A solution is made by mixing one mole of volatile liquid A with 3 moles of volatile liquid B. The vapour pressure of pure A is 200 mm Hg and that of the solution is 500 mm Hg. The vapour pressure of pure B and the least volatile component of the solution, respectively, are:
- 1400 mm Hg, A
- 1400 mm Hg, B
- 600 mm Hg, A
- 600 mm Hg, B
Answer
(3) 600 mm Hg, A
Solution
Mole fractions: xA = 11+3 = 0.25, xB = 34 = 0.75
By Raoult's law, ptotal = pA0 xA + pB0 xB
500 = 200 0.25 + pB0 0.75
0.75 pB0 = 450
pB0 = 600 mm Hg
pA0 = 200 mm Hg < pB0 = 600 mm Hg, A is the least volatile component.
Answer: (3)