Depression in Freezing Point Method and Molecular Weight of Benzoic Acid in Benzene

Depression in Freezing Point Method:
The depression in freezing point method is a technique used to determine the molecular weight of a solute in a solvent. It is based on the principle that when a solute is dissolved in a solvent, it lowers the freezing point of the solvent. This lowering of freezing point is directly proportional to the concentration of the solute in the solvent.

Molecular Weight of Benzoic Acid in Benzene:
In this case, the molecular weight of benzoic acid in benzene is determined using the depression in freezing point method. When benzoic acid is dissolved in benzene, it forms dimers through intermolecular hydrogen bonding. Each dimer consists of two molecules of benzoic acid held together by hydrogen bonds.

Dimerization of Benzoic Acid:
The formation of dimers in the solution of benzoic acid in benzene affects the freezing point depression. The presence of dimers increases the effective concentration of the solute in the solution, leading to a greater depression in freezing point.

Explanation of Correct Answer:
The correct answer to the question is option B, which states that the depression in freezing point method corresponds to the dimerization of benzoic acid. This is because the formation of dimers in the solution of benzoic acid in benzene is responsible for the observed depression in freezing point.

The presence of dimers increases the effective concentration of benzoic acid in the solution, leading to a greater depression in freezing point. This can be explained by the fact that the formation of dimers reduces the number of free solute particles in the solution, resulting in a lower concentration of solute particles available to lower the freezing point.

Therefore, the depression in freezing point method measures the degree of dimerization of benzoic acid in benzene, which in turn provides information about the molecular weight of benzoic acid in benzene.

In conclusion, the depression in freezing point method is used to determine the molecular weight of benzoic acid in benzene, and the observed depression corresponds to the dimerization of benzoic acid in the solution.