How will you account for the acidic nature of carboxylic acid ?

Explanation

The Carboxylic acid molecule is resonance hybrid of the following two structures.

In structure (II) the oxygen atom of the -OH group carries +ve charge. Therefore the electron pair of O-H bond is displaced towards O-atom. Due to this displacement of electrons, the release of proton `(H^(+))` and a carboxylate in we formed.
`RCOOH hArr RCOO^(-) + H^(+)`
The carboxylica ion `(RCOO^(-))` formed is also resonance stabilised as shown below.

Thus we find that both carboxylic acid as well as carboxylate ion are resonance stabilised. However resonance stabilisation of carboxylate ion is letter than that of carboxylic acids as explained below.
(a) The two resonating structures for carboxylic acid are not equivalent, while the two resonating structures for carboxylate anion are equivalent.
(b) The resonating structures (II) for carboxylic acid involves charge separation. Thus it has higher energy and hence lesser contribution towards resonance hybrid. The two resonating structures for carboxylate ion are of equal energy and as such contribute equally towards resonance hybrid.
Therefore, carboxylate ion is more resonance stabilised than carboxylic acid. Thus carboxylic acids readily give a proton to form stable carboxylate ion
`RCOOH hArr RCOO^(-) + H^(+)`