UPSC Combined Geo-Scientist, Mains · 2026 · Mains Paper II

Q1(i). Galvanic cell for 2 Cu⁺leftharpoonsCu²⁺+Cu

Question

Construct a galvanic cell in which the following spontaneous reaction will happen. 2 Cu⁺(aq)leftharpoonsCu²⁺(aq)+Cu(s).

Pt | Cu²⁺, Cu⁺ | Cu⁺ | Cu; E^°=0.52-0.153=+0.37 V.

Cu⁺ → Cu²⁺ + e⁻ E^°(Cu²⁺/Cu⁺)=+0.153 V (inert Pt dips in a Cu⁺/Cu²⁺ solution).
Cathode (reduction): Cu⁺ + e⁻ → Cu E^°(Cu+/Cu)=+0.52 V.
Pt | Cu²⁺(aq), Cu⁺(aq) | Cu⁺(aq) | Cu(s); E^°_(cell)=E^°_R-E^°_L=0.52-0.153=0.37 V, positive, so the reaction is spontaneous (K=10^(0.37/0.0591)≈2×10⁶).

The full model answer

Worked out step by step, as it should go in the answer booklet. The solution sheet follows it.

Anode (oxidation): Cu⁺ → Cu²⁺ + e⁻ E^°(Cu²⁺/Cu⁺)=+0.153 V (inert Pt dips in a Cu⁺/Cu²⁺ solution).
Cathode (reduction): Cu⁺ + e⁻ → Cu E^°(Cu+/Cu)=+0.52 V.
Cell: Pt | Cu²⁺(aq), Cu⁺(aq) | Cu⁺(aq) | Cu(s); E^°_(cell)=E^°_R-E^°_L=0.52-0.153=0.37 V, positive, so the reaction is spontaneous (K=10^(0.37/0.0591)≈2×10⁶).

Coverscell notationGalvanic cell for 2 Cu⁺leftharpoonsCu²⁺+Cu