Question

Although phenoxide ion has more number of resonating structures than carboxylate ion, carboxylic acid is a stronger acid than phenol. Why?

Answer 1

Although phenoxide ion has more number of resonating structures than carboxylate ion, carboxylic acid is a stronger acid than phenol.
This is explained as below.
In case of phenoxide ion, the negative charge is present on one electronegative oxygen atom and the lesser electronegative carbon atoms.
The contribution of resonance structures towards resonance stabilization of phenoxide ion is less.
In case of carboxylate ion, the negative charge is present on two electronegative oxygen atoms.
The contribution of resonance structures towards resonance stabilization of carboxylate ion is more.
Hence, the carboxylate ion is more resonance stabilized than the phenoxide ion. Due to this, carboxylate ion is more stable than phenoxide ion.
Higher stability leads to greater acidic strength.