Second Method: In the electrochemical series, iron is located above copper. Hence the electrode potential of iron is less than the electrode potential of copper.
Fe2+ + 2e ⇌ Fe
Cu2+ + 2e ⇌ Cu
The reduction potential of the first half-reaction is low and the oxidation potential is high. The reduction potential of the second half-reaction is high. And oxidation potential is low. Hence Fe will be oxidized to Fe and Cu will be reduced to Cu.
Fe → Fe2+ + 2e
Cu2+ + 2e → Cu
Copper sulphate solution contains Cu copper cations. Adding iron to it will cause oxidation of iron and reduction of Cu.
Fe + Cu2+ → Fe2+ + Cu
Fe + CuSO4 → FeSO4 + Cu
As copper(Cu) becomes free, it gets deposited on iron nails.