Why carboxylic acids are more acidic than alcohols?

Carboxylic acids are more acidic than alcohols. Carboxylic acids react with Na, NaOH, Na2CO3 and NaHCO3. But alcohols only reacts with Na. Reson is, carboxylate anion is more stable than alkoxide anion.


Now we look stability of these carboxylate anion and alkoxide anion.


How do we know carboxylic acids are more acidic than alcohols?

  1. Carboxylic acid reacts with Na, NaOH. But alcohols only reacts with Na.
  2. Carboxylic react with Na2CO3 and NaHCO3. But alcohols doesn't.
  3. In same concentration solutions of carboxylic acids and alcohols, pH of carboxylic acid is low.
  4. Ka of ethanol = 10-18 moldm-3 , Ka of ethanoic acid = 1.8 * 10-5 moldm-3


Now, we look why carboxylic acids are more acidic than alcohols.

The main reason is the stability of anions of alcohols and carboxylic acids.


Carboxylic acid solution

The anion forming, when H is removed from carboxylic acid is called as carboxylate anion.

carboxylic acid gives carboxylate anion

Carboxylate anion can show resonance structures. Therefore carboxylate anion can spread it's negative charge by carbonyl group. So that brings a stability to the carboxylate anion and equilibrium goes to the right side.

Resonance structures of carboxylate anion

resonance structures of carboxylate anion


Alcoholic solution

The anion forming, when H is removed from alcohol is called as alkoxode anion.

alcohol alkoxide ion

Alkokside anion can't show resonance structures. Therefore stability of alkoxide is low. So equilibrium goes to the left side.



What is more acidic, benzoic acid or acetic acid?

Benzoic acid is much acidic than acetic acid. Benzoate ion is more stable than acetate ion.