Explanation:
According to Bronsted-Lowry, an acid is defined as the specie which is able to donate hydrogen ions when dissolved in water.
For example, [tex]HCl \rightarrow H^{+} + Cl^{-}[/tex]
On the other hand, bases are the species which are able to donate hydroxide ions when dissolved in water.
For example, [tex]NaOH \rightarrow Na^{+} + OH^{-}[/tex]
It is known that the full form of PABA is para-aminobenzoic acid. It's chemical formula is [tex]C_{7}H_{7}NO_{2}[/tex]. This compound can take up a proton and also it is able to lose a proton.
Therefore, PABA acts as both an acid and a base.
The carboxylic group has a chemical formula COOH and it can easily donate a hydrogen ion. Therefore, it is an acid.
And, [tex]NH_{2}[/tex] contains a lone pair of electrons and it is difficult for it to lose a hydrogen ion but it can readily gain a hydrogen ion. Therefore, this group acts as a base.
Thus, we can conclude that PABA is both an acid and a base. The molecule contains both a C O O H; carboxylic group and an − N H 2; amine group. It can act like an [tex]H^{+}[/tex] donor or acceptor.
