Question

The vapour pressure of a dilute aqueous solution of glucose is 750 mm of Hg at 373 K. Calculate molality.

Answer 1

$P^o=760;P_s=750mm$
$\frac{P^o-P_s}{P^o}={\chi }_2$
$\Rightarrow \frac{760-750}{760}={\chi }_2\Rightarrow {\chi }_2=0.013;{\chi }_1=1-0.013=0.968$
$m=\frac{{\chi }_2\times 1000}{{\chi }_1\times M{w}_1}=\frac{0.013\times 1000}{0.986\times 18}=0.732$