What is the reaction when hydrogen peroxide, dish washing liquid and potassium iodide are mixed ?

hydrogen peroxide
manganese dioxide
potassium iodide
You're describing the famous 'elephant's toothpaste' demonstration. Take a large (500 mL) graduated cylinder and place about 50 mL of 30% hydrogen peroxide in the bottom. Add a squirt of liquid dishwashing soap. Place the graduated cylinder on a wide tray. Add a teaspoon of powdered potassium iodide and stand back. The reaction is

2 H2O2(aq) O2(aq) + 2 H2O(aq)

A foam of oxygen bubbles and soap will rise quickly up the cylinder and out the top, like toothpaste squirting out of a tube. (Let a little food dye run down the sides of the cylinder before you add the iodide, so the foam comes out of the tube striped like toothpaste.)

You may be wondering why there isn't any iodide in the reaction above. The iodide acts as a catalyst- that is, it speeds up the reaction without being produced or consumed in the reaction. Manganese dioxide can also be used as a catalyst.

This demonstration is potentially dangerous. Wear gloves and goggles. 30% hydrogen peroxide solution can cause serious burns and damage to the eyes. It can also bleach hair and clothing. If you add too much iodide, the peroxide may spray violently out of the top of the tube- and all over you and your audienc.

Related Links

Elephant's Toothpaste (ThinkQuest)
The recipe for the "elephant's toothpaste" demonstration- a classic! This student-constructed site also includes a RealMedia clip of the demonstration in action.
http://library.advanced.org/10429/high/cool/labs/elephantlab.htm (3/22/99)

Author: Fred Senese senese@antoine.frostburg.edu

General Chemistry Online! What is the reaction when hydrogen peroxide, dish washing liquid and potassium iodide are mixed ?

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