Electroplating
Have you won an award recently? Was it a cup or a trophy with a footballer or netball player on it? If you have, the cup or trophy is most likely on proud display somewhere in your home. Its silver surface will shine and reflect light to make it stand out for all to see.
Perhaps someone in your home won a trophy years ago. It will still shine, if it is kept polished, but bits of the silver may have peeled off. Underneath is a duller, greyer metal. Cups and trophies are rarely made of solid silver. They just have a silver coat. The reason for this is that silver is an expensive metal. Few organisations could afford to award solid silver cups and trophies to every winner so most organisations give silver-coated awards instead.

Imagine you have won a cup. It was first formed from a cheap metal. This was heated until it melted then was poured into a mould. When the metal had cooled and set into a solid again, it was removed from the mould and sent to be electroplated. In this process, a silver coating was added to the cup by using electricity.

Silver does not just exist as a metal: it forms other substances too. One substance is a liquid called silver nitrate. This liquid is used to coat your cup in silver. First, your cup is dipped into the silver nitrate. Simply dipping the cup in the liquid does not work. If you were to pull out the cup after dipping it in the silver nitrate would just drip from it leaving a dull grey surface behind. Electricity is needed to make the silver stick.

The cup in the silver nitrate is connected up to the negative terminal of the electricity supply and a piece of silver is connected to the positive terminal of the electricity supply. The piece of silver is then dipped into the silver nitrate and the current of electricity is switched on. The current of electricity causes some of the silver connected to the positive terminal to dissolve in the silver nitrate. As some of the silver metal dissolves some of the silver in the silver nitrate settles on the cup and forms a coating. The cup is left in the liquid until all of it is covered in a thick coating of silver. This forming of a coating is an irreversible change. The silver will not fall off when the cup is taken out of the liquid. It is bonded to the cheaper metal underneath. Over the years it may get chipped and some of it may eventually flake away but most of it will stay in place to remind you of the proud day you won an award.

Bath taps are covered in shiny metal. Have they been electroplated?
Yes, they have. The metal used is not silver. It is chromium. This metal is used because it has an attractive shine like silver. It is much cheaper than silver and it is also different in that it does not tarnish like silver. Chromium does not rust and was once widely used to coat steel parts such as bumpers and radiator grills on cars.

Is silver cutlery electroplated?
Most of it is electroplated. If it has a silver coating it is called EPNS. These letters stand for Electroplated Nickel Silver. If you look in a catalogue of household items you may find in the cutlery section that some sets of cutlery are EPNS silverware.

Is gold used in the electroplating process?
Yes. Gold is very expensive. By electroplating it on to cheaper metals attractive jewellery can be made which many people can then afford. Gold is used in microprocessors in computers because it does not rust or tarnish and conducts electricity very well. It is placed on the microprocessor by electroplating.

Is electroplating used for any other processes?
Yes. It is used to purify copper. Copper ore contains other substances besides copper. Two of these substances are iron and sulphur. The copper is separated from them by roasting the ore in a furnace. This is an irreversible process but it produces copper with bubbles of gas in it and the copper looks as if it is covered in blisters. This copper is called blister copper and also contains other metals mixed up with it. The blister copper is connected to the positive terminal of the electricity supply and a piece of pure copper is connected to the negative terminal. The two pieces of metal are then dipped in a liquid containing a copper substance and the current of electricity is switched on. This makes the blister copper dissolve in the liquid and copper from the liquid settle on the piece of pure copper. As the blister copper dissolves the metal impurities sink to the bottom of the tank. They are collected because they are expensive metals - gold and silver.

Is electricity used to take metal from their ores?
It is used to take aluminium from its ore. The ore of aluminium is bauxite. It contains a substance called aluminium oxide. This substance is heated strongly until it melts. A powerful current of electricity is then passed through a tank of the liquid aluminium oxide. The current makes the aluminium and oxygen in the aluminium oxide take part in an irreversible change - they separate. The oxygen escapes from the top of the tank as a gas and molten aluminium forms a liquid at the bottom of the tank and is drawn off through a tap to cool and turn into a solid.