Question

The correct order of increasing acid strength is

• A. Phenol $<$ Ethanol $<$ Chloroacetic acid $<$ Acetic acid
• B. Chloroacetic acid $<$ Acetic acid $<$ Ethanol $<$ Phenol
• C. Ethanol $<$ Phenol $<$ Acetic acid $<$ Chloroacetic acid
• D. Phenol $<$ Acetic acid $<$ Chloroacetic acid $<$ Ethanol

Hint:

Acid strength increases when the conjugate base is stabilized. Resonance and $-I$ effects (electron withdrawing groups) strongly enhance acidity.

Answer 1

The Correct Option is C

Step 1: Compare Ethanol and Phenol.
- Ethanol (\(CH_3CH_2OH\)) is a neutral alcohol with very weak acidic character because the \(O–H\) bond is not easily ionizable.
- Phenol (\(C_6H_5OH\)) is more acidic than ethanol because the phenoxide ion formed after deprotonation is stabilized by resonance in the benzene ring.
\[ $\Rightarrow$ Ethanol < Phenol \]

Step 2: Compare Phenol and Acetic acid.
- Acetic acid (\(CH_3COOH\)) is much more acidic than phenol because the acetate ion is stabilized by resonance involving two oxygen atoms.
\[ $\Rightarrow$ Phenol < Acetic acid \]

Step 3: Compare Acetic acid and Chloroacetic acid.
- Chloroacetic acid (\(ClCH_2COOH\)) is stronger than acetic acid because the electron-withdrawing chlorine atom shows the $-I$ (inductive) effect, which stabilizes the conjugate base (chloroacetate ion).
\[ $\Rightarrow$ Acetic acid < Chloroacetic acid \] Final Order:
\[ \text{Ethanol} < \text{Phenol} < \text{Acetic acid} < \text{Chloroacetic acid} \] Thus, the correct option is (C).