BellevueCollege|Chemistry162LabManual
Chem& 162 ~ Reaction Kinetics: An Iodine Clock Reaction
6
CAUTION: I
2
is toxic and corrosive! It can damage eyes and skin on contact. It is readily
absorbed through skin and harmful if inhaled in high concentrations.
9. Use forceps to remove the stir bar from the beaker. Rinse the stir bar and test tubes with tap water, then
DI water, and then acetone between trials. Place the test tubes upside down to dry.
10. Repeat this process for the other two trials of Run 2, so you will have three reaction times for Run 2.
11. Repeat the procedure for Run 1, 3, 4, or 5 as assigned by your instructor.
12. Write your raw data on the board, or post on the class forum if your class uses one. Copy posted
data into your data table for use in the calculations.
Note: The same test tube B can be used for all trials of Runs 1-3 because the same amounts of
(NH
4
)
2
S
2
O
8
and (NH
4
)
2
SO
4
are used in all three Runs. However, use a different test tube B for each
subsequent Run, Runs 4 and 5, because the composition of the (NH
4
)
2
S
2
O
8
and (NH
4
)
2
SO
4
mixture is
different for these runs.
Part II: Effect of a Catalyst
Repeat Run 2 (at room temperature) one more time, adding one drop of 0.020 M Cu(NO
3
)
2
to the mixture
in the Test Tube B. Since there are no calculations using this result, one trial should be sufficient. Record
your time, and calculate the rate with the catalyst.
Part III: Effect of Temperature and the Activation Energy
Run 2 provides the reaction time at room temperature, and the temperature study requires reaction times for
Run 2 at another temperature . Perform a single run at one of the following temperatures, as assigned by
your instructor: one at least 15°C colder than room temperature, one about 15°C warmer than room
temperature, and another about 25°C warmer than room temperature.
Make sure to do the cold temperature run first and only perform one trial at each temperature.
1. If preparing a cold water bath: Use a small beaker that is large enough to prop up two test tubes. Use
tap water to mostly-fill the beaker, and add small pieces of ice. The test tubes should sit in an ice-water
slurry, but don’t add too much ice. Rather, maintain a cool temperature by adding pieces of ice
periodically as they melt.
2. If preparing a warm water bath: Use a small beaker by mixing the warm water on the hot plate with
an appropriate amount of tap water. Verify that the temperature of the water baths are within the
appropriate ranges.
3. Prepare three each of Test Tubes A and Test Tubes B, as described in Part I for Run 2. Place both
Test Tubes A & B in a water bath containing either an ice-water slurry or warm water, depending on the
desired temperature. Allow the solutions to remain in the water bath (separately, not yet mixed!) until
their temperatures have equilibrated (about 10 minutes), and measure the temperature of Tube A. Make
sure to record into your data table the temperatures of the solutions just before you combine them. Then
combine the mixtures, and time the reaction as before. For the reactions at temperatures above room
temperature, the reaction will occur very quickly.
4. Repeat this for each temperature of water bath.