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UPSC Combined Geo-Scientist

Chemist

  • 3 descriptive papers
  • 200 marks each
  • 3 h per paper

Mains Paper II covers physical chemistry.

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.

Model answer to Q1(k), 2016 Mains Paper II: solution pages 5 and 6
Solution pages 5 and 6 of 19

CoversElectrolysis of copper sulfateElectrochemistry