Transference-number measurements of silver nitrate in pure and mixed solvents using the electromotive force method

Abstract

An e.m.f. cell with transference similar in design to that developed by Rupert and recently used by Braun and Weingaertner has been fabricated. Using this cell transference numbers of NO₃^–(t_NO3^–) in AgNO₃ have been measured in the concentration range 0.01538–0.2000 mol dm^–3 in water (H₂O), acetonitrile (AN), methanol (MeOH), N,N-dimethylformamide (DMF), dimethyl sulphoxide (DMSO) and in AN–H₂O, AN–MeOH, AN–DMF and AN–DMSO mixtures containing 20, 40, 60 and 80 mol% AN at 25 °C. The method is fast and reliable for transference-number measurements of AgNO₃ in mixed non-aqueous solvents. The transference numbers of NO₃^– show practically no change with a change in AgNO₃ concentration. The limiting transference numbers of NO₃^–(t°_NO3^–) in various solvent systems have been obtained by calculating the average of the transference-number values of NO₃^– at different AgNO₃ concentrations. The limiting transference numbers of NO₃^– in mixed solvents vary significantly with solvent composition. They show a maximum and a minimum in AN–H₂O mixtures, a maximum in AN–MeOH mixtures and a continuous decrease in AN–DMF and AN–DMSO mixtures with an increase in [AN]. By combining t°_NO3^– values with the Λ₀ values of AgNO₃ in various solvent systems, λ°_Ag⁺ and λ°_NO3^– values have been calculated and their Walden product plotted as a function of solvent composition.