Question

If 0.2 mol $NaCl$ is added in 2 mol water, then vapour pressure of the solution is:

(vapour pressure of pure water is 760 torr)

• A. 33.33 torr
• B. 690.90 torr
• C. 345.45 torr
• D. 316.67 torr

Answer 1

The correct option is B 690.90 torr

$\begin{array}{c}\begin{array}{c}\text{vapour pressure of given solution}=P^{\circ }{X}_{\text{solvent}}\\ \text{where}{P}^{\circ }⟶\text{vapour pressure of pure solvent.}\\ X_{\text{solvent}}\to \text{mole fraction of solvent.}\end{array}\end{array}$

$\begin{array}{cc}\text{So, vapour pressure}& =760\times \frac{2}{2.2}\text{Torr}\\ & =690.90\text{Torr.}\end{array}$