Question

The vapour pressure of solvent decreases by 1 O mm Hg, if mole fraction of non-volatile solute is 0.2. Calculate vapour pressure of solvent.

Options

• 70 mm of Hg

• 40 mm of Hg

• 50 mm of Hg

• 60 mm of Hg

Answer 1

50 mm of Hg

Explanation:

Given, Lowering of vapour pressure

`("p"_4^circ - "p"_"A")` = 10 mm Hg

Mole fraction of non-volatile solution (χ_A) = 0.2

Mole fraction of solution,

`chi_"A" = ("p"_4^circ - "p"_"A")/"p"_"A"`

`0.2 = (100  "mm"  "Hg")/"p"_"A"`

`=> "p"_"A" = 10/0.2`mm Hg = 50 mm of Hg