14.3 Catalytic Decomposition of H2O2 I – “Elephant’s Toothpaste”
Subjects: Kinetics, catalysis, exothermic reactions
Description: When a catalyst is added to hydrogen peroxide along with some dish soap, a large amount of foam is produced.
- 1 L graduated cylinder*
- plastic tray (or use sink)
- 50 mL 30% H2O2‡
- dishwashing detergent
- Solid KI or NI (~1/4 spatula)‡
*1L graduated cylinder is located on the prep shelf.
‡The 30% H2O2 is located in the refrigerator. The KI and NaI are located in the general chemical storage cabinets.
Note: Perform this demo in the sink or in an extra demo bin.
1. Place H2O2 in the cylinder.
2. Add the dishwashing detergent drop wise down the side of the cylinder to produce a layer of soap.
3. Add the KI or NaI.
4. The oxygen evolved produces a large volume of foam with the dish soap. The toothpaste-like foam will rise from the graduated cylinder (i.e. elephant’s toothpaste).
The decomposition of H2O2 to O2 and water occurs on its own. The rate of the reaction can be substantially increased with the addition of a catalyst. Several substances, including potassium iodide, sodium iodide and manganese dioxide are known to catalyze the reaction.
Overall reaction: 2H2O2(aq) –> 2H2O(l) + O2(g) + heat
Hydrogen peroxide is catalyzed by iodide ion in a two step prcess shown below. The IO- ion is believed to be the reaction intermediate:
H2O2(aq) + I-(aq) –> H2O(l) + OI-(aq)
H2O2(aq) + OI-(aq) –> H2O(l) + O2(g) + I-(aq)
The oxygen generated creates bubbles in the soap to produce a toothpaste-like foam. A glowing splint can be used to test that the gas produced is oxygen. This experiment demonstrates the concept and utility of catalysts.
Concentrated H2O2 can cause burns. Be sure to wear gloves and goggles when performing this experiment.
The reaction contents can be flushed down the drain with plenty of water.
1. L. Summerlin, J. Ealy; Chemical Demonstrations: A Sourcebook for Teachers; Volume 1; 1985; p. 71.
2. NCSU Department of chemistry lecture demonstration website: