Chemistry Demonstration: Catalytic Decomposition of Hydrogen Peroxide (Elephant’s Toothpaste)

Introduction

Hydrogen peroxide (H₂O₂) naturally decomposes to produce oxygen and water. However, this process takes a very long time. It may be sped up by the addition of a catalyst. In this experiment, we will use the iodide ion (I^–) present in potassium iodide or sodium iodide as a catalyst to speed up the decomposition of hydrogen peroxide. The reaction is also exothermic, meaning that it releases heat.

The catalyzed reactions are shown below:

H₂O_{2 (aq)} + I^–_(aq) –> H₂O_(l) + IO^–_(aq)

IO^–_(aq) + H₂O_{2 (aq)} –> H₂O_(l) + O_{2 (g)}

The overall reaction is as follows:

2 H₂O_{2 (aq)} –> 2 H₂O_(l) + O_{2 (g)}

Materials

• 30% Hydrogen Peroxide (H₂O₂)
• Potassium iodide or Sodium iodide
• Food Coloring
• Liquid dish detergent (Palmolive)
• 1 Liter Graduated Cylinder
• A large basin or tarp to facilitate cleanup
• glowing splint (optional)

Procedure

1. Place the 1 Liter graduated cylinder in the center of the large basin or tarp.
2. Pour 50 mL of 30% hydrogen peroxide into the graduated cylinder. Add two to four drops of food coloring. Add a small layer of liquid dish detergent to the mixture.
3. Prepare a saturated solution of potassium iodide or sodium iodide by adding an excess of salt to deionized water. The supernate of these solutions is used to carry out the reaction.
4. Swirl the contents of the cylinder and quickly add 5 mL of saturated potassium iodide solution before the agitation has subsided. This reaction occurs rapidly, so stand back immediately after adding the potassium or sodium iodide solution.
5. The reaction produces water and oxygen gas. The oxygen gas is trapped in the foam bubbles of the soap solution. To test for the presence of oxygen, you can introduce a glowing splint to the graduated cylinder.

Safety

This experiment utilizes 30% hydrogen peroxide, which is a strong oxidizing agent (household hydrogen peroxide is typically about 3%). Concentrated hydrogen peroxide can cause burns. Wear latex gloves, safety glasses, and avoid contact with the skin and mucous membranes.

A safer version of this demonstration that utilizes 3% (household) hydrogen peroxide instead of 30% hyrogen peroxide is also available. See reference #2 below.

Disposal of Waste Products

All waste products may be safely disposed of down the drain upon addition of plenty of water.

References

1. Conklin, A.R.; Kessinger, A. Demonstration of the catalytic decomposition of hydrogen peroxide. J. Chem. Educ., 1996, 73(9), 838.
2. Trujillo, C.A. A modified demonstration of the catalytic decomposition of hydrogen peroxide. J. Chem. Educ., 2005, 82(6), 855.