Question

Identify the strongest acid among: acetic acid, chloroacetic acid, dichloroacetic acid, and trichloroacetic acid.

• A. Acetic acid
• B. Chloroacetic acid
• C. Dichloroacetic acid
• D. Trichloroacetic acid

Hint:

Electron-withdrawing groups such as halogens increase acidity by stabilizing the conjugate base through the \(-I\) effect.

Answer 1

The Correct Option is D

Concept: The strength of carboxylic acids increases with the presence of electron-withdrawing groups. These groups stabilize the conjugate base through the inductive effect (\(-I\) effect). Chlorine is a strong electron-withdrawing group.

Step 1: Compare the number of chlorine atoms. \[ \text{CH}_3\text{COOH} \] Acetic acid has no electron-withdrawing substituents. \[ \text{ClCH}_2\text{COOH} \] Chloroacetic acid has one chlorine atom. \[ \text{Cl}_2\text{CHCOOH} \] Dichloroacetic acid has two chlorine atoms. \[ \text{Cl}_3\text{CCOOH} \] Trichloroacetic acid has three chlorine atoms.

Step 2: Greater the number of chlorine atoms, stronger the \(-I\) effect and higher the acidity. Thus the acidity order is \[ \text{Trichloroacetic acid}>\text{Dichloroacetic acid}>\text{Chloroacetic acid}>\text{Acetic acid} \]

Step 3: Final result. \[ \boxed{\text{Trichloroacetic acid}} \]