Which acid is stronger or Which is most acidic `:`

Options

A. `Cl_(2) CHCOOH`
B. `ClCH_(2)COOH`
C. `CH_(3)COOH`
D. `Cl_(3)COOH`

Answer

To determine which acid is stronger among the given acetic acid derivatives, we need to analyze the stability of the anions formed after the removal of a hydrogen ion (H⁺) from each acid. The more stable the anion, the stronger the acid.

### Step-by-Step Solution:

1. **Identify the Acids**: We have four acids to compare:
- Trichloroacetic acid (CCl₃COOH)
- Dichloroacetic acid (CCl₂HCOOH)
- Monochloroacetic acid (CClH₂COOH)
- Acetic acid (CH₃COOH)

2. **Understand the Concept of Acidity**: The acidity of an acid is determined by the stability of its conjugate base (anion) after losing H⁺. The more stable the anion, the stronger the acid.

3. **Determine the Conjugate Bases**:
- The conjugate base of trichloroacetic acid is CCl₃COO⁻.
- The conjugate base of dichloroacetic acid is CCl₂HCOO⁻.
- The conjugate base of monochloroacetic acid is CClH₂COO⁻.
- The conjugate base of acetic acid is CH₃COO⁻.

4. **Analyze the Effects of Substituents**:
- Chlorine atoms are electronegative and exert a -I (inductive) effect, which stabilizes the negative charge on the conjugate base by dispersing it.
- The more chlorine atoms present, the greater the -I effect, leading to increased stability of the anion.

5. **Compare the Stability of Conjugate Bases**:
- Trichloroacetic acid (3 Cl) will have the most stable anion due to the strong -I effect from three chlorine atoms.
- Dichloroacetic acid (2 Cl) will be less stable than trichloroacetic acid but more stable than monochloroacetic acid.
- Monochloroacetic acid (1 Cl) will be less stable than dichloroacetic acid.
- Acetic acid (0 Cl) will be the least stable as it has no electronegative substituents to stabilize the negative charge.

6. **Rank the Acids**: Based on the stability of their conjugate bases, we can rank the acids from strongest to weakest:
- Trichloroacetic acid > Dichloroacetic acid > Monochloroacetic acid > Acetic acid.

7. **Conclusion**: The strongest acid among the given options is **trichloroacetic acid**.

### Final Answer:
The most acidic acid is **trichloroacetic acid**.

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