Question

When two moles of a non-volatile solute are dissolved in three moles of a solvent, the vapour pressure of the solution relative to that of the pure solvent is:

• A. $\frac{3}{5}$
• B. $\frac{2}{5}$
• C. $\frac{5}{3}$
• D. $\frac{5}{2}$

Answer 1

The correct option is A $\frac{3}{5}$

We know,

$\frac{p^{\circ }-p}{p^{\circ }}=\frac{n_{solute}}{(n_{solute}+n_{solvent})}$

The vapour pressure of the solution relative to that of the pure solvent

$\Rightarrow \frac{p}{p^{\circ }}=\frac{n_{solute}}{(n_{solute}+n_{solvent})}$

Therefore,

$\frac{p}{p^{\circ }}=\frac{3}{5}$