Question

When pure crystalline amino acids are heated, decomposition generally occurs before the solid melts. Account for this observation.

(Hint: Crystalline amino acids exist ascalled zwitterions.

Short answer

When pure crystalline amino acids are heated, decomposition generally occurs before the solid melts. Because strong intermolecular ionic forces occur.

Step-by-step solution

Introduction of zwitterions

Ions containing two functional groups are called zwitterion ions. A single ion containing both negative and positive electrical charges is called an ion with double charges. As a result, zwitterions are mostly electrically neutral (the net formal charge is usually zero). Sometimes, zwitterions are called "inner salts".

To account for the observation

Crystalline amino acids are zwitterions because each amino acid possesses both charges (positive and negative). Between those zwitterions, strong ionic forces occur between the opposite charges. Ionic species are known for having high melting point because of ionic forces. Therefore, decomposition of amino acids may occur before crystalline melts down.

Hence strong intermolecular ionic forces occur.