How are metals refined by the electrolytic process? Describe the electrolytic refining of copper with the help of a neat labeled diagram.

For the refining of an impure metal by the process of electrolysis, a thick block of impure metal is made anode (connected to +ve terminal of the battery) and a thin strip of the pure metal is made cathode (connected to the -ve terminal of the battery). A water-soluble salt (of the metal to be refined) is taken as the electrolyte. On passing current, impure metal dissolves from the anode and goes into the electrolyte solution. And pure metal from the electrolyte deposits on the cathode.

Electrolytic refining of copper: In an electrolytic tank, acidified copper sulphate (CuSO₄ + dilute H₂SO₄₎ solution forms the electrolyte. A block of impure copper is made into an anode by connecting the positive terminal of a power supply (battery). A thin strip of highly pure copper metal is the cathode of the cell. The negative terminal of the power supply is connected to it.

A small electric current is passed through the cell. Atoms from the anode enter the electrolyte. The copper from the anode gets converted into copper sulphide. An equal number of copper atoms from the solution get deposited on the cathode. This is to keep the concentration of the solution constant. Impurities from the anode block either remain in solution or collect below the anode, as they are unable to displace copper from the sulphate solution. The insoluble impurities remain in the electrolyte and are called anode mud.

Copper sulphate solution contains ions of Cu²⁺ and SO₄^2–.

The following reactions take place when an electric current is passed.

At cathode: $Cu^{2^{+}} + 2e^{–} → Cu$

At anode: $Cu - 2e^{-} → Cu^{2^{+}}$

Pure copper is removed from the cathode.