3.17 Uses of electrolysis Purification of copper: Impure copper extracted from its ore by heating the ore with carbon (smelting) – a mixture of copper with other elements and compounds – is purified on an industrial scale using electrolysis. Electrolyte: copper sulphate solution Electrodes: anode: a block of impure copper cathode: a thin sheet of pure copper 1

3.17 Uses of electrolysis Purification of copper: Reactions at the electrodes: Reaction at anode: The copper atoms lose two electrons and become copper ions which dissolve into the solution: Cu(s)  Cu2+(aq) + 2e- Reaction at cathode: The copper ion picks up 2 electrons from the cathode and gets deposited as pure copper: Cu2+(aq) + 2e-  Cu(s) 2

Electrolyte: solution containing ions of the plating metal Electrodes: 3.17 Uses of electrolysis Electroplating: Electroplating uses electrolysis to deposit a thin layer of a metal on the surface of another to improve the appearance and/or the resistance to corrosion of the latter. Electrolyte: solution containing ions of the plating metal Electrodes: anode: the pure metal which is to make up the coating cathode: the object to be plated 3

Electrolysis Electroplating: Uses: Silver or gold plating gives an attractive appearance and is cheaper than making the object out of the pure metal. Electroplating protects the plated metal by preventing contact with air and water so preventing corrosion. Galvanised steel is steel coated with zinc. The protection against rusting works even when the coating gets scratched because zinc is more reactive. 4

Oxidation and reduction Addition of oxygen, eg. burning of magnesium: 2Mg(s) + O2(g)  2MgO(s) Loss of electrons, eg. magnesium atoms turn into magnesium ions by losing two electrons: Mg  Mg2+ + 2e- magnesium atom magnesium ion Reduction: Removal of oxygen, eg. reduction of iron (III) oxide: 2Fe2O3(s)  4Fe(s) + 3O2(g) Gain of electrons, eg. Iron (III) ions are converted into iron atoms by gaining three electrons: Fe3+ + 3e-  Fe iron(III) ion iron atom 5