Variation of transference numbers with concentration: a test of the Fuoss–Onsager and the Pitts equations

Abstract

Computer calculations have been carried out to test how well the variation with concentration of moving boundary transference numbers is described by 3 theories: the standard Fuoss–Onsager transference equation, a transference equation based on the revised 1963 Fuoss–Onsager electrophoretic expression, and the Pitts conductance equation arranged into its transference form. The fit of all three theories leaves something to be desired. Many aqueous transference data are less than adequately described by the theoretical equations, and several sets of non-aqueous results are fitted well only by use of distances of closet approach (a) that are physically unreasonable, even absurd. The revised Fuoss–Onsager theory often produces more sensible a values but at the price of poorer fitting to the experimental data. Suggestions are made as to why the theoretical equations apply less well to transference numbers than they do to conductances.