Question

A binary solution is formed by mixing two volatile liquids $A(P_A^O=100\text{torr})$ and $B(P_B^O=400\text{torr})$ .
What is the mole fraction of $A$ in solution when the mole fraction of $A$ is double than that of $B$ in vapour phase?

• A. $\frac{8}{9}$
• B. $\frac{1}{5}$
• C. $\frac{1}{2}$
• D. $\frac{9}{8}$

Answer 1

The correct option is A $\frac{8}{9}$

$P_A=P_A^O{x}_A=100x_A$

$=2P_B=2P_B^O{x}_B=2\times 400(1-x_A)$

$\Rightarrow 100x_A=800-800x_A$

$\Rightarrow x_A=\frac{8}{9}$