A mixture of aniline ( b.p. $=457 \mathrm{~K}$ ) and water ( b.p. $=373 \mathrm{~K}$ ) boils at 371.

Question

A mixture of aniline ( b.p. $=457 \mathrm{~K}$ ) and water ( b.p. $=373 \mathrm{~K}$ ) boils at 371.5 K and 1 bar pressure. Vapour pressure of water is 724 mm at 371.5 K . The relative masses of aniline and water in the distillate will be\

Professor PC Thomas Classes · Answer

Vapour pressure of aniline $=p_{1}$ Vapour pressure of water $=p_{2}$\ $\mathrm{p}_{1}+\mathrm{p}_{2}=760 \mathrm{~mm}$\ $\mathrm{p}_{1}=760-\mathrm{p}_{2}=760-724=36 \mathrm{~mm}$\ Pressure is proportional to no. of moles 
$ \begin{aligned} & \frac{P_{1}}{P_{2}}=\frac{w_{1} / M_{1}}{w_{2} / M_{2}}=\frac{w_{1}}{w_{2}} \frac{M_{2}}{M_{1}} \ & \frac{w_{1}}{w_{2}}=\frac{P_{1} \mathrm{M}_{1}}{P_{2} \mathrm{M}_{2}}=\frac{36 	imes 93}{724 	imes 18}=0.25 \end{aligned} $ 
$ \begin{aligned} 	ext { Mass ratio of aniline }: 	ext { water }= & 0.25: 1 \ & =1: 4 \end{aligned} $