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

Options

A. 250 mm, 550 mm
B. 350 mm, 450 mm
C. 350 mm, 700 mm
D. 550 mm, 250 mm

Answer

D

Explanation

Molar ratio of `1:1` means `x_(X)=x_(y)=0.5`
`P_("total")=x_(X)p_(X)^(@)+x_(Y)p_(Y)^(@)`
`therefore" "400=0.5p_(X)^(@)+0.5p_(Y)^(@)`
`"or "p_(X)^(@)+p_(Y)^(@)=800" ...(i)"`
`"Molar ratio of 1 : 2 means , "x_(A)=(1)/(3), x_(Y)=(2)/(3)`
`therefore" "350 =(1)/(3)p_(X)^(@)+(2)/(3)p_(Y)^(@)`
`"or "p_(X)^(@)+2p_(Y)^(@)=1050" ...(ii)"`
Eqn. (ii) - Eqn. (i) gives `p_(Y)^(@)=250mm`
Putting in (i), we get `p_(X)^(@)=550 mm`