When a non-volatile solute is added to a liquid to form a dilute solution, the form of Raoult's law

Question

When a non-volatile solute is added to a liquid to form a dilute solution, the form of Raoult's law applicable states that relative lowering of vapour pressure is

Professor PC Thomas Classes · Answer

Relative lowering of vapour pressure is equal to the mole fraction of the solute. $\frac{p_{1}^{0}-p_{1}}{p_{1}^{0}}=\chi_{2}$ This follows from the Raoult's law for two liquids. When the solute is non-volatile, $p_{2}=0 p_{1}=p_{1}^{0} \chi_{1} p_{1}^{0}\left(1-\chi_{2}\right)=p_{1}^{0}-p_{1}^{0} \chi_{2} p_{1}^{0} \chi_{2}=p_{1}^{0}-p_{1} \frac{p_{1}^{0}-p_{1}}{p_{1}^{0}}=\chi_{2}$