Electrolyte solutions in liquid ammonia. Part 6.—Mean molal activity coefficients and cation transference numbers of silver(I), copper(II) and lead(II) nitrates in liquid ammonia at 233 K

Abstract

An improved apparatus for the determination of e.m.f. values of concentration cells with transport containing AgNO₃, Cu(NO₃)₂ and Pb(NO₃)₂ solutions in liquid ammonia is described and the mean molal ionic activity coefficients have been obtained for solutions with concentrations between 10^–5 and 5 × 10^–2 mol kg^–1.

The transference numbers, t^°_Ag+= 0.3827, t^°_Cu2+= 0.3477, t^°_Pb2+= 0.3385 in NO^–₃ solutions at 233 K, indicate much lower relative mobilities for the Cu²⁺ and Pb²⁺ ions and that these ions are much more heavily solvated in liquid ammonia than in water.

Very low activity coefficients are obtained; γ±= 0.237 and 0.063 for AgNO₃, 0.477 and 0.017 for Cu(NO₃)₂ and 0.278 and 0.010 for Pb(NO₃)₂, at 10^–4 and 10^–2 mol kg^–1, respectively. The divergence of the observed values of γ± from those calculated by the Debye–Hückel equation indicates a very high degree of ion-pairing for all three salts even at very low concentrations. In Pb(NO₃)₂ and Cu(NO₃)₂ solutions, the ion associates are believed to be substantially in the form of solvent-separated and solvent-shared species.