Question

Which of the following solutions shows positive deviation from Raoult's law?

• A. Ethanol + Acetone
• B. Chloroform + Acetone
• C. Benzene + Toluene
• D. Phenol + Aniline

Hint:

If mixing two liquids breaks existing hydrogen bonds (like adding a non-polar or less polar solvent to an alcohol), expect a positive deviation. If mixing them creates new hydrogen bonds (like mixing an acid and a base), expect a negative deviation!

Answer 1

The Correct Option is A

Step 1: Know what positive deviation means.
It happens when the new mixed forces between unlike molecules are weaker than the forces in the pure liquids. The molecules escape more easily, so vapour pressure rises.

Step 2: Scan the pairs.
Chloroform with acetone makes new hydrogen bonds, so that is negative. Phenol with aniline also bonds strongly, again negative. Benzene with toluene is nearly ideal.

Step 3: Pick the loose one.
Adding acetone to ethanol breaks ethanol's hydrogen bonds and puts weaker forces in their place, so this shows positive deviation.
\[ \boxed{\text{Ethanol + Acetone}} \]