Question

Two liquids $A$ and $B$ form an ideal solution at temperature $T$. When the total vapour pressure above the solution is $600$ atm, the mole of the fraction of $A$ in the vapour phase is $0.30$ in the liquid phase is $0.80$, then :

• A. liquid $A$ is more volatile
• B. liquid $B$ is more volatile
• C. both are equally volatile
• D. cannot be predicted

Answer 1

Answer: (B)

liquid $B$ is more volatile

$P_{solution}=600atm$

$y_{A_{vapor}}=\frac{P_A^o{X}_{A}liquid}{P_{solution}}$

$0\cdot 3=\frac{P_A^o\times 0\cdot 8}{600}$

$P_A^o=\frac{600\times \cdot 3}{0\cdot 8}=225atm$

Similarly,

$P_B^o=\frac{600\times \cdot 7}{0\cdot 2}=2100atm$

So, $P_B>P_A$

Liquid B is more volatile.