Vapour pressure of chloroform $\left(\mathrm{CHCl}_{3}ight)$ and dichloromethane $\left(\mathrm{CH}_{2}…

Vapour pressure of chloroform $\left(\mathrm{CHCl}_{3}ight)$ and dichloromethane $\left(\mathrm{CH}_{2} \mathrm{Cl}_{2}ight)$ at $25^{\circ} \mathrm{C}$ are $200 \mathrm{~mm} \mathrm{Hg}$
and $41.5 \mathrm{~mm}$ Hg respectively. Vapour pressure of the solution obtained by mixing $25.5 \mathrm{~g}$ of $\mathrm{CHCl}_{3}$ and $40 \mathrm{~g}$ of $\mathrm{CH}_{2} \mathrm{Cl}_{2}$ at the same temperature will be: (Molecular mass of $\mathrm{CHCl}_{3}=119.5 \mathrm{u}$ and molecular mass of $\mathrm{CH}_{2} \mathrm{Cl}_{2}=85 \mathrm{u}$ ).
  1. $90.92 \mathrm{~mm} \mathrm{Hg}$
  2. $115.0 \mathrm{~mm} \mathrm{Hg}$
  3. $147.9 \mathrm{~mm} \mathrm{Hg}$
  4. $285.5 \mathrm{~mm} \mathrm{Hg}$

Solution

$\mathrm{n}_{\mathrm{CHCl}_{3}}=\frac{25.5}{119.5}=0.213$
$\mathrm{n}_{\mathrm{CH}_{2} \mathrm{Cl}_{2}}=\frac{40}{85}=0.47$
$\mathrm{P}_{\mathrm{T}}=\mathrm{P}_{\mathrm{A}}^{\mathrm{o}} \mathrm{X}_{\mathrm{A}}+\mathrm{P}_{\mathrm{B}}^{\mathrm{o}} \mathrm{X}_{\mathrm{B}}$
$=200 \times \frac{0.213}{0.683}+41.5 \times \frac{0.47}{0.683}$
$=62.37+28.55=90.92$ *

Asked in: JEE-TOPICTESTS-CHEMISTRY

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