What Is Polyprotic Acid Chemistry Definition

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-, HPO42-, and PO43-. 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.