Elephants’ Toothpaste

A tower of foam emerges from a graduated cylinder

Purpose

To observe the rapid decomposition of hydrogen peroxide when treated with a catalyst

Demonstration The hydrogen peroxide had a few

drops of detergent in it

When potassium iodide KI was added it catalyzed the decomposition of the hydrogen peroxide

The oxygen gas bubbled causing the detergent to foam

2H2O2 2H2O + O2

bubble

bubble

bubble

Concepts

1. Decomposition Reactions

2. Peroxides

3. Gases

1. Decomposition Reactions Any reaction of the general form

AB A + B

In a decomposition reaction a single substance breaks into two or more substances

We say the original substance has “decomposed” which means it has broken apart

2. Peroxides A compound which has an oxygen-

oxygen bond

Hydrogen peroxide is a common peroxide

Chemical formula H2O2

Chemical structure

H O O H

3. Gases Occupy much greater volume than

the solid or liquid substances from which they are formed

Expand to fill or escape the container they are in

Will foam in the presence of a detergent as in this demonstration

Conclusions Hydrogen peroxide decomposed to

form oxygen gas and water when treated with a catalyst

When trapped in detergent, the oxygen gas bubbles expanded and a foaming tower was produced

Comments Many different peroxides are

known to exist

Benzoyl peroxide is a peroxide used in acne medication which released oxygen to kill facial bacteria