Question

If SR = 100 torr and PR = 350 torr then the mole fraction of $A$ in vapour phase and mole fraction of $A$ in liquid phase respectively are:

• A. $\frac{3}{10},\frac{2}{9}$
• B. $\frac{7}{9},\frac{3}{10}$
• C. $\frac{2}{9},\frac{7}{10}$
• D. $\frac{2}{9},\frac{3}{10}$

Answer 1

The correct option is D $\frac{2}{9},\frac{3}{10}$

$PQ=SR=P_A=100\text{torr}$
and $PR=P_B=350\text{torr}$
$P_T=P_A+P_B=100+350=450\text{torr}$
and $P_B=P_B^{\circ }\times X_B^{\prime }$
$X_B^{\prime }\left(\text{vapour phase}\right)=\frac{P_B}{P_T}=\frac{350}{450}=\frac{7}{9}$
$350=500X_B\Rightarrow X_B=7/10$
$X_A^{\prime }=1-X_B^{\prime }=\frac{2}{9}$
$X_A=1-X_B=\frac{3}{10}$