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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 · 2020 · Mains Paper II

Q4. Barium sulfate solubility product

Question

At 298 K, Δ_fG°/(RT) for BaSO₄(s), Ba²⁺(aq) and SO₄²⁻(aq) is -549.53, -226.21 and -300.34. (i) Calculate thermodynamic Kₛₚ. (ii) Compare with 0.246 mg BaSO₄ dissolved in 0.1 L water, taking M=233.38 g mol⁻¹ and unit activity coefficients. (iii) Explain the difference.

Answer in brief

(i) Kₛₚ=1.047×10⁻¹⁰; (ii) the concentration estimate is 1.111×10⁻¹⁰.

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CoversBarium sulfate solubility productIonic equilibrium