Question

Consider the following statements about the solutions formed by mixing two liquids.

• [A.] An ideal solution thus formed obeys Raoult's law throughout the composition range.

• [B.] Mixture of chloroform and acetone shows negative deviation from Raoult's law.

• [C.] Mixture of aniline and phenol shows positive deviation from Raoult's law.
Select

• A. A and C only
• B. A and B only
• C. B and C only
• D. A only

Hint:

Whenever mixing two components results in the formation of new, stronger bonds (like hydrogen bonding between chloroform-acetone or phenol-aniline), the molecules are held tightly in the liquid phase. This always results in a lower vapor pressure, meaning a negative deviation from Raoult's Law.

Answer 1

The Correct Option is B

Step 1: Understand what we are checking.
We have three statements about liquid-liquid solutions, and we must decide which are true. The key idea is comparing the strength of the new A-B interactions formed on mixing with the original A-A and B-B interactions in the pure liquids.
Step 2: Recall the ideal solution rule.
An ideal solution is defined as one that obeys Raoult's law at every composition. By definition the partial pressure of each component is proportional to its mole fraction across the whole range, so Statement A is true.
Step 3: Set up the deviation logic.
If A-B forces are stronger than A-A and B-B, molecules escape less easily, vapour pressure drops, and we get a negative deviation. If A-B forces are weaker, escape is easier, vapour pressure rises, and we get a positive deviation.
Step 4: Test chloroform and acetone (Statement B).
When these mix, the acidic H of \(CHCl_3\) forms a new hydrogen bond with the carbonyl O of acetone. This A-B bond is stronger than the original dipole-dipole forces, so the escaping tendency falls and the mixture shows a negative deviation. Statement B is true.
Step 5: Test aniline and phenol (Statement C).
Phenol's O-H proton hydrogen bonds strongly with the lone pair on aniline's nitrogen. This new A-B interaction is stronger than self-association in either pure liquid, so this mixture actually shows a negative deviation, not a positive one. Statement C is false.
Step 6: Combine and conclude.
Only A and B are correct, while C is wrong. That matches the option "A and B only".
\[ \boxed{\text{A and B only}} \]