Question

3 moles of A ($P_A^0$=200mm of Hg) and 2 moles of B($P_B^0$ =300mm of Hg) are mixed at a fixed temperature. The vapours above the solution are collected and condensed. Than:

• A. The vapour pressure of condensate is 250 mm of Hg
• B. The mole fraction in vapour phase of B for condensate is greater than the mole fraction of B in original solution.
• C. On fractional distillation vapour of A will be separated first.
• D. The vapour will become richer in vapours of B on repeated distillations.

Answer 1

Answer: (A), (B), (D)

The correct options are
A

The vapour pressure of condensate is 250 mm of Hg

B

The mole fraction in vapour phase of B for condensate is greater than the mole fraction of B in original solution.

D

The vapour will become richer in vapours of B on repeated distillations.

$X_A=\frac{3}{5},X_B=\frac{2}{5}{P}_A=\frac{3}{5}\times 200$ = 120 mm of Hg
$P_B=\frac{2}{5}\times 300$ = 120 mm of Hg
$P_T=240mmofHg{Y}_A=0.5,Y_B=0.5$
Now, $X_A$ (molefraction condensate) $=Y_A=0.5$
$X_B$ (molefraction in condensate) $=Y_B=0.5)$
$P_A=100mm{P}_B=150mm{P}_T=250mm{Y}_A=\frac{100}{250}=\frac{2}{5};Y_B=\frac{150}{250}=\frac{3}{5}Hence;X_B<Y_B$
On fractional distillation B will be separated out as it is more volatile.