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The Henderson–Hasselbalch equation can be used to estimate the pH of a buffer solution by approximating the actual concentration ratio as the ratio of the analytical concentrations of the acid and of a salt, MA. The equation can also be applied to bases by specifying the protonated form of the base as the acid.
After rearranging the expression defining the acid dissociation constant, and putting pH = −log 10 [H +], one obtains pH = pK a – log ( [AH]/[A −] ) This is a form of the Henderson-Hasselbalch equation. It can be deduced from this expression that when the acid is 1 % dissociated, that is, when [AH]/[A −] = 100, pH = pK a − 2
This is the Henderson–Hasselbalch equation, from which the following conclusions can be drawn. At half-neutralization the ratio [A −] / [HA] = 1; since log(1) = 0, the pH at half-neutralization is numerically equal to pK a. Conversely, when pH = pK a, the concentration of HA is equal to the concentration of A −.
From the titration of protonatable group, one can read the so-called pK a 1 ⁄ 2 which is equal to the pH value where the group is half-protonated (i.e. when 50% such groups would be protonated). The pK a 1 ⁄ 2 is equal to the Henderson–Hasselbalch pK a (pK HH a) if the titration curve follows the Henderson–Hasselbalch equation. [14]
Hence, the pK of each buffer will dictate the ratio of the concentrations of its base and weak acid forms at the given pH, in accordance with the Henderson-Hasselbalch equation. Any condition that changes the balance of one of the buffer systems, also changes the balance of all the others because the buffer systems actually buffer one another ...
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.
The pH can be calculated approximately by the Henderson–Hasselbalch equation: [1] = + where K a is the acid dissociation constant. 3. The pH at the equivalence point depends on how much the weak acid is consumed to be converted into its conjugate base.
Karl Albert Hasselbalch (Danish pronunciation: [ˈkʰɑˀl ˈælˀpɐt ˈhæsl̩ˌpælˀk]; 1 November 1874 – 19 September 1962) was a Danish physician and chemist known for his work on the Henderson–Hasselbalch equation.