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". This sometimes is known as the "Marshmallow Experiment", but is unrelated to the psychological Stanford marshmallow experiment.
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.
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 iodide ion changes the mechanism by which the reaction occurs:
- "Elephant's Toothpaste" (PDF). University of Utah Chemistry Demonstrations. University of Utah. Retrieved 21 March 2014.
- "Elephant's Toothpaste - Kid Version". Steve Spangler Science. Retrieved 21 March 2014.
- "Catalytic Decomposition of H2O2 - Elephant's Toothpaste" (PDF). NCSU Department of Chemistry Lecture Demonstrations. North Carolina State University. Retrieved 21 March 2014.
- "Elephant's Toothpaste (slow motion)". Periodic Table of Videos. The University of Nottingham.
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- The Elephant's Toothpaste Experiment sciencebob.com