How do you explain the amphoteric behaviour of amino acids?

Explanation

Amino acids have basic `(NH_(2))` and acidic (COOH) groups. These are therefore, amphoteric in nature. However, they exhibit these characters in the amino acid molecule itself i.e., `NH_(2)` group (basic) accepts a proton from COOH group (acidic) in the same molecule. Therefore, `alpha`-amino acid exists as a dipolar ion.
`H_(2)overset(..)(N)-underset(R )underset(|)(C )H-COOH hArr H_(3)overset(+)(N)-underset(R )underset(|)(C )H-COO^(-)` (Dipolar ion)