Today I’m going to do this common experiment that is used in chemistry classes called the elephant’s toothpaste. Elephant’s toothpaste is a foamy substance caused by the rapid decomposition of hydrogen peroxide. This is often used for classroom demonstrations because it requires only a small number of ingredients and makes a “volcano of foam”.
Things you’ll need: a plastic container (as shown on the picture), potassium iodide, food coloring, latex gloves, dishwasher soap, hydrogen peroxide 6%, and a graduated cylinder.
- Place the graduated cylinder in the middle of the plastic container (it will be very messy so prepare some paper towels).
- Wear the latex gloves and pour 50 ml of hydrogen peroxide into the graduated cylinder.
- Pour food coloring and dishwasher soap into the graduated cylinder.
- Put 2 grams of potassium iodide. The reaction will start.
This is a fun experiment. You could see the liquid just flows out nicely.
The reaction ended in about 30 seconds. Very fun for young kids.
Concentrated (>30%) hydrogen peroxide is first mixed with liquid soap. Then a catalyst, often potassium iodide 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. Often some food coloring is also added before the catalyst to spice up the experiment, and make it more colorful and fun.
This experiment shows the catalyzed decomposition of hydrogen peroxide. Hydrogen peroxide (H2O2) decomposes into water and oxygen gas, but normally the reaction is too slow to be easily perceived or measured:
The iodide ion from potassium iodide acts as a catalyst—it speeds up the reaction without being consumed in the reaction process. The reaction is exothermic; the foam produced is hot. A glowing splint can be used to show that the gas produced is oxygen.