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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 · 2018 · Mains Paper II

Q5. Molar mass from vapour-pressure lowering

Question

Benzene vapour pressure at 60.6° C falls from 53.3 to 51.5 kPa when 19.0 g nonvolatile solute is dissolved in 500.0 g benzene. Find the solute molar mass, taking benzene as 78.0 g mol⁻¹.

Answer in brief

M₂=84.8 g mol⁻¹ using the full ideal-solution Raoult expression.

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