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Starch-Iodine Clock Reaction Mark as Favorite (10 Favorites)

LAB in Reaction Rate. Last updated August 19, 2019.

Summary

In this lab, students perform an iodine clock reaction to determine how concentration and temperature effect the reaction rate.

Grade Level

Middle and high school

AP Chemistry Curriculum Framework

This lab supports the following unit, topic and learning objective:

  • Unit 5: Kinetics
    • Topic 5.5: Collision Model
      • TRA-4.B: Explain the relationship between the rate of an elementary reaction and the frequency, energy, and orientation of molecular collisions.

Objectives

By the end of this lesson, students should be able to

  • measure the rate of reaction.
  • determine the effect of a change in concentration on the rate of a reaction.
  • explain the effect of a change in temperature on the rate of reaction.

Chemistry Topics

This lesson supports students’ understanding of

  • Kinetics

Time

Teacher Preparation: 1 day (letting the vitamin C sit in water overnight)

Lesson: 60 minutes +

Materials

Solution preparation

  • Vitamin C tablet
  • Mortar and pestal
  • 150-mL beaker (3)
  • Water
  • Hot plate
  • 2% iodine
  • 10-mL graduated cylinder (3)
  • 3% hydrogen peroxide
  • Liquid starch

For the students

  • Test tube rack
  • Test tubes (5)
  • Solution A
  • Solution B
  • Water
  • 10-mL graduated cylinder (3)
  • Hot bath
  • Cold bath
  • Thermometer
  • Stop watch

Safety

  • Always wear safety goggles when working with chemicals in a laboratory setting.
  • Students should wash their hands thoroughly before leaving the lab.
  • When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.

Teacher Notes

  • These instructions prepare 65 mL of solution A and 77 mL of solution B. For each group to complete all parts, they each need 46 mL of each solution. Scale up the preparation according to how many groups you’ll have completing the activity.
    • Crush 1,000 mg of vitamin C. Fill a beaker with 60 mL of water and heat it up on a hot plate. Once the water is hot, mix the vitamin C with the water until most of the vitamin C has dissolved. Turn the hot plate off. Let the solution sit for 24 hours.
    • To prepare solution A: After 24 hours has passed, mix 5 mL of the vitamin C solution in a beaker with 60 mL of water and 5 mL of Tincture of iodine (2% iodine).
    • To prepare solution B: Mix 60 mL of warm water with 15 mL of hydrogen peroxide (3%), and 2.5 mL of liquid starch. Allow the solution to cool to room temperature.
  • In each part, students should use a graduated cylinder to measure out the volumes of each solution. They should use one graduated cylinder for solution A and a different graduated cylinder for solution B so the reaction doesn’t begin before the solutions are mixed in the test tube.

For the Student

Lesson

Purpose

  1. To measure the rate of reaction
  2. To measure the effect of a change in concentration of rate of a reaction
  3. To measure the effect on a change in temperature on the rate of reaction

Procedure

In each part, use a graduated cylinder to measure out the volumes. Use one graduated cylinder for solution A and a different graduated cylinder for solution B.

Part I: test how fast the reaction will occur by increasing the amount of solution A

  1. Add 1 mL of solution A to a test tube.
  2. Add 1 mL of solution B to the test tube.
  3. Time how long it takes for the solution to turn color.
  4. To a new test tube, add 2 mL of solution A.
  5. Add 1 mL of solution B to the test tube.
  6. Time how long it takes for the solution to turn color.
  7. Continue following the chart.

Solution A

Solution B

Time (seconds)

1 mL

1 mL

2 mL

1 mL

3 mL

1 mL

4 mL

1 mL

5 mL

1 mL

Part II: test how fast the reaction will occur by increasing the amount of solution B

  1. Add 1 mL of solution A to a test tube.
  2. Add 1 mL of solution B to the test tube.
  3. Time how long it takes for the solution to turn color.
  4. To a new test tube, add 1 mL of solution A.
  5. Add 2 mL of solution B to the test tube.
  6. Time how long it takes for the solution to turn color.
  7. Continue following the chart.

Solution A

Solution B

Time (seconds)

1 mL

1 mL

1 mL

2 mL

1 mL

3 mL

1 mL

4 mL

1 mL

5 mL

Part III: test how fast the reaction will occur by diluting solution A

  1. Add 5 mL of solution A to a test tube.
  2. Add 1 mL of solution B to the test tube.
  3. Time how long it takes for the solution to turn color.
  4. To a new test tube, add 4 mL of solution A.
  5. Add 1 mL of water to the test tube.
  6. Add 1 mL of solution B to the test tube.
  7. Time how long it takes for the solution to turn color.
  8. Continue following the chart.

Solution A

Solution B

Water

Time (seconds)

5 mL

1 mL

0 mL

4 mL

1 mL

1 mL

3 mL

1 mL

2 mL

2 mL

1 mL

3 mL

1 mL

1 mL

4 mL

Part IV: test how fast the reaction will occur by diluting solution B

  1. Add 1 mL of solution A to a test tube.
  2. Add 5 mL of solution B to the test tube.
  3. Time how long it takes for the solution to turn color.
  4. To a new test tube, add 1 mL of solution A.
  5. Add 1 mL of water to the test tube.
  6. Add 4 mL of solution B to the test tube.
  7. Time how long it takes for the solution to turn color.
  8. Continue following the chart.

Solution A

Solution B

Water

Time (seconds)

1 mL

5 mL

0 mL

1 mL

4 mL

1 mL

1 mL

3 mL

2 mL

1 mL

2 mL

3 mL

1 mL

1 mL

4 mL

Part V: test how fast the reaction will occur at different temperatures

  1. Add 2 mL of solution A to a test tube.
  2. Put A into a cold water bath for two minutes.
  3. Take the temperature of the water.
  4. After two minutes, add 2 mL of solution B to the test tube.
  5. Time how long it takes for the solution to turn color.
  6. In a new test tube, add 2 mL of solution A.
  7. Put A into a hot water bath for two minutes.
  8. Take temperature of the water.
  9. After two minutes, add 2 mL of solution B to the test tube.
  10. Time how long it takes for the solution to turn color.
  11. In a new test tube, add 2 mL of solution A.
  12. Take temperature of the air.
  13. Add 2 mL of solution B to the test tube.
  14. Time how long it takes for the solution to turn color.

Solution A

Solution B

Temperature

Time (seconds)

2 mL

2 mL

2 mL

2 mL

2 mL

2 mL

Analysis

  1. Create three graphs showing what happened in part I, part II, and part V.
  2. In part I, as the amount of solution A increased, the rate of reaction changed how?
  3. How long do you think it would take for the reaction to occur if solution A was increased to 6 mL?
  4. In part II, as the amount of solution B increased, the rate of reaction changed how?
  5. How long do you think it would take for the reaction to occur if solution B was increased to 6 mL?
  6. In parts III and IV, did adding water effect the rate of reaction?
  7. In part III, as the amount of water increased and solution A decreased, the rate of reaction changed how?
  8. In part IV, as the amount of water increased and solution B decreased, the rate of reaction changed how?
  9. Was there a difference in the rate of reaction between part III and part IV? What was the difference?
  10. What effect did lowering the temperature have on the reaction?
  11. What effect did raising the temperature have on the reaction?
  12. So in general, how does changing the temperature effect the rate of reaction?
  13. Explain why, in terms of molecular collisions, there was an increase in the reaction rate when the concentrations were increased.
  14. Explain why, in terms of molecular collisions, there was an increase in the reaction rate when temperature was increased.