Monica Hernandez
Kinetics Lab Iodine Clock
03/30/10
Chemical Kinetics; Iodine clock Lab
90 minutes
MN educational standards 9C.1.3.4.1, 9C.2.1.2.1, 9C.2.1.2.3, 9C.2.1.3.6
Anticipatory set: I will open this lab by talking about the reactions that will take place; what the
limiting reagent is and how the color change will come about. In addition I will discuss the one
variable rule and also have the students predict the affects of temperature and concentration
on the rate of the reaction. I will engage the students and also interest them by having the
prediction, and also talk about the color change and chemical reaction that is occurring
Objective: Students will be able to predict the affect that temperature and concentration have
on the rate of a given reaction.
Input: The information presented will be the reactions and information about limiting
reagents. Some of which the students will try to answer in the prelab worksheet, then we will
go over it as a group in the prelab discussion. The procedure and questions are in the following
lab attachment. The information delivered by this lab is the effect of temperature and
concentration on the rate of a reaction.
Modeling: I will be showing the students written chemical equations that will occur during lab.
No demonstration or examples will be given as this is a lab and they will be conducting it
independently along with their lab partner.
Checking for Understanding: I will check to make sure the students are understating what is
going on by stopping them at the end of the concentration trial, and the end of the
temperature trials, and discussing whether or not their predictions were correct. In addition
there will be questions about the lab on the kinetics unit test.
Guided Practice: I will go around and make sure students are getting reasonable results from
the trials. If they aren’t, then I will observe their lab technique in order to detect errors.
Independent Practice: As homework the students are the take home the post lab, complete
questions and graph results in excel.
Closure: The lesson will be ended the following day by discussing post lab questions and excel
graphs. I will also point out how one may predict rate of reactions by using the excel graphs for
data that they didn’t obtain in lab.
Monica Hernandez
Kinetics Lab Iodine Clock
03/30/10
Pre Lab
-
1. If we need to make a 0.024M KIO3 (Potassium Iodate ) solution, how many grams of
KIO3- would need to be added to 1L of water?
2. If we add 1.7g of NaHSO3 to 1L of water what is the molarity of the solution?
Monica Hernandez
Kinetics Lab Iodine Clock
03/30/10
SAFETY
OVERVIEW
The Iodine Clock Reaction is a “classic”
experiment demonstrating the effects of
concentration and temperature on reaction rate.
In this experiment two solutions are mixed. The
reaction takes place in two steps.
Step 1:
IO3- (aq) + 3HSO3- (aq) → I-(aq) +3SO42- (aq)
+ 3H+(aq)
Step 2:
5I-(aq) + 6H+(aq) + IO3-(aq) → 3I2(aq) +
3H2O(l)
The iodine, I2, produced in Step 2 will react
with starch (not shown in the equations),
producing a deep blue-black solution.
The rate of the entire reaction can be measured
by timing how long it takes before the blue color
appears once the two solutions are mixed.
By altering the concentration of one of the
reactants (Part A) and by changing the reaction
temperature (Part B), the effects of these factors
on reaction rate can be determined.
PURPOSE



To measure the rate of a reaction.
To measure the effect of changing
reactant concentration on reaction rate.
To measure the effect of changing
temperature on reaction rate
Avoid getting either solution on your skin or
clothes. Wash any splashes with cold water.
Wear safety goggles
EQUIPMENT AND MATERIALS
 Solution A (contains IO3- ions)
 Solution B (contains HSO3- & starch)
 distilled water
 ice cubes
 beakers, 250 mL and 100 mL (2)
 graduated cylinders, 10 mL (2)
 LARGE test tubes (2)
 thermometer
 water baths
 timer (stop watch or clock with second
hand)
 safety goggles
 magnetic stirrer, optional
PROCEDURE
Part A. Effect of Concentration
1. For Trial 1 measure exactly 10.0 mL of
solution A and pour into a 100 mL beaker
2. Use a different graduated cylinder to
measure exactly 10.0 mL of solution B and
pour it into a second 100 mL beaker
3. You will begin recording reaction time
as soon as you first mix the two solutions.
One person should record the time of
reaction while the other partner mixes the
solutions. Pour one of the solutions into the
other, then pour the solutions back and forth
sever times to ensure thorough mixing. Then
wait for the completion of the reaction.
4. Record the time at the instant the deep
blue-black color first appears.
Monica Hernandez
Kinetics Lab Iodine Clock
03/30/10
5. You will repeat Steps 1 – 4 using different
concentrations of solution A. Obtain the
dilutions by adding distilled water to Solution
A, according to the following table:
Trial
Solution A
Distilled
(mL)
Water
1
10.0
0.0
2
9.0
1.0
3
8.0
2.0
4
7.0
3.0
5
6.0
4.0
6
5.0
5.0
7
4.0
6.0
8
3.0
7.0
Rinse and dry the beakers and graduated
cylinders between each trial to avoid
contamination/early mixing of reactants.
If time is short, half the class may be assigned
trials 2, 4, 6, 8 and the other half should do
trials 3, 5, 7. All groups should do the 1st trial.
At the end of the lab data should be shared
between groups.
Part B. Effect of Temperature
1. You will follow the same procedure as you
used for Trial 1 of Part A, mixing 10.0 mL of
Solution A with 10.0 mL of Solution B. The
concentrations will be kept constant, but you
will vary the temperature of the solutions before
mixing. As with Part A, different groups of
students may be assigned different temperatures.
2. Class data should be obtained for the
following temperatures.
Each group of students should do trials at four
temperatures:
Set 1: 5°C 15°C 25°C 35°C
Set 2: 10°C 20°C 30°C 40°C
3. Prepare water baths for your set of solutions.
Fill a 250 mL beaker about two third full with
water of the appropriate temperature. For water
baths below room temperature, use ice to chill
the water. For warmer baths use warm water
from the tap or a kettle. There should be enough
water in the beakers so that the solutions in the
test tubes are well beneath the water level in the
baths.
4. As before, measure out exactly 10.0 mL of
Solution A and B, pouring each into their own
test tube. Place the two test tubes in your water
baths, allowing them to remain for about 10
minutes to allow the solution temperatures to
reach the temperature of the water baths. Use the
thermometer to monitor water bath
temperatures. Try to keep the water bath
temperature within 0.5°C of your assigned
temperature. Add more ice or warm water as
necessary. Record your water bath temperature
just before mixing the solutions in the data table.
5. Once the solutions are at the desired
temperatures, prepare to record time and mix the
two solutions. Pour the mixture back and forth
between the two test tubes several times to
ensure mixing. Then place the test tube
containing the mixed solutions back in the water
bath. Record the time it takes from initial mixing
until the deep blue-black color appears. At the
end of the lab, share temperature and reaction
rate data between groups.
Monica Hernandez
Kinetics Lab Iodine Clock
03/30/10
RESULTS
Conclusions and Questions
Results may be recorded in the following data
tables.
Part A. Effect of Concentration
Trial
1
2
3
4
5
6
7
8
Trial
Volume
KIO3
(mL)
Distilled
Water
(mL)
10.0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
Time to
Completion
(s)
1
2
3
4
5
6
7
8
Solution
Temperature
(°C)
2. Based on your results what can you conclude
regarding the effect of concentration on reaction
rate? Use the collision theory to explain this
effect.
3. Based on your results what conclusion can
you make regarding the effect of temperature on
reaction rate? Explain this in terms of the
collision theory.
Part B. Effect of Temperature
Trial
1. Using Excel plot your results for Part A and
Part B on two graphs. Graph A – plot mL
Solution A vs reaction time Graph B – plot
Temperature vs reaction time
Time to
Completion
(s)
Monica Hernandez
Kinetics Lab Iodine Clock
03/30/10
Teachers Lab Guide
Kinetics Lab AP Chemistry
Iodine Clock Reaction
Solutions:
A- 0.024M KIO3- (Potassium Iodate )
Weigh 5.1g of KIO3- (solid) and mix with 1 L of water. Sake vigorously until dissolved.
B- 0.016M NaHSO3 (Sodium Bissulfite) and 1% starch
In large beaker heat .5-1L of water to a boil. Add 10g of Starch (soild). Stir until dissolved.
Weigh 1.7g of NaHSO3 and add to starch solution. Add enough water to make 1 L.

Note to students that the color change of the mixture of solutions A and B will happen rapidly.
(Less than 1 second) It will not be difficult to notice the color change so be ready with your
timing device.