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. `0.3`

Answer

B

Explanation

This question is based on Raoult’s law. It represent that the partial pressure of each component in the solution is directly proportional to its mole fraction for a solution i.e., `P _(A) prop X _(A) and p _(B) prop X _(B).`
From Aaoult.s law
`p ^(@) - p _(s) = p ^(@) xx `Mole fraction of solute
`10 = p ^(@) xx 0.2 `
`20 = p ^(@) xx X _(2)`
`therefore X _(2) = 0.4`
and `X _(1) = 1 - 0.4 = 0.6`
`X _(1) =` mole fraction of solvent