Describe the electrolytic refining of copper. Include a labelled diagram.

Electrolytic refining is the most widely used method for refining impure metals like copper. In this process, the impure metal is made the anode, and a thin strip of pure metal is made the cathode. An aqueous solution of a salt of the metal (e.g., acidified copper sulphate for copper) is used as the electrolyte. When an electric current is passed:

• At the anode (impure copper), the impure metal oxidizes, and metal ions (e.g., Cu2+) dissolve into the electrolyte. More reactive impurities also dissolve, while less reactive impurities settle down as 'anode mud'.
• At the cathode (pure copper), the metal ions from the electrolyte gain electrons and deposit as pure metal.

The overall effect is the transfer of pure metal from the anode to the cathode.