Question

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

• A. 0.5
• B. 0.6
• C. 0.27
• D. 0.73

Answer 1

Answer: (C)

0.27

For the equimolar solution of benzene and toluene, the mole fraction of benzene and toluene are $0.5$ each.

Total pressure $P=P_B+P_T=P_B^0{X}_B+P_T^o{X}_T$

$P=160\times 0.5+60\times 0.5$

$P=110$

The mole fraction of toluene in the vapour phase in contact with an equimolar solution of benzene and toluene.

$Y_T=\frac{P_T}{P}$

$Y_T=\frac{P_T^o{X}_T}{P}$

$Y_T=\frac{60\times 0.5}{110}=0.27$

Hence, the correct option is C.