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Journal/Book: Reprinted from: RECUEIL DES TRAVAUX CHIMIQUES DES PAYS-BAS edited by the Koninklijke Nederlandse Chemische Vereniging (The Hague Holland) T. 86 - No. 10 - October 1967 N.V. UITGEVERIJ W. P. VAN STOCKUM & ZOON - 'S-GRAVENHAGE. 1967;

Abstract: Laboratory for Analytical Chemistry ** State University of Utrecht The Netherlands * This work has been taken from the thesis of M. Alfenaar Utrecht (1966). ** Address: Croesestraat 77a Utrecht. *** M. Alfenaar and C. L. de Ligny to be published. 1 E. A. Guggenheim J. Phys. Chem. 33 842 (1929). Existing methods for the estimation of the primary medium effect for individual ions are critically reviewed and an improved method for its estimation is developed. By this method the primary medium effect of the hydrogen ion has been determined for the transfer from water to methanol-water mixtures and methanol. The medium effect of the alkali and the halide ions are then also known. The accuracy of the values so obtained for the individual ions is of the same order as the accuracy of experimentally determined values for electroneutral combinations of ions. 1. Introduction In his paper "The conceptions of electrical potential differences between two phases and the individual activities of ions" Guggenheim1 stated that: "If one sets out to measure the activity or chemical potential of an individual ion one is trying to measure a quantity which physically does not exist". Though this statement is undoubtedly true another statement by Guggenheim that activities of-individual ions do not have physical significance is not endorsed by us. As will be shown *** activity coefficients of individual ions can give information about physical processes which is not easily obtained in any other way. Therefore though exact measurement of these quantities is impossible it is worthwhile to try to estimate the activity or chemical potential of individual ions. When solutions in different solvents are considered one must account for "Salt effects" and for "primary medium effects". The salt effects can be estimated in many cases by the generally accepted Debye-Hückel theory. For the estimation of the primary medium effect several theories exist none of which are however fully satisfactory. ___MH

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