Question

According to Raoult's law, relative lowering of vapour pressure for a solution containing a non-volatile solute is equal to

• A. mole fraction of solvent
• B. moles of solute
• C. moles of solvent
• D. mole fraction of solute

Hint:

Relative lowering of vapour pressure is a colligative property and depends only on the number of solute particles present, not their nature.

Answer 1

The Correct Option is D

Step 1: Statement of Raoult's law.
According to Raoult's law, the vapour pressure of a solvent in a solution is directly proportional to its mole fraction. For a solution containing a non-volatile solute, the vapour pressure decreases due to the presence of solute particles.

Step 2: Relative lowering of vapour pressure.
The relative lowering of vapour pressure is defined as:
\[ \frac{P^0 - P}{P^0} \] where \( P^0 \) is the vapour pressure of pure solvent and \( P \) is the vapour pressure of the solution.

Step 3: Mathematical relation.
For dilute solutions, the relative lowering of vapour pressure is equal to the mole fraction of the solute.

Step 4: Conclusion.
Thus, the correct answer is (D) mole fraction of solute.