The vapour pressure of a solvent decreased by 10 mm of Hg when a non-volatile solute was added to the solvent. The mole fraction of solute in solution is 0.2, what would be the mole fraction of solvent if the decrease in vapour pressure is 20 mm of Hg?

Options

A. 0.8
B. 0.6
C. 0.4
D. 0.2

Answer

B

Explanation

`"Mole fraction of solute"="lowering in vapour pressure"/"vapour pressure of solvent"`
Comparing under the two conditions,
`0.2/"mole fraction of solute"=10/20`
or mole fraction of solute = 0.4
mole fraction of solvent = (1 – 0.4) = 0.6