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

Demonstration  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 O 2 (g)+ 2Cl - (aq) Catalyst NaClO(aq)

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

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

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+BA+B

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

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

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

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