Henderson Equation
The Henderson–Hasselbalch equation describes the derivation of pH as a measure of acidity in biological and chemical systems. The equation is also useful for estimating the pH of a buffer solution and finding the equilibrium pH in acid-base reactions .
An equation expressing the pH of a buffer solution as a function of theconcentration of the weak acid or base and the salt components of thebuffer. Henderson Hasselbalch Equation Definition: an approximate equation that shows the relationship between the pH or pOH of a solution and the pKa or pKb and the ratio of theconcentrations of the dissociated chemical species.
7) The acid dissociation constant (Ka) for this reaction would be given by the equation
$$ K _{a} = \frac {[H^{+}][A^{-}] }{ [HA] } $$This equation can be rearranged to isolate the hydrogen ion concentration on the left, because, remember, we want an equation relating the pH of the solution to the pKa and the extent of ionization of the weak acid. The rearranged form of the equation is
$$ \frac{1 } {[H^{+}]} = 1 / [K _{b}]* [A^{-}] / [HA] $$