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

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

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