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

Step 1: Classify the azeotrope.
The boiling point of the mixture is higher than that of both pure components. This identifies it as a maximum boiling azeotrope.
Step 2: Reason for maximum boiling point.
Maximum boiling azeotropes form when A-B intermolecular interactions are stronger than A-A and B-B interactions. Molecules are held more tightly in solution, reducing the tendency to escape into the vapour phase.
Step 3: Deviation from Raoult's law.
Because molecules escape less readily, the actual vapour pressure is lower than what Raoult's law predicts. This is negative deviation. A lower vapour pressure means a higher boiling temperature.
\[ \boxed{\text{Negative deviation from Raoult's law}} \]