Final answer:
Zwitterions can only form at the isoelectric point when the net charge on an amino acid is zero.
Step-by-step explanation:
Zwitterions are compounds that have a positive charge on one atom and a negative charge on another atom in the same molecule. They are commonly found in amino acids. The isoelectric point (pI) is the specific pH at which the net charge on an amino acid is zero, meaning it exists as a zwitterion. At this pH, the positive and negative charges on the amino acid are balanced.
For example, consider the amino acid glycine, which has a pI of approximately 6.0. Below pH 6.0, glycine carries a net positive charge and exists predominantly as a positively charged species. Above pH 6.0, glycine carries a net negative charge and exists predominantly as a negatively charged species. At pH 6.0, glycine is neutral and exists as a zwitterion.