Diprotic and Polyprotic Acids: Two or more dissociable protons Consider the carbonic acid equilibrium

Consider the phosphoric acid equilibrium

 What about the third equivalence point?  Why is first equivalence point “acidic” and second “basic”?

Amino Acids Amphoteric and zwitterionic e.g. Glycine Behaves like a base when titrated with hydrochloric acid Behaves like an acid when titrated with sodium hydroxide

Titration curve for 0.1 M Glycine with equivalent amounts of HCl and NaOH

The Isoelectronic Point (pI) When species is electrically neutral (e.g. zwitterionic glycine) it is said to be isoelectric. The pH is the isoelectric point (pI). Species does not migrate in an electric field. Consider aspartic acid: Only this species is isoelectric, and so

Consider histidine: Stepwise dissociation of a fully protonated histidine molecule