Science, Tech, Math › Science Henderson Hasselbalch Equation Definition What Is the Henderson Hasselbalch Equation in Chemistry? Share Flipboard Email Print The Henderson-Hasselbalch equation is used to estimate buffer pH. sfe-co2 / 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 August 10, 2019 The Henderson Hasselbalch equation is an approximate equation that shows the relationship between the pH or pOH of a solution and the pKa or pKb and the ratio of the concentrations of the dissociated chemical species. In order to use the equation, the acid dissociation constant must be known. Equation There are multiple ways to write the equation. Two of the most common are: pH = pKa + log ([conjugate base]/[weak acid]) pOH = pKa + log ([conjugate acid]/[weak base]) History An equation to calculate the pH of a buffer solution was derived by Lawrence Joseph Henderson in 1908. Karl Albert Hasselbalch rewrote this formula in logarithmic terms in 1917. Sources Hasselbalch, K. A. (1917). "Die Berechnung der Wasserstoffzahl des Blutes aus der freien und gebundenen Kohlensäure desselben, und die Sauerstoffbindung des Blutes als Funktion der Wasserstoffzahl." Biochemische Zeitschrift. 78: 112–144.Henderson, Lawrence J. (1908). "Concerning the relationship between the strength of acids and their capacity to preserve neutrality." Am. J. Physiol. 21: 173–179.