Question

The vapour pressures 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
$x_{A} = x_{B} = 0.5$
$p_{benzene} = 160 × 0.5 = 80\, torr,$
$p_{toluene} = 60 × 0.5 = 30\, torr$
$p_{total} = 80 + 30 = 110\, torr$
Mole fraction of toluene in vapour phase
$= \frac{partial\, vapour \, pressure\, of \, toluene}{total\, vapour\, pressure} = \frac{30}{110} = 0.27$