Question

If $P_A^0$ and $P_B^0$ are $108$ and $36$ torr respectively. What will be the mole fraction of $A$ is vapour phase if $B$ has mole fraction in solution $0.5$:

• A. $0.25$
• B. $0.75$
• C. $0.60$
• D. $0.35$

Answer 1

Answer: (B)

$0.75$

$P=X_A{P}_A^0+X_B{P}_B^0$

$=0.5\times 108+0.5\times 36$

$=54+18=72$ torr

$Now,X_a=\frac{P_a}{P}=0.5\times \frac{108}{72}=\frac{54}{72}=0.75$

Hence, the correct option is $A$