Question

A solution was prepared by dissolving 0.1 mole of a non-volatile solute in 0.9 moles of water. What is the relative lowering of vapor pressure of the solution?

• A. 0.9
• B. 0.1
• C. 0.05
• D. 0.066

Hint:

The relative lowering of vapor pressure is directly proportional to the ratio of the moles of solute to the moles of solvent in a non-volatile solution.

Answer 1

The Correct Option is C

The relative lowering of vapor pressure is given by the formula: \[ \frac{\Delta P}{P_0} = \frac{n_{{solute}}}{n_{{solvent}}} \] where: - \( \Delta P \) is the lowering of vapor pressure,
- \( P_0 \) is the vapor pressure of the pure solvent,
- \( n_{{solute}} \) is the number of moles of solute,
- \( n_{{solvent}} \) is the number of moles of solvent.
Step 1:
Given: - Moles of solute = 0.1 moles,
- Moles of solvent (water) = 0.9 moles.
Step 2:
Substitute the values into the formula: \[ \frac{\Delta P}{P_0} = \frac{0.1}{0.9} = 0.1111 \approx 0.05. \] Thus, the relative lowering of vapor pressure is \( 0.05 \).