Question

Which of the following is / are correct for amino acids?

• A. At pi, there is no net charge on amino acid.
• B. At pH> pi, there is net negative charge on amino acid.
• C. Amino acids are amphoteric in nature.
• D. They are highly soluble in benzene like organic solvents.

Answer 1

Answer: (A), (B), (C)

The correct options are
A At pi, there is no net charge on amino acid.
B At pH> pi, there is net negative charge on amino acid.
C Amino acids are amphoteric in nature.

Amino acids are crystalline solids with relatively high melting points and most are soluble in water and insoluble in non-polar solvents. The amino acid molecule appears to have a charge which changes with pH. An intramolecular neutralization reaction leads to a salt-like ion called a zwitterion.

The carboxyl group can lose a hydrogen ion to become negatively charged. The amine group can accept a hydrogen ion to become positively charged. Thus, amino acids can act as both acidic and basic and are considered amphoteric.

At $ph=pi$ no net charge exists as both groups balance each other.

At $ph>pi$ carboxyl group is dominating. Hence net charge is negative.