Jerry Brounsteinl
University of Maine Orono. Maine
I 1 I
Electromotive Forte of Molten Salt Concentration Cells and Association Equilibria in Solution
Research on the properties of molten salts is not new, and there is a steadily increasing body of theory and experiment on this interesting class of substances (1-3). Molten salts are of growing technological importance in metallurgy, glasses, fuel cells, and, more recently, in the development of nuclear reactors. Theoretical studies of molten salts lead to a better understanding of electrolyte solutions. Nevertheless, although many experiments with molten salts illustrate principles of the physical chemistry of electrolyte solutions more readily than do experiments with aqueous electrolyte solutions, and are well suited for student experiments, there has not been widespread use of experiments with molten salts in the teaching of physical chemistry. The purpose of this paper is to show how experiments with molten salts can be used to demonstrate some aspects of the thermodynamics of electrolyte solutions. The electromotive force of molten salt concentration cells is discussed in connection with the verification of the Nernst equation, the evaluation of activity coefficients in electrolyte solutions, and the evaluation of thermodynamic association constants. Measurements of the emf of molten salt concentration cells are described using equipment generally available in the undergraduate physical chemistry laboratory. The first part of this paper deals with concentration units and activities in molten salt solutions, the Nernst equation and Henry's law in dilute solutions in molten salts, the evaluation of activity coefficients, and the calculation of association constants. The latter part of the paper describes the experimental details for measuring the emf of concentration cells in molten alkali nitrate solvents. Concentrafions, Acfivities, and Henry's Law
The activity, a
