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

From Raoult's law
`p_(@) - p_(s) = p_(@)xx"Mole fraction of soule"`
`10 = p^(@)xx0.2 rArr 20 = p^(@) xx X_(2)`
`:. X_(2) = 0.4` and `X_(1) = 1 - 0.4 = 0.6`
`X_(1) =` mole fractiono of solvent