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UPSC Combined Geo-Scientist

Chemist

  • 2 objective papers
  • 120 questions each
  • 2 h per paper
  • 100 + 300 marks

Prelims Paper II covers chemistry.

UPSC Combined Geo-Scientist, Prelims · 2020 · Paper II, Chemistry · Q70 of 120

Geo-Scientist Prelims 2020 Chemistry Q70: What will be the ratio of mole fractions of O₂ and N₂ dissolved in…

QuestionSolutions / Henry's law

What will be the ratio of mole fractions of O₂ and N₂ dissolved in water at 25˚C? (Given that Henry’s law constant (in torr) for O₂ and N₂ are 3.3 × 10⁷ and 6.5 × 10⁷ respectively at 25˚C; mole fractions of O₂ and N₂ in air are taken as 0.2 and 0.8 respectively)

  1. (a) ~ 0.51
  2. (b) ~0.66
  3. (c) ~0.25
  4. (d) ~0.49

Answer: (d) ~0.49

x = p/KH. x(O₂)/x(N₂) = (0.2/3.3 × 10⁷)/(0.8/6.5 × 10⁷) = (0.2 × 6.5)/(0.8 × 3.3) = 0.49 → (d). O₂ is about twice as soluble as N₂, so dissolved air is O₂-rich.

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