Question

The vapour pressure of pure benzene and toluene are $160$ and $60$ torr respectively. The mole fraction of toluene in vapour phase in contact with equimolar solution of benzene and toluene is

• A. 0.50
• B. 0.16
• C. 0.27
• D. 0.73

Answer 1

Answer: (C)

For equimolar solution, let us take

$x_{A}=x_{B}=0.5$

$P_{\text {benzene }}=160 \times 0.5=80 $ torr,

$P_{\text {toluene }}=60 \times 0.5=30$ torr

$P_{\text {total }}=80+30=110 $ torr

Mole fraction of toluene in vapour phase

$=\frac{\text { Partial vapour pressure of toluene }}{\text { Total vapour pressure }}$

$=\frac{30}{110}=0.27$