Rapid Oxidation

Introduction

Teach oxidation–reduction reactions to your students with an amazing fire and smoke demonstration. By adding glycerin to potassium permanganate students will witness the oxidation of the glycerin by permanganate.

Concepts

• Oxidation–reduction reaction
• Exothermic reaction

Background

Oxidation–reduction reactions are a major class of chemical reactions. An oxidation-reduction, or redox, reaction is defined as any reaction in which electrons are transferred from one substance to another. Oxidation occurs when a substance loses electrons. Because any electrons lost by one reactant must be transferred to another reactant, oxidation and reduction always occurs together. Reduction occurs when a substance gains electrons.

Substances that are used to cause the oxidation or reduction of another substance are called oxidizing and reducing agents. The substance that accepts electrons in a redox reaction is called the oxidizing agent—by accepting electrons, it is itself reduced but it causes the oxidation of another substance. Similarly, the substance that loses electrons in a redox reaction is called the reducing agent because it causes the reduction of another substance.

The equation for the reaction demonstrated is shown in Equation 1.

Materials

Safety Precautions

Potassium permanganate is a powerful oxidizing agent; may react violently with easily oxidized substances and can explode on sudden heating in a closed container. Some people are allergic to glycerin and may experience irritation to their skin and eyes. Contact with strong oxidants (chromium trioxide, potassium chlorate, potassium permanganate) may cause an explosion. The quantities used in this lab are considered to be a safe demonstration when all safety precautions are taken. Wear chemical splash goggles, chemical-resistant gloves and chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory. Follow all laboratory safety guidelines. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. Wash the lab table thoroughly with water to clean up any un-reacted potassium permanganate. All soluble solid products should be disposed of according to Flinn Suggested Disposal Method #26b. All insoluble products should be rinsed with water and then disposed of according to Flinn Suggested Disposal Method #26a.

Procedure

1. Place a safety shield between students and the reaction vessel.
2. Place 15 g of potassium permanganate into a clean evaporating dish.
3. Pour 1 mL of glycerin into the middle of the pile of potassium permanganate. Immediately stand back.
4. The reaction will smoke and then burst into flames within a few minutes. It will occur almost instantaneously for very fine crystals.

Student Worksheet PDF

12544_Student1.pdf

Teacher Tips

• The reaction will start faster by making the size of the potassium permanganate crystals smaller. The finer the crystals, the greater the surface area and the faster the heat will be liberated.
• The crystals can be ground with a DRY mortar and pestle.

Answers to Questions

1. Describe what happened in this demonstration.
   

   A small amount of glycerin was poured into an evaporating dish containing solid potassium permanganate. Almost immediately, the reaction began to smoke and burst into flames.

2. The two chemicals used in this demonstration were potassium permanganate and glycerin. Which do you think was the oxidizing agent?
   

   The oxidizing agent was potassium permanganate.

3. What would happen if the potassium permanganate crystals were smaller?
   

   If the potassium permanganate crystals were smaller, then the reaction would be faster. Smaller crystals means a greater surface area, and greater surgace area allows heat to be released quicker.

4. What is an oxidation–reduction reaction?
   

   An oxidation–reduction (or “redox”) reaction occurs when one or more electrons are transferred between molecules. Oxidation refers to a loss of electrons (and rise in oxidation state), and reduction refers to a gain of electrons (and subsequent decrease in oxidation state).

References

Special thanks to Jim and Julie Ealy, The Peddie School, Hightstown, NJ, who provided us with the instructions for this activity.

Haight, G.P. and D.J. Phillipson, J. Chem. Educ., 1980, 57, 325.

Scheer, R., J. Chem. Educ., 1959, 36, A219.