Question

The boiling point of an azeotropic mixture of water and nitric acid is more than that of pure water and nitric acid. The mixture shows :

• A. no deviation from Raoult's law
• B. that solution is an ideal solution
• C. positive deviation from Raoult's law
• D. negative deviation from Raoult's law

Hint:

Maximum boiling azeotrope → Negative deviation from Raoult's law. Minimum boiling azeotrope → Positive deviation from Raoult's law.

Answer 1

The Correct Option is D

Concept: An azeotrope is a mixture that boils at a constant temperature and possesses the same composition in liquid and vapour phases. Azeotropes are of two types:

• Minimum boiling azeotrope

• Maximum boiling azeotrope

Step 1: Understand the given statement. The boiling point of the mixture is higher than the boiling points of both pure components. Therefore, the mixture is a: Maximum boiling azeotrope

Step 2: Relation with intermolecular forces. Maximum boiling azeotropes arise when: \[ A-B \text{ interactions} \] are stronger than \[ A-A \text{ and } B-B \text{ interactions} \] As a result, molecules escape less easily into the vapour phase.

Step 3: Vapour pressure behaviour. Stronger intermolecular attraction causes the vapour pressure to become lower than predicted by Raoult's law. Thus the solution exhibits: Negative deviation from Raoult's law.

Step 4: Final answer. \[ \boxed{\text{Negative deviation from Raoult's law}} \] Hence option (D) is correct.