14.16: How do you explain the amphoteric behaviour of amino acids?

In aqueous solution, the carboxyl group of an amino acid can lose a proton and the amino group can accept a proton to give a dipolar ion known as zwitter ion.

                   O                                                       R-CH-C-O-HR-CH-C-O-                                             |      :NH2                                   N+H3                                             Zwitter ion 

Therefore, in zwitter ionic form, the amino acid can act both as an acid and as a base.

Thus, amino acids show amphoteric behaviour.