Question

Which has highest acidity? ____.

• A. Ethanol
• B. Phenol
• C. Acetic acid
• D. Methanol

Hint:

Carboxylic acids are generally stronger acids than phenols because the negative charge in the carboxylate ion is shared by two oxygens, whereas in phenoxide, the charge spends most of its time on less electronegative carbon atoms.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Acidity is determined by the stability of the conjugate base formed after the loss of a proton ($H^+$). The more stable the anion, the stronger the acid.

Step 2: Detailed Explanation:
1. Alcohols (Ethanol/Methanol): Form alkoxide ions. These are the least stable because there is no resonance to spread the negative charge. 2. Phenol: Forms a phenoxide ion. The negative charge is delocalized over the benzene ring via resonance, making it much more acidic than alcohols. 3. Acetic acid: Forms an acetate ion ($CH_3COO^-$). Here, the negative charge is delocalized over two highly electronegative oxygen atoms. Resonance between equivalent oxygen atoms provides much greater stability than resonance in a carbon ring.

Step 3: Final Answer:
Acetic acid has the highest acidity among the given options.