Science, Tech, Math › Science Conjugate Acid Definition in Chemistry Conjugate Acid-Base Pairs Share Flipboard Email Print A conjugate acid is formed when a base gains a hydrogen or proton. Jutta Klee / 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 March 06, 2019 Conjugate Acid Definition Conjugate acids and bases are Bronsted-Lowry acid and base pairs, determined by which species gains or loses a proton. When a base dissolves in water, the species that gains a hydrogen (proton) is the base's conjugate acid. Acid + Base → Conjugate Base + Conjugate Acid In other words, a conjugate acid is the acid member, HX, of a pair of compounds that differ from each other by gain or loss of a proton. A conjugate acid can release or donate a proton. A conjugate base is the name given to the species that remains after the acid has donated its proton. The conjugate base can accept a proton. Conjugate Acid Example When the base ammonia reacts with water, the ammonium cation is the conjugate acid that forms: NH3(g) + H2O(l) → NH+4(aq) + OH−(aq) Source Zumdahl, Stephen S., Zumdahl, Susan A. (2007). Chemistry. Houghton Mifflin. ISBN 0618713700.