THE DEFINITION AND MEANING OF pH

Abstract

After a critical review of the meanings that are attached to the term "pH," the author makes the following recommendations: 1. Wherever the term "pH" is used in exact thermodynamic equations it should mean only the negative logarithm of the hydrogen ion concentration and should always be written "pHa". Activity coefficients should appear explicitly in a separate term. 2. Where "pH" is used as an empirical means of specifying the acid-base properties of solns., derived from some particular means of measurement, it should be written without subscript. In giving its value, the method of measurement, its standardization, and details of the composition of the soln. (such as the- kinds and concs, of buffer and neutral salts) should also always be specified. 3. The use of the concept of "membrane potential" should be avoided. 4. The term "pH" should never be used with reference to interphases.