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.