Liquid A and B form an ideal solution. The vapour pressures of pure liquids A and B are 350 and 750 mm Hg respectively at the same temperature. If xA and xB are the mole fraction of A and B in solution while yA and yB are the mole fraction of A and B in vapour phase, then,
- (xA - yA) < (xB - yB)
- xAxB = yAyB
- xAxB < yAyB
- xAxB > yAyB
Answer
(4) xAxB > yAyB
Solution
By Raoult's law and Dalton's law:
yA = pA xAptotal, yB = pB xBptotal
yAyB = pA pB xAxB = 350750 xAxB
350750 < 1
yAyB < xAxB, i.e. xAxB > yAyB
(Also, B is more volatile, so yB > xB and yA < xA xA - yA > 0 > xB - yB; option (1) is wrong.)
Answer: (4)