Question

Aqueous solution of nickel sulphate contains Ni²⁺ and SO₄²⁻ ions.
(a) Which ion moves towards the cathode?
(b) What is the product at the anode?

Answer 1

(a) Ni²⁺ ions (positively charged) move towards cathode (negatively charged terminal).
(b) Ions migrating to anode would be SO₄^2-, OH^-. The product at anode depends on the nature of electrode.

• If the electrode at anode is reactive, say nickel electrode, neither of the anions get discharged due to the reactive nature of the electrode. Nickel anode itself loses electrons to form nickel ions in the electrolyte.
• If the electrode at anode is inert, say platinum or carbon, the ion that is preferentially discharged at anode is ${\mathrm{OH}}^{-}$ as it is located lower than ${\mathrm{SO}}_4^{2-}$ in the electrochemical series. These ${\mathrm{OH}}^{-}$ ions lose electrons, becoming neutral OH particles and react with themselves to form oxygen gas and water. Oxygen gas is liberated at anode.