Question

At $T(K)$, the vapor pressure of water is $x$ kPa. What is the vapor pressure (in kPa) of 1 molal solution containing non-volatile solute?

• A. \(1.018x\)
• B. \(0.8x\)
• C. \(0.972x\)
• D. \(0.982x\)

Hint:

For solutions of non-volatile solutes, the vapor pressure of the solution is proportional to the mole fraction of the solvent.

Answer 1

The Correct Option is D

Using Raoult’s Law for the vapor pressure of a solution: \[ P_{\text{solution}} = P_{\text{solvent}} \times X_{\text{solvent}} \] Where \(P_{\text{solution}}\) is the vapor pressure of the solution, \(P_{\text{solvent}}\) is the vapor pressure of the pure solvent, and \(X_{\text{solvent}}\) is the mole fraction of the solvent. Given that the solute is non-volatile, the mole fraction of the solvent is approximately \(1 - \text{molality of the solution}\), which leads to a slight reduction in vapor pressure. The vapor pressure is then given by \(0.982x\).