What electrolysis is

Near the gold shops of almost every town you may have seen travelling traders who offer to gold-plate your gold or silver jewellery on the spot.

If you have not, look carefully at the equipment of such a trader when you next meet one. There is a battery that supplies electricity, wires connected to it, and a vessel holding some solution. One electrode is a thin sheet of gold; the other electrode is the piece of jewellery you gave to be polished. With this equipment the trader gold-plates the jewellery.

In this process the trader lets an electric current pass through the solution he uses, and gold is laid down on the jewellery.

A cell run backwards

Compare this with the zinc-copper cell. There a chemical reaction happened by itself, and the electrons it released were made to flow as a current: chemical energy became electrical energy. In electrolysis the direction is reversed. A battery pushes electrons into the liquid, and they force a chemical change that would not happen on its own: electrical energy becomes chemical energy. The same words apply to both — anode, cathode, oxidation, reduction — so what you learned in 12.1 carries straight over. Only the signs of the electrodes change, as you will see on the next pages.