UPSC Combined Geo-Scientist, Mains · 2016 · Mains Paper II
Q1(k). Electrolysis of copper sulfate
Question
A current of 800 mA passes through dilute CuSO₄ for 20 minutes. Identify the anode and cathode products and calculate their amounts.
Answer in brief
For inert electrodes and quantitative current efficiency: 0.316 g Cu at the cathode and 0.0796 g O₂ at the anode.
Key points
- The charge is Q=It=0.800×1200=960 C; use F=96485 C mol⁻¹.
- Cathode: Cu²⁺ + 2e⁻ → Cu. Thus n_(Cu)=Q/(2F)=4.975×10⁻³ mol and m=0.316 g.
- Inert anode: 2H₂O → O₂ + 4H⁺ + 4e⁻. Thus n_(O₂)=Q/(4F)=2.487×10⁻³ mol, or 0.0796 g.
- Electrode material is unspecified: a copper anode instead dissolves by Cu → Cu²⁺ + 2e⁻, losing about 0.316 g, rather than evolving oxygen under ordinary…
The full model answer
As written for the answer booklet: the diagram carries the working, the lines stay short. Read here only; it is not offered as a download.

CoversElectrolysis of copper sulfateElectrochemistry
All parts of Question 1
- 1(a) Virial equation5 marks
- 1(b) Inclined capillary5 marks
- 1(c) Entropy and diffraction5 marks
- 1(d) Equipartition in hydrogen5 marks
- 1(e) Expansion cooling of helium5 marks
- 1(f) Temperature dependence of equilibrium5 marks
- 1(g) Ammonium chloride pH5 marks
- 1(h) Reverse osmosis5 marks
- 1(i) Rate-law determination5 marks
- 1(j) Monolayer surface area5 marks
- 1(k) Electrolysis of copper sulfate5 marks
- 1(l) Ionization of helium ion5 marks
- 1(m) Photochemical quantum yield5 marks
- 1(n) Momentum in a box5 marks
- 1(o) Formaldehyde electronic transitions5 marks
- 1(p) NMR distinction of ethers5 marks