Question

What would be the vapour pressure of 0.5 molal solution of non volatile solute in benzene at ${30}^{o}C$ ? The vapour pressure of pure benzene at ${30}^{o}C$ is 119.6 torr.

• A. 119.6 torr
• B. 121.23 torr
• C. 118.52 torr
• D. None of these

Answer 1

The correct option is C 118.52 torr

$\frac{△p}{p^0}=x_2$

$\frac{△p}{p^0}=\frac{n_2}{n_1}$

$=\frac{m_2\times M_1}{M_2\times m_1}$

$=\frac{m\times m_1}{1000}$

$\frac{△p}{p^0}=\frac{0.5\times 18}{1000}$

$=0.009$

$\frac{p^0-p}{p^0}=0.009$

$[m=molarity=\frac{m_2}{M_2}\times \frac{1000}{m_1}$

$\frac{119.6-p}{119.6}=009$

$19.6-p=1.0764$

$p=118.52torr$