Question

The relative lowering of the vapour pressure is equal to the ratio between the number

• A. solute molecules to the solvent molecules
• B. solute molecules to the total molecules the solution
• C. solvent molecules to the total molecules B in the solution
• D. solvent molecules to the total number ions of the solute

Answer 1

Answer: (B)

According to Raoulfs law, relative lowering in vapour pressure is directly proportional to the mole fraction of solute, ie, $\frac{P^o-P}{P^o}{\chi }_s$ where ${\chi }_s=\frac{n_s}{n_s+N}=\frac{molesofsolute}{totalnumberofmoles}$ $\therefore$ relative lowering of vapour pressure $=\frac{n_2}{n_1+n_2}=\frac{solutemolecules}{totalmoleculesinthesolution}$