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 options, we will analyze the effects of substituents on the acidity of carboxylic acids. The presence of electron-withdrawing groups (EWGs) increases the acidity of the acid by stabilizing the negative charge on the conjugate base.

### Step-by-Step Solution:

1. **Understanding Acidity**: The acidity of a compound is determined by its ability to donate a proton (H⁺). The more stable the conjugate base (the species formed after the acid donates a proton), the stronger the acid.

2. **Identifying Electron-Withdrawing Groups**: Electron-withdrawing groups (like -Cl, -Br, -NO₂) increase the acidity of carboxylic acids by stabilizing the negative charge on the conjugate base. In this case, we will focus on the chlorine substituent.

3. **Comparing Acids**: We will compare the acidity of the following acids:
- Trichloroacetic acid (Cl₃COOH)
- Dichloroacetic acid (Cl₂COOH)
- Monochloroacetic acid (ClCOOH)
- Acetic acid (CH₃COOH)

4. **Analyzing the Effects of Chlorine Substituents**:
- **Trichloroacetic Acid (Cl₃COOH)**: The three chlorine atoms exert a strong -I (inductive) effect, significantly stabilizing the conjugate base (Cl₃COO⁻).
- **Dichloroacetic Acid (Cl₂COOH)**: The two chlorine atoms still provide a -I effect, but it is less than that of trichloroacetic acid.
- **Monochloroacetic Acid (ClCOOH)**: The single chlorine atom has a weaker -I effect compared to the previous two acids.
- **Acetic Acid (CH₃COOH)**: The methyl group (-CH₃) is an electron-donating group (+I effect), which decreases acidity compared to the chlorinated acids.

5. **Ranking the Acids**: Based on the strength of the -I effect from the chlorine substituents, we can rank the acids in order of acidity:
- **Most Acidic**: Trichloroacetic acid (Cl₃COOH)
- Dichloroacetic acid (Cl₂COOH)
- Monochloroacetic acid (ClCOOH)
- Least Acidic: Acetic acid (CH₃COOH)

6. **Conclusion**: Therefore, the most acidic compound among the given options is trichloroacetic acid (Cl₃COOH).

### Final Answer:
The most acidic acid is **trichloroacetic acid (Cl₃COOH)**.

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