Question

When a non-volatile solute is added to a pure solvent, the:
A. Vapor pressure of the solution becomes lower than that of the pure solvent
B. Rate of evaporation of the pure solvent is reduced
C. Solute does not affect the rate of condensation
D. Rate of the evaporation of the solution is equal to the rate of condensation of the solution at a lower vapor pressure than that in the case of the pure solvent.

Answer 1

Hint: The solute is a chemical which is present in a less amount compared to the amount of solvent. Non-volatile solute means the chemical which does not evaporate into gas in normal existing conditions. Means non-volatile solute has low vapor pressure.

Complete answer:
- In the question it is given that a non-volatile solute is added to a pure solvent.
- We have to find which option is going to suit after adding a non-volatile solute to a pure solvent.
- When we are going to add a non-volatile solute to the solvent, few of the non-volatile solute occupies the surface of the solvent and won’t allow the solvent to evaporate easily.
- Hence the vapor pressure of the solution becomes less when compared to the vapor pressure of the pure solvent.
- Therefore when a non-volatile solute is added to a pure solvent, the vapor pressure of the solution becomes lower than that of the pure solvent.


- So, the correct option is A.

Note: Vapor pressure of a solvent can be defined as the pressure applied by the vapors of the pure solvent with itself. When we are going to add a non-volatile solute to the solvent the number of solvent molecules is going to decrease on the surface of the pure solvent.