Elephant's Toothpaste, Ever Hear of This??

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Did you know that the Elephant toothpaste is a foamy substance and often used for classroom demonstrations to make a "volcano of foam". You can learn more such experiments at Science-In-Box experience zone. 

This reaction is sometimes known as the "Marshmallow Experiment". It creates foam that shoots up out of the bottle. After a minute or so, it begins to come out in a moving stream that looks like toothpaste being squeezed out of a tube. 

Procedure

  1. Mix Concentrated (30%) hydrogen peroxide with liquid soap. 
  2. Add a catalyst, often potassium iodide, to make the hydrogen peroxide decompose very quickly. 
  3. Hydrogen peroxide breaks down into oxygen and water. 
  4. As a small amount of hydrogen peroxide generates a large volume of oxygen, the oxygen quickly pushes out of the container. 
  5. The soapy water traps the oxygen, creating bubbles, and turns into foam.

Chemistry Behind

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:
2H2O2 → 2H2O(l) + O2(g)
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:
H2O2 + I H2O + IO
H2O2 + IO H2O + O2 + I

2H2O2 2H2O(l) + O2(g) ΔrH° = −196 kJ/mol
The reaction is exothermic; the foam produced is hot. Everyone can play with the foam as it is just soap and water with oxygen bubbles. 



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