In the process of electrolysis of copper sulphate solution, copper metal is used as electrode. The copper sulphate dissociate as Cu2+ and (SO4 )2- ions. As cation move towards cathode the Cu2+ will move toward catode , gain electrons and deposite there in form of copper metal. (SO4 )2- anode but it dose not lose electrons so water molecules from solution release O2 at anode after the removal of electron. Since there is a loss of copper from the copper sulphate solution.Thus to maintain the concentration of the solution constant copper from the positive electrode(anode) comes into copper sulphate solution.Hence, the concentration of the copper sulphate solution remains the same and also it retain its blue colour.
The reaction at electrodes can be written as:
Cathode reaction: Cu2+(aq) + 2e- → Cu(s)
Anode reaction: 2H2O(l) → O2(g) + 4H+(aq) + 4e-