Question

Identify the correct statement from the following.

• A. Vapour pressure of a solution containing a non-volatile solute is always less than vapour pressure of pure solvent.
• B. Liquids having greater intermolecular forces have lower boiling points.
• C. Boiling point of pure solvent is always greater than boiling point of its solution containing a non-volatile solute.
• D. Vapour pressure of a solution containing a non-volatile solute is always greater than vapour pressure of pure solvent.

Hint:

Adding a non-volatile solute to a solvent lowers the vapour pressure of the solution compared to the pure solvent.

Answer 1

The Correct Option is A

Step 1: Understanding the effect of non-volatile solutes.
When a non-volatile solute is added to a solvent, it lowers the vapour pressure of the solution compared to the pure solvent. This phenomenon is explained by Raoult’s law. Non-volatile solutes do not evaporate, so they reduce the number of solvent molecules at the surface, which decreases the vapour pressure.
Step 2: Analyzing the options.
(A) Vapour pressure of a solution containing a non-volatile solute is always less than vapour pressure of pure solvent: This is correct, as explained by Raoult’s law.
(B) Liquids having greater intermolecular forces have lower boiling points: This is incorrect, as stronger intermolecular forces usually lead to higher boiling points.
(C) Boiling point of pure solvent is always greater than boiling point of its solution containing a non-volatile solute: This is incorrect; the boiling point of a solution is higher than that of the pure solvent (boiling point elevation).
(D) Vapour pressure of a solution containing a non-volatile solute is always greater than vapour pressure of pure solvent: This is incorrect. The presence of a non-volatile solute lowers the vapour pressure.
Step 3: Conclusion.
The correct statement is (A).