Henderson Hasselbalch Equation Definition

What Is the Henderson Hasselbalch Equation in Chemistry?

Colored buffer solutions
The Henderson-Hasselbalch equation is used to estimate buffer pH.

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The Henderson Hasselbalch equation is an approximate equation that shows the relationship between the pH or pOH of a solution and the pKa or pKb and the ratio of the concentrations of the dissociated chemical species. In order to use the equation, the acid dissociation constant must be known.

Equation

There are multiple ways to write the equation. Two of the most common are:

pH = pKa + log ([conjugate base]/[weak acid])

pOH = pKa + log ([conjugate acid]/[weak base])

History

An equation to calculate the pH of a buffer solution was derived by Lawrence Joseph Henderson in 1908. Karl Albert Hasselbalch rewrote this formula in logarithmic terms in 1917.

Sources

  • Hasselbalch, K. A. (1917). "Die Berechnung der Wasserstoffzahl des Blutes aus der freien und gebundenen Kohlensäure desselben, und die Sauerstoffbindung des Blutes als Funktion der Wasserstoffzahl." Biochemische Zeitschrift. 78: 112–144.
  • Henderson, Lawrence J. (1908). "Concerning the relationship between the strength of acids and their capacity to preserve neutrality." Am. J. Physiol. 21: 173–179.