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).