Question

Predict the products of electrolysis in each of the following:

(i) An aqueous solution of AgNO₃ with silver electrodes. 

(ii) An aqueous solution of AgNO₃ with platinum electrodes. 

(iii) A dilute solution of H₂SO₄ with platinum electrodes. 

(iv) An aqueous solution of CuCl₂ with platinum electrodes.

Answer 1

(i) At cathode: 

The following reduction reactions compete to take place at the cathode 

Ag⁺(aq) + e^- → Ag(s); E^θ = 0.80 V 

H⁺ (aq) + e^- → H₂ (g); E^θ = 0.00V 

The reaction with a higher value of E^θ takes place of the cathode. 

Therefore, deposition of silver will take place at the cathode. 

At anode: The Ag anode is attacked by NO^3- ions. 

Therefore, the silver electrode at the anode dissolves in the solution to form Ag⁺. 

(ii) At cathode: Same as above At anode: Anode is not attackable and hence OH^- ions have lower discharge potential than NO^3- ions and OH^- ions react to give O₂ 

OH^- → OH + e^- 

4OH → 2H₂O + O₂ (g)

(iii) H₂SO₄ → 2H⁺ + SO₂^-4 

HO₂ ⇌ H⁺ + OH^- 

At cathode: 

2H⁺ + 2e^- → H₂ 

At anode: 4OH^- → 2H₂O + O₂ + 4e^- 

i. e., H₂ will be liberated at cathode and O₂ at anode. 

(iv) CuCl₂ → Cu²⁺ + 2Cl^- 

At Cathode: Cu²⁺ ions will be reduced in preference to H⁺ ions 

Cu²⁺ + 2e → Cu At anode: Cl^- ions will be oxidised in preference to OH^- ions. 

2Cl^- → Cl₂ + 2e^- 

i.e., Cu will be deposited on the cathode and Cl₂ will be liberated at the anode.