Solutions and Colligative Properties - Result Question 56
####27. The vapour pressure of pure benzene is $639.70 mm$ of $Hg$ and the vapour pressure of solution of a solute in benzene at the same temperature is $631.9 mm$ of $Hg$. Calculate the molality of the solution.
(1981, 3M)
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Solution:
- According to Raoult’s law :
$$ \begin{aligned} & & p=p _0 \chi _1 \Rightarrow 631.9=639.7 \quad \chi _1 \ \Rightarrow & \chi _1 & =0.9878 \Rightarrow \chi _2=0.0122 \ \Rightarrow & \text { Molality } & =\frac{0.0122}{0.9878 \times 78} \times 1000=0.158 \end{aligned} $$
