Elephant’s toothpaste is a foamy substance caused by the rapid decomposition of hydrogen peroxide using potassium iodide or yeast and warm water as a catalyst. How rapidly the reaction proceeds will depend on the concentration of hydrogen peroxide. Because it requires only a small number of ingredients and makes a “volcano of foam”, this is a popular experiment for children to perform in school or at parties.
About 50 ml of concentrated (>30%) hydrogen peroxide is first mixed with liquid soap or dishwashing detergent. Then, a catalyst, often around 10 ml potassium iodide solution or catalase from baker’s yeast, is added to make the hydrogen peroxide decompose very quickly. Hydrogen peroxide breaks down into oxygen and water. As a small amount of hydrogen peroxide generates a large volume of oxygen, the oxygen quickly pushes out of the container. The soapy water traps the oxygen, creating bubbles, and turns into foam. About 5-10 drops of food colouring could also be added before the catalyst to dramatise the effect. How rapidly the reaction occurs will depend on the concentration of hydrogen peroxide used.