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Lesson 21:

Chemical Kinetics

Concepts conveyed | Materials | Procedure | Resource

Concepts conveyed:

The purpose of this demonstration is display the idea of chemical reactions through the use of an oscillating reaction. This reaction is a visual example of how concentrations, reaction rates (kinetics), and molecular transport all play a role.

Materials:

Solution A: (this solution takes a while to dissolve)
  • 3 mL concentrated sulfuric acid
  • 21.4 g potassium iodate
  • 500 mL water
Solution B:
  • 1.9 g manganese sulfate dihydrate (MnSO4*2H2O)
  • 7.8 g malonic acid
  • 500 mL water
Solution C:
  • 0.5 g starch (add a little water to make a paste)
  • 100 mL boiling water
Solution D:
  • 180 mL of 30% hydrogen peroxide (use protective clothing and caution in handling!)
  • 320 mL water
Other items:
  • 3, 500 mL flasks
  • 3, 100 mL graduated cylinders
  • 1, 100 mL flask
  • 1, 10 mL graduated cylinder
  • 1 glass stirring rod
  • 1, 500 mL beaker

Procedure:

Prepare solutions A, B, C, and D just prior to the class period:

To carry out the reaction pour 90 mL of A, 90 mL of B, 8 mL of C, and 90 mL of D into a 500 mL beaker and stir. The reaction will oscillate from the color blue to yellow or colorless for five minutes or more. Note how when the solution is stationary, one part of the solution changes color and then the rest. It is as if the solution is not homogeneous. Stirring will allow a more homogeneous change.

Oscillating reactions are very complex. There is a great interest in studying them in order to understand how concentration, kinetics, and molecular transport all play a role and how these can be manipulated to control reactions. There are many examples in nature where chemical reactions do not occur homogeneously. Some believe that oscillating reactions serve as simple models to help us understand the heterogeneity of life and its processes.

Resource:

  • Chemistry for Museums: A Manual of Chemistry Demonstrations; Center of Science and Industry: Columbus, OH, 1976; Show #11, Demonstration #5; Project Funded by a National Science Foundation Grant #7423549.