ABSTRACT
Although the material included here should have been part of Chapter 18, keeping with the structure of this book, the permanent structure of classical thermodynamics has been kept separate from material that may change with time. The measurability of the activity of individual ions may not be considered to be definitely settled, as there are people who still maintain that these measurements are impossible to achieve in concentrated solutions above 0.01 m. A historical perspective of roots of that point of view is given elsewhere [1] and discussed briefly in the closing comments of this chapter. In addition, two discussions available in the literature illustrate the extent of the disagreement on this matter [2–10]. In both cases, the editor of the respective journal closed the debate once the informed reader could judge how much each of the two sides knew about the subject. Being a matter of experimental measurements, this topic can only be resolved with independent laboratory tests. The arguments in favor of the measurability of the activity of individual ions have been presented elsewhere [1,2,6,11–30]. This chapter presents the main points supporting these views, compares experimental results obtained by different researchers in concentrated electrolyte solutions, and briefly mentions recent theoretical advances in the field.
