PURIFYING COPPER
If a current is passed through copper sulphate solution, positive copper ions move from the impure copper anode to the cathode, where they are deposited as pure copper metal.
Electrolysis
Electrolysis involves the input of a direct electric current, via electrodes, to produce chemical change in an electrolyte. Any electrolyte by definition contains ions that are free to move, and they are therefore normally liquids – either liquid salts, such as molten sodium chloride, or solutions in which ions are dissolved.
Copper
The element copper is a lustrous reddish-brown transition metal. It is malleable and ductile, and is a good conductor of electricity. It was first used about 5,000 years ago in the form of bronze (an alloy of copper and tin) to make tools, but was later replaced by iron. It has also been used in coins, and today is used in electrical cables, wires, and other components, and also in plumbing.
Properties and Uses
The reddish-brown colour of copper is due to a thin film of oxide, and when the film is removed the colour of the pure metal is rosy pink. It is an extremely tough metal, and can be drawn out into a thin wire or hammered into a thin leaf. Small impurities considerably reduce this high ductility and malleability. When heated nearly to its melting point it becomes brittle and can be powdered.
Copper is an extremely good electrical conductor, second only to silver, and it is therefore used for electrical wiring. Since it is relatively chemically unreactive, it is also used to make pipes for plumbing. It may be combined with a number of other metals to make a wide range of useful alloys.
Electrolysis
This method is sometimes used for extracting copper from the ore, but is usually employed as a means of refining the already purified metal. Commercial copper refined in this way is one of the purest commercial metals, with a purity of about 99.9 per cent. Ingots of the unrefined metal are placed in copper sulphate, and these form the anodes, while sheets of pure copper function as cathodes. As a current is passed through the solution, the anode is eaten away and pure copper is deposited at the cathodes. The impurities pass into solution, unless they are silver and gold, which settle as slime on the bottom of the tank and can be recovered.