Author(s): Henry N Po, N M Senozan
The Henderson–Hasselbalch equation plays a pivotal role in teaching acid–base equilibrium and therefore receives considerable attention in general, analytical, and biochemistry courses. Buffer problems, titration curves, and a host of related phenomena, including the extent of ionization and electrical charge on a polypeptide, can be discussed with relative ease using this equation or its non-logarithmic form. As is often the case, however, for a subject that has moved from one generation of textbooks to the next for much of the century, certain subtleties of the Henderson–Hasselbalch equation have become lost and the distinction between exact and approximate results has blurred. This article presents a critical evaluation of the reliability of the Henderson– Hasselbalch equation and comments on its history, including the development of the pH scale.