Question

Why is observed molar mass of acetic acid in benzene greater than actual molar mass?

• A. Due to ionization of solute particles
• B. Due to association of solute particles
• C. Due to hydrolysis of solute
• D. Due to dissociation of solute particles

Hint:

In solvents like benzene, some solutes can form dimers or higher-order aggregates, which leads to an increase in observed molar mass compared to the theoretical value.

Answer 1

The Correct Option is B

Step 1: Understanding molar mass in different solvents.
In solvents like benzene, acetic acid undergoes association, which means the molecules of acetic acid tend to form dimers. This increases the observed molar mass as the dimers are considered as a single entity during the measurement.
Step 2: Analyzing the options.
(A) Due to ionization of solute particles: Incorrect. Ionization would lead to a decrease in the observed molar mass due to the formation of ions, which is not the case here.
(B) Due to association of solute particles: Correct — In benzene, acetic acid molecules associate, forming dimers, which increases the observed molar mass.
(C) Due to hydrolysis of solute: Incorrect. Hydrolysis is not involved in this process.
(D) Due to dissociation of solute particles: Incorrect. Dissociation would lead to a decrease in observed molar mass, which is not the case here.
Step 3: Conclusion.
The correct answer is (B) Due to association of solute particles, as acetic acid forms dimers in benzene, leading to an increase in observed molar mass.