Moderate

At 60° C, vapour pressure of methanol and water are 84.562 kPa and 19.953 kPa respectively. An aqueous solution of methanol at 60° C exerts a pressure of 39.223 kPa; the liquid phase and vapour phase mole fractions of methanol are 0.1686 and 0.5714 respectively. Activity co-efficient of methanol is__________________?

Correct answer: A. 1.572

  • A. 1.572
  • B. 1.9398
  • C. 3.389
  • D. 4.238

Explanation

For methanol, modified Raoult's law gives yP = xγP°; thus γ = (0.5714 × 39.223)/(0.1686 × 84.562) ≈ 1.572. The activity coefficient exceeds one because the solution shows positive deviation from Raoult's law.

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