility of results where measurements have been repeated

♦ carry out quantitative stoichiometric calculations

♦ interpret spectral data

♦ appropriately use a positive control, for example a known substance, to validate a

technique or procedure

Stoichiometry is the study of mole relationships involved in chemical reactions.

Chemical equations, using formulae and state symbols, can be written and balanced to

show the mole ratio(s) of reactants and products, including multi-step reactions.

The mass of a mole of any substance, in grams (g), is equal to the gram formula mass

(GFM) and can be calculated using relative atomic masses.

Version 3.1 31

Researching chemistry (continued)

Calculations can be performed using the relationship between the mass and the number of

moles of a substance.

For solutions, the mass of solute (grams or g), the number of moles of solute (moles or

mol), the volume of solution (litres or l), or the concentration of the solution (moles per litre

or mol l

-1

), can be calculated from data provided.

Percentage by mass is the mass of solute made up to 100 cm

of solution.

Percentage by volume is the number of cm

of solute made up to 100 cm

of solution.

The unit ppm stands for parts per million and refers to 1 mg per kg or 1 mg per litre.

Calculations can be performed using data, including:

♦ GFM

♦ masses

♦ number of moles

♦ concentrations and volumes of solutions

♦ volumes of gases

♦ reactant excess

♦ theoretical and percentage yield

♦ empirical formulae

Theoretical yields can be calculated and compared with actual yields, leading to

determining the percentage yield. The percentage yield is reduced by:

♦ mass transfer or mechanical losses

♦ purification of product

♦ side reactions

♦ equilibrium position

Candidates must be able to carry out stoichiometric calculations for all of the skills and

techniques in the course where appropriate.

Version 3.1 32

Researching chemistry (continued)

(d) Gravimetric analysis

Candidates must be familiar with the technique of gravimetric analysis, including use of:

♦ an accurate electronic balance, including the tare function

♦ a weighing boat

♦ weighing by difference

♦ the term ‘weighing accurately approximately’

♦ heating to constant mass:

— heating a substance

— allowing to cool in a desiccator to prevent absorption of water

— weighing

— repeating the steps of heating, cooling and weighing until no further changes in

mass are observed

Gravimetric analysis is used to determine the mass of an element or compound in a

substance.

The substance is converted into another substance of known chemical composition, which

can be readily isolated and purified.

The conversion can occur either through precipitation or volatilisation.

In precipitation conversion the substance undergoes a precipitation reaction. The

precipitate is separated from the filtrate and the filtrate tested to ensure the reaction has

gone to completion. The precipitate is washed, dried to constant mass and then weighed.

In volatilisation conversion the substance is heated and any volatile products (often water)

are evaporated. The substance is heated to constant mass and the final mass recorded.

(e) Volumetric analysis

Candidates must be familiar with use of the technique of volumetric analysis, including:

♦ preparing a standard solution

♦ accurate dilution

♦ standardising solutions to determine accurate concentration

♦ titrating to obtain concordancy using burettes, pipettes and volumetric flasks

♦ choosing an appropriate indicator

Version 3.1 33

Researching chemistry (continued)

(e) Volumetric analysis (continued)

A solution of accurately known concentration is known as a standard solution.

A standard solution can be prepared by:

♦ weighing a primary standard accurately

♦ dissolving in a small volume of solvent (usually deionised or distilled water) in a beaker

♦ transferring the solution and rinsings into a volumetric flask

♦ making up to the graduation mark with solvent

♦ stoppering and inverting

Standard solutions can also be prepared by accurate dilution by pipetting an appropriate

volume of a standard solution into a volumetric flask, making up to the graduation mark

with solvent, stoppering and inverting.

A primary standard must:

♦ be available in a high state of purity

♦ be stable when solid and in solution

♦ be soluble

♦ have a reasonably high GFM

Examples of primary standards include:

♦

sodium carbonate, Na CO

♦

22 4 2

hydrated oxalic acid, H C O ·2H O

♦

84 4

potassium hydrogen phthalate, KH(C H O )

♦

silver nitrate, AgNO

♦

potassium iodate, KIO

♦

2 27

potassium dichromate, K Cr O

Sodium hydroxide is not a primary standard as it has a relatively low GFM, is unstable as a

solid (absorbs moisture) and unstable as a solution. Sodium hydroxide solution must be

standardised before being used in volumetric analysis.

Version 3.1 34

Researching chemistry (continued)

(e) Volumetric analysis (continued)

Candidates must be familiar with use of the following types of volumetric analysis:

♦ acid-base titrations

♦ redox titrations based on reactions between oxidising and reducing agents

♦ complexometric titrations based on reactions in which complexes are formed — EDTA

is an important complexometric reagent and can be used to determine the

concentration of metal ions in solution

♦ back titrations used to find the number of moles of a substance by reacting it with an

excess volume of a reactant of known concentration. The resulting mixture is then

titrated to work out the number of moles of the reactant in excess. From the initial

number of moles of that reactant, the number of moles used in the reaction can be

determined. The initial number of moles of the substance being analysed can then be

calculated. A back titration is useful when trying to work out the quantity of substance

in a solid with a low solubility.

(f) Practical skills and techniques

Candidates must be familiar with use of the technique of colorimetry, including:

♦ preparing a series of standard solutions of appropriate concentration

♦ choosing an appropriate colour or wavelength of filter complementary to the colour of

the species being tested

♦ using a blank

♦ preparing a calibration graph

Colorimetry uses the relationship between colour intensity of a solution and the

concentration of the coloured species present.

A colorimeter or a spectrophotometer is used to measure the absorbance of light of a

series of standard solutions, and this data is used to plot a calibration graph.

The concentration of the solution being tested is determined from its absorbance and by

referring to the calibration curve.

The concentration of coloured species in the solution being tested must lie in the straight

line section of the calibration graph.

Candidates must be familiar with use of the technique of distillation. Distillation is used for

identification and purification of organic compounds.

The boiling point of a compound, determined by distillation, is one of the physical

properties that can be used to confirm its identity.

Distillation can be used to purify a compound by separating it from less volatile substances

in the mixture.

Version 3.1 35

Researching chemistry (continued)

(f) Practical skills and techniques (continued)

Candidates must be familiar with use of the technique of heating under reflux. Heating

under reflux allows heat energy to be applied to a chemical reaction mixture over an

extended period of time without volatile substances escaping.

When carrying out heating under reflux, the reaction mixture is placed in a round-bottomed

flask with anti-bumping granules and the flask is fitted with a condenser. The flask is then

heated using an appropriate source of heat.

Candidates must be familiar with use of the technique of vacuum filtration. Vacuum

filtration involves carrying out a filtration under reduced pressure and provides a faster

means of separating a precipitate from a filtrate. A Büchner, Hirsch or sintered glass funnel

can be used during vacuum filtration.

Candidates must be familiar with use of the technique of recrystallisation to purify an

impure solid involving:

♦ dissolving an impure solid gently in a minimum volume of a hot solvent

♦ hot filtration of the resulting mixture to remove any insoluble impurities

♦ cooling the filtrate slowly to allow crystals of the pure compound to form, leaving

soluble impurities dissolved in the solvent

♦ filtering, washing and drying the pure crystals

The solvent for recrystallisation is chosen so that the compound being purified is

completely soluble at high temperatures and only sparingly soluble at lower temperatures.

Candidates must be familiar with use of the technique of solvent extraction. Solvent

extraction involves isolating a solute from a liquid mixture or solution by extraction using an

immiscible solvent in which the solute is soluble.

When carrying out a solvent extraction, the two immiscible solvents form two layers in the

separating funnel. The solute dissolves in both solvents and an equilibrium establishes

between the two layers. The ratio of solute dissolved in each layer is determined by the

equilibrium constant,

. The lower layer is run off into a container and the upper layer is

poured into a second container. This process is repeated to maximise the quantity of

solute extracted.

Version 3.1 36

Researching chemistry (continued)

(f) Practical skills and techniques (continued)

The quantity of solute extracted is greater if a number of extractions using smaller volumes

of solvent are carried out rather than a single extraction using a large volume of solvent.

The solvent used should be:

♦ immiscible with the liquid mixture or solution (usually water)

♦ one in which the solute is more soluble in than the liquid mixture or solution

(usually water)

♦ volatile to allow the solute to be obtained by evaporation of the solvent

♦ unreactive with the solute

Candidates must be familiar with use of the techniques of melting point and mixed melting

point determination. The melting point of a substance is the temperature range over which

the solid first starts to melt, to when all of the solid has melted.

The identity of a pure compound can be confirmed by melting point analysis and a

comparison of the experimentally determined melting point with a literature or known

melting point value.

Determination of the melting point of a compound can give an indication of the purity of a

compound. The presence of impurities in the compound lowers the melting point and

broadens its melting temperature range due to the disruption in intermolecular bonding in

the crystal lattice.

Determination of a mixed melting point involves mixing a small quantity of the product with

some of the pure compound and determining the melting point. The melting point value

and the range of the melting temperature can be used to determine if the product and the

pure compound are the same substance.

Candidates must be familiar with use of the technique of thin-layer chromatography.

Chromatography is a technique used to separate the components present within a mixture.

Chromatography separates substances by making use of differences in their polarity or

molecular size.

Thin-layer chromatography (TLC) uses a fine film of silica or aluminium oxide spread over

glass, aluminium foil or plastic. A small sample of the mixture being tested is spotted onto

the base (pencil) line of the chromatogram. A solvent dissolves the compounds in the spot

and carries the compounds up the chromatogram. How far the compounds are carried

depends on how soluble the compounds are in the chosen solvent and how well they

adhere to the plate. A developing agent or ultraviolet light is normally required to visualise

the spots on the chromatogram.

Version 3.1 37

Researching chemistry (continued)

(f) Practical skills and techniques (continued)

values can be calculated:

distance travelled by the sample

distance travelled by the solvent

Under the same conditions (temperature, solvent, and saturation levels) a compound

always has the same

value (within experimental error).

The identity of a compound can be confirmed by:

♦ comparing the experimentally determined

values with a literature or known value

determined under the same conditions

♦ making a direct comparison on a TLC plate between the compound being tested and

the pure substance — a co-spot could be used

TLC is used to assess the purity of substances. A pure substance, when spotted and

developed on a TLC plate, should appear as a single spot (some impurities may not be

visible by TLC analysis). The presence of more than one spot shows that impurities are

present.

Skills, knowledge and understanding included in the course are appropriate to the SCQF level of

the course. The SCQF level descriptors give further information on characteristics and expected

performance at each SCQF level, and are available on the SCQF website.

Version 3.1 38

Skills for learning, skills for life and skills for work

This course helps candidates to develop broad, generic skills. These skills are based on SQA’s

Skills Framework: Skills for Learning, Skills for Life and Skills for Work and draw from the following

main skills areas:

Literacy

1.1

Reading

1.2

Writing

Numeracy

2.1

Number processes

2.2

Money, time and measurement

2.3

Information handling

Thinking skills

5.3

Applying

5.4

Analysing and evaluating

5.5

Creating

Teachers and/or lecturers must build these skills into the course at an appropriate level, where

there are suitable opportunities.

Version 3.1 39

Course assessment

Course assessment is based on the information in this course specification.

The course assessment meets the purposes and aims of the course by addressing:

♦ breadth — drawing on knowledge and skills from across the course

♦ challenge — requiring greater depth or extension of knowledge and/or skills

♦ application — requiring application of knowledge and/or skills in practical or theoretical contexts

as appropriate

This enables candidates to apply:

♦ breadth and depth of skills, knowledge and understanding from across the course to answer

questions in chemistry

♦ skills of scientific inquiry, using related knowledge, to carry out a meaningful and appropriately

challenging project in chemistry and communicate findings

Course assessment structure: question paper

Question paper 110 marks

The question paper has 110 marks. This is scaled by SQA to represent 75% of the overall marks

for the course assessment.

The question paper has 2 sections.

Section 1 contains multiple-choice questions and has 25 marks.

Section 2 contains restricted-response and extended-response questions and has 85 marks.

A data booklet is provided.

The majority of the marks are awarded for applying knowledge and understanding. The other

marks are awarded for applying skills of scientific inquiry, scientific analytical thinking and problem

solving.

The question paper gives candidates an opportunity to demonstrate the following skills, knowledge

and understanding:

♦ making accurate statements

♦ describing information, providing explanations and integrating knowledge

♦ applying knowledge of chemistry to new situations, interpreting information and solving

problems

♦ planning and designing chemical experiments/investigations, including safety measures to

make a discovery, demonstrate a known fact, illustrate particular effects or test a hypothesis

♦ selecting information from a variety of sources

♦ presenting information appropriately in a variety of forms

Version 3.1 40

♦ processing information and data (using calculations, significant figures and units, where

appropriate)

♦ making predictions and generalisations based on evidence and/or information

♦ drawing valid conclusions and giving explanations supported by evidence and/or justification

♦ evaluating experiments and suggesting improvements

Setting, conducting and marking the question paper

The question paper is set and marked by SQA, and conducted in centres under conditions

specified for external examinations by SQA.

Candidates have 3 hours to complete the question paper.

Specimen question papers for Advanced Higher courses are published on SQA’s website. These

illustrate the standard, structure and requirements of the question papers. The specimen papers

also include marking instructions.

Course assessment structure: project

Project 25 marks

The project has 25 marks. This is scaled by SQA to represent 25% of the overall marks for the

course assessment.

The project allows candidates to carry out an in-depth investigation of a chemistry topic and

produce a project report. Candidates are required to individually plan and carry out a chemistry

investigation.

Candidates should keep a record of their work (lab book) as this will form the basis of their project

report. This record should include details of their research, experiments and recorded data.

The project assesses the application of skills of scientific inquiry and related chemistry knowledge

and understanding. It gives candidates an opportunity to demonstrate the following skills,

knowledge and understanding:

♦ extending and applying knowledge of chemistry to new situations, interpreting and analysing

information to solve more complex problems

♦ planning, designing and safely carrying out chemical experiments/investigations, including risk

assessments to make a discovery, demonstrate a known fact, illustrate particular effects or test

a hypothesis

♦ recording systematic detailed observations and collecting data

♦ selecting information from a variety of sources

♦ presenting detailed information appropriately in a variety of forms

♦ processing and analysing chemical information and data (using calculations, significant figures

and units, where appropriate)

♦ making reasoned predictions and generalisations from a range of evidence and/or information

♦ drawing valid conclusions and giving explanations supported by evidence and/or justification

♦ critically evaluating experimental procedures by identifying sources of uncertainty and

suggesting and implementing improvements

Version 3.1 41

♦ drawing on knowledge and understanding of chemistry to make accurate statements, describe

complex information, provide detailed explanations and integrate knowledge

♦ communicating chemical findings and information fully and effectively

♦ analysing and evaluating scientific publications and media reports

Project overview

Candidates carry out an in-depth investigation of a chemistry topic. Candidates choose their topic

and individually investigate/research its underlying chemistry. Candidates must discuss potential

topics with their teacher or lecturer to ensure that they do not waste time researching unsuitable

topics. This is an open-ended task that may involve candidates carrying out a significant part of the

work without close supervision.

Throughout the project candidates work autonomously, making independent and rational decisions

based on evidence and interpretation of scientific information, which involves analysing and

evaluating results. Through this, candidates further develop and enhance their scientific literacy

skills.

The project offers challenge by requiring candidates to apply skills, knowledge and understanding

in a context that is one or more of the following:

♦ unfamiliar

♦ familiar but investigated in greater depth

♦ integrating a number of familiar contexts

Candidates will produce a project report that has a logical structure.

Refer to the Advanced Higher Chemistry Project Assessment Task for detailed advice on the

content of the project report.

Version 3.1 42

Setting, conducting and marking the project

Setting

The project is set:

♦ by centres within SQA guidelines

♦ at a time appropriate to the candidate’s needs

♦ within teaching and learning and includes experimental work at a level appropriate to Advanced

Higher

Conducting

The project is conducted:

♦ under some supervision and control

♦ in time to meet a submission date set by SQA

♦ independently by the candidate

Marking

The project has 25 marks.

The table below gives the mark allocation for each assessment category of the project report.

Section Expected response

Mark

allocation

Abstract

A brief abstract (summary) stating the overall aim and

conclusion of the project

Underlying

chemistry

A description of the underlying chemistry that:

♦ is relevant to the project

♦ demonstrates an understanding of the chemistry theory

underpinning the project

♦ is of a level of demand commensurate with Advanced

Higher Chemistry

Data collection and

handling

Procedure(s) clearly described in the past tense and use

the impersonal voice

Statement of appropriate safety measure(s) with

justification(s)

Data collected using methods of appropriate complexity,

including one procedure and at least one of the following:

♦ a second procedure

♦ a modification in light of experience

♦ a control experiment

♦ standardisation of any solution where the accuracy of

the concentration is crucial in an analysis

Experimental results providing evidence that the

procedure(s) has (have) been carried out in duplicate

Version 3.1 43

Section Expected response

Mark

allocation

A description of the correct use of the appropriate

apparatus, chemicals and any other substances to achieve

the required levels of precision and/or accuracy

All relevant raw data is recorded

Numerical data is appropriately presented

Citations and references for three sources of

internet/literature data, using any relevant referencing

system

Data analysis

Analysis of data of a level of demand commensurate with

Advanced Higher Chemistry. Analysis to include, as

appropriate:

♦ values calculated correctly using a chemical

relationship

♦ scatter, line or bar graph

♦ chromatograms

♦ spectra

Calculated values stated to an appropriate number of

significant figures

Conclusion

A valid conclusion that relates to the aim and is supported

by all the data in the report

Analysis

A valid comparison of the experimental data with data from

the internet/literature source(s), or a comparison of

duplicate experimental data if no internet/literature source

is available

Evaluation

Evaluation of the investigation including, as appropriate:

♦ evaluation of data from the internet/literature

♦ evaluative statements supported by justification

♦ quantitative treatment of uncertainties

Structure

A clear and concise report with an informative title,

contents page and page numbers

Total 25

The project report is submitted to SQA for external marking.

All marking is quality assured by SQA.

Version 3.1 44

Assessment conditions

Time

Candidates should start their project at an appropriate point in the course. SQA does not prescribe

a maximum time allocation for the project but it is expected that candidates will spend 10-15 hours

on experimental work. Candidates may choose to spend additional time on experimental work.

Supervision, control and authentication

The project is conducted under some supervision and control. This means that candidates may

complete part of the work outwith the learning and teaching setting.

Teachers and lecturers must make sure candidates understand the requirements of the project

from the outset.

Teachers and lecturers must ensure that the project is the work of the individual candidate, for

example by:

♦ having regular progress meetings with candidates

♦ conducting spot-check interviews with candidates

♦ regularly reviewing candidates’ lab books

♦ completing checklists to record candidates’ progress

Teachers and lecturers must exercise their professional responsibility to ensure that the project

report submitted by a candidate is the candidate’s own work.

Resources

There are no restrictions on the resources to which candidates may have access.

Reasonable assistance

The term ‘reasonable assistance’ is used to try to balance the need for support with the need to

avoid giving too much assistance, for example, drawing out or teasing out points without leading

candidates. Candidates sometimes get stuck at a particular part of a task. In such cases, a teacher

or lecturer could assist by raising other questions that make the candidate think about the original

problem, therefore giving them the opportunity to answer their own questions without supplying the

actual answers.

Teachers and lecturers must be careful that the integrity of the assessment is not compromised.

Centres must not provide model answers.

Version 3.1 45

Evidence to be gathered

The following candidate evidence is required for this assessment:

♦ a project report

The project report is submitted to SQA, within a given timeframe, for marking.

The same project report cannot be submitted for more than one subject.

Volume

The project report should be between 2500 and 4500 words in length, excluding the title page,

contents page, tables of data, graphs, diagrams, calculations, references and acknowledgements.

Candidates must include their word count on the project report flyleaf.

If the word count exceeds the maximum by more than 10%, a penalty is applied.

Version 3.1 46

Grading

Candidates’ overall grades are determined by their performance across the course assessment.

The course assessment is graded A–D on the basis of the total mark for both course assessment

components.

Grade description for C

For the award of grade C, candidates will typically have demonstrated successful performance in

relation to the skills, knowledge and understanding for the course by:

♦ retaining knowledge and scientific skills over an extended period of time

♦ integrating knowledge and understanding and scientific skills acquired throughout the course

♦ applying knowledge and understanding and scientific skills in a variety of contexts

♦ applying knowledge and understanding and scientific skills to solve problems

♦ selecting, analysing and presenting relevant information collected through experimental,

observational or research work

♦ reporting in a scientific manner that communicates the chemistry

Grade description for A

For the award of grade A, candidates will typically have demonstrated a consistently high level of

performance in relation to the skills, knowledge and understanding for the course by:

♦ retaining an extensive range of knowledge and scientific skills over an extended period of time

♦ integrating an extensive range of knowledge and understanding and scientific skills acquired

throughout the course

♦ applying knowledge and understanding and scientific skills in a variety of complex contexts

♦ integrating knowledge and understanding and scientific skills to solve problems in a variety of

complex contexts

♦ showing proficiency in selecting, analysing and presenting relevant information, collected

through experimental, observational or research work

♦ showing proficiency in reporting in a scientific manner that communicates the chemistry by

analysing and interpreting information in a critical and scientific manner, and demonstrating

depth of knowledge and understanding

Version 3.1 47

Equality and inclusion

This course is designed to be as fair and as accessible as possible with no unnecessary barriers to

learning or assessment.

Guidance on assessment arrangements for disabled candidates and/or those with additional

support needs is available on the assessment arrangements web page:

www.sqa.org.uk/assessmentarrangements

Version 3.1 48

Further information

♦ Advanced Higher Chemistry subject page

♦ Assessment arrangements web page

♦ Building the Curriculum 3–5

♦ Guide to Assessment

♦ Guidance on conditions of assessment for coursework

♦ SQA Skills Framework: Skills for Learning, Skills for Life and Skills for Work

♦ Coursework Authenticity: A Guide for Teachers and Lecturers

♦ Educational Research Reports

♦ SQA Guidelines on e-assessment for Schools

♦ SQA e-assessment web page

The SCQF Framework, level descriptors and handbook are available on the SCQF website.

Version 3.1 49

Appendix: course support notes

Introduction

These support notes are not mandatory. They provide advice and guidance to teachers and

lecturers on approaches to delivering the course. Please read these course support notes in

conjunction with the course specification, the specimen question paper and the project assessment

task.

Approaches to learning and teaching

This section provides you with advice and guidance on learning and teaching. You should use a

variety of learning and teaching approaches to allow candidates with different needs and prior

attainment to demonstrate achievement. You have considerable flexibility to select contexts that

stimulate and challenge candidates, offering both breadth and depth.

Discussion and questioning are effective ways of developing candidates’ knowledge and

understanding of chemical concepts. Teachers, lecturers and candidates should make full use of

models to develop the understanding of concepts in chemistry, and use information communication

technology to support learning and to process data. As well as using computers as a learning tool,

computer animations and simulations can help candidates understand chemical concepts.

Computer-interfacing equipment can detect changes in variables, allowing experimental results to

be recorded and processed. Results can also be displayed in real time, helping to improve

understanding.

Advanced Higher courses encourage independent study. Candidates should be given opportunities

to work independently, collaboratively, co-operatively and as a whole class.

You should adopt a holistic approach to encourage the simultaneous development of candidates’

conceptual understanding and skills. Practical and investigative skills are strongly recommended to

be progressively developed throughout the course. This allows practical techniques to be

introduced and practised within real-life contexts, and for candidates to make the connections

between theory and practical applications. You should encourage candidates to see risk

assessment as part of the planning process for any practical activity. Throughout the course,

candidates should have the opportunity to assess risks and make informed decisions regarding the

use of appropriate control measures. During the project, candidates must identify safety measures

taken to minimise risk during their experimental work.

Although the mandatory knowledge and skills may be similar in Higher and Advanced Higher

courses, there are differences in the:

♦ depth of underpinning knowledge and understanding

♦ complexity and sophistication of the applied skills

♦ ways that candidates learn — they take more responsibility for their learning at Advanced

Higher, and work more autonomously

The mandatory content is described in four areas: inorganic chemistry; physical chemistry; organic

chemistry and instrumental analysis; and researching chemistry. Centres can deliver the course

content in whichever order best meets the needs of their candidates.

Version 3.1 50

Partnership working can enhance the learning experience. You could invite guest speakers from,

industry, further education and higher education to share their knowledge of particular aspects of

chemistry.

Assessment should be integral to and improve learning and teaching. The approach should involve

candidates and provide supportive feedback. Self- and peer-assessment techniques are

encouraged, wherever appropriate. Assessment information should be used to set learning targets

and next steps and provide supportive feedback.

Examples of possible learning and teaching activities can be found in the following table.

The first column matches the ‘Skills, knowledge and understanding for the course assessment’

section in the course specification. The second column offers suggestions for activities that you

could use to enhance teaching and learning.

All resources named were correct at the time of publication and may be subject to change.

The Strathclyde resource, and the RSC site, require you to register, but registration is free.

Version 3.1 51

Inorganic chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(a) Electromagnetic radiation and atomic spectra

Electromagnetic radiation can be described in terms of waves and

characterised in terms of wavelength and/or frequency.

The relationship between these quantities is given by

Frequency is often quoted in Hz, which is the same



as s

-1

The different types of radiation arranged in order of wavelength is

known as the electromagnetic spectrum.

Wavelengths of visible light are normally expressed in nanometres

(nm).

Electromagnetic radiation can be described as a wave (has a

wavelength and frequency), and as a particle, and is said to have a

dual nature.

A variety of different resources on this topic are available from RSC

education resources, including:

♦ a printable handout containing a chart of the electromagnetic

spectrum

♦ a vignette showing the quantisation of energy levels within an

atom

When electromagnetic radiation is absorbed or emitted by matter it

behaves like a stream of particles. These particles are known as

photons.

A photon carries quantised energy proportional to the frequency of

radiation.

When a photon is absorbed or emitted, energy is gained or lost by

electrons within the substance.

Video tutorials on light and the electromagnetic spectrum are

available from Khan Academy.

Version 3.1 52

Inorganic chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(a) Electromagnetic radiation and atomic spectra (continued)

The photons in high frequency radiation can transfer greater amounts

of energy than photons in low frequency radiation.

The energy associated with a single photon is given by:

E hf E

= =

The values for the constants are h = 6·63 × 10

–34

s and

L = 6·02 × 10

mol

–1

and are given in the data booklet.

L is Avogadro’s constant and is the number of formula units in one

mole of the substance. (Formula units can be atoms, molecules or

groups of ions, depending on the type of bonding present.)

The energy associated with one mole of photons is given by:

Lhc

E Lhf E

= =

Energy is often in units of kJ mol

-1

When energy is transferred to atoms, electrons within the atoms may

be promoted to higher energy levels.

An atom emits a photon of light energy when an excited electron

moves from a higher energy level to a lower energy level.

To calculate the energy of one mole of photons in kJ mol

-1

, it may be

more convenient to use:

1000 1000

Lhf Lhc

= =

The light energy emitted by an atom produces a spectrum that is

made up of a series of lines at discrete (quantised) energy levels.

This provides direct evidence for the existence of these energy

levels.

Chemguide explains the atomic emission spectrum of hydrogen.

Version 3.1 53

Inorganic chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(a) Electromagnetic radiation and atomic spectra (continued)

A number of resources detail activities relating to atomic emission

spectroscopy, including:

♦ RSC education resources:

— spray bottle flame test demonstration

— flame test class experiment

♦ SSERC:

— flame test demonstration

— instructions for making a spectroscope from a CD, a DVD, or

using a smart phone

♦ chemistry hypermedia project — provides information about

atomic emission instrumentation

Each element in a sample produces characteristic absorption and

emission spectra. These spectra can be used to identify and quantify

the element.

Khan Academy provides a video tutorial explaining the difference

between atomic absorption and emission spectroscopy.

Version 3.1 54

Inorganic chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(a) Electromagnetic radiation and atomic spectra (continued)

In absorption spectroscopy, electromagnetic radiation is directed at

an atomised sample. Radiation is absorbed as electrons are

promoted to higher energy levels.

An absorption spectrum is produced by measuring how the intensity

of absorbed light varies with wavelength.

In emission spectroscopy, high temperatures are used to excite the

electrons within atoms.

As the electrons drop to lower energy levels, photons are emitted.

An emission spectrum of a sample is produced by measuring the

intensity of light emitted at different wavelengths.

In atomic spectroscopy, the concentration of an element within a

sample is related to the intensity of light emitted or absorbed.

A number of activities demonstrate atomic absorption spectroscopy,

including:

♦ SSERC — an activity with filter paper soaked in brine

used to

observe the sodium absorption spectrum

♦ vapour discharge lamps or fluorescent tube lamps used to

observe the emission spectrum of mercury (a series of purple

lines) when viewed through a spectroscope

RSC education resources has an interesting anecdote describing a

forensic use of atomic absorption spectroscopy in an

investigation of

lead in hair treated with products to reduce greyness. An applet from

the University of Oregon shows the absorption and emission spectra

of elements by clicking on the appropriate element on a periodic

table.

(b) Atomic orbitals, electronic configurations and the periodic table

The discrete lines observed in atomic spectra can be explained if

electrons, like photons, also display the properties of both particles

and waves.

Animated videos explaining the behaviour of electrons as waves and

particles are available online.

Version 3.1 55

Inorganic chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(b) Atomic orbitals, electronic configurations and the periodic table (continued)

Electrons behave as standing (stationary) waves in an atom. These

are waves that vibrate in time but do not move in space. There are

different sizes and shapes of standing wave possible around the

nucleus, known as orbitals. Orbitals can hold a maximum of two

electrons.

The different shapes of orbitals are identified as s, p, d and f

(knowledge of the shape of f orbitals is not required).

Electrons within atoms have fixed amounts of energy called quanta.

It is possible to describe any electron in an atom using four quantum

numbers:

♦ the principal quantum number

indicates the main energy level

for an electron and is related to the size of the orbital

♦ the angular momentum quantum number

determines the shape

of the subshell and can have values from zero to

1n −

♦ the magnetic quantum number

determines the orientation of

the orbital and can have values between

and ll−+

♦ the spin magnetic quantum number

determines the direction of

spin and can have values of

+−

A number of resources provide details of activities relating to atomic

orbitals and the quantum mechanical model of the atom:

♦ ChemTube3D, available through RSC education resources,

has

an illustration of the shapes of atomic orbitals

♦ Chemguide has information about atomic orbitals, including

electronic configurations

♦ Khan Academy has videos and tutorials giving information on:

— the quantum mechanical model of the atom

— electronic configurations

— quantum numbers

♦ RSC education resources has an interactive gridlocks game on

subshells

Version 3.1 56

Inorganic chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(b) Atomic orbitals, electronic configurations and the periodic table (continued)

Electrons within atoms are arranged according to:

♦ the aufbau principle — electrons fill orbitals in order of increasing

energy (‘aufbau’ means ‘building up’ in German)

♦ Hund’s rule — when degenerate orbitals are available, electrons

fill each singly, keeping their spins parallel before spin pairing

starts

♦ the Pauli exclusion principle — no two electrons in one atom can

have the same set of four quantum numbers, therefore, no orbital

can hold more than two electrons and these two electrons must

have opposite spins

An interesting audio discussion of Pauli’s exclusion principle and the

life of Wolfgang Pauli is available for download from BBC Radio 4 —

In Our Time.

In an isolated atom the orbitals within each subshell are degenerate.

The relative energies corresponding to each orbital can be

represented diagrammatically using orbital box notation for the first

four shells of a multi-electron atom.

Electronic configurations using spectroscopic notation and orbital box

notation can be written for elements of atomic numbers 1 to 36.

The periodic table is subdivided into four blocks (s, p, d and f)

corresponding to the outer electronic configurations of the elements

within these blocks.

There are a number of online resources providing tutorial notes

covering electronic configuration, spectroscopic notation and orbital

box notation, including

Chemistry Libretexts and Chemguide.

Version 3.1 57

Inorganic chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(b) Atomic orbitals, electronic configurations and the periodic table (continued)

The variation in first, second and subsequent ionisation energies with

increasing atomic number for the first 36 elements can be explained

in terms of the relative stability of different subshell electronic

configurations. This provides evidence for these electronic

configurations. Anomalies in the trends of ionisation energies can be

explained by considering the electronic configurations.

A graph of first ionisation energies against atomic number shows

anomalies, which provides good evidence of s and p orbitals being

filled. Chemguide

explains these anomalies.

There is a special stability associated with half-filled and full

subshells. The more stable the electronic configuration, the higher

the ionisation energy.

VSEPR (valence shell electron pair repulsion) theory can be used to

predict the shapes of molecules and polyatomic ions.

The number of electron pairs surrounding a central atom can be

found by:

♦ taking the total number of valence (outer) electrons on the central

atom and adding one for each atom attached

♦ adding an electron for every negative charge

♦ removing an electron for every positive charge

♦ dividing the total number of electrons by two to give the number

of electron pairs

Although valence shell electron pair repulsion (VSEPR) theory does

not describe the actual molecular orbitals in a molecule, the shapes

predicted are usually quite accurate. Bristol University ChemLabS

has

instructions for working out electron pairs with worked examples.

RSC education resources has a number of vignettes on

bonding

theory and VSEPR.

Version 3.1 58

Inorganic chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(b) Atomic orbitals, electronic configurations and the periodic table (continued)

Electron pairs are negatively charged and repel each other. They are

arranged to minimise repulsion and maximise separation.

A fun practical using soap bubbles to demonstrate the concept of

VSEPR is available from Boise State University.

The arrangement of electron pairs around a central atom is:

♦ linear for two electron pairs

♦ trigonal planar for three electron pairs

♦ tetrahedral for four electron pairs

♦ trigonal bipyramidal for five electron pairs

♦ octahedral for six electron pairs

Shapes of molecules or polyatomic ions are determined by the

shapes adopted by the atoms present based on the arrangement of

electron pairs. Electron dot diagrams can be used to show these

arrangements.

Electron pair repulsions decrease in strength in the order:

non-bonding pair/non-bonding pair

non-bonding pair/bonding pair

bonding pair/bonding pair

Version 3.1 59

Inorganic chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

The d-block transition metals are metals with an incomplete d

subshell in at least one of their ions.

The filling of the d orbitals follows the aufbau principle, with the

exception of chromium and copper atoms.

These exceptions are due to the special stability associated with the

d subshell being half-filled or completely filled.

When atoms from the first row of the transition elements form ions, it

is the 4s electrons that are lost first rather than the 3d electrons.

An element is said to be in a particular oxidation state when it has a

specific oxidation number.

The oxidation number can be determined by the following:

♦ uncombined elements have an oxidation number of 0

♦ ions containing single atoms have an oxidation number that is the

same as the charge on the ion

♦ in most of its compounds, oxygen has an oxidation number of

2−

♦ in most of its compounds, hydrogen has an oxidation number of

♦ the sum of all the oxidation numbers of all the atoms in a neutral

compound must add up to zero

♦ the sum of all the oxidation numbers of all the atoms in a

polyatomic ion must be equal to the charge on the ion

A display of sample bottles containing salts or compounds of the first

30 elements arranged on a large (A1 or A2 size) periodic table show

that only the d-block compounds are coloured.

Candidates may also

notice that zinc compounds are white, indicating that, although lying

in the central region of the periodic table, zinc is different from the

transition metals. Scandium is also different since it forms only the 3

ion, which has no d electrons.

Khan Academy has a number of video tutorials on transition metals

and electronic configurations of d-block elements.

Version 3.1 60

Inorganic chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

A transition metal can have different oxidation states in its

compounds.

Compounds of the same transition metal in different oxidation states

may have different colours.

Oxidation can be defined as an increase in oxidation number.

Reduction can be considered as a decrease in oxidation number.

Changes in oxidation number of transition metal ions can be used to

determine whether oxidation or reduction has occurred.

Compounds containing metals in high oxidation states are often

oxidising agents, whereas compounds with metals in low oxidation

states are often reducing agents.

Ligands may be negative ions or molecules with non-bonding pairs of

electrons that they donate to the central metal atom or ion, forming

dative covalent bonds.

Ligands can be classified as monodentate, bidentate, up to

hexadentate.

It is possible to deduce the ligand classification from a formula or

structure of the ligand or complex.

A number of resources provide instructions for experiments involving

oxidation states of transition metals and transition metal complexes,

including:

♦ RSC education resources:

— oxidation states of vanadium

— transition elements — a microscale investigation

— preparation of nickel complexes (Skills’ block 2, page 10)

— complexes of cobalt (Discovery block 4, page 20)

♦ SSERC:

— oxidation states of vanadium

— oxidation states of manganese

— colour change chameleon

— ligands of copper complexes

— copper amino complexes

— microscale iron drops practical

♦ Science in School:

— a redox reaction using lollipops

Version 3.1 61

Inorganic chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

The total number of bonds from the ligands to the central transition

metal is known as the coordination number.

RSC education resources has a gridlocks game to aid revision of

shapes of complex ions and coordination numbers.

Names and formulae can be written according to IUPAC rules for

complexes containing:

♦ central metals that obey the normal IUPAC rules

♦ copper (cuprate) and iron (ferrate)

♦ ligands, including water, ammonia, halogens, cyanide, hydroxide,

and oxalate

In a complex of a transition metal, the d orbitals are no longer

degenerate.

Nomenclature of Inorganic Chemistry (Red Book) has information

about IUPAC rules for naming complexes.

Splitting of d orbitals to higher and lower energies occurs when the

electrons present in approaching ligands cause the electrons in the

orbitals lying along the axes to be repelled.

Ligands that cause a large difference in energy between subsets of d

orbitals are strong field ligands. Weak field ligands cause a small

energy difference.

Ligands can be placed in an order of their ability to split d orbitals.

This is called the spectrochemical series.

Candidates can investigate the spectrochemical series and discover

how the position of a ligand in the series may affect the colour of the

complex. RSC Education in Chemistry details an experiment that can

be used to demonstrate the spectrochemical

series.

Version 3.1 62

Inorganic chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

Colours of many transition metal complexes can be explained in

terms of d-d transitions.

Light is absorbed when electrons in a lower energy d orbital are

promoted to a d orbital of higher energy.

If light of one colour is absorbed, then the complementary colour will

be observed.

Electrons transition to higher energy levels when energy

corresponding to the ultraviolet or visible regions of the

electromagnetic spectrum is absorbed.

Chemguide explains colours of transition metal complexes.

RSC education resources hosts an exciting Nuffield Foundation

experiment involving transition metal ions in coloured glass

as an

interesting introduction, and looks at an everyday life application of

the use of transition metal chemistry.

STEM Learning details the RSC Classic Chemistry Demonstrations

No. 93, page 261, that shows different colours of nickel complexes

with water and ethylenediamine as ligands in different ratios.

UV-visible spectrometers and colorimeters measure the intensity of

radiation transmitted through a sample, and compares this with the

intensity of incident radiation.

Chemistry Practical Guide — Support

Materials (2012), produced by Education Scotland and available

through SSERC, details an experiment to determine the manganese

content in steel using the practical technique of colorimetry.

The wavelength ranges are approximately 200–400 nm for ultraviolet

and 400–700 nm for visible light.

Version 3.1 63

Inorganic chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

Transition metals and their compounds can act as catalysts.

Heterogeneous catalysts are in a different state to the reactants.

Heterogeneous catalysis can be explained in terms of the formation

of activated complexes and the adsorption of reactive molecules onto

active sites. The presence of unpaired d electrons or unfilled d

orbitals is thought to allow activated complexes to form. This can

provide reaction pathways with lower activation energies compared to

the uncatalysed reaction.

Chemguide has a range of information on catalysts starting with an

introduction to catalysts.

Homogeneous catalysts are in the same state as the reactants.

Homogeneous catalysis can be explained in terms of changing

oxidation states with the formation of intermediate complexes.

The demonstration of cobalt(II) chloride as a homogeneous transition

metal catalyst in the oxidation of Rochelle salt may have been carried

out at Higher, but can now be discussed in terms of oxidation states.

There are a number of online resources detailing the instructions for

this, including:

♦ RSC education resources:

— a visible activated complex

— catalysts in reactions

♦ SSERC:

— catalysts at work

Version 3.1 64

Physical chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(a) Chemical equilibrium

A chemical reaction is in equilibrium when the composition of the

reactants and products remains constant indefinitely.

The equilibrium constant (

) characterises the equilibrium

composition of the reaction mixture.

For the general reaction

aA bB cC dD++

the equilibrium

expression is:

[ ] [ ]

You should reinforce the links between equilibrium where applicable

in the ‘Organic chemistry and instrumental analysis’, and

‘Researching Chemistry areas.

Chemguide’s An introduction to equilibrium

has a useful recap of

prior knowledge of equilibrium.

RSC education resources,

Advanced starters for ten: section 2

‘Equilibria’, has a selection of easily editable short quizzes and

activities.

[ ] [ ] [ ] [ ]

, , and ABC D

are the equilibrium concentrations of

, , and

ABC D

and

, , and abc d

are the stoichiometric coefficients in

the balanced reaction equation.

The value of equilibrium constants can be calculated.

A number of tutorials on equilibrium constant are available online, for

example:

♦ Khan Academy — The equilibrium constant K

♦ Chemguide — Equilibrium constants: K

The value of an equilibrium constant indicates the position of

equilibrium.

Equilibrium constants have no units.

Partition coefficients could be included as a specific example of an

equilibrium constant. RSC education resources has details of a

practical on the partition of iodine across two immiscible liquids

Version 3.1 65

Physical chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(a) Chemical equilibrium (continued)

The concentrations of pure solids and pure liquids at equilibrium are

taken as constant and given a value of 1 in the equilibrium

expression.

Introduce thin-layer chromatography (TLC) and solvent extraction

activities to reinforce the concept of equilibria through practical

applications and to reinforce links to the ‘Researching chemistry’

area.

The numerical value of the equilibrium constant depends on the

reaction temperature and is independent of concentration and/or

pressure.

For endothermic reactions, a rise in temperature causes an increase

and the yield of the product is increased.

For exothermic reactions, a rise in temperature causes a decrease in

and the yield of the product is decreased.

The presence of a catalyst does not affect the value of the equilibrium

constant.

Chemguide explains the relationship between equilibrium constant

and Le Chatelier’s principle.

In water and aqueous solutions there is an equilibrium between the

water molecules and hydronium (hydrogen) and hydroxide ions.

This ionisation of water can be represented by:

( ) ( )

() ()

22 3

HO HO HO aq OH aq

−

++ 

Chemguide has a good explanation about the ionic product of water.

RSC education resources, Advanced starters for ten: section 3,

‘Acids and bases’, has a selection of easily editable short quizzes

and activities relating to the ionic product of water.

Version 3.1 66

Physical chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(a) Chemical equilibrium (continued)

()

H O aq

represents a hydronium ion, a hydrated proton. A

shorthand representation of

()

H O aq

)

H (aq

Water is amphoteric (can react as an acid and a base).

The dissociation constant for the ionisation of water is known as the

ionic product and is represented by

–

H O OH

  

  

The value of the ionic product varies with temperature.

At 25°C the value of

is approximately

-14

1 × 10

The relationship between pH and the hydrogen ion concentration is

given by:

log

10 3 3

pH H O and H O 10

+ +−

 

=−=

 

There are a number of virtual lab simulations on acids and bases

available, including:

♦ Chemcollective — acid-base chemistry

♦ RSC education resources — pH scale simulation

In water and aqueous solutions with a pH value of 7 the

concentrations of

()

H O aq

and

OH (aq)

−

are both

-7

mol l

-1

25°C.

Version 3.1 67

Physical chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(a) Chemical equilibrium (continued)

If the concentration of

()

H O aq

or the concentration of

OH (aq)

−

known, the concentration of the other ion can be calculated using

or by using

pH pOH 14

The Brønsted-Lowry definitions of acids and bases state that an acid

is a proton donor and a base is a proton acceptor.

For every acid there is a conjugate base, formed by the loss of a

proton.

For every base there is a conjugate acid, formed by the gain of a

proton.

Online tutorials available include:

♦ Khan Academy:

— pH, pOH and the pH scale

— Brønsted-Lowry acid-base theory

♦ Chemguide:

— theories of acids and bases

, which provides information on

Brønsted Lowry acids and bases, conjugate acids and bases,

and amphoteric substances

Strong acids and strong bases are completely dissociated into ions in

aqueous solution.

Weak acids and weak bases are only partially dissociated into ions in

aqueous solution.

Examples of strong acids include hydrochloric acid, sulfuric acid and

nitric acid.

Ethanoic acid, carbonic acid and sulfurous acid are examples of

weak acids.

Investigate the pH of strong and weak acids and bases and different

metal and non-metal hydroxide solutions. Ideas for investigations

include:

♦ Salters’ archive — investigating acid-base reactions

♦ STEM learning — strong and weak acids — the common ion effect

Version 3.1 68

Physical chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(a) Chemical equilibrium (continued)

Solutions of metal hydroxides are strong bases.

Ammonia and amines are examples of weak bases.

The weakly acidic nature of solutions of carboxylic acids, sulfur

dioxide and carbon dioxide can be explained by reference to

equations showing the equilibria.

The weakly alkaline nature of a solution of ammonia or amines can

be explained by reference to an equation showing the equilibrium.

Equimolar solutions of weak and strong acids (or bases) have

different pH values, conductivity, and reaction rates, but the

stoichiometry of reactions are the same.

The acid dissociation constant is represented by

[ ]

HO A

+−

  

  

Chemguide has tutorial notes available on strong and weak acids and

bases.

RSC education resources

Advanced starters for ten: section 3, ‘Acids

and bases’, offers easily editable short quizzes and activities covering

acids and bases.

To highlight the difference between strong and weak acids, one

possible activity involves calculating the pH of a 0·1 mol l

-1

solution of

a weak acid, and confirming the result by measurement. The solution

can then be diluted tenfold to show that the pH rises by 0·5 rather

than by 1, as it would when diluting a strong acid such as 0·1 mol l

-1

HCl. This is also a good opportunity for candidates to practise the

technique of accurate dilution.

or by:

log

p where p

a aa

KKK= −

The approximate pH of a weak acid can be calculated using:

log

pH p c

K= −

Version 3.1 69

Physical chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(a) Chemical equilibrium (continued)

A soluble salt of a strong acid and a strong base dissolves in water to

produce a neutral solution.

A soluble salt of a weak acid and a strong base dissolves in water to

produce an alkaline solution.

A soluble salt of a strong acid and a weak base dissolves in water to

produce an acidic solution.

The name of the salt produced depends on the acid and base used.

Using the appropriate equilibria, the changes in concentrations of

and

−

ions of salt solutions can be explained.

RSC education resources provides resources relating to the pH of

salt solutions:

♦ Titration screen experiment: Titration 2 and titration 3

provide a

good explanation of pH curves

♦ Problem-based practical activities ‘Acid erosion’, problem 6,

contains practice calculations and a practical activity relating to pH,

pH curves, strong and weak acids, and

values.

Further information about

pH (titration) curves, pH of salts and choice

of indicator is available on Chemguide.

ChemCollective has a concept test on acids and bases.

Candidates can calculate the pH of a given salt solution and confirm

the value obtained by measuring the pH (examples of salt solutions

include: sodium carbonate; sodium sulphite; sodium stearate;

ammonium chloride; ammonium nitrate). Candidates can carry out

titration experiments measuring the pH after each small addition of an

acid or base, and plotting the results on a graph to create pH curves.

Data logging equipment can be used and the pH curves plotted can

be used to introduce indicator solutions.

Version 3.1 70

Physical chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(a) Chemical equilibrium (continued)

A buffer solution is one in which the pH remains approximately

constant when small amounts of acid, base or water are added.

An acid buffer consists of a solution of a weak acid and one of its salts

made from a strong base.

In an acid buffer solution the weak acid provides hydrogen ions when

these are removed by the addition of a small amount of base. The

salt of the weak acid provides the conjugate base, which can absorb

excess hydrogen ions produced by the addition of a small amount of

acid.

A basic buffer consists of a solution of a weak base and one of its

salts.

In a basic buffer solution the weak base removes excess hydrogen

ions, and the conjugate acid provided by the salt supplies hydrogen

ions when these are removed.

Candidates can prepare buffer solutions, calculate their pH and

confirm the value obtained by measuring the pH. A pH meter could

be first calibrated using a buffer solution, and then used to measure

the pH, and so provide a practical application of the use of a buffer

solution.

Khan Academy has a range of resources including:

♦ pH and pKa relationship in buffers

♦ buffer solution pH calculations

♦ introduction to buffer systems, which regulate pH in blood

Version 3.1 71

Physical chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(a) Chemical equilibrium (continued)

An approximate pH of an acid buffer solution can be calculated from

its composition and from the acid dissociation constant:

[ ]

log

acid

pH p

salt

K= −

Indicators are weak acids for which the dissociation can be

represented as:

In ( ) In ( )

H (aq) H O H O (aq) aq

+−

++

Candidates can determine the pH range over which an indicator

changes colour. Natural indicators extracted from plants could be

used.

Use pH curves to explain how appropriate indicators for titration

reactions are selected. Khan Academy has a video explaining

titration curves and acid-base indicators

The acid indicator dissociation constant is represented as

and is

given by the following expression:

[ ]

−

  

  

In aqueous solution the colour of an acid indicator is distinctly

different from that of its conjugate base.

Demonstrate the colour changes of the various indicators present in

Universal Indicator with an effervescent rainbow. Instructions are

available through the

RSC education resources.

Version 3.1 72

Physical chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(a) Chemical equilibrium (continued)

The colour of the indicator is determined by the ratio of

[ ]

In In

H to

−





The theoretical point at which colour change occurs is when

In3

HO K





The colour change is assumed to be distinguishable when

[ ]

In InH and

−





differ by a factor of 10.

The pH range over which a colour change occurs can be estimated

by the expression:

pH p 1K= ±

Suitable indicators can be selected from pH data, including titration

curves.

Version 3.1 73

Physical chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(b) Reaction feasibility

The standard enthalpy of formation,

H∆°

, is the enthalpy change

when one mole of a substance is formed from its elements in their

standard states.

The standard state of a substance is its most stable state at a

pressure of 1 atmosphere and at a specified temperature, usually

taken as 298 K.

The standard enthalpy of a reaction can be calculated from the

standard enthalpies of formation of the reactants and products:

()

()products reactants

HH H∆°=Σ∆° −Σ∆°

RSC education resources, Advanced starters for ten: section 10,

offers editable lesson resources on thermodynamic definitions,

enthalpy, entropy and free energy.

The entropy (S) of a system is a measure of the degree of disorder of

the system.

The greater the degree of disorder, the greater the entropy.

Solids have low disorder and gases have high disorder.

Entropy increases as temperature increases.

There is a rapid increase in entropy at the melting point of a

substance and an even more rapid and larger change in entropy at

the boiling point.

The second law of thermodynamics states that the total entropy of a

reaction system and its surroundings always increases for a

spontaneous process.

Khan Academy has a video that introduces entropy.

Chemguide has useful information relating to entropy:

♦ an introduction to entropy

♦ taking entropy changes further, which links to free energy

A fun flash animation of entropy using an Einstein quote

is available

from the University of Toronto.

An audio discussion of the second law of thermodynamics is

available for download from BBC Radio 4 — In Our Time

Version 3.1 74

Physical chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(b) Reaction feasibility (continued)

Heat energy released by the reaction system into the surroundings

increases the entropy of the surroundings.

Heat energy absorbed by the reaction system from the surroundings

decreases the entropy of the surroundings.

The third law of thermodynamics states that the entropy of a perfect

crystal at 0 K is zero.

The standard entropy of a substance is the entropy value for the

substance in its standard state.

The change in standard entropy for a reaction system can be

calculated from the standard entropies of the reactants and products:

()SS S∆°=Σ° −Σ°(products) reactants

RSC education resources has details for the endothermic solid-solid

reaction between barium hydroxide and ammonium chloride.

Chemicool has ideas and examples of other spontaneous

endothermic reactions.

The change in free energy for a reaction is related to the enthalpy

and entropy changes:

G H TS∆ °=∆ °− ∆ °

If the change in free energy (

G∆°

) between reactants and products is

negative, a reaction may occur and the reaction is said to be feasible.

A feasible reaction is one that tends towards the products rather than

the reactants. This does not give any indication of the rate of the

reaction.

Education in Chemistry magazine provides an article outlining an

experiment involving exploding soap bubbles that can be used to link

between entropy changes and free energy by calculating the entropy

change for the reaction of methane and oxygen.

Chemguide provides an introduction to Gibbs free energy.

RSC education resources has two problem-solving activities:

♦ Thermodynamics

♦ What makes it go?

Version 3.1 75

Physical chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(b) Reaction feasibility (continued)

The standard free energy change for a reaction can be calculated

from the standard free energies of formation of the reactants and

products using the relationship:

()

(products) reactantsGG G∆°=Σ∆° −Σ∆°

The feasibility of a chemical reaction under standard conditions can

be predicted from the calculated value of the change in standard free

energy (

G∆°

The temperatures at which a reaction may be feasible can be

estimated by considering the range of values of

for which

0.G∆ °<

Under non-standard conditions any reaction is feasible if

G∆

negative.

At equilibrium,

0G∆=

A reversible reaction will proceed spontaneously until the composition

is reached where

0G∆=

Carry out an experiment to verify a thermodynamic prediction using,

for example, NaHCO

(s).

The rate of a chemical reaction normally depends on the

concentrations of the reactants.

RSC education resources, Advanced starters for ten: section 1, offers

editable lesson resources on kinetics.

Version 3.1 76

Physical chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

Orders of reaction are used to relate the rate of a reaction to the

reacting species.

If changing the concentration of a reactant

has no effect on the

rate of the reaction, then the reaction is zero order with respect to

If doubling the concentration of a reactant

doubles the rate of the

reaction, then the reaction is first order with respect to

. The rate

can be expressed as:

[ ]

rate kA=

where

is the rate constant and

[ ]

is the

concentration of reactant

in mol l

-1

Chemguide has information on orders of reaction and rate equations

and order of reaction and organic mechanisms.

A video tutorial is also available on Khan Academy.

If doubling the concentration of a reactant

increases the rate of the

reaction fourfold, then the reaction is second order with respect to

The rate can be expressed as:

[

]

rate kA=

The order of a reaction with respect to any one reactant is the power

to which the concentration of that reactant is raised in the rate

equation.

The overall order of a reaction is the sum of the powers to which the

concentrations of the reactants are raised in the rate equation.

Version 3.1 77

Physical chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

The order of a reaction can only be determined from experimental

data.

The rate equation and the rate constant, including units, can be

determined from initial rate data for a series of reactions in which the

initial concentrations of reactants are varied. These can be zero, first,

second or third order.

Reactions usually occur by a series of steps called a reaction

mechanism.

The rate of reaction is dependent on the slowest step, which is called

the ‘rate determining step’.

Experimentally determined rate equations can be used to determine

possible reaction mechanisms.

A number of instructions for practical activities are available:

♦ RSC education resources problem-based practical activities

provides problem-solving activities and experimental details for

the propanone and iodine reaction

♦ SSERC describes an experiment to determine the rate constant

and order of reaction using bleach and blue food dye

, and also

provides an opportunity to introduce the practical technique of

colorimetry

♦ the University of Strathclyde has details of an experiment,

determination of the rate of a reaction that includes detailed

kinetics information, as well as the experimental procedure

Version 3.1 78

Organic chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(a) Molecular orbitals

VSEPR cannot explain the bonding in all compounds. Molecular

orbital theory can provide an explanation for more complex

molecules.

There are websites available with information and animations

showing sigma bonds, pi bonds and hybridisation.

Molecular orbitals form when atomic orbitals combine. The number of

molecular orbitals formed is equal to the number of atomic orbitals

that combine. The combination of two atomic orbitals results in the

formation of a bonding molecular orbital and an antibonding orbital.

The bonding molecular orbital encompasses both nuclei. The

attraction of the positively charged nuclei and the negatively charged

electrons in the bonding molecular orbital is the basis of bonding

between atoms. Each molecular orbital can hold a maximum of two

electrons.

In a non-polar covalent bond, the bonding molecular orbital is

symmetrical about the midpoint between two atoms. Polar covalent

bonds result from bonding molecular orbitals that are asymmetric

about the midpoint between two atoms. The atom with the greater

value for electronegativity has the greater share of the bonding

electrons. Ionic compounds are an extreme case of asymmetry, with

the bonding molecular orbitals being almost entirely located around

just one atom, resulting in the formation of ions.

Molecular orbitals that form by end-on overlap of atomic orbitals

along the axis of the covalent bond are called sigma (

) molecular

orbitals or sigma bonds.

RSC education resources has a series of vignettes covering

molecular orbitals, hybridisation, aromaticity and conjugation.

Version 3.1 79

Organic chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(a) Molecular orbitals (continued)

Molecular orbitals that form by side-on overlap of parallel atomic

orbitals that lie perpendicular to the axis of the covalent bond are

called pi (

) molecular orbitals or pi bonds.

The electronic configuration of an isolated carbon atom cannot

explain the number of bonds formed by carbon atoms in molecules.

The bonding and shape of molecules of carbon can be explained by

hybridisation.

Hybridisation is the process of mixing atomic orbitals within an atom

to generate a set of new atomic orbitals called hybrid orbitals. These

hybrid orbitals are degenerate.

In alkanes, the 2s orbital and the three 2p orbitals of carbon hybridise

to form four degenerate sp

hybrid orbitals. These adopt a tetrahedral

arrangement. The sp

hybrid orbitals overlap end-on with other

atomic orbitals to form

bonds.

The bonding in alkenes can be described in terms of sp2

hybridisation. The 2s orbital and two of the 2p orbitals hybridise to

form three degenerate sp2 hybrid orbitals. These adopt a trigonal

planar arrangement. The hybrid sp2 orbitals overlap end-on to form

bonds. The remaining 2p orbital on each carbon atom of the

double bond is unhybridised and lies perpendicular to the axis of the

bond. The unhybridised p orbitals overlap side-on to form

bonds.

ChemTube3D, available through RSC education resources, contains

interactive 3D models for some important organic molecules including

methane, ethane, ethyne and benzene. The model view can be

altered to show the hybrid orbitals.

Version 3.1 80

Organic chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(a) Molecular orbitals (continued)

The bonding in benzene and other aromatic systems can be

described in terms of sp

hybridisation. The six carbon atoms in

benzene are arranged in a cyclic structure with

bonds between the

carbon atoms. The unhybridised p orbitals on each carbon atom

overlap side-on to form a

molecular system, perpendicular to the

plane of the

bonds. This

molecular system extends across all

six carbon atoms. The electrons in this system are delocalised.

The bonding in alkynes can be described in terms of sp hybridisation.

The 2s orbital and one 2p orbital of carbon hybridise to form two

degenerate hybrid orbitals. These adopt a linear arrangement. The

hybrid sp orbitals overlap end-on to form

bonds. The remaining

two 2p orbitals on each carbon atom lie perpendicular to each other

and to the axis of the

bond. The unhybridised p orbitals overlap

side-on to form two

bonds.

Molecular orbital theory can be used to explain why organic

molecules are colourless or coloured. Electrons fill bonding molecular

orbitals, leaving higher energy antibonding orbitals unfilled. The

highest bonding molecular orbital containing electrons is called the

highest occupied molecular orbital (HOMO). The lowest antibonding

molecular orbital is called the lowest unoccupied molecular orbital

(LUMO).

Absorption of electromagnetic energy can cause electrons to be

promoted from HOMO to LUMO.

Most organic molecules appear colourless because the energy

difference between HOMO and LUMO is relatively large. This results

in absorption of light from the ultraviolet region of the spectrum.

Khan Academy has a series of videos covering molecular orbitals,

HOMO and LUMO, and UV/Vis spectroscopy in organic molecules as

well as explaining the link between conjugation and colour in organic

molecules. These videos compare the absorptions of molecules with

different degrees of conjugated systems.

ChemTube3D, available through RSC education resources, has

many useful resources including a graphic showing the difference in

energy between HOMO and LUMO in linear polyenes as well as

models showing the conjugation in a number of dyes.

A PowerPoint presentation introducing molecules and colour is a

resource produced by Education Scotland, and available on the

Science NQ GLOW portal.

Version 3.1 81

Organic chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(a) Molecular orbitals (continued)

Some organic molecules contain chromophores. A chromophore is a

group of atoms within a molecule that is responsible for absorption of

light in the visible region of the spectrum. Light can be absorbed

when electrons in a chromophore are promoted from the HOMO to

the LUMO.

Chemistry in your cupboard is a resource available on RSC

education resources, and links the action of the stain remover Vanish

to the structure of coloured organic molecules, providing a real-life

example of the importance of understanding the chemistry of colour.

Chromophores exist in molecules containing a conjugated system —

a system of adjacent unhybridised p orbitals that overlap side-on to

form a molecular orbital across a number of carbon atoms. Electrons

within this conjugated system are delocalised. Molecules with

alternating single and double bonds, and aromatic molecules have

conjugated systems.

The more atoms in the conjugated system the smaller the energy gap

between HOMO and LUMO. A lower frequency of light (longer

wavelength, lower energy) is absorbed by the compound. When the

wavelength of light absorbed is in the visible region, the compound

will exhibit the complementary colour.

Colourful Chemistry infographics from RSC education resources has

a visually stimulating and informative infographic about colours of

organic molecules including the colours of autumn leaves, poinsettia

plants and glow sticks.

The Science of Sunscreen infographic from RSC

education

resources has information about organic molecules with conjugated

systems that are used to absorb UV light.

Compounds highlighting the effect of increasing the length of the

conjugated system on the colour can be compared. For example,

vitamin A (yellow) can be compared with β-carotene (orange).

Ninhydrin reacts with amino acids and forms a highly conjugated

product that absorbs light in the visible region, and an intense purple

colour (λ

max

750 nm) is observed. This is used in the detection of

amino acids both as a locating agent in chromatography and in

detecting latent fingerprints in crime scenes.

Molecule of the Month:

April 2018 outlines the steps involved in formation of one of these

conjugated products.

Version 3.1 82

Organic chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(a) Molecular orbitals (continued)

Explain the colours observed for the indicator phenolphthalein by

looking at the degree of conjugation in the molecule in both acid and

in base conditions. Structures of the two forms of phenolphthalein

can be seen on the

Elmhurst College website.

An experiment to synthesise phenolphthalein and its derivatives

available through the University of Strathclyde website.

Prepare a variety of dyes and examine their structures to identify the

chromophore. RSC education resources has instructions for the

microscale synthesis of an azo dye and the

microscale synthesis of

indigo-dye. The University of Strathclyde has instructions for the

synthesis of methyl orange.

A number of online resources allow complementary colours to be

explained by demonstrating colour mixing. One example is hosted by

Stanford University

and has sliders to change the colour of light being

transmitted or absorbed.

Candidates can use simple spectroscopes made from DVDs or using

a smart phone — available from SSERC —to view light transmitted or

reflected by coloured compounds. SSERC has

instructions for

making spectroscopes.

Version 3.1 83

Organic chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(b) Synthesis

When an organic reaction takes place, bonds in the reactant

molecules are broken and bonds in the product molecules are made.

The process of bond breaking is known as bond fission.

There are two types of bond fission, homolytic and heterolytic.

Homolytic fission:

♦ results in the formation of two neutral radicals

♦ occurs when each atom retains one electron from the

covalent

bond and the bond breaks evenly

♦ normally occurs when non-polar covalent bonds are broken

Reactions involving homolytic fission tend to result in the formation of

very complex mixtures of products, making them unsuitable for

organic synthesis.

Heterolytic fission:

♦ results in the formation of two oppositely charged ions

♦ occurs when one atom retains both electrons from the

covalent bond and the bond breaks unevenly

♦ normally occurs when polar covalent bonds are broken

Reactions involving heterolytic fission tend to result in far fewer

products than reactions involving homolytic fission, and so are better

suited for organic synthesis.

The University of Bath offers a PowerPoint presentation

that covers

homolytic and heterolytic fission, along with curly arrow notation, and

definitions of nucleophiles and electrophiles.

Version 3.1 84

Organic chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(b) Synthesis (continued)

The movement of electrons during bond fission and bond making can

be represented using curly arrow notation where:

♦ a single-headed arrow indicates the movement of a single

electron

♦ a double-headed arrow indicates the movement of an electron

pair

♦ the tail of the arrow shows the source of the electron(s)

♦ the head of the arrow indicates the destination of the electron(s)

♦ two single-headed arrows starting at the middle of a covalent

bond indicate homolytic bond fission is occurring

♦ a double-headed arrow starting at the middle of a covalent bond

indicates heterolytic bond fission is occurring

♦ an arrow drawn with the head pointing to the space between two

atoms indicates that a covalent bond will be formed between

those two atoms

Chemguide has information on use of curly arrows.

The University of Edinburgh has a curly arrow resource

that provides

activities that test understanding of curly arrows in a number of

different reaction types.

RSC Mechanism Inspector has information and interactive activities

relating to single and double-headed

curly arrows, electrophiles and

nucleophiles.

Education in Chemistry magazine provides an article, ‘

End curly

arrow anxiety’, which has a downloadable exercise to practice curly

arrow mechanisms.

RSC education resources has a set of activity sheets

to aid

understanding of curly arrows and reaction mechanisms.

The University of Southampton has created a set of exam-style self-

assessment questions covering various aspects of

organic reactions

and mechanisms.

In reactions involving heterolytic bond fission, attacking groups are

classified as nucleophiles or electrophiles.

RSC Mechanism Inspector has information and interactive activities

relating to electrophiles and nucleophiles.

RSC education resources has a series of vignettes

covering

mechanism theory including electrophiles, nucleophiles and curly

arrow notation.

Version 3.1 85

Organic chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(b) Synthesis (continued)

Nucleophiles are:

♦ negatively charged ions or neutral molecules that are electron

rich, such as

Cl , Br , OH , CN

−− − −

NH and H O

♦ attracted towards atoms bearing a partial

()

or full positive

charge

♦ capable of donating an electron pair to form a new covalent bond

Electrophiles are:

♦ positively charged ions or neutral molecules that are electron

deficient, such as

and SO

♦ attracted towards atoms bearing a partial

()

−

or full negative

charge

♦ capable of accepting an electron pair to form a new covalent bond

RSC education resources, Starters for ten: chapters 1-11, section 5

‘Organic Chemistry’, offers a selection of easily editable short quizzes

and activities covering curly arrows and electrophiles and

nucleophiles.

The following reaction types can be identified from a chemical

equation:

♦ substitution

♦ addition

♦ elimination

♦ condensation

♦ hydrolysis

♦ oxidation

♦ reduction

♦ neutralisation

National 5 and Higher courses cover some of the reaction types.

Candidates should revise these in the context of this course.

Organic Chemistry

infographics from RSC education resources has a

visually stimulating and informative infographic relating different

reaction types in organic chemistry.

It is important that you give candidates many varied, real-life contexts

for these reactions. Similarities between the different reaction types

should be reinforced and opportunities given to make connections

between reaction types and to develop skills that enable synthetic

routes to be devised for given products.

Version 3.1 86

Organic chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(b) Synthesis (continued)

Synthetic routes can be devised, with no more than three steps, from

a given reactant to a final product.

The possible reactions of a particular molecule can be deduced by

looking at the structural formula.

Which Compound? Which Route?

is available on RSC education

resources, and has an activity to plan a synthetic route for a drug.

RSC education resources has details on Synthesis Explorer

that

allow synthetic routes to be devised, and shows details of reagents

involved. A help sheet for this is

available.

The structure of any molecule can be drawn as a full, shortened or

skeletal structural formula.

In a skeletal structural formula, neither the carbon atoms, nor any

hydrogens attached to the carbon atoms, are shown. The presence

of a carbon atom is implied by a ‘kink’ in the carbon backbone, and at

the end of a line.

Given a full or shortened structural formula for a compound, the

skeletal structural formula can be drawn.

Given a skeletal structural formula for a compound, the full or

shortened structural formula can be drawn.

Molecular formulae can be written from a full, shortened or skeletal

structural formula.

Chemguide provides information about skeletal formula.

Organic chemistry infographics

from RSC education resources has a

visually stimulating and informative infographic showing the different

types of organic formulae.

Molecular drawing packages such as ChemSketch

(a free

downloadable application) can be set to display structures in skeletal

representation if required. Wireframe, stick, ball and stick, and space-

filling representations should all be familiar. Molecules can be rotated

around the x, y and z axes to align any chosen bond horizontally or

vertically; to align any three atoms in a given plane; to zoom in and

out; and to switch on and off atom labels. Molecules sketched in 2D

mode can be converted into 3D representations in ChemSketch.

Candidates can create and manipulate 3D representations of

relatively small molecules (fewer than 10 carbon atoms) containing

common functional groups using Molymods or other molecular model

kits.

Version 3.1 87

Organic chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(b) Synthesis (continued)

ChemSpider has a searchable library of molecules that can be

viewed as skeletal formula or as 3D molecules.

Straight and branched chain alkanes; alkenes; alcohols; carboxylic

acids; aldehydes and ketones; haloalkanes; and ethers can be

systematically named, indicating the position of the functional group

where appropriate, from structural formulae containing no more than

eight carbon atoms in their longest chain. Straight chain esters can

be systematically named from the names of their parent alcohol and

carboxylic acid or their structural formula.

Molecular formulae can be written and structural formulae drawn from

systematic names of straight and branched chain alkanes; alkenes;

alcohols; carboxylic acids; aldehydes and ketones; haloalkanes; and

ethers containing no more than eight carbon atoms in their longest

chain. Molecular formulae can be written and structural formulae

drawn for esters from the systematic name or the structural formulae

of their parent alcohol and carboxylic acid.

The RSC education resource, Gridlocks, has some activities that may

help to revise naming rules from previous courses.

Chemguide has useful information that explains the

naming of all

types of organic compound.

Orgchem101, produced by the University of Ottawa, has an

interactive organic nomenclature quiz

Haloalkanes (alkyl halides) are substituted alkanes in which one or

more of the hydrogen atoms is replaced with a halogen atom.

A podcast on the environmental significance and the chemistry of

haloalkanes is available on RSC education resources.

RSC education resources details a Nuffield Foundation experiment to

synthesise bromoethane from ethanol in a test tube.

Version 3.1 88

Organic chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(b) Synthesis (continued)

Monohaloalkanes:

♦ contain only one halogen atom

♦ can be classified as primary, secondary or tertiary according to

the number of alkyl groups attached to the carbon atom

containing the halogen atom

♦ take part in elimination reactions to form alkenes using a strong

base, such as potassium or sodium hydroxide in ethanol

RSC education resources, Starters for ten: chapters 1-11, section 5

‘Organic Chemistry’, offers a selection of easily editable short quizzes

and activities relating to haloalkanes.

Chemguide has a description of the different kinds of haloalkanes

well as elimination and nucleophilic reactions.

♦ take part in nucleophilic substitution reactions with:

— aqueous alkalis to form alcohols

— alcoholic alkoxides to form ethers

— ethanolic cyanide to form nitriles (chain length increased by

one carbon atom) that can be hydrolysed to carboxylic acids

The University of York has instructions for the reaction involving a

haloalkane and water.

A monohaloalkane can take part in nucleophilic substitution reactions

by one of two different mechanisms.

Education in Chemistry magazine provides an article outlining an

investigation into the mechanism of the

hydrolysis of 2-bromo-2-methylpropane.

1 is a nucleophilic substitution reaction with one species in the rate

determining step and occurs in a minimum of two steps via a trigonal

planar carbocation intermediate.

RSC Mechanism Inspector has information and interactive activities

about nucleophilic substitution reactions.

Version 3.1 89

Organic chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(b) Synthesis (continued)

2 is a nucleophilic substitution reaction with two species in the rate

determining step and occurs in a single step via a single five-centred,

trigonal bipyramidal transition state.

The reaction mechanisms for S

1 and S

2 reactions can be

represented using curly arrows. Steric hindrance and the inductive

stabilisation of the carbocation intermediate can be used to explain

which mechanism will be preferred for a given haloalkane.

The University of Edinburgh has a curly arrow resource that provides

activities that test understanding of the mechanism of nucleophilic

substitution reactions.

The University of Oxford has an interactive quiz to test knowledge of

nucleophilic substitution reactions

and curly arrow mechanisms.

ChemTube3D, available through RSC education resources, has

simple

animated mechanisms and 3D models showing nucleophilic

substitution reactions as well as showing more complex examples.

Khan Academy has videos showing the mechanism of both S

1 and

2 reactions.

RSC education resources, Starters for ten: chapters 1-11, section 5

‘Organic Chemistry’, offers a selection of easily editable short quizzes

and activities relating to substitution reactions and elimination

reactions of haloalkanes.

Version 3.1 90

Organic chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(b) Synthesis (continued)

Alcohols are substituted alkanes in which one or more of the

hydrogen atoms is replaced with a hydroxyl functional group, –OH

group.

RSC education resources, Starters for ten: chapters 1-11, section 5

‘Organic Chemistry’, offers a selection of easily editable short quizzes

and activities testing knowledge of alcohols and their reactions.

Alcohols can be prepared from:

♦ haloalkanes by substitution

♦ alkenes by acid-catalysed hydration (addition)

♦ aldehydes and ketones by reduction using a reducing agent such

as lithium aluminium hydride

Reactions of alcohols include:

♦ dehydration to form alkenes using aluminium oxide, concentrated

sulfuric acid or concentrated phosphoric acid

♦ oxidation of primary alcohols to form aldehydes and then

carboxylic acids and secondary alcohols to form ketones, using

acidified permanganate, acidified dichromate or hot copper(II)

oxide

♦ formation of alcoholic alkoxides by reaction with some reactive

metals such as potassium or sodium, which can then be reacted

with monohaloalkanes to form ethers

♦ formation of esters by reaction with carboxylic acids using

concentrated sulfuric acid or concentrated phosphoric acid as a

catalyst

RSC education resources provides a range of activities on reactions

of alcohols:

♦ dehydration of ethanol to ethene

using porcelain chips as a

catalyst

♦ preparation of cyclohexene from cyclohexanol (Skills – Block 1,

page 39) with purification by distillation and solvent extraction and

testing the product for unsaturation

♦ oxidation of ethanol – the alcohol is oxidised to ethanal and, with

further oxidation, to ethanoic acid

♦ the ‘breathalyser’ reaction is a quick demonstration of the reaction

used in early forms of breathalysers

♦ a microscale oxidation of alcohols allows the difference in the

oxidation reactions of primary, secondary and tertiary alcohols to

be observed by the addition of acidified dichromate(VI)

♦ properties of alcohols details the reaction of sodium with ethanol

♦ Alcohols (16-19) is a game and resource based on naming,

classifying and identifying the products of oxidation

♦ making esters from alcohols and acids

♦ microscale synthesis of ethyl benzoate

♦ Chemguide, which has an explanation of the properties of

alcohols in relation to hydrogen bonding

Version 3.1 91

Organic chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(b) Synthesis (continued)

♦ formation of esters by reaction with acid chlorides ( ) —

this gives a faster reaction than reaction with carboxylic acids,

and no catalyst is needed

Hydroxyl groups make alcohols polar, which gives rise to hydrogen

bonding. Hydrogen bonding can be used to explain the properties of

alcohols including boiling points, melting points, viscosity and

solubility or miscibility in water.

Ethers can be regarded as substituted alkanes in which a hydrogen

atom is replaced with an alkoxy functional group, –OR, and have the

general structure R' – O – R'', where R' and R'' are alkyl groups.

Ethers are named as substituted alkanes. The alkoxy group is named

by adding the ending ‘oxy’ to the alkyl substituent, and this prefixes

the name of the longest carbon chain.

Ethers can be prepared in a nucleophilic substitution reaction by

reacting a monohaloalkane with an alkoxide.

Due to the lack of hydrogen bonding between ether molecules, they

have lower boiling points than the corresponding isomeric alcohols.

Methoxymethane and methoxyethane are soluble in water. Larger

ethers are insoluble in water due to their increased molecular size.

Ethers are commonly used as solvents since they are relatively inert

chemically and will dissolve many organic compounds.

SSERC has details of the Ether Runway demonstration, which

provides an interesting introduction to ethers, illustrating their

flammability.

ChemistryWorld magazine has a podcast and transcript

providing

some of the history of diethyl ether.

Khan Academy has a video that explains IUPAC naming of ethers

well as describing some of their properties. Another video describes

the

Williamson ether synthesis of an alcohol and alkyl halide using a

strong base such as sodium hydride.

Version 3.1 92

Organic chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(b) Synthesis (continued)

Alkenes can be prepared by:

♦ dehydration of alcohols using aluminium oxide, concentrated

sulfuric acid or concentrated phosphoric acid

♦ base-induced elimination of hydrogen halides from

monohaloalkanes

Chemistry Practical Guide — Support Materials (2012),produced by

Education Scotland and available through SSERC, has details of the

preparation of cyclohexene from cyclohexane using concentrated

phosphoric acid and provides an opportunity to introduce the practical

techniques or distillation and solvent extraction (only one extraction is

carried out in this procedure).

Alkenes take part in electrophilic addition reactions with:

♦ hydrogen to form alkanes in the presence of a catalyst

♦ halogens to form dihaloalkanes

♦ hydrogen halides to form monohaloalkanes

♦ water using an acid catalyst to form alcohols

RSC education resources has a number of experiments and activities

relating to alkenes including:

♦ dehydration of ethanol to ethene

using porcelain chips as a

catalyst

♦ preparation of cyclohexene from cyclohexanol with purification by

distillation and solvent extraction

♦ Starters for ten: chapters 1-11, section 5 ‘Organic Chemistry’

offers a selection of easily editable short quizzes and activities

testing knowledge of electrophilic addition reactions of alkenes,

including reaction mechanisms

RSC Mechanism Inspector has information and interactive activities

about electrophilic addition reactions.

Version 3.1 93

Organic chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(b) Synthesis (continued)

Markovnikov’s rule states that when a hydrogen halide or water is

added to an unsymmetrical alkene, the hydrogen atom becomes

attached to the carbon with the most hydrogen atoms attached to it

already. Markovnikov’s rule can be used to predict major and minor

products formed during the reaction of a hydrogen halide or water

with alkenes.

The reaction mechanisms for the addition of a hydrogen halide and

the acid-catalysed addition of water can be represented using curly

arrows and showing the intermediate carbocation. The inductive

stabilisation of intermediate carbocations formed during these

reactions can be used to explain the products formed.

The reaction mechanism for the addition of a halogen can be

represented using curly arrows and showing the cyclic ion

intermediate.

Carboxylic acids can be prepared by:

♦ oxidising primary alcohols using acidified permanganate, acidified

dichromate and hot copper(II) oxide

♦ oxidising aldehydes using acidified permanganate, acidified

dichromate, Fehling’s solution and Tollens’ reagent

♦ hydrolysing nitriles, esters or amides

Khan Academy has a video that explains Markovnikov’s rule, using

curly arrows and inductive stabilisation of carbocation intermediates.

Chemguide has mechanisms for electrophilic addition reactions

alkenes with hydrogen halides and halogens.

The Khan Academy video hydration of an alkene

shows the

mechanism for the reaction of an alkene with water and a sulphuric

acid catalyst.

The University of Edinburgh has a curly arrow resource

that provides

activities that test understanding of the mechanism of electrophilic

addition reactions of alkenes.

Version 3.1 94

Organic chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(b) Synthesis (continued)

Reactions of carboxylic acids include:

♦ formation of salts by reactions with metals or bases

♦ condensation reactions with alcohols to form esters in the presence

of concentrated sulfuric or concentrated phosphoric acid

♦ reaction with amines to form alkylammonium salts that form

amides when heated

♦ reduction with lithium aluminium hydride to form primary alcohols

RSC education resources provides a range of resources relating to

carboxylic acids:

♦ Advanced starters for ten: section 4, ‘Carbonyl Chemistry’

has

easily editable short quizzes on reactions of carboxylic acids

♦ oxidation of ethanol experiment

♦ salicylic acid infographic provides information relating to the wide-

ranging use of this carboxylic acid

♦ reactions of ethanoic acid compares the pH of ethanoic acid and

hydrochloric acid as well as their reactions with magnesium and

sodium carbonate

♦ microscale preparation of ethyl benzoate

♦ microscale synthesis of aspirin

♦ synthesis of aspirin, which also provides an opportunity to

introduce important practical techniques including reflux,

recrystallisation, melting point analysis, thin layer chromatography

and % yield calculations. A similar procedure can also be found in

Chemistry Practical Guide — Support Materials (2012), produced

by Education Scotland and available through SSERC

♦ The First Year Undergraduate Chemistry Laboratory Course

Manual 2011-2012 provides experimental details that include use

of important practical techniques (including reflux, vacuum

filtration, recrystallisation, melting point analysis and % yield

calculations) for preparation of the ester propyl ethanoate as well

as the preparation of benzoic acid from methyl benzoate

Version 3.1 95

Organic chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(b) Synthesis (continued)

Chemistry Practical Guide — Support Materials (2012), produced by

Education Scotland and available through SSERC, has details of an

experiment to hydrolyse ethyl benzoate to prepare benzoic acid, and

provides an opportunity to introduce important practical techniques

including reflux, recrystallisation, melting point analysis, thin layer

chromatography and % yield calculations. This guide also contains

experimental details to prepare ethyl ethanoate.

Amines are organic derivatives of ammonia in which one or more

hydrogen atoms of ammonia has been replaced by an alkyl group.

Amines can be classified as primary, secondary or tertiary according to

the number of alkyl groups attached to the nitrogen atom.

Amines react with acids to form salts.

Primary and secondary amines, but not tertiary amines, display

hydrogen bonding. As a result, primary and secondary amines have

higher boiling points than isomeric tertiary amines.

Primary, secondary and tertiary amine molecules can hydrogen-bond

with water molecules, thus explaining the appreciable solubility of the

shorter chain length amines in water.

Amines like ammonia are weak bases and dissociate to a slight extent

in aqueous solution. The nitrogen atom has a lone pair of electrons

which can accept a proton from water, producing hydroxide ions.

RSC education resources, Advanced starters for ten: section 6,

‘Compounds with amine groups’, has easily editable short quizzes on

reactions and properties of amines.

Chemguide has useful information about amines

including

descriptions of the different classifications and their properties and

reactions.

The University of Purdue has some information about

amine-based

drugs and discusses the solubility of some of the available forms.

Version 3.1 96

Organic chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(b) Synthesis (continued)

Benzene (C

) is the simplest member of the class of aromatic

hydrocarbons.

The benzene ring has a distinctive structural formula. The stability of

the benzene ring is due to the delocalisation of electrons in the

conjugated system. The presence of delocalised electrons explains

why the benzene ring does not take part in addition reactions.

Bonding in benzene can be described in terms of sp

hybridisation,

sigma and pi bonds, and electron delocalisation.

A benzene ring in which one hydrogen atom has been substituted by

another group is known as the phenyl group. The phenyl group has the

formula –C

Benzene rings can take part in electrophilic substitution reactions.

Reactions at benzene rings include:

♦ halogenation by reaction of a halogen using aluminium chloride or

iron(III) chloride for chlorination and aluminium bromide or iron(III)

bromide for bromination

♦ alkylation by reaction of a haloalkane using aluminium chloride

♦ nitration using concentrated sulfuric acid and concentrated nitric

acid

♦ sulfonation using concentrated sulfuric acid

ChemistryWorld magazine has a podcast and transcript providing

some of the history of benzene.

Many everyday consumer products have very distinctive smells as a

result of the presence of key aromatic compounds. Create a display

of household products containing these aromatic compounds to

capture interest. Examples could include well known antiseptics and

disinfectants containing tricholorophenol or

4-chloro-3,5-dimethylphenol, or permanent markers containing xylene

or toluene.

ChemGuide provides a good explanation about:

♦ the bonding in benzene

♦ the modern representation of benzene

♦ electrophilic substitution reactions

RSC education resources,

Advanced starters for ten: section 5,

‘Aromatic Chemistry’, has easily editable short quizzes and activities

on reactions and properties of aromatic compounds.

RSC education resources,

Advanced starters for ten: section 5,

‘Aromatic Chemistry’, has easily editable short quizzes and activities

on reactions and properties of aromatic compounds.

Version 3.1 97

Organic chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(b) Synthesis (continued)

There are many important compounds that contain benzene rings.

The RSC education resources provides details about:

♦ aspirin

♦ paracetamol

♦ ibuprofen (Nurofen)

RSC education resources has details of a

micro-scale preparation of

TCP, as well as the nitration of methyl benzoate.

Electrophilic aromatic substitution reactions

, available through the

University of Strathclyde, provides details for carrying out some

electrophilic aromatic substitution reactions and also provides an

opportunity to introduce the practical techniques of recrystallisation,

melting point analysis and thin layer chromatography.

Molecules that have the same molecular formula but different

structural formulae are called isomers.

Khan Academy has a short video that introduces structural and

stereo isomerism.

Structural isomers occur when the atoms are bonded together in a

different order in each isomer.

Candidates can create and manipulate 3D representations of

relatively small molecules (fewer than 10 carbon atoms) using

Molymods or other molecular model kits, to show the difference in

structures of geometric and optical isomers.

Version 3.1 98

Organic chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

Stereoisomers occur when the order of the bonding in the atoms is

the same but the spatial arrangement of the atoms is different in each

isomer. There are two types of stereoisomer, geometric and optical.

Geometric isomers:

♦ can occur when there is restricted rotation around a carbon-

carbon double bond or a carbon-carbon single bond in a cyclic

compound

♦ must have two different groups attached to each of the carbon

atoms that make up the bond with restricted rotation

♦ can be labelled cis or trans according to whether the substituent

groups are on the same side (cis) or on different sides (trans) of

the bond with restricted rotation

♦ have differences in physical properties, such as melting point and

boiling point

♦ can have differences in chemical properties

RSC education resources Starters for ten: chapters 1-11, section 5

‘Organic Chemistry’ offers a selection of easily editable short quizzes

and activities testing knowledge of structural and geometric isomers.

Videos explaining the difference in physical and chemical properties

of geometric isomers are available online.

A useful article produced by the American Chemical Society

discusses saturated, unsaturated and cis and trans fats

, and some of

the health concerns relating to trans fats.

ChemistryWorld magazine has a podcast and transcript

about the

anticancer drug cis-platin.

An experiment to synthesise cis and trans complexes of cobalt

available through the University of Strathclyde.

Optical isomers:

♦ occur in compounds in which four different groups are arranged

tetrahedrally around a central carbon atom (chiral carbon or chiral

centre)

♦ are asymmetric

♦ are non-superimposable mirror images of each other

♦ can be described as enantiomers

The Khan Academy video available through RSC education

resources introduces chirality and provides worked examples of

molecules with and without chiral carbon atoms.

RSC education resources has details of two short activities to look at

the differences in properties of the two optical isomers of limonene as

well as those for carvone (caraway and spearmint). There is also an

experiment to explore the optical rotation of sugars.

Version 3.1 99

Organic chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

♦ have identical physical properties, except for their effect on plane-

polarised light

♦ have identical chemical properties, except when in a chiral

environment such as that found in biological systems (only one

optical isomer is usually present)

♦ rotate plane-polarised light by the same amount but in opposite

directions and so are optically active

♦ when mixed in equal amounts are optically inactive because the

rotational effect of the plane-polarised light cancels out — this is

called a racemic mixture

Candidates can build their own polarimeters. The University of

Strathclyde has instructions for a cardboard box and a coffee cup

polarimeter, as well as a zero cost, technology enabled polarimeter

using a smart phone. Stem Learning has details of the RSC Classic

Chemistry Demonstrations No.13, page 26,

The Optical Activity of

Sucrose, which also has instructions for constructing a polarimeter.

ChemTube3D, available through RSC education resources, has a

tutorial that discusses the differences between

chiral and non-chiral

molecules, including an activity in which the molecules can be rotated

to show they are non-superimposable.

The University of Bristol’s, Molecule of the Month, July 2000

, features

thalidomide and discusses the uses of the drug, the enantiomeric

forms and the associated consequences of the use of thalidomide in

pregnant women. Limonene features as

Molecule of the Month:

March 2008.

RSC education resources features

Chemistry in your Cupboard:

Nurofen, which is normally sold as a mixture of two optical isomers,

one of which is an effective pain-killing drug and the other of which is

inactive.

One enantiomer of the drug naproxen is a pain reliever and the other

enantiomer is a liver toxin. Information about the structure and optical

activity of these enantiomers is available online.

Version 3.1 100

Organic chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(d) Experimental determination of structure

In organic chemistry a number of experimental techniques are carried

out to verify the chemical structure of a substance.

The RSC website SpectraSchool provides many resources relating to

spectroscopy techniques, with animations, videos and interactive

spectra.

Spectroscopy in a suitcase

is an RSC outreach activity giving

candidates the opportunity to learn about spectroscopy through

hands-on experience. As well as covering the principles of

spectroscopic techniques, the activities use real-life contexts to

demonstrate the applications of the techniques. There is also a

student resource that introduces spectroscopy, as well as providing

background information on mass spectrometry, infrared spectroscopy

and

H NMR spectroscopy.

RSC education resources,

Advanced starters for ten: section 8,

‘Structure Determination’, has easily editable short quizzes testing

knowledge of functional groups, mass spectrometry and NMR

spectroscopy. Problem-based practical activities —

Compound

confusion, problem 8 offers a problem-solving activity using various

spectroscopic and analytical techniques.

RSC education resources Following a synthetic route

exemplifies the

use of spectroscopy techniques to monitor reactions.

Elemental microanalysis is used to determine the masses of C, H, O,

S and N in a sample of an organic compound in order to determine its

empirical formula.

RSC education resources, Starters for ten: chapters 1-11, section 5

‘Organic Chemistry’, offers a selection of easily editable short quizzes

and activities providing the opportunity to practise empirical formula

calculations.

Version 3.1 101

Organic chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(d) Experimental determination of structure (continued)

An empirical formula shows the simplest ratio of the elements in a

molecule.

ChemCollective, produced by the National Science Foundations, has

a video tutorial: determining the empirical formula from an elemental

analysis that shows a worked example of an empirical formula

calculation from combustion product masses.

Elemental microanalysis can be determined from:

♦ combustion product masses

♦ percentage product by mass

Khan Academy has two videos, empirical formula from mass

composition and another mass composition problem, that show

worked examples of empirical formulae calculations from percentage

product by mass.

Mass spectrometry can be used to determine the accurate gram

formula mass (GFM) and structural features of an organic compound.

In mass spectrometry, a small sample of an organic compound is

bombarded by high-energy electrons. This removes electrons from

the organic molecule generating positively charged molecular ions

known as parent ions. These molecular ions then break into smaller

positively charged ion fragments. A mass spectrum is obtained

showing a plot of the relative abundance of the ions detected against

the mass-to-charge (m/z) ratio.

The mass-to-charge ratio of the parent ion can be used to determine

the GFM of the molecular ion, and so a molecular formula can be

determined using the empirical formula.

The fragmentation data can be interpreted to gain structural

information.

Chemguide has useful information about mass spectrometry

including an outline of the process of obtaining a mass spectrum of a

sample, fragmentation patterns and molecular ions.

A PowerPoint presentation introducing mass spectroscopy is a

resource produced by Education Scotland and is available on the

Science NQ GLOW portal.

Spectroscopy in a suitcase, available through the RSC education

resources website, has a Students mass spectrometry exercise

providing a forensic basis to analysing mass spectra.

Version 3.1 102

Organic chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(d) Experimental determination of structure (continued)

Infrared spectroscopy is used to identify certain functional groups in

an organic compound.

When infrared radiation is absorbed by organic compounds, bonds

within the molecule vibrate (stretch and bend). The wavelengths of

infrared radiation that are absorbed depend on the type of atoms that

make up the bond and the strength of the bond.

A PowerPoint presentation introducing Infrared Spectroscopy is a

resource produced by Education Scotland and available on the

Science NQ GLOW portal.

Chemguide has useful information about infrared spectroscopy

including an outline of the process of obtaining an infrared spectrum,

fingerprint regions and functional group analysis.

In infrared spectroscopy, infrared radiation is passed through a

sample of the organic compound and then into a detector that

measures the intensity of the transmitted radiation at different

wavelengths. The absorbance of infrared radiation is measured in

wavenumbers, the reciprocal of wavelength, in units of cm

-1

Characteristic absorptions by particular vibrations are given in the

data booklet.

RSC education resources has a handout, Modern chemical

techniques — infrared, that contains some spectra that candidates

can analyse.

Khan Academy has a number of videos explaining

infrared

spectroscopy, including practice examples.

Proton nuclear magnetic resonance spectroscopy (proton NMR or

NMR) can give information about the different chemical environments

of hydrogen atoms (protons or

H) in an organic molecule, and about

how many hydrogen atoms there are in each of these environments.

RSC education resources has a handout, Modern chemical

techniques — nuclear magnetic resonance spectroscopy, that

contains some spectra that candidates can analyse.

Khan Academy has a number of videos

explaining

NMR

spectroscopy, including practice examples.

Version 3.1 103

Organic chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(d) Experimental determination of structure (continued)

H nuclei behave like tiny magnets and in a strong magnetic field

some align with the field (lower energy), whilst the rest align against it

(higher energy). Absorption of radiation in the radio frequency region

of the electromagnetic spectrum causes the

H nuclei to ‘flip’ from the

lower to the higher energy alignment. As they fall back from the

higher to the lower energy alignment the emitted radiation is detected

and plotted on a spectrum.

In a

H NMR spectrum the chemical shift,

, (peak position) is related

to the environment of the

H atom and is measured in parts per

million (ppm).

Chemical shift values for

H in different chemical environments are

given in the data booklet.

The area under the peak is related to the number of

H atoms in that

environment and is often given by an integration curve on a

spectrum. The height of an integration curve is proportional to the

number of

H atoms in that environment, and so a ratio of

H atoms in

each environment can be determined.

The standard reference substance used in

H NMR spectroscopy is

tetramethylsilane (TMS), which is assigned a chemical shift value

equal to zero.

H NMR spectra can be obtained using low-resolution or high-

resolution NMR.

RSC education resources has a handout, Modern chemical

techniques — nuclear magnetic resonance spectroscopy, that

contains some spectra that candidates can analyse.

Khan Academy has a number of videos

explaining

NMR

spectroscopy, including practice examples.

Chemguide has useful information about

H NMR spectroscopy,

including an outline of the process of obtaining a spectrum of a

sample, low- and high-resolution spectroscopy and integration of

peaks.

Education Scotland has a number of resources available on the

Science NQ GLOW portal including:

♦ PowerPoint presentations introducing Proton NMR Spectroscopy

♦ learners’ workbooks and answers

♦ an organic spectroscopy structural determination workshop that

provides an opportunity for candidates to use mass, IR and

NMR spectra to determine the structure of a molecule

Version 3.1 104

Organic chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(d) Experimental determination of structure (continued)

High-resolution

H NMR uses higher radio frequencies than those

used in low-resolution

H NMR and provides more detailed spectra.

In a high-resolution

H NMR an interaction with

H atoms on

neighbouring carbon atoms can result in the splitting of peaks into

multiplets. The number of

H atoms on neighbouring carbon atoms

will determine the number of peaks within a multiplet and can be

determined using the n+1 rule, where n is the number of

H atoms on

the neighbouring carbon atom.

Low- and high-resolution

H NMR spectra can be analysed, and low-

resolution

H NMR spectra can be sketched for any given compound.

(e) Pharmaceutical chemistry

Drugs are substances that alter the biochemical processes in the

body.

Drugs that have beneficial effects are used in medicines.

A medicine usually contains the drug plus other ingredients such as

fillers to add bulk or sweeteners to improve the taste.

RSC education resources, Making medicines video, provides a useful

introduction to drug development.

Encyclopaedia Britannica has a good introduction to different types of

drug action

The articles ‘Big picture on drug development’ and ‘

Drug formulation’,

available through Stem Learning, introduces the process of drug

development and formulation.

The Association of the British Pharmaceutical Industry has the

resource making medicines that gives background information about

the drug development process and also has interesting information

about the history of medicine through to development of modern

medicines.

Version 3.1 105

Organic chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(e) Pharmaceutical chemistry (continued)

The RSC Education in Chemistry article ‘Pain relief: from coal tar to

paracetamol’ discusses the development of paracetamol, its mode of

action and the importance of correct doses. The Guardian article,

‘

Does paracetamol do you more harm than good?’, also provides

some useful information.

Drugs generally work by binding to specific protein molecules. These

protein molecules can be found on the surface of a cell (receptor) or

can be specific enzyme molecules within a cell.

Drugs that act on receptors can be classified as agonists or

antagonists.

♦ An agonist mimics the natural compound and binds to the

receptor molecules to produce a response similar to the natural

active compound.

♦ An antagonist prevents the natural compound from binding to the

receptor, and so blocks the natural response from occurring.

Many drugs that act on enzymes are classified as enzyme inhibitors

and act by binding to the active site of the enzyme and blocking the

reaction normally catalysed there.

The Conversation article, ‘Explainer: how do drugs work’, provides a

condensed explanation about agonist and antagonist drugs.

Edinformatics has an article that discusses how drugs work

and

provides examples of enzyme inhibitors, agonist and antagonist

drugs, as well as having 3D models of a number of drugs bound to

active sites.

The British Heart Foundation has short videos with a brief

explanation of how aspirin

prevents blood clots (enzyme inhibition)

forming and how beta blockers work (receptor antagonists).

RSC education resources has details about aspirin

, including a short

explanation of its action as an enzyme inhibitor and the history of its

development. There are also details of experiments to synthesise,

purify, and characterise aspirin that include important practical

techniques such as recrystallisation, melting point and thin layer

chromatography analysis.

The overall shape and size of a drug is such that it interacts with a

receptor binding site or to the active site of an enzyme. The types of

interactions formed can include van der Waals forces and/or ionic

bonds.

Khan Academy has a video, Beta-lactam antibiotics, which discusses

the chemistry of beta-lactam derivatives and how they act as enzyme

inhibitors.

Version 3.1 106

Organic chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(e) Pharmaceutical chemistry (continued)

The structural fragment of a drug molecule that allows it to form

interactions with a receptor binding site or to an enzyme active site

normally consists of different functional groups correctly orientated

with respect to each other.

By comparing the structures of drugs that have similar effects on the

body, the structural fragment that is involved in the drug action can

be identified.

The article ‘Caffeine: The chemistry behind the world’s most popular

drug’ discusses the antagonist nature of caffeine and compares the

structure of caffeine to the natural molecule adenosine.

RSC education resources Nurofen worksheet

provides some

information about how Nurofen acts.

The website Protein Data Bank has a large number of protein

structures to view. For example, the structure of the enzyme

neurominidase

, involved in influenza, is shown with its natural

substrate as well as with two active drugs.

An interactive resource from the RSC education resources is

masterminding molecules. This resource combines learning with

game-play and involves cracking a code to reveal hidden chemical

concepts involved in the design of drugs and medicines.

A PowerPoint presentation, Medicinal Chemistry, is a resource

produced by Education Scotland and available on the Science NQ

GLOW portal. It provides some examples of drugs, their active

structural fragments, and their interactions with the active sites.

World of Molecules

has a selection of 3D drug molecules that can be

viewed, as well as an explanation about the mode of action and the

history of their development. Another resource available gives the

structure of some drug molecules and allows for comparison of the

key functional groups necessary for biological activity.

Explain it with

molecules has information about caffeine.

Version 3.1 107

Researching chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(a) Common chemical apparatus

Candidates must be familiar with the use(s) of the following types of

apparatus:

♦ conical flask

♦ digital balance

♦ pipette with safety filler

♦ burette

♦ volumetric (standard) flask

♦ distillation (round-bottomed) flask

♦ condenser

♦ thermometer

♦ Buchner or Hirsch or sintered glass funnel

♦ glassware with ground glass joints (‘Quickfit’ or similar)

♦ thin-layer chromatography apparatus

♦ colorimeter

♦ melting point

♦ separating funnel

RSC education resources provide details of standard pieces of

laboratory equipment in The interactive lab primer — lab apparatus.

The interactive lab primer — weighing compounds using a balance

available through RSC education resources, contains a video and an

online simulation that allows candidates to become familiar with the

correct use of chemical balances.

Version 3.1 108

Researching chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(b) Skills involved in experimental work

Candidates must be able to:

♦ tabulate data using appropriate headings and units of

measurement

♦ represent data as a scatter graph with suitable scales and labels

♦ sketch a line of best fit (straight or curved) to represent the trend

observed in the data

♦ calculate average (mean) values

♦ identify and eliminate rogue points

♦ qualitatively appreciate the relative accuracy of apparatus used to

measure the volume of liquids

♦ comment on the reproducibility of results where measurements

have been repeated

♦ carry out quantitative stoichiometric calculations

♦ interpret spectral data

♦ appropriately use a positive control, for example a known

substance, to validate a technique or procedure

RSC education resources offer a number of activities related to

experimental work:

♦ a guide to keeping a lab book

gives useful advice to candidates

about how to keep a good lab book to help with planning their

projects

♦ The nature of science: measurement, accuracy and precision

supports the teaching of reproducibility, and identifying rogue

points and uncertainties

A Guide to Practical Work (2012)

, produced by Education Scotland,

is available through SSERC and contains useful information about

errors and uncertainty calculations (that may be useful for candidates

carrying out data analysis as part of their project work).

Why do scientists do what scientist do

describes and explains how to

use a positive control in an experiment. It also gives an introduction

to and video on accuracy, precision, errors and statistics.

Many of the suggested experiments show the appropriate use of a

positive control to validate a technique or procedure.

Chemistry

Practical Guide — Support Materials (2012), produced by Education

Scotland and available through SSERC, has details of the

determination of vitamin C by titration with iodine using a sample of

pure ascorbic as a positive control.

Version 3.1 109

Researching chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

Stoichiometry is the study of mole relationships involved in chemical

reactions.

Chemical equations, using formulae and state symbols, can be

written and balanced to show the mole ratio(s) of reactants and

products, including multi-step reactions.

The mass of a mole of any substance, in grams (g), is equal to the

gram formula mass (GFM) and can be calculated using relative

atomic masses.

Calculations can be performed using the relationship between the

mass and the number of moles of a substance.

For solutions, the mass of solute (grams or g), the number of moles

of solute (moles or mol), the volume of solution (litres or l), or the

concentration of the solution (moles per litre or mol l

-1

), can be

calculated from data provided.

Percentage by mass is the mass of solute made up to 100 cm

solution.

Percentage by volume is the number of cm

of solute made up to 100

of solution.

The unit ppm stands for parts per million and refers to 1 mg per kg or

1 mg per litre.

Integrating stoichiometric calculations throughout the course and

practical work offers the opportunity to link with real-life examples,

leading to deeper understanding.

RSC education resources,

Starters for ten: chapters 1-11, section 1

‘Quantitative Chemistry’, offers a selection of easily editable short

quizzes and activities testing stoichiometric calculations.

Version 3.1 110

Researching chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(c)Stoichiometric calculations (continued)

Calculations can be performed using data, including:

♦ GFM

♦ masses

♦ number of moles

♦ concentrations and volumes of solutions

♦ volumes of gases

♦ reactant excess

♦ theoretical and percentage yield

♦ empirical formulae

Theoretical yields can be calculated and compared with actual yields,

leading to determining the percentage yield. The percentage yield is

reduced by:

♦ mass transfer or mechanical losses

♦ purification of product

♦ side reactions

♦ equilibrium position

Candidates must be able to carry out stoichiometric calculations for

all of the skills and techniques in the course where appropriate.

Possible experiments to determine number of moles, reactant excess

and theoretical and percentage yields include:

♦ preparation of aspirin — the RSC offers two aspirin preparations:

— the Aspirin book

contains details of a number of experiments

relating to aspirin, including the synthesis, recrystallisation,

melting point and TLC analysis of aspirin

— The microscale synthesis of aspirin

provides instructions for

producing small quantities of aspirin that could be used to

determine the percentage yield of aspirin produced

♦ Chemistry Practical Guide — Support Materials (2012)

, produced

by Education Scotland and available through SSERC, has details

of the theory of percentage yield and also has instructions for

experiments that can be used to practise percentage yield

calculations and evaluations:

— preparation of potassium trioxalatoferrate(III) also provides an

opportunity to introduce the practical technique of hot filtration

— preparation of benzoic acid by hydrolysis of ethyl benzoate

also provides an opportunity to introduce the practical

techniques of reflux, recrystallisation, melting point analysis

and thin layer chromatography

Version 3.1 111

Researching chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

♦ the University of Strathclyde

provides details of experiments that

can be used in practising percentage yield calculations and also

involve other practical techniques such as recrystallisation,

melting point and thin layer chromatography:

— synthesis and analysis of aluminium compounds prepared

from Coke cans

— electrophilic aromatic substitution organic photosynthesis

reactions

— preparation of cis- and trans- complexes of cobalt

RSC education resources,

Starters for ten: chapters 1-11, section 1

‘Quantitative Chemistry’, offers a selection of easily editable short

quizzes and activities that includes percentage yield calculations.

(d) Gravimetric analysis

Candidates must be familiar with the technique of gravimetric

analysis, including use of:

♦ an accurate electronic balance, including the tare function

♦ a weighing boat

♦ weighing by difference

♦ the term ‘weighing accurately approximately’

♦ heating to constant mass:

— heating a substance

— allowing to cool in a desiccator to prevent absorption of water

— weighing

Chemistry Practical Guide — Support Materials (2012), produced by

Education Scotland and available through SSERC, contains useful

theory about gravimetric analysis as well as details of the following

experiments:

♦ gravimetric determination of water in hydrated barium chloride by

volatilisation

♦ gravimetric determination of Ni using dimethylglyoxime by

precipitation

Version 3.1 112

Researching chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(d) Gravimetric analysis (continued)

— repeating the steps of heating, cooling and weighing until no

further changes in mass are observed

Gravimetric analysis is used to determine the mass of an element or

compound in a substance.

The substance is converted into another substance of known

chemical composition, which can be readily isolated and purified.

The conversion can occur either through precipitation or volatilisation.

In precipitation conversion the substance undergoes a precipitation

reaction. The precipitate is separated from the filtrate and the filtrate

tested to ensure the reaction has gone to completion. The precipitate

is washed, dried to constant mass and then weighed.

In volatilisation conversion the substance is heated and any volatile

products (often water) are evaporated. The substance is heated to

constant mass and the final mass recorded.

Preparation and characterisation of transition metal-oxalate ligand

complexes, available through the University of Strathclyde, details the

preparation of potassium trioxalatoferrate(III), followed by gravimetric

analysis to determine the water of hydration as well as volumetric

analysis of oxalate and iron(III) content.

Version 3.1 113

Researching chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(e) Volumetric analysis

Candidates must be familiar with use of the technique of volumetric

analysis, including:

♦ preparing a standard solution

♦ accurate dilution

♦ standardising solutions to determine accurate concentration

♦ titrating to obtain concordancy using burettes, pipettes and

volumetric flasks

♦ choosing an appropriate indicator

A solution of accurately known concentration is known as a standard

solution.

A standard solution can be prepared by:

♦ weighing a primary standard accurately

♦ dissolving in a small volume of solvent (usually deionised or

distilled water) in a beaker

♦ transferring the solution and rinsings into a volumetric flask

♦ making up to the graduation mark with solvent

♦ stoppering and inverting

Standard solutions can also be prepared by accurate dilution by

pipetting an appropriate volume of a standard solution into a

volumetric flask, making up to the graduation mark with solvent,

stoppering and inverting.

Chemistry — a practical guide, support materials (2012), produced by

Education Scotland and available through SSERC, contains useful

theory about volumetric analysis as well as details of possible

experiments including:

♦ preparation of a standard solution of 0·1 mol l

-1

oxalic acid

♦ standardisation of a solution of sodium hydroxide using oxalic

acid

♦ determination of the ethanoic acid content of vinegar

♦ preparation of a standard solution of 0·1 mol l

-1

sodium carbonate

♦ standardisation of a solution of hydrochloric acid using sodium

carbonate solution

♦ determination of the purity of marble by back titration

♦ determination of nickel in a nickel(II) salt using EDTA

♦ determination of vitamin C by titration with iodine

The water testing

resources produced by SSERC contain details of

complexometric titrations using EDTA. The Cobalt complexes booklet

has details on the preparation and analysis by titration of a cobalt

complex and also involves vacuum filtration.

Version 3.1 114

Researching chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(e) Volumetric analysis (continued)

A primary standard must:

♦ be available in a high state of purity

♦ be stable when solid and in solution

♦ be soluble

♦ have a reasonably high GFM

Examples of primary standards include:

♦

, Na COsodium carbonate

♦

22 4 2

hydrated oxalic acid, H C O ·2H O

♦

84 4

potassium hydrogen phthalate, KH(C H O )

♦

silver nitrate, AgNO

♦

potassium iodate, KIO

♦

2 27

potassium dichromate, K Cr O

Sodium hydroxide is not a primary standard as it has a relatively low

GFM, is unstable as a solid (absorbs moisture) and unstable as a

solution. Sodium hydroxide solution must be standardised before

being used in volumetric analysis.

RSC education resources has a number of resources relating to

volumetric analysis:

♦ a video with instructions on making a standard solution

♦ the interactive lab primer — standard solution, apparatus guide,

and mass and concentration calculators

♦ the interactive lab primer — titration has a video, apparatus guide

and information relating to pH curves and indicators as well as

instructions for correct use of pipettes and burettes

♦ titration screen experiment provides videos, animations and

interactive quizzes relating to titration, including acid base and

redox titrations

♦ a redox titration using wine video and experiment instructions

The University of Strathclyde details a number of experiments

involving volumetric analysis, including:

♦ preparation and characterisation of transition metal-oxalate ligand

complexes — preparation of potassium trioxaatoferrate(III)

followed by gravimetric analysis to determine the water of

hydration, as well as volumetric analysis of oxalate and iron(III)

content

♦ Build-a-stomach: antacid study — direct and back titration

experiment with antacid treatments

Version 3.1 115

Researching chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(e) Volumetric analysis (continued)

Candidates must be familiar with use of the following types of

volumetric analysis:

♦ acid-base titrations

♦ redox titrations based on reactions between oxidising and

reducing agents

♦ complexometric titrations based on reactions in which complexes

are formed — EDTA is an important complexometric reagent and

can be used to determine the concentration of metal ions in

solution

♦ back titrations used to find the number of moles of a substance by

reacting it with an excess volume of a reactant of known

concentration. The resulting mixture is then titrated to work out

the number of moles of the reactant in excess. From the initial

number of moles of that reactant, the number of moles used in

the reaction can be determined. The initial number of moles of the

substance being analysed can then be calculated. A back titration

is useful when trying to work out the quantity of substance in a

solid with a low solubility

Version 3.1 116

Researching chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(f) Practical skills and techniques

Candidates can carry out practical skills and techniques as individual

activities or combined together during single experiments. Some of

the suggestions listed below allow candidates to use a number of

practical skills and techniques in a single experiment.

The RSC website ‘SpectraSchool

’ provides many resources relating

to spectroscopy techniques with animations, videos and interactive

spectra.

‘Spectroscopy in a suitcase’ is an RSC outreach activity

giving candidates the opportunity to learn about spectroscopy

through hands-on experience. As well as covering the principles of

spectroscopic techniques, the activities use real-life contexts to

demonstrate the applications of the techniques. You can use this to

teach colorimetry. There is also a

student resource that introduces

spectroscopy as well as providing background information the

technique of colorimetry.

Candidates must be familiar with use of the technique of colorimetry,

including:

♦ preparing a series of standard solutions of appropriate

concentration

♦ choosing an appropriate colour or wavelength of filter

complementary to the colour of the species being tested

♦ using a blank

♦ preparing a calibration graph

Challenging medicines resource, available through RSC education

resources, details colorimetric analysis of 2-hydroxybenzoic acid,

aspirin and paracetamol. Also available through RSC

education

resources is challenging plants

that details colorimetric analysis of

soil samples.

Chemistry Practical Guide — Support Materials (2012)

, produced by

Education Scotland and available through SSERC, contains useful

theory about colorimetric analysis as well as instructions for the

determination of manganese in steel experiment.

Version 3.1 117

Researching chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(f) Practical skills and techniques (continued)

Colorimetry uses the relationship between colour intensity of a

solution and the concentration of the coloured species present.

A colorimeter or a spectrophotometer is used to measure the

absorbance of light of a series of standard solutions, and this data is

used to plot a calibration graph.

The concentration of the solution being tested is determined from its

absorbance and by referring to the calibration curve.

The concentration of coloured species in the solution being tested

must lie in the straight line section of the calibration graph.

SSERC provides a method for determination of iron and manganese

in tea using colorimetry.

Colorimetric determination of iron content

, available through the

University of Strathclyde, provides theory as well as instructions for

determination of iron in Irn Bru, iron tablets and spinach.

Candidates must be familiar with use of the technique of distillation.

Distillation is used for identification and purification of organic

compounds.

The boiling point of a compound, determined by distillation, is one of

the physical properties that can be used to confirm its identity.

Distillation can be used to purify a compound by separating it from

less volatile substances in the mixture.

Theory of the organic techniques distillation, heating under reflux,

vacuum filtration, solvent extraction, recrystallisation, melting point

and mixed melting point determination and thin layer chromatography

are available in

Chemistry Practical Guide — Support Materials

(2012), produced by Education Scotland and available through

SSERC.

RSC education resources provides a number of resources for

distillation:

♦ interactive lab primer — distillation

contains a video, animation

and apparatus guide to distillation

♦ extracting limonene from oranges by steam distillation

Version 3.1 118

Researching chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(f) Practical skills and techniques (continued)

Chemistry Practical Guide — Support Materials (2012), produced by

Education Scotland and available through SSERC, contains details of

two experiments that involve distillation:

♦ preparation of ethyl ethanoate

♦ preparation of cyclohexene from cyclohexanol

Oils and spices

, available through the University of Strathclyde,

details the extraction of essential oils by steam distillation followed by

solvent extraction.

Candidates must be familiar with use of the technique of heating

under reflux. Heating under reflux allows heat energy to be applied to

a chemical reaction mixture over an extended period of time without

volatile substances escaping.

When carrying out heating under reflux, the reaction mixture is placed

in a round-bottomed flask with anti-bumping granules and the flask is

fitted with a condenser. The flask is then heated using an appropriate

source of heat.

RSC education resources provides a number of resources for heating

under reflux:

♦ interactive lab primer — heating under reflux

has a video,

animation and apparatus guide

♦ the synthesis of aspirin also provides an opportunity to introduce

other important practical techniques including recrystallisation,

vacuum filtration, melting point analysis, thin layer

chromatography and % yield calculations. A similar procedure is

available in

Chemistry Practical Guide — Support Materials

(2012)

♦ the RSC aspirin screen experiment gives an opportunity to learn

about the synthesis of aspirin before beginning practical work. It

provides videos, animations and interactive quizzes relating to the

synthesis of aspirin, purification by recrystallisation and analysis

by TLC and relates these experiments to the functional groups

and properties of aspirin

Version 3.1 119

Researching chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(f) Practical skills and techniques (continued)

♦ The First Year Undergraduate Chemistry Laboratory Course

Manual 2011-2012 provides experimental details for the

preparation of ester propyl ethanoate and the preparation of

benzoic acid from methyl benzoate, and also provides an

opportunity to include other important practical techniques

(vacuum filtration, recrystallisation, melting point analysis and %

yield calculations)

Chemistry Practical Guide — Support Materials (2012)

, produced by

Education Scotland and available through SSERC, contains details of

an experiment to hydrolyse ethyl benzoate, by heating under reflux,

to prepare benzoic acid. It also provides an opportunity to include

other important practical techniques (recrystallisation, vacuum

filtration, melting point analysis, thin layer chromatography and %

yield calculations). This guide also contains experimental details for

preparation of ethyl ethanoate.

The University of Strathclyde details a number of experiments

involving heating under reflux

♦ preparation and characterisation of methyl esters details

experimental procedures to make two solid methyl esters, and

involves the practical techniques of solvent extraction and melting

point determination as well as providing some spectral data

♦ using an inorganic complex to catalyse an organic molecular

reaction provides an opportunity to carry out vacuum filtration,

solvent extraction and thin layer chromatography

Version 3.1 120

Researching chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(f) Practical skills and techniques (continued)

Candidates must be familiar with use of the technique of vacuum

filtration. Vacuum filtration involves carrying out a filtration under

reduced pressure and provides a faster means of separating a

precipitate from a filtrate. A Büchner, Hirsch or sintered glass funnel

can be used during vacuum filtration.

RSC education resources interactive lab primer — vacuum filtration

contains a video and an apparatus guide.

There are many experiments that could include vacuum filtration. A

selection provided in

Chemistry Practical Guide — Support Materials

(2012) includes:

♦ preparation of potassium trioxalatoferrate(III)

♦ preparation of aspirin

♦ preparation of benzoic acid by hydrolysis of ethyl benzoate

The University of Strathclyde also details the following experiments

that use vacuum filtration

♦ cis- and trans-complexes of cobalt

♦ methyl orange synthesis

♦ electrophilic aromatic substitution reactions provides an

opportunity to introduce the practical techniques of

recrystallisation, melting point analysis and thin layer

chromatography

Version 3.1 121

Researching chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(f) Practical skills and techniques (continued)

Candidates must be familiar with use of the technique of

recrystallisation to purify an impure solid involving:

♦ dissolving an impure solid gently in a minimum volume of a hot

solvent

♦ hot filtration of the resulting mixture to remove any insoluble

impurities

♦ cooling the filtrate slowly to allow crystals of the pure compound

to form, leaving soluble impurities dissolved in the solvent

♦ filtering, washing and drying the pure crystals

The solvent for recrystallisation is chosen so that the compound

being purified is completely soluble at high temperatures and only

sparingly soluble at lower temperatures.

In addition to the previous suggested experiments that could include

recrystallisation, RSC education resources also provides:

♦ interactive lab primer – recrystallisation

, including a video,

animation and an apparatus guide as well as details about hot

filtration

♦ preparation of paracetamol

There are many experiments that could include recrystallisation. A

selection provided in

Chemistry Practical Guide — Support Materials

(2012) includes:

♦ preparation of aspirin

♦ preparation of benzoic acid by hydrolysis of ethyl benzoate

Candidates must be familiar with use of the technique of solvent

extraction. Solvent extraction involves isolating a solute from a liquid

mixture or solution by extraction using an immiscible solvent in which

the solute is soluble.

RSC education resources provides a number of resources for solvent

extraction including:

♦ interactive lab primer — solvent extraction

, which has a video,

animation and apparatus guide

Version 3.1 122

Researching chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(f) Practical skills and techniques (continued)

When carrying out a solvent extraction, the two immiscible solvents

form two layers in the separating funnel. The solute dissolves in both

solvents and an equilibrium establishes between the two layers. The

ratio of solute dissolved in each layer is determined by the equilibrium

constant,

. The lower layer is run off into a container and the upper

layer is poured into a second container. This process is repeated to

maximise the quantity of solute extracted.

The quantity of solute extracted is greater if a number of extractions

using smaller volumes of solvent are carried out rather than a single

extraction using a large volume of solvent.

The solvent used should be:

♦ immiscible with the liquid mixture or solution (usually water)

♦ one in which the solute is more soluble in than the liquid mixture

or solution (usually water)

♦ volatile to allow the solute to be obtained by evaporation of the

solvent

♦ unreactive with the solute

♦ extracting iodine from seaweed by solvent extraction (only one

extraction is carried out in this procedure)

♦ preparation of cyclohexene from cyclohexanol with purification by

distillation and solvent extraction

Chemistry Practical Guide — Support Materials (2012)

, produced by

Education Scotland and available through SSERC, details

experiments that provide an opportunity to introduce the practical

techniques of distillation and solvent extraction (only one extraction is

carried out in both of these experiments):

♦ preparation of cyclohexene from cyclohexane using concentrated

phosphoric acid

♦ preparation of ethyl ethanoate

The University of Strathclyde also details the following experiments

that use solvent extraction

♦ extraction of caffeine from tea provides an opportunity to perform

melting point analysis and percentage yield calculations

♦ plant pigments and pH indicators provides an opportunity to carry

out thin layer chromatography

♦ selective reductions with sodium borohydride provides an

opportunity to monitor reactions using thin layer chromatography

Version 3.1 123

Researching chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(f) Practical skills and techniques (continued)

Candidates must be familiar with use of the techniques of melting

point and mixed melting point determination. The melting point of a

substance is the temperature range over which the solid first starts to

melt, to when all of the solid has melted.

The identity of a pure compound can be confirmed by melting point

analysis and a comparison of the experimentally determined melting

point with a literature or known melting point value.

Determination of the melting point of a compound can give an

indication of the purity of a compound. The presence of impurities in

the compound lowers the melting point and broadens its melting

temperature range due to the disruption in intermolecular bonding in

the crystal lattice.

Determination of a mixed melting point involves mixing a small

quantity of the product with some of the pure compound and

determining the melting point. The melting point value and the range

of the melting temperature can be used to determine if the product

and the pure compound are the same substance.

Candidates must be familiar with use of the technique of thin-layer

chromatography. Chromatography is a technique used to separate

the components present within a mixture. Chromatography separates

substances by making use of differences in their polarity or molecular

size.

In addition to the previous suggested experiments that could include

melting point determination, RSC education resources interactive lab

primer has a video and apparatus guide to

melting point

determination.

As well as learning about the practical technique of melting point

analysis, candidates could explain the effect impurities have on the

melting point of a solid in terms of the strengths of intermolecular

forces of attraction. The University of Rhode Island

explains the effect

impurities have on melting point, in relation to strength of

intermolecular forces.

Version 3.1 124

Researching chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(f) Practical skills and techniques (continued)

Thin-layer chromatography (TLC) uses a fine film of silica or

aluminium oxide spread over glass, aluminium foil or plastic. A small

sample of the mixture being tested is spotted onto the base (pencil)

line of the chromatogram. A solvent dissolves the compounds in the

spot and carries the compounds up the chromatogram. How far the

compounds are carried depends on how soluble the compounds are

in the chosen solvent and how well they adhere to the plate. A

developing agent or ultraviolet light is normally required to visualise

the spots on the chromatogram.

values can be calculated:

distance travelled by the sample

distance travelled by the solvent

Under the same conditions (temperature, solvent, and saturation

levels) a compound always has the same

value (within

experimental error).

The identity of a compound can be confirmed by:

♦ comparing the experimentally determined

values with a

literature or known value determined under the same conditions

♦ making a direct comparison on a TLC plate between the

compound being tested and the pure substance — a co-spot

could be used

In addition to the previous suggested experiments that could include

TLC, RSC education resources interactive lab primer has a video,

animation and apparatus guide to thin layer chromatography

The University of Strathclyde details

electrophilic aromatic

substitution reactions that include instructions for carrying out TLC,

as well as providing IR spectra for analysis.

Version 3.1 125

Researching chemistry

Mandatory knowledge

Suggested learning activities and resources, and/or further

guidance on mandatory knowledge

(f) Practical skills and techniques (continued)

TLC is used to assess the purity of substances. A pure substance,

when spotted and developed on a TLC plate, should appear as a

single spot (some impurities may not be visible by TLC analysis). The

presence of more than one spot shows that impurities are present.

Version 3.1 126

Preparing for course assessment

The course is assessed by a question paper and a project. To help candidates prepare for

the course assessment, you should give them opportunities to practise activities similar to

those expected in the course assessment, for example:

♦ practising question paper techniques and revising for the question paper. To support this

learning, you may find it helpful to refer to: Advanced Higher Chemistry Specimen

Question Paper and Guidance on the use of past papers for Advanced Higher Chemistry

♦ preparing for the project: selecting topics; gathering and researching information/data;

evaluating and analysing findings; developing and justifying conclusions; and presenting

the information/data (as appropriate). You may find it helpful to refer to the Advanced

Higher Chemistry coursework assessment task

Developing skills for learning, skills for life and skills

for work

You should identify opportunities throughout the course for candidates to develop skills for

learning, skills for life and skills for work.

Candidates should be aware of the skills they are developing and you can provide advice on

opportunities to practise and improve them.

SQA does not formally assess skills for learning, skills for life and skills for work.

There may also be opportunities to develop additional skills depending on the approach

centres use to deliver the course. This is for individual teachers and lecturers to manage.

Some examples of potential opportunities to practise or improve these skills are provided

below.

Literacy

Writing means the ability to create texts which communicate ideas, opinions and information,

to meet a purpose and within a context. In this context, ‘texts’ are defined as word-based

materials (sometimes with supporting images) which are written, printed, Braille or displayed

on screen. These are technically accurate for the purpose, audience and context.

Version 3.1 127

1.1 Reading

Candidates understand and interpret a variety of scientific texts.

1.2 Writing

Candidates use skills to effectively communicate key areas of chemistry, make informed

decisions and explain, clearly, chemistry issues in various media forms. Candidates have the

opportunity to communicate applied knowledge and understanding throughout the course.

There are opportunities to develop the literacy skills of listening and reading when gathering

and processing information in chemistry.

Numeracy

This is the ability to use numbers in order to solve problems by counting, doing calculations,

measuring, and understanding graphs and charts. This is also the ability to understand the

results.

Candidates extract, process and interpret information presented in numerous formats

including tabular and graphical. Practical work provides opportunities to develop time

management and measurement skills.

2.1 Number processes

Number processes means solving problems through: carrying out calculations, when dealing

with data and results from experiments/investigations and class work; making informed

decisions based on the results of these calculations, and understanding these results.

2.2 Money, time and measurement

The accuracy of measurements is important when handling data in a variety of chemistry

contexts, including practical and investigative. Candidates should consider uncertainties.

2.3 Information handling

Candidates experience information handling opportunities when dealing with data in tables,

charts and other graphical displays, to draw conclusions with justifications throughout the

course. This involves interpreting the data, and considering its reliability in making reasoned

deductions and informed decisions with justifications.

Thinking skills

This is the ability to develop the cognitive skills of remembering and identifying,

understanding and applying.

The course allows candidates to develop skills of applying, analysing and evaluating.

Candidates can analyse and evaluate practical work and data by reviewing the process,

identifying issues and forming valid conclusions. They can demonstrate understanding and

application of concepts and explain and interpret information and data.

Version 3.1 128

5.3 Applying

Candidates plan experiments and investigations throughout the course and use existing

information to solve problems in different contexts.

5.4 Analysing and evaluating

During practical work, candidates review and evaluate experimental procedure and identify

improvements. Candidates use their judgement when drawing conclusions from experiments.

Analysis is the ability to solve problems in chemistry and make decisions that are based on

available information.

It may involve reviewing and evaluating relevant information and/or prior knowledge to

provide an explanation.

It may build on selecting and/or processing information, so is a higher skill.

5.5 Creating

This is the ability to design something innovative or to further develop an existing thing by

adding new dimensions or approaches. Candidates can demonstrate creativity, in particular,

when planning and designing experiments/investigations. They have the opportunity to be

innovative in their approach, and to make, write, say or do something new.

Candidates also have opportunities to develop the skills of working with others, creating, and

citizenship.

Working with others

Learning activities provide many opportunities, in all areas of the course, for candidates to

work with others. Practical activities and investigations, in particular, offer opportunities for

group work, which is an important aspect of chemistry.

Citizenship

Candidates develop citizenship skills, when considering the applications of chemistry on our

lives, as well as the implications for the environment and society.

Version 3.1 129

Administrative information

Published: April 2021 (version 3.1)

History of changes

Version Description of change Date

2.0

Amendments made in ‘Skills knowledge and understanding’

section:

♦ ‘

Inorganic Chemistry’ section, sub-section ‘(c) transitiona

etals’: information about heterogeneous catalysts,

heterogeneous catalysis and homogeneous catalysis clarified.

♦ ‘

Physical Chemistry’ section, sub-section ‘(b) reacti

easibility’: error in entropy equation corrected.

♦ ‘Organic Chemistry and instrumental analysis’ section, sub-

section ‘(b) synthesis’: reference to Markonikov’s rule clarified.

Course support notes added as appendix.

September

2019

3.0

Error in terminology corrected on p9 and p59 — ‘…in a molecule

or neutral ion’ changed to ‘…in a neutral compound’.

October

2020

3.1

Fixed software formatting error that occurred in version 3.0 on p12

and p15.

April 2021

ote: please check SQA’s website to ensure you are using the most up-to-date version of

this document.

Scottish Qualifications Authority 2014, 2019, 2020, 2021