Question

According to the graph given below, zwitterions for an amino acid X are most likely to be obtained in a solution of pH

• A. 1
• B. 2
• C. 6
• D. 10

Answer 1

The correct option is C 6

When an amino acid is dissolved in water at a particular pH, it exists in solution as dipolar ion or zwitterion. The ionisable nature of $N{H}_2$ and COOH groups can cause them to form $N{H}_3^{+}$ and $CO{O}^{-}$ by gain and loss of a proton respectively at a particular range of pH. At this point, the net charge on an amino acid becomes zero and the amino acid is said to be in the zwitterionic form. The pH at which an amino acid exists in zwitterion is called its iso-electric pH. From the graph, it is quite evident that the net charge on the amino acid is zero near pH=6. At this pH, the amino acid occurs as zwitterions.