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

Abstract

Transference numbers of NO–3(tNO–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 (Aη) 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 (ri) 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.