Now invert —log [HA]/[A ], which involves changing its sign, to obtain the Henderson-Hasselbalch equation:

Stated more generally, pH = pKa + log

[proton acceptor] [proton donor]

This equation fits the titration curve of all weak acids and enables us to deduce a number of important quantitative relationships. For example, it shows why the p^a of a weak acid is equal to the pH of the solution at the midpoint of its titration. At that point, [HA] equals [A—], and pH = pKa + log 1 = pKa + 0 = pKa

As shown in Box 2-3, the Henderson-Hasselbalch equation also allows us to (1) calculate pKa, given pH and the molar ratio of proton donor and acceptor; (2) calculate pH, given pKa and the molar ratio of proton donor and acceptor; and (3) calculate the molar ratio of proton donor and acceptor, given pH and pKa.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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