Activity coefficients of aqueous thiocyanic acid solutions from electromotive force, transference number, and freezing-point depression measurements

Abstract

Accurate values of the activity coefficients of thiocyanic acid in aqueous solution have been obtained for concentrations of up to 0.1 molal at 25 °C by combining results for transference-number experiments with those for cells with transport. The transference-number experiments were done with the moving-boundary method, the transference-number at infinite dilution being calculated from measured conductivities of the thiocyanic acid. For the electromotive force (e.m.f.) measurements, conventional glass electrodes were used in conjunction with a high input-impedance electrometer.The results obtained electrochemically were checked by determining activity coefficients from freezing-point depression measurements which also extended the range of concentrations to 1 molal.The results of the two types of measurement are in good agreement.