Acetic acid shows a molecular mass of 120 when dissolved in benzene. This is because of

Options

A. Solvation process
B. Intermolecular H-bonding
C. Presence of H atom at `alpha` C
D. Dimerisation

Answer

To solve the question regarding why acetic acid shows a molecular mass of 120 when dissolved in benzene, we can follow these steps:

### Step 1: Understand the Molecular Mass of Acetic Acid
Acetic acid (CH₃COOH) has the following molecular formula:
- Carbon (C): 2 atoms × 12 g/mol = 24 g/mol
- Hydrogen (H): 4 atoms × 1 g/mol = 4 g/mol
- Oxygen (O): 2 atoms × 16 g/mol = 32 g/mol

Calculating the total:
\[ \text{Molecular mass of acetic acid} = 24 + 4 + 32 = 60 \text{ g/mol} \]

### Step 2: Identify the Behavior of Acetic Acid in Benzene
When acetic acid is dissolved in benzene, it undergoes dimerization. This means that two molecules of acetic acid combine to form a dimer.

### Step 3: Calculate the Molecular Mass of the Dimer
Since the dimer consists of two acetic acid molecules, the molecular mass of the dimer is:
\[ \text{Molecular mass of dimer} = 2 \times 60 \text{ g/mol} = 120 \text{ g/mol} \]

### Step 4: Explain the Reason for Dimerization
The dimerization occurs due to intermolecular hydrogen bonding between the acetic acid molecules. This interaction stabilizes the dimer formation in the benzene solvent.

### Conclusion
Thus, the molecular mass of acetic acid appears to be 120 g/mol when dissolved in benzene due to the dimerization of acetic acid molecules, which is facilitated by intermolecular hydrogen bonding.

### Final Answer
The reason acetic acid shows a molecular mass of 120 when dissolved in benzene is due to dimerization, which is a result of intermolecular hydrogen bonding.

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