How do you explain the amphoteric behaviour of amino acids?
Amino acids exhibit amphoteric behavior because they contain both an amino group (-NH₂) and a carboxyl group (-COOH) as substituents on the same α-carbon.
A particular property of amino acids is the ionizable nature of these -NH₂ and -COOH groups. In solutions of different pH, the structure of amino acids changes. They can exist in different ionic forms depending on the pH of the medium.
The amino acid can exist as a zwitterion (dipolar ion) where the amino group is protonated (NH₃⁺) and the carboxyl group is deprotonated (COO⁻). This allows amino acids to react with both acids and bases, exhibiting amphoteric nature.
Explanation
The textbook explains that amino acids are organic compounds containing both an amino group and an acidic (carboxyl) group on the same α-carbon. The ionizable nature of these groups allows amino acids to change structure in solutions of different pH, forming zwitterions. This dual presence of acidic and basic groups enables amino acids to behave as amphoteric substances.