Question

What is refining of metals? Explain with diagram the method of electrolysis by which copper is purified.

Answer 1

The metal obtained by reduction method is not very pure. The method to obtain about hundred percent pure metal by removing impurities present in very small amounts in the metal is called refining.
Refining of copper metal is carried out by the electrolysis method: The rod of impure copper is arranged as the anode and the rod of pure copper is arranged as a cathode. The aqueous solution of copper sulphate is taken as the electrolyte. A little dilute sulphuric acid is added to it. When an electric current is passed through the electrolyte, the proportion in which copper from the anode is dissolved in aqueous solution of copper sulphate, copper in the same proportion from copper sulphate solution is deposited at the cathode. Thus, the copper deposited at the cathode in this way has almost 100% purity.
Anode (Positive pole): $Cu\left(s\right)$ (Impure) $\to$ $C{u}_2+\left(aq\right)+2e^{-}$ (oxidation)
Cathode (Negative pole): $C{u}^{2+}$ (aq) + 2e- $\to$ $Cu\left(s\right)$ (reduction)
Net reaction: $Cu\left(s\right)$ (Impure) $\to$ $Cu\left(s\right)$ (Pure)