JEE Main · 2024 · 27 Jan 2024 · Shift 1 · Solutions

A solution of two miscible liquids showing negative deviation from Raoult's law will have :

(A)increased vapour pressure, increased boiling point
(B)increased vapour pressure, decreased boiling point
(C)decreased vapour pressure, decreased boiling point
(D)decreased vapour pressure, increased boiling point✓ Correct

Answer: (D)

Solution

Negative deviation from Raoult's law means A–B interactions are stronger than the average of A–A and B–B interactions, which suppresses escape of molecules into the vapour phase:

P_{T} < P_{A}^{0} X_{A} + P_{B}^{0} X_{B}

A lower vapour pressure means a higher temperature is needed to reach the external pressure, so the boiling point increases. The solution shows decreased vapour pressure and increased boiling point.

JEE Main · 2024 · 27 Jan 2024 · Shift 1 · Single correct option

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