Question

Two liquids X and Y form an ideal solution. The mixture has a vapour pressure of 400 mm at 300 K when mixed in the molar ratio 1:1. when mixed in the molar ratio of 1:2 at the same temperatre the vapour pressure of the mixture is 350 mm. The vapour pressure of the two pure liquids X and Y respectively are
A. 250mm,550mm
B. 350mm,450mm
C. 350mm,700mm
D. 550mm,250mm

Answer 1

Correct Answer - D
In lst case, when liquids X and Y are mixed in the molar ratio 1:1.
`"Mole fraction of "X(Xx)=(1)/(2)"and mole fraction of " Y(Xx)=(1)/(2) `
We know that
`p=p_(x)^(@)x_(x)+p_(y)^(@)x_(y)(p="total pressure of mixture")`
`400xx2=p_(x)^(@)+p_(y)^(@)` . . .(i)
In case llnd, when liquids are mixed in the molar ratio of 1:2.
`"Mole fraction of "X(x_(x))=(1)/(3)xx"Mole fraction of " Y(x_(x))=(2)/(3)`
`p=p_(x)^(@)x_(x)+p_(y)^(@)x_(y)`
`350xx3=p_(x)^(@)+2p_(y)^(@)` . . . (ii)
Form Eqs. (i) and (ii), we get
`p_(x)^(@)=500mmandp_(y)^(@)=250mm`