Question

mole fraction of A in vapour phase above the ideal liquid solution of A and B (xA=0.4) will be (p°A= 100mm, p°B=200mm)
(1) 0.4 (2) 0.8 (3) 0.25 (4) none of these

Answer 1

Given that,

Mole fraction of A, xA = 0.4

so, Mole fraction of B, xB = 1 - 0.4 = 0.6

First, let us find the total Vapour Pressure 'P'

P = pA + pB

P = p°A(xA) + p°B(xB)

P = 100(0.4) + 200(0.6)

P = 40 + 120

P = 160 mm

Now, let the mole fraction of A in vapour phase be 'yA'

yA = pA/P

yA = 40/160

yA = 0.25

∴ The mole fraction of A in vapour phase is 0.25.

Hope it helps!!

Answer 2

Answer:

0.25 is the right ans.