Question

At a certain temperature, the vapour pressures of benzene and toluene are 119 torr and 37 torr, respectively. The mole fraction of toluene in the vapour phase, which is in equilibrium with a solution of benzene and toluene in 1 : 1 molar ratio, is

• (A) 0.237
• (B) 0.5
• (C) 0.763
• (D) None of these

Answer 1

The Correct Option is A

Explanation:
Assuming ideal behaviour,Pbenzene $={\mathrm{X}}_{\text{benzene }}{P}_{\text{ben sene }}^o=0.5\times 119$ torr $=59.5$ torr$P_{\text{toluene }}=X_{\text{toluene }}{P}_{\text{tod }}^0=0.5\times 37$ torr $=18.5$ torr$P_{\text{total }}=59.5+18.5=78.0$ torr$x_{\mathrm{tol}}^{\mathrm{vap}}=P_{\mathrm{toluene}/{\mathrm{P}}_{\mathrm{total}}}=18.5/78.0=0.237$Thus,(1) is the correct option.