Question

What happens to the vapour pressure of a liquid when a volatile solute dissolves in it?

Answer 1

1. When a volatile solute is dissolved in a volatile solvent, the vapour pressure of the solution lies between the vapour pressures of the pure solvent and the pure solute, depending on their mole fractions.
2. This is because both components contribute to the total vapour pressure.
3. According to Raoult’s Law, the total vapour pressure increases or decreases depending on whether the solute has a higher or lower vapour pressure than the solvent.
4. Thus, the final vapour pressure is a weighted average of the two, based on their proportions in the solution.