Liquids A and B form an ideal solution at a fixed temperature, with $p_{A}^{0} = 300 torr$ and $p_{B}^{0} = 100 torr$ . A liquid mixture has $x_{A} = 0.25$ . Which statements are correct?

AThe vapour is richer in B than the liquid is
BThe total vapour pressure above the liquid is $150 torr$
CThe mole fraction of A in the vapour is $0.50$
DIf the first vapour is condensed completely and the condensate is allowed to reach vapour-liquid equilibrium at the same temperature, the new vapour has $y_{A} = 0.75$

Answer: B, C, D

P = 0.25 (300) + 0.75 (100) = 150 torr

and

y_{A} = 75/150 = 0.50

. The vapour is richer in the more volatile component A (

y_{A} = 0.50 > x_{A} = 0.25

), so the fourth statement is false. The condensate has

x_{A} = 0.50

, giving

P = 0.5 (300) + 0.5 (100) = 200 torr

and

y_{A} = 150/200 = 0.75