Question

The vapour pressures of two volatile liquids A and B at 25°C are 50 Torr and 100 Torr, respectively. If the liquid mixture, contains 0.3 mole fraction of A, then the mole fraction of liquid B in the vapour phase is $\frac {x}{17}$. The value of x is _____.

Answer 1

$P_T = P^0_A . x_A + P^0_B . x_B$
$PT= 50 × 0.3 + 100 × 0.7$
$= 85$ mm Hg
$y_B = \frac {70}{85} = \frac {x}{17}$
$\frac {x}{17} = 14$

So, the answer is $14$.