Will a non-volatile solute always lower the vapor pressure of the pure solvent in solution? Why or why not?
Yes, it will ALWAYS.
Why? Think Raoult's Law.
p = X*Po and since X of the solvent will ALWAYS be lower than 1 (when mixed with the solute) so the partial pressure must always be lower than Po, the normal vapor pressure of the pure solvent.
To determine whether a non-volatile solute will lower the vapor pressure of the pure solvent in solution, we need to understand the concept of vapor pressure and its relation to solute-solvent interactions.
Vapor pressure is the pressure exerted by the vapor phase of a substance in equilibrium with its liquid or solid phase at a specific temperature. In a pure solvent, the vapor pressure depends on the temperature and the intermolecular forces between solvent molecules, usually expressed as a measure of volatility.
When a solute is added to the solvent to form a solution, the solute-solvent interactions influence the vapor pressure of the system. Two possibilities can occur:
1. If the solute-solvent interactions are similar or stronger than the solvent-solvent interactions, the solute is considered volatile. In this case, the vapor pressure of the solution will decrease compared to that of the pure solvent.
2. If the solute-solvent interactions are weaker than the solvent-solvent interactions, the solute is considered non-volatile. In this case, the vapor pressure of the solution will not be significantly affected, and it will remain close to the vapor pressure of the pure solvent.
To answer the question, a non-volatile solute does not always lower the vapor pressure of the pure solvent in a solution. It depends on the relative strength of the solute-solvent interactions compared to the solvent-solvent interactions.