Chemistry - Liquid Solution Question with Solution | TestHub

Number of moles of sucrose, $n_2=\frac{136.8}{342}=0.4$ mol

Number of moles of water, $n_1=\frac{1000}{18}=55.55$ mol

Mole fraction of sucrose, $x_2=\frac{n_2}{n_1+n_2}=\frac{0.4}{55.55+0.4}=\frac{0.4}{55.95}=0.00715$

Relative lowering of vapour pressure is given by:

$\frac{P^0-P_s}{P^0}=x_2$

$P^0-P_s=P^0{x}_2=18\times 0.00715=0.1287$ mm Hg

$P_s=18-0.1287=17.87$ mm Hg

Answer: $17.87\text{mm Hg}$