Formic acid and acetic acid can be distinguished with

Options

A. sodium
B. `HgCl_2`
C. 2, 4 - dinitropenyl hydrazine
D. `CH_3CH_2overset(-+)(ONa)`

Answer

To distinguish between formic acid (HCOOH) and acetic acid (CH3COOH), we can analyze their reactions with different reagents. Here’s a step-by-step solution:

### Step 1: Reaction with Sodium (Na)
- **Formic Acid:**
\[ \text{HCOOH} + \text{Na} \rightarrow \text{HCOO}^- + \text{Na}^+ + \frac{1}{2} \text{H}_2 \]
- **Acetic Acid:**
\[ \text{CH}_3\text{COOH} + \text{Na} \rightarrow \text{CH}_3\text{COO}^- + \text{Na}^+ + \frac{1}{2} \text{H}_2 \]
- **Conclusion:** Both acids react similarly with sodium, thus they cannot be distinguished using this reagent.

### Step 2: Reaction with Mercuric Chloride (HgCl2)
- **Formic Acid:**
\[ \text{HCOOH} + \text{HgCl}_2 \rightarrow \text{Hg}_2\text{Cl}_2 + \text{CO}_2 + \text{HCl} \]
- This reaction produces a white precipitate (Hg2Cl2).

- **Acetic Acid:**
\[ \text{CH}_3\text{COOH} + \text{HgCl}_2 \text{ does not produce a precipitate.} \]
- **Conclusion:** Formic acid gives a white precipitate with HgCl2, while acetic acid does not. Thus, this test can distinguish between the two acids.

### Step 3: Reaction with 2,4-Dinitrophenylhydrazine (2,4-DNP)
- Both formic acid and acetic acid contain carbonyl groups and can react with 2,4-DNP to form hydrazones.
- **Conclusion:** This reagent does not distinguish between the two acids as both will react similarly.

### Step 4: Reaction with Ethoxide Ion (CH3CH2O^-)
- **Formic Acid:**
\[ \text{HCOOH} + \text{CH}_3\text{CH}_2\text{O}^- \rightarrow \text{CH}_3\text{CH}_2\text{OH} + \text{HCOO}^- \]

- **Acetic Acid:**
\[ \text{CH}_3\text{COOH} + \text{CH}_3\text{CH}_2\text{O}^- \rightarrow \text{CH}_3\text{CH}_2\text{OH} + \text{CH}_3\text{COO}^- \]
- **Conclusion:** Both acids react similarly with ethoxide ion, thus this test cannot distinguish between them.

### Final Conclusion:
The only reagent that can distinguish between formic acid and acetic acid is mercuric chloride (HgCl2), which gives a white precipitate with formic acid but not with acetic acid.