Mean Activity Coefficients of NaNO3 and the Mixing Ion-Interaction Parameters in the Ternary System (NaNO3 + CsNO3 + H2O) at 298.15 K by EMF Method

Ion-selective electrodes directly respond to the activity of target ions without destroying the existing form of the original electrolyte, so ion-selective electrodes have been widely used in various fields. Mean activity coefficient of NaNO3 in the ternary system (NaNO3 + CsNO3 + H2O) at 298.15 K was measured by electromotive force (EMF) with the cell: Na+ ion-selective electrode (Na-ISE)|NaNO3 (mA), CsNO3 (mB)|NO3- ion-selective electrode (NO3-ISE) with total ionic strengths from 0.01 to 4.5 mol·kg-1 at different ionic strength fractions (0, 0.1, 0.2, 0.4, 0.6, and 0.8). The results showed that the Na-ISE and NO3-ISE have a good Nernst response, and the mean activity coefficients of NaNO3 are obtained via the Nernst equation. Based on the data of mean activity coefficients of NaNO3, the relationship diagrams of activity coefficients of NaNO3 against ion strengths in the ternary system were demonstrated, and the Pitzer mixing ion-interaction parameters θ Na , Cs and ψ Na , Cs , N O 3 were obtained.