Question

In case of association, abnormal molar mass of solute will:

• A. decrease
• B. increase
• C. remain same
• D. first increase and then decrease

Hint:

In case of association, the abnormal molar mass tends to decrease due to the aggregation of solute molecules.

Answer 1

The Correct Option is B

To solve the problem, we need to understand what happens to the molar mass of a solute when association occurs in a solution.

1. Understanding Association in Solutions:
Association refers to the process in which solute molecules or ions combine to form larger aggregates or clusters, typically due to intermolecular forces such as hydrogen bonding. This happens mostly in polar solvents like water, where molecules like acids, bases, or other solutes tend to form dimers, trimers, etc.

2. Effect on Molar Mass:
When association occurs, the apparent molar mass of the solute will appear to be greater than the actual molar mass. This is because the association leads to fewer particles in solution (fewer particles are dissociated), and hence, the observed colligative properties (such as freezing point depression or boiling point elevation) will be less than expected for the number of particles, which makes the calculated molar mass higher.

3. Key Concept:
Abnormal molar mass refers to the measured molar mass that is higher than the expected value due to association. For example, when a dimer is formed, the apparent molar mass will be double the actual molar mass of the solute.

Final Answer:
In case of association, the abnormal molar mass of the solute will increase.