Q19 / 160 · AP EAMCET 2016 · Chemistry

The vapour pressure of pure benzene and toluene are 160 and $60 \mathrm{~mm} \mathrm{Hg}$ respectively. The mole fraction of benzene in vapour phase in contact with equimolar solution of benzene and toluene is

  • A
    $0.073$
  • B
    $0.027$
  • C
    $0.27$
  • Correct answer
    D
    $0.73$

Solution

For equimolar solution, $\begin{aligned} & \chi_b=\chi_t=0.5 \\ & \mathrm{p}_b=\chi_b \times \mathrm{p}_b^0=0.5 \times 160 \\ & =80 \mathrm{~mm} \\ & \mathrm{p}_b=\chi_t \times \mathrm{p}_b^0=0.5 \times 60 \\ & =30 \mathrm{~mm}\end{aligned}$ $\mathrm{p}_{\text {total }}=80+30=110 \mathrm{~mm}$ Mole fraction of benzene in vapour phase $=\frac{\mathrm{p}_b}{\mathrm{p}_{\text {total }}}=\frac{80}{110}=0.727=0.73$

Hence, the correct answer is option: 'D'.

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