Chemistry - Liquid Solution Question with Solution | TestHub

In equimolar solution of benzene and toluene, mole fraction of benzene,

${\mathrm{X}}_{\mathrm{b}}=$mole-fraction of toluene,${\mathrm{X}}_{\mathrm{t}}=\frac{1}{1+1}=0.5$

So partial pressure of benzene,

${\mathrm{p}}_{\mathrm{b}}={\mathrm{X}}_{\mathrm{b}}.{\mathrm{p}}_{\mathrm{b}}^{\mathrm{o}}=0.5\times 160$torr = 80 torr and partial pressure of toluene,

${\mathrm{p}}_{\mathrm{t}}={\mathrm{X}}_{\mathrm{t}}{\mathrm{p}}_{\mathrm{t}}^{\mathrm{o}}=0.5\times 60$torr = 30 torr

Hence, vapour pressure of solution = 80 torr + 30 torr = 110 torr

According to Dalton's law of partial pressure,

Partial vapour pressure of toluene,

${\mathrm{p}}_{\mathrm{t}}=$mole fraction of touene in vapour phase$\times$total pressure$\left({\mathrm{p}}_{\mathrm{t}\mathrm{o}\mathrm{t}\mathrm{a}\mathrm{l}}\right)$

or mole fraction of toluene in vapour phase$=\frac{{\mathrm{p}}_{\mathrm{t}}}{{\mathrm{p}}_{\mathrm{t}\mathrm{o}\mathrm{t}\mathrm{a}\mathrm{l}}}=\frac{30\text{ torr}}{110\text{ torr}}=0.27$