Question

Vapour pressure of solvent 'A' is 0.90 atm, when a non-volatile solute is added, vapour pressure drops to 0.60 atm. What is mole fraction of A in solution?

• A. 0.300
• B. 0.333
• C. 0.500
• D. 0.667

Hint:

To find the mole fraction of a solvent in a solution, use Raoult's Law, considering the change in vapour pressure.

Answer 1

The Correct Option is D

Step 1: Using Raoult's Law.
Raoult's Law states that the mole fraction of solvent \( A \) can be calculated using: \[ P_A = P_A^0 \times X_A \] Where: - \( P_A^0 \) is the vapour pressure of pure solvent A (0.90 atm), - \( P_A \) is the vapour pressure of the solution (0.60 atm), - \( X_A \) is the mole fraction of A.
Step 2: Calculation.
From Raoult's Law, \[ X_A = \frac{P_A}{P_A^0} = \frac{0.60}{0.90} = 0.667 \] Step 3: Conclusion.
The correct answer is (D) 0.667.