Question

Explain the electrolysis of copper sulphate solution using a platinum anode and a copper cathode.

Answer 1

When an aqueous solution of CuSO₄ is electrolyzed using an inert platinum anode and an active copper cathode:

Ions present: Cu²⁺, H⁺, \[\ce{SO^2-_4}\] and OH⁻

Reaction at Cathode (Copper electrode): Cu²⁺ ions have a lower discharge potential than H⁺ ions. They move to the cathode, gain electrons, and deposit as reddish-pink copper metal.

\[\ce{Cu^{2+} + 2e- -> Cu}\]

Reaction at Anode (Platinum electrode): OH⁻ ions have a lower discharge potential than \[\ce{SO^2-_4}\] ions. They move to the platinum anode, lose electrons, and evolve as oxygen gas.

\[\ce{OH^- -> OH + e-}\]

\[\ce{4OH -> 2H2O + O2 ^}\]

Observation: The blue colour of the solution fades away gradually because Cu²⁺ ions are continuously removed from the solution and not replaced.