Phenol and benzoic acid may be distinguished by their reaction with :

Options

A. NaOH
B. `Na HCO_(3)`
C. `Na_(2) CO_(3)`
D. `H_(2) SO_(4)`

Answer

To distinguish between phenol and benzoic acid, we can analyze their reactions with various reagents. Here’s a step-by-step breakdown of the solution:

### Step 1: Understand the Structures
- **Phenol** has the structure: C6H5OH (a hydroxyl group attached to a benzene ring).
- **Benzoic Acid** has the structure: C6H5COOH (a carboxylic acid group attached to a benzene ring).

### Step 2: Identify the Acidity
- Both phenol and benzoic acid are acidic, but benzoic acid is a stronger acid than phenol.
- **Phenol** is a weak acid, while **benzoic acid** is a stronger acid due to the stability of its conjugate base (benzoate ion) through resonance.

### Step 3: Analyze the Reactions with Sodium Hydroxide (NaOH)
- When phenol reacts with NaOH, it forms sodium phenoxide:
\[ \text{C6H5OH} + \text{NaOH} \rightarrow \text{C6H5O}^- \text{Na}^+ + \text{H2O} \]
- When benzoic acid reacts with NaOH, it forms sodium benzoate:
\[ \text{C6H5COOH} + \text{NaOH} \rightarrow \text{C6H5COO}^- \text{Na}^+ + \text{H2O} \]
- **Conclusion**: Both phenol and benzoic acid react with NaOH to form soluble salts, so NaOH cannot distinguish between them.

### Step 4: Analyze the Reactions with Sodium Bicarbonate (NaHCO3)
- **Phenol** does not react with NaHCO3, and no effervescence occurs.
- **Benzoic Acid** reacts with NaHCO3, producing sodium benzoate and releasing carbon dioxide (effervescence):
\[ \text{C6H5COOH} + \text{NaHCO3} \rightarrow \text{C6H5COO}^- \text{Na}^+ + \text{H2O} + \text{CO2} \uparrow \]
- **Conclusion**: The effervescence of CO2 when reacting with benzoic acid allows us to distinguish it from phenol.

### Step 5: Analyze the Reactions with Sodium Carbonate (Na2CO3)
- Similar to NaHCO3, phenol does not react with Na2CO3, resulting in no effervescence.
- Benzoic acid will react with Na2CO3, producing sodium benzoate and releasing CO2, albeit more slowly than with NaHCO3:
\[ \text{C6H5COOH} + \text{Na2CO3} \rightarrow \text{C6H5COO}^- \text{Na}^+ + \text{H2O} + \text{CO2} \uparrow \]
- **Conclusion**: Na2CO3 can also distinguish between phenol and benzoic acid due to the release of CO2.

### Step 6: Analyze the Reaction with Sulfuric Acid (H2SO4)
- Both phenol and benzoic acid undergo sulfonation when treated with H2SO4, but this does not lead to a clear distinction:
- Phenol reacts to form ortho and para sulfonated products.
- Benzoic acid reacts to form a meta sulfonated product.
- **Conclusion**: The sulfonation does not provide a clear distinction in a practical sense, as both products will still be soluble.

### Final Conclusion
The reagents that can be used to distinguish between phenol and benzoic acid are:
- **Sodium Bicarbonate (NaHCO3)**: Produces effervescence with benzoic acid but not with phenol.
- **Sodium Carbonate (Na2CO3)**: Also produces effervescence with benzoic acid but at a slower rate.

Thus, the correct answer is **B (NaHCO3)** and **C (Na2CO3)**.

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