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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.
He wrote the Henderson equation in 1908 to describe the use of carbonic acid as a buffer solution. Karl Albert Hasselbalch later expressed the equation in logarithmic terms, creating the Henderson–Hasselbalch equation. [3] In addition, he described blood gas transport and the general physiology of blood as physico-chemical system (1920–1932).
Speciation of ions refers to the changing concentration of varying forms of an ion as the pH of the solution changes. [1]The ratio of acid, AH and conjugate base, A −, concentrations varies as the difference between the pH and the pK a varies, in accordance with the Henderson-Hasselbalch equation.
This is why weak acids are better absorbed from the stomach and weak bases from intestine where the pH is alkaline. When pH of a solution is equal to pKa of dissolved drug, then 50% of the drug is ionized, another 50% is unionized. This is described by the Henderson-Hasselbalch equation. [citation needed]
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 ...
The Henderson-Hasselbalch equation offers a way to determine the proportion of a substance that is ionized at a given pH. In the stomach, drugs that are weak acids (such as aspirin ) will be present mainly in their non-ionic form, and weak bases will be in their ionic form.
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.
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