Activities of Electrolytes

Abstract

The consideration of the solutions of electrolytes by using the notion of activity is that which, very highly, has been the matter of the largest number of studies, in any case in the realm of the study of activities. The handling of the activities is quasi-imperative as soon as one is faced with solutions of electrolytes since, among all the solutions, the latter are those which exhibit the most strong nonideality effects. This is due to the charges brought by ions. For example, even when the “concentrations” of electrolytes are weak, equilibria constants in which ions intervene are not constant, on the contrary to the solutions of nonelectrolytes. Then, it is imperative to work with very weak “concentrations” so that these constants can be considered as being constant.

Therefore, as soon as a solution does contain ions, the chemical potentials of the different solutes must be the matter of supplementary theoretical and practical considerations with respect to the solutions of nonelectrolytes. One is induced, indeed, not only to define the activity and the activity coefficient of the whole electrolyte but also for the ions coming from its dissociation.

The chapter is focused on the setting up of relations linking all these kinds of activities. However these relations are fundamentally the same in the cases of strong and weak electrolytes. Actually, it is clearer to successively treat both kinds rather than to do that simultaneously. The study shows that a parameter of great importance is the electric charge of the different intervening ions.