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.
AP Chemistry Curriculum Framework
- Big Idea 3: Changes in matter involve the rearrangement and/or reorganization of atoms and/or the transfer of electrons.
- 3.9: The student is able to design and/or interpret the results of an experiment involving a redox titration.
- 3.10 The student is able to evaluate the classification of a process as a physical change, chemical change, or ambiguous change based on both macroscopic observations and the distinction between rearrangement of covalent interactions and noncovalent interactions.
- Big Idea 4: Rates of chemical reactions are determined by details of the molecular collisions.
- 4.1 The student is able to design and/or interpret the results of an experiment regarding the factors (i.e., temperature, concentration, surface area) that may influence the rate of a reaction.
- Big Idea 5: The laws of thermodynamics describe the essential role of energy and explain and predict the direction of changes in matter.
- 5.3 The student can generate explanations or make predictions about the transfer of thermal energy between systems based on this transfer being due to a kinetic energy transfer between systems arising from molecular collisions.
- 5.4 The student is able to use conservation of energy to relate the magnitudes of the energy changes occurring in two or more interacting systems, including identification of the systems, the type (heat versus work), or the direction of energy flow.
- 5.5 The student is able to use conservation of energy to relate the magnitudes of the energy changes when two nonreacting substances are mixed or brought into contact with one another.
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.
This lesson supports students’ understanding of
- Chemical change
- Redox reaction
Teacher Preparation: 10 minutes
Lesson: 10 minutes
- Powdered KMnO4
- Paper towel
- Pie plate
- Glycerin (glycerol)
- 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.
- Wet a paper towel and lay it flat on a flame resistant surface.
- Put a pie pan upside down on top of the paper towel.
- Pour a silver-dollar sized pile of powdered potassium permanganate onto the middle of the pie pan.
- 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.