Science, Tech, Math › Science Polyprotic Acids Introduction to Polyprotic Acids Share Flipboard Email Print Phosphoric acid is a polyprotic acid. Laguna Design / Getty Images Science Chemistry Basics Chemical Laws 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 March 06, 2017 There are many different types of acids. This is an introduction to polyprotic acids, with an example of the ionization steps of a polyprotic acid. What Is a Polyprotic Acid? + + Ka1 > Ka2 > Ka3 Example of a Polyprotic Acid 3 4 H3PO4(aq) ⇔ H+(aq) + H2PO4-(aq)Ka1 = [H+][H2PO4-]/[H3PO4] = 7.5 x 10-3H2PO4-(aq) ⇔ H+(aq) + HPO42-(aq)Ka2 = [H+][HPO42-]/[H2PO4-] = 6.2 x 10-8HPO42-(aq) ⇔ H+(aq) + PO43-(aq)Ka3 = [H+][PO43-]/[HPO42-] = 4.8 x 10-13 Learn More