Question

Define the term zwitterion.

Short answer

Provide an example in your explanation. A zwitterion is a molecule that has both positive and negative charges but is overall electrically neutral. These molecules typically contain an internal acid-base pair that results in the formation of charged groups within the same molecule. Zwitterions form when molecules containing both acidic and basic functional groups transfer a proton (\(H^+\)) from the acidic group to the basic group within the molecule, making the molecule electrically neutral. This process occurs at a specific pH value called the isoelectric point (pI). A common example of compounds that form zwitterions are amino acids, which contain both an acidic carboxyl group \((-COOH)\) and a basic amino group \((-NH_2)\). At their isoelectric point, the carboxyl group loses a proton, forming a negatively charged carboxylate ion \((-COO^-\)), and the amino group gains a proton, forming a positively charged ammonium ion \((NH_3^+)\), resulting in a zwitterion with overall neutral charge.

Step-by-step solution

Define zwitterion

A zwitterion is a molecule that has both positive and negative charges, but is overall electrically neutral. These molecules typically contain an internal acid-base pair that results in the formation of charged groups within the same molecule.

Explain why zwitterions form

Zwitterions commonly form in molecules containing both acidic and basic functional groups. The transfer of a proton (\(H^+\)) from the acidic group to the basic group within the molecule results in the formation of charged groups, making the molecule a zwitterion. This internal transfer of protons is in response to the molecule's stability and occurs at a specific pH value called the isoelectric point (pI), where the molecule is electrically neutral.

Provide an example

Amino acids are a common example of compounds that form zwitterions. Amino acids contain both an acidic carboxyl group \((-COOH)\) and a basic amino group \((-NH_2)\). At their isoelectric point, the carboxyl group loses a proton, forming a negatively charged carboxylate ion \((-COO^-\)), and the amino group gains a proton, forming a positively charged ammonium ion \((NH_3^+)\). As a result, the amino acid molecule becomes a zwitterion with overall neutral charge.