General procedure for the easy calculation of pH in an introductory course of general or analytical chemistry

Abstract

All pH calculations for simple acid-base systems used in introductory courses on general or analytical chemistry can be carried out by using a general procedure requiring the use of predominance diagrams. In particular, the pH is calculated as the sum of an independent term equaling the average pKa values of the acids involved in the diagram step and a concentration-dependent value, calculated as the ratio between pC (that is, -log Cacid + log Cbase, corresponding to the predominant species involved in the predominance diagram step) and the number of pH-controlling acid-base pairs involved in the diagram step (one or two for conjugate or nonconjugate systems, respectively). A number of acid-base features can be readily explained via this procedure. This methodology can be extended to complexation equilibria. © 2014 The American Chemical Society and Division of Chemical Education, Inc.