Transference number, conductance and viscosity studies of some 1 : 1 electrolytes in pyridine–methanol mixtures at 25 °C

Abstract

Transference numbers of NO^–₃(t_NO^–3) in AgNO₃ have been measured at several concentrations in the range 0.01538–0.2000 mol dm^–3 in pyridine–methanol (Py–MeOH) mixtures containing 90, 70, 40 and 10 mol % Py at 25 °C using the e.m.f. method. The limiting transference numbers of Ag⁺(t^°_Ag+) in all cases have been obtained by applying the Logsworth method in the form suggested by Kay and Dye. The t^°_Ag+ value in Py–MeOH mixtures varies significantly with the solvent composition. Molar conductances and viscosities of Bu₄NBPh₄, Bu₄NClO₄, Bu₄NI, NaClO₄, NaBPh₄,CuClO₄·4AN, AgClO₄ and AgNO₃ in Py–MeOH mixtures have also been measured in the concentration range (1–68)× 10^–4 and (17–655)× 10^–4 mol dm^–3 respectively, at 25 °C. The conductance data by the Jones–Dole equation for the unassociated as well as for the associated electrolytes. The A and B coefficients of the Jones–Dole equation are positive in all cases. The A coefficients are in reasonably good agreement with the limiting theoretical values (A_η) calculated by using Falkenhagen–Vernon equation. The limiting-ion conductances for Ag⁺(λ^°_Ag+) in Py–MeOH mixtures have been obtained by combining the Λ₀ value of AgNO₃ with t^°_Ag+. Using λ^°_Ag+ in various solvent systems studied, the λ°_i values for several other ions have been computed. The variation of the actual solvated radii (r_i) as well as the ionic B₊ and B_– coefficients with the solvent composition in Py–MeOH mixtures shows a heteroselective preferential solvation of AgNO₃, AgClO₄ and CuClO₄ with the cations preferentially solvated by Py and the anions preferentially solvated by MeOH. NaClO₄, however, shows a homoselective preferential solvation in Py–MeOH mixtures, with both Na⁺ adn ClO^–₄ ions preferentially solvated by MeOH in the MeOH-rich region of the mixtures.