What You Need
- empty 20-oz plastic bottle (or other container)
- 3% hydrogen peroxide solution (available at nearly any store)
- packet of active yeast (from the grocery store)
- liquid dishwashing detergent (such as Dawn™)
- warm water
- food coloring (optional, but it looks nice)
- Pour 1/2 cup hydrogen peroxide solution, 1/4 cup dishwashing soap, and a few drops of food coloring into the bottle. Swish the bottle around to mix the ingredients. Set the bottle in a sink or outdoors or some other place where you won't mind getting wet foam everywhere.
- In a separate container, mix a packet of active yeast with a little warm water. Give the yeast about 5 minutes to activate before proceeding to the next step.
- When you are ready to do the demo, pour the yeast mixture into the bottle.
Hydrogen peroxide (H2O2) is a reactive molecule that readily decomposes into water (H2O) and oxygen:
2H2O2 → 2H2O + O2(g)
In this demonstration, yeast catalyzes the decomposition so that it proceeds much more rapidly than normal. The dishwashing detergent captures the oxygen that is released, making foam. Food coloring can color the film of the bubbles so that you get colored foam. In addition to being a nice example of a decomposition reaction and a catalyzed reaction, the elephant toothpaste demo is exothermic, so heat is produced.