Question

State Raoult's law for a solution containing a non-volatile solute.

Hint:

{Non-volatile solute → Lowers vapor pressure} Raoult’s law: \( P = P^0 \times X_{\text{solvent}} \)

Answer 1

Concept: Raoult's law describes the relationship between the vapor pressure of a solvent and the presence of a solute in a solution. It is especially applicable to dilute solutions and ideal solutions. Statement: For a solution containing a non-volatile solute, Raoult's law states that: \begin{quote} The vapor pressure of the solvent over the solution is directly proportional to the mole fraction of the solvent present in the solution. \end{quote} Mathematically, \[ P = P^0 \times X_{\text{solvent}} \] where:

• \( P \) = vapor pressure of the solvent in the solution
• \( P^0 \) = vapor pressure of the pure solvent
• \( X_{\text{solvent}} \) = mole fraction of the solvent

Since the solute is non-volatile, it does not contribute to vapor pressure. Its presence lowers the vapor pressure of the solvent compared to the pure solvent. Conclusion: Thus, in a solution containing a non-volatile solute, the vapor pressure of the solvent decreases in proportion to the mole fraction of the solvent.