Question

The phase diagram for the pure solvent (solid lines) and the solution (non - volatile, solute, dashed line) and recorded below:

Here T is the temperature at which the solvent boils. Which quantity indicates relative lowering vapor pressure?

• A. $\frac{AB}{AC}$
• B. $\frac{AB}{BC}$
• C. $\frac{AD}{AE}$
• D. $\frac{AD}{DE}$

Answer 1

The correct option is A $\frac{AB}{AC}$

$AB=AC-BC=P_o-P_s$
$AC=\text{Vapour pressure of pure solvent,}{P}_o$
Thus, $\frac{AB}{AC}=\frac{P_o-P_s}{P_o}$
Hence $\frac{AB}{AC}$ is the relative lowering of vapour pressure.