In chemistry and biochemistry, the pH of weakly acidic chemical solutions can be estimated using the Henderson-Hasselbalch Equation:
The equation relates the pH of the weak acid to the numerical value of the acid dissociation constant, Ka, of the acid, and the ratio of the concentrations of the acid and its conjugate base.
Lawrence Joseph Henderson (June 3, 1878 – February 10, 1942) was an American physiologist, chemist, biologist, philosopher, and sociologist. He became one of the leading biochemists of the early 20th century. His work contributed to the Henderson–Hasselbalch equation, used to calculate pH as a measure of acidity.
View the full Wikipedia page for Lawrence Joseph HendersonThe Hammett acidity function (H0) is a measure of acidity that is used for very concentrated solutions of strong acids, including superacids. It was proposed by the physical organic chemist Louis Plack Hammett and is the best-known acidity function used to extend the measure of Brønsted–Lowry acidity beyond the dilute aqueous solutions for which the pH scale is useful.
In highly concentrated solutions, simple approximations such as the Henderson–Hasselbalch equation are no longer valid due to the variations of the activity coefficients. The Hammett acidity function is used in fields such as physical organic chemistry for the study of acid-catalyzed reactions, because some of these reactions use acids in very high concentrations, or even neat (pure).
View the full Wikipedia page for Hammett acidity function![{\displaystyle {\mathrm {pH} }={\mathrm {p} }K_{\mathrm {a} }+\log _{10}\left({\frac {[{\mathrm {Base} }]}{[{\mathrm {Acid} }]}}\right)}](https://wikimedia.org/api/rest_v1/media/math/render/svg/092fb635dc84d06b9de5a2622a393f10057d5a06)