The osmotic pressure of a solution of benzoic acid dissolved in benzene is less than expected because:

Options

A. benzoic acid is an organic solute
B. benzene is a non-polar solvent
C. benzoic acid dissociates in benzene
D. benzoic acid gets associated in benzene

Answer

To solve the question regarding the osmotic pressure of a solution of benzoic acid in benzene being less than expected, we can break down the reasoning step by step:

### Step 1: Understand Osmotic Pressure
Osmotic pressure is the pressure required to stop the flow of solvent into a solution through a semipermeable membrane. It is directly related to the concentration of solute particles in the solution. The more particles present, the higher the osmotic pressure.

**Hint:** Remember that osmotic pressure depends on the number of solute particles in the solution.

### Step 2: Identify the Nature of Benzoic Acid
Benzoic acid (C6H5COOH) is an organic compound that can exist in a dimeric form when dissolved in non-polar solvents like benzene. In a typical scenario, we would expect it to dissociate into individual molecules.

**Hint:** Consider how solutes behave in non-polar solvents compared to polar solvents.

### Step 3: Analyze the Solvent
Benzene is a non-polar solvent. Non-polar solvents do not stabilize ions or polar molecules effectively, which can lead to different interactions between solute and solvent.

**Hint:** Think about how the polarity of the solvent affects the behavior of the solute.

### Step 4: Dimerization of Benzoic Acid
In benzene, benzoic acid tends to dimerize. This means that two molecules of benzoic acid combine to form a dimer (C6H5COOH)2. As a result, instead of contributing two particles to the solution, they contribute only one particle (the dimer).

**Hint:** Recall that dimerization reduces the number of effective solute particles in the solution.

### Step 5: Effect on Osmotic Pressure
Since the dimerization reduces the number of solute particles in the solution, the osmotic pressure will be lower than expected. This is because osmotic pressure is proportional to the number of particles in solution; fewer particles mean lower osmotic pressure.

**Hint:** Connect the reduction in particle number to the decrease in osmotic pressure.

### Conclusion
The osmotic pressure of the solution of benzoic acid dissolved in benzene is less than expected because benzoic acid gets associated (or dimerizes) in benzene, leading to a decrease in the number of solute particles.

**Final Answer:** The correct choice is option D: The osmotic pressure of the solution of benzoic acid dissolved in benzene is less than expected because benzoic acid gets associated in benzene.