Summary

In this demo, students witness two chemicals that take some time to react. The KMnO₄ and glycerin come into contact and appear not to react, but then a flame results. This is an example of an exothermic redox reaction.

Grade Level

High school

AP Chemistry Curriculum Framework

This demonstration supports the following units, topics, and learning objectives:

• Unit 4: Chemical Reactions
  • Topic 4.7: Types of Chemical Reactions
    • TRA-2.A: Identify a reaction as acid-base, oxidation-reduction, or precipitation.
• Unit 6: Thermodynamics
  • Topic 6.1: Endothermic and Exothermic Processes
    • ENE-2.A: Explain the relationship between experimental observations and energy changes associated with a chemical or physical transformation.

Objectives

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

• Recognize that a chemical change doesn’t have to happen immediately.
• Understand that one chemical is giving up electrons and another chemical is accepting them (redox).
• Realize that the resulting flame indicates an exothermic reaction.

Chemistry Topics

This lesson supports students’ understanding of

• Chemical change
• Redox reaction
• Exothermic
• Kinetics

Time

Teacher Preparation: 10 minutes

Lesson: 10 minutes

Materials

• Powdered KMnO₄
• Paper towel
• Water
• Ceramic dish/evaporating dish (optional: use layer of sand)
• Glycerin (glycerol)

Safety

• Always wear safety goggles when handling chemicals in the lab.
• It’s recommended to wear gloves when carrying out this demonstration.
• Students should be warned not to approach the experiment area when the reaction is in progress. It takes a moment for the reaction to begin, so they may be tempted to lean in to get a closer look. Do not allow this to happen.
• The reaction takes between 20 and 60 seconds to get going.
• Always use caution around open flames. Keep flames away from flammable substances.
• An operational fire extinguisher should be in the classroom.
• This demonstration should be completed in the fume hood with the sash closed as sparks may be produced. Alternatively, using a polycarbonate shield to surround the reaction would also be beneficial.

Teacher Notes

• Wet a paper towel and lay it flat on a flame resistant surface.
• Put an evaporating dish upside down on top of the paper towel.
• Pour a silver-dollar sized pile of powdered potassium permanganate onto the middle of the dish.
• Make a divot with a pencil or a spoon so the powder looks like a volcano.
• Fill the opening of the volcano with glycerin.
• The reaction takes between 20 and 60 seconds to get going, and then it will smoke and burst into flames.
• I have noticed that if you add too much glycerin it doesn't react.
• Extensions to the kinetics of the reaction could be explored by changing the size of the divot, or not making a divot at all.