Question

A mixture of two immiscible liquids nitrobenzene and water boiling at ${97}^{o}C$ has a partial vapor pressure of water 733 mm and that of nitrobenzene 27 mm. The ratio of the weights of water to nitrobenzene in the distillate is:

• A. 4
• B. 5
• C. 3
• D. 7

Answer 1

The correct option is A 4

$P^{\prime }=P_M\times {\chi }_A$ where ${\chi }_A$ is the mole fraction in the gaseous phase
$27=P_M\times \frac{\frac{W_2}{123}}{\frac{W_1}{18}\times \frac{W_2}{123}}$ (for nitrobenzene) .............(1)

$733=P_M\times \frac{\frac{W_1}{18}}{\frac{W_1}{18}\times \frac{W_2}{123}}$ (for water) .............(2)
On dividing equation 2 by equation 1, we get-

$\frac{733}{27}=\frac{W_1}{18}\times \frac{123}{W_2}$

$\frac{W_1}{W_2}=4$

Hence, option A is correct.