Activity coefficients in mixed-electrolyte solutions

Abstract

The limitations of Guggenheim's equations for the activity coefficients of mixed electrolytes are well known. Some examples of these limitations are given. Modern theories of mixed-electrolyte solutions may be regarded as building on the Guggenheim treatment by adding terms for binary interactions of ions of the same sign and also ternary interactions involving two ions of one sign and one of opposite sign. The Scatchard treatment probably includes other short-range interactions as well and is very complicated. A simple physical interpretation of the interaction parameters appears to be lacking. The Pitzer treatment offers a more compact and convenient formalism with fewer parameters. These two approaches are outlined and some of the problems associated with their applications are discussed.