During electrolysis of aqueous copper sulphate solution using platinum electrodes, the blue colour of the electrolytic solution fades and towards the end of the process bubbles appear at the cathode. Why ? Also comment on the change in pH of solution due to electrolysis

Explanation

Dissociation of electrolyte
`CuSO_(4) rarr Cu^(2+) + SO_(4)^(2-)`
`H_(2)O rarr H^(+) + OH^(-)`
Cathode : `Cu^(2+)+ 2e^(-) rarr Cu`
`Cu^(2+)` discharge in preference to `H^(+)` due to low discharge potential. Due to this the blue colour of the solution fades as `Cu^(2+)` ions gradually migrate or discharge at cathode and as the electrolyte or whole `Cu^(2+)` ions are exhausted, `H^(+)` ions get discharged and are liberated as `H_(2)` gas at the cathode.
`:.` Bubbles appear at cathode.
`H^(+) + e^(-) rarr H`
`H + H rarr H_(2)`
In the beginning `OH^(-)` ions get discharged at anode and `H^(+)` ions remain in the solution. Therefore, pH of the solution decreases. Once all `Cu^(+2)` ions are consumed, `H^(+)` ions start getting discharged at cathode. Therefore, pH of the solution increases.