Science, Tech, Math › Science Conjugate Base Definition (Chemistry) Bronsted Lowry Acids and Bases Share Flipboard Email Print The conjugate base of hydrochloric acid is the chloride anion. Josh Westrich / 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 Base Definition The Bronsted-Lowry acid-base theory includes the concepts of conjugate acids and conjugate bases. When an acid dissociates into its ions in water, it loses a hydrogen ion. The species that is formed is the acid's conjugate base. A more general definition is that a conjugate base is the base member, X-, of a pair of compounds that transform into each other by gaining or losing a proton. The conjugate base is able to gain or absorb a proton in a chemical reaction. The conjugate acid donates the proton or hydrogen in the reaction. In an acid-base reaction, the chemical reaction is: Acid + Base ⇌ Conjugate Base + Conjugate Acid Key Takeaways: Conjugate Base Conjugate acids and bases are part of the Bronsted-Lowry theory of acids and bases.According to this theory, the species that donates a hydrogen cation or proton in a reaction is a conjugate acid, while the remaining portion or the one that accepts a proton or hydrogen is the conjugate base.The conjugate base may be recognized as an anion. Conjugate Base Examples The general chemical reaction between a conjugate acid and a conjugate base is: HX + H2O ↔ X− + H3O+ In an acid-base reaction, you can recognize the conjugate base because it is an anion. For hydrochloric acid (HCl), this reaction becomes: HCl + H2O ↔ Cl− + H3O+ Here, the chloride anion, Cl−, is the conjugate base. Sulfuric acid, H2SO4 forms two conjugate bases as hydrogen ions are successively removed from the acid: HSO4- and SO42-.