This experiment is often used as a fun science demo for kids...It is called "Elephant's Toothpaste."

Hydrogen peroxide

is catalytically decomposed by the potasium iodide. By the idodide ion, actually.

Oxygen gas

is rapidly formed. You put a squirt of dish soap and a drop of food coloring into 50 mL of 30% hydrogen peroxide... Then when you add 1 or 2 grams of potassium iodide... the released oxygen gas is trapped in soap bubbles... you get a huge amount of foamy suds!!!

The reaction sequence is as follows:

H202 (aq) + I- (aq) --> H20 (l) + OI- (aq)

H202 (aq) + OI- (aq) --> H20 (l) + O2 (g) + I- (aq)

The iodide ion is not consumed by the reaction, therefore it is a CATALYST.

Hydrogen peroxide mixed with potassium iodide









This is what happens when