Polyprotic Acid Definition in Chemistry

A polyprotic acid is an acid that can donate more than one proton or hydrogen atom per molecule to an aqueous solution. In contrast, a monoprotic acid (e.g., HCl) can only donate one proton per molecule.

Polyprotic Acid Examples

Sulfuric acid (H₂SO₄) is a polyprotic acid because it can donate two hydrogen atoms to an aqueous solution. Specifically, sulfuric acid is a diprotic acid because it has two available hydrogen atoms.

Orthophosphoric acid (H₃PO₄) is a triprotic acid. Successive deprotonations yield H₂PO₄^-, HPO₄^2-, and PO₄^3-. In this acid, the positions of the original three hydrogen atoms are equivalent on the molecule, but removal of subsequent protons becomes less energetically favorable.