Science, Tech, Math › Science Henderson-Hasselbalch Equation and Example Share Flipboard Email Print JazzIRT / 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. Anne Marie Helmenstine, Ph.D. Facebook Twitter 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. Learn about our Editorial Process Updated on November 28, 2022 You can calculate the pH of a buffer solution or the concentration of the acid and base using the Henderson-Hasselbalch equation. Here's a look at the Henderson-Hasselbalch equation and a worked example that explains how to apply the equation. Henderson-Hasselbalch Equation The Henderson-Hasselbalch equation relates pH, pKa, and molar concentration (concentration in units of moles per liter): apH = pK + log ([A-]/[HA]) [A-] = molar concentration of a conjugate base [HA] = molar concentration of an undissociated weak acid (M) The equation can be rewritten to solve for pOH: pOH = pKb + log ([HB+]/[ B ]) [HB+] = molar concentration of the conjugate base (M) [ B ] = molar concentration of a weak base (M) Example Problem Applying the Henderson-Hasselbalch Equation Calculate the pH of a buffer solution made from 0.20 M HC2H3O2 and 0.50 M C2H3O2- that has an acid dissociation constant for HC2H3O2 of 1.8 x 10-5. This is a straightforward example because all of the terms are given. Solve this problem by plugging the values into the Henderson-Hasselbalch equation for a weak acid and its conjugate base. pH = pKa + log ([A-]/[HA]) pH = pKa + log ([C2H3O2-] / [HC2H3O2]) pH = -log (1.8 x 10-5) + log (0.50 M / 0.20 M) pH = -log (1.8 x 10-5) + log (2.5) pH = 4.7 + 0.40 pH = 5.1 Cite this Article Format mla apa chicago Your Citation Helmenstine, Anne Marie, Ph.D. "Henderson-Hasselbalch Equation and Example." ThoughtCo, Nov. 28, 2022, thoughtco.com/henderson-hasselbalch-equation-and-example-603648. Helmenstine, Anne Marie, Ph.D. (2022, November 28). Henderson-Hasselbalch Equation and Example. Retrieved from https://www.thoughtco.com/henderson-hasselbalch-equation-and-example-603648 Helmenstine, Anne Marie, Ph.D. "Henderson-Hasselbalch Equation and Example." ThoughtCo. https://www.thoughtco.com/henderson-hasselbalch-equation-and-example-603648 (accessed May 29, 2023). copy citation