Science, Tech, Math › Science Polyprotic Acid Definition in Chemistry Share Flipboard Email Print Sulfuric acid is a polyprotic acid, able to donate two hydrogen ions to aqueous solution. LAGUNA DESIGN / Getty Images Science Chemistry Chemical Laws Basics Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated July 03, 2019 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.