Preparation of Oxygen Gas from Bleach

1. Preparation of Oxygen Gas from Bleach When bleach is treated with a catalyst the rapid evolution of oxygen gas ensues

2. Demonstration NaClO(aq) • The commercial bleach was a solution of sodium hypochlorite in water • When treated with a small amount of cobalt(II)chloride the hypochlorite decomposed • 2ClO- (aq) • The bubbles given off were the oxygen gas as concluded from • Pine splint test Catalyst O2(g) + 2Cl-(aq)

3. Purpose • To use a catalyst to decompose bleach • To collect the decomposition product • To test for the presence of oxygen gas

4. Concepts 1. Decomposition Reactions 2. Catalysts 3. Collection and Determination of Oxygen

5. 1. Decomposition Reactions • Decomposition reactions are of the kind A-B • In decomposition reactions, a single substance is converted to more than one new substance • In this demonstration hypochlorite ion decomposes into oxygen gas and chloride ion A + B

6. 2. Catalysts • A catalyst is a substance which enables a chemical change to occur • A catalyst assists the reactants to convert to products • The catalyst itself may be used over and over: It itself is not changed • When a catalyst is present it is written over the reaction arrow • Addition of a catalyst will speed the rate of many chemical reactions allowing them to occur faster than they otherwise would

7. 3. Collection and Determination of Oxygen • Oxygen is a gas and is conveniently collected by the displacement of water • A glowing--but not burning--pine splint will burst into flame if oxygen gas is present

8. Conclusions • Oxygen gas was a decomposition product of bleach • A catalyst was used to cause rapid decomposition • Oxygen was easily collected • Oxygen supported combustion reactions • with a glowing pine splint

9. Comments • This reaction is not only a decomposition, but also a redox reaction • Bleach should NEVER be mixed with any household chemicals!!!