Question

Which of the following pairs forms an ideal solution?

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

Hint:

Common examples of ideal solutions: \[ \text{Benzene + Toluene} \] \[ n\text{-Hexane + }n\text{-Heptane} \] Similar molecular size and similar intermolecular forces generally favor ideal behavior.

Answer 1

The Correct Option is C

Concept: An ideal solution obeys Raoult's law throughout the entire range of concentration. For an ideal solution: \[ \Delta H_{\text{mix}}=0 \] and \[ \Delta V_{\text{mix}}=0. \] The intermolecular forces between unlike molecules are nearly equal to those between like molecules.

Step 1: Analyze Acetone + Chloroform. Strong hydrogen bonding develops between acetone and chloroform molecules. This causes negative deviation from Raoult's law. Hence it is not ideal.

Step 2: Analyze Ethanol + Acetone. Hydrogen bonding interactions change considerably on mixing. Therefore it is non-ideal.

Step 3: Analyze Phenol + Aniline. Strong intermolecular hydrogen bonding exists between the components. Hence it is non-ideal.

Step 4: Analyze Benzene + Toluene. Both are non-polar aromatic hydrocarbons having similar molecular size and intermolecular forces. The interactions \[ A-A,\quad B-B,\quad A-B \] are almost equal. Therefore the mixture obeys Raoult's law closely.

Step 5: Final conclusion. The ideal solution is \[ \boxed{\text{Benzene + Toluene}} \] Hence, \[ \boxed{\text{Option (3)}} \]