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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 p K a .
Lawrence Henderson was born in Lynn, Massachusetts the son of a business man Joseph Henderson and his wife. He entered Harvard at the age of 16 in 1894. His father was a ship chandler whose principal business was located in nearby Salem, but who also conducted business in Saint Pierre and Miquelon, a French Overseas collectivity off the coast of Canada.
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 ] Most p K a calculation methods silently assume that all titration curves are Henderson–Hasselbalch shaped, and p K a values in p K a calculation programs are therefore often determined in this way.
The Henderson–Hasselbalch equation, which is derived from the law of mass action, can be modified with respect to the bicarbonate buffer system to yield a simpler equation that provides a quick approximation of the H + or HCO − 3 concentration without the need to calculate logarithms: [7]
That is, when several buffers are present together in the same solution, they are all exposed to the same hydrogen ion activity. 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.
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.