Measurements and Calculations mean activity coefficients of KI in the KI–KCl–H2O ternary system at 298.15 K

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Compared to the current popular methods for measuring the mean activity coefficient of the ternary aqueous solution, electromotive force method has certain advantages of rapidity and sensitivity. Herein, The electromotive force measurements were performed on the cell of the type: K–ISE|KI (m1), KCl (m2)|I–ISE, which consists of a potassium-ion combination ion selective electrode (ISE) and iodide-ion combination ion selective electrode (ISE) without a liquid junction. We chose the total ionic strength I range from 0.0100 to 1.0000 mol·kg−1 for different ionic strength fractions yb of KCl with yb = (0.0, 0.2, 0.4, 0.6, 0.8). The experimental results show that the mean activity coefficients of KI can be calculated well by using the Pitzer models and Nernstian equation. Moreover, the Pitzer ion interaction parameters of θCl,I and ψK,I,Cl were fitted using Pitzer’s equations, and the two parameters were used to calculated the mean activity coefficients of KCl in the KI–KCl–H2O ternary system. Accordingly, the osmotic coefficients, water activities, and excess Gibbs free energies in the mixtures were studied in the KI–KCl–H2O ternary system.