Thermodynamic study of electrolyte mixture (KCl + KNO3 + water + proline) by potentiometric measurements at T = 298.2 and 303.2 K

In this work, the thermodynamic properties of the mixed electrolyte system (KCl + KNO3 + water + proline), using the potentiometric method, are reported. The potentiometric measurements were performed on the galvanic cells without liquid junction of the type: Ag–AgCl|KCl (m1), KNO3 (m2), (100-wt%) H2O + wt% proline|K-ISE, NO3-ISE|KNO3 (m1), (100-wt%) H2O + wt% proline|K-ISE over total ionic strengths from 0.001 to 3.000 mol kg−1 for different series of salt molal ratios r   (r=mKCl/mKNO3=0.1,1,2.5,5.0,10.0r=mKCl/mKNO3=0.1,1,2.5,5.0,10.0) and pure KCl in mixed solvent system containing 5% mass fraction of proline at T = 298.2 and 303.2 K. The PVC based potassium and nitrate ion selective electrodes (K, NO3-ISE) and Ag–AgCl electrode used in this work were prepared in our laboratory and had a reasonably Nernst response. The activity coefficients data were interpreted based on the Harned rule and Pitzer model. The unknown Pitzer mixing interaction parameters (θClNO3,ψKClNO3θClNO3,ψKClNO3) were evaluated for the studied mixed electrolyte system according to Pitzer graphical method .Then, the parameters obtained with the Pitzer model were used to calculate the values of the mean activity coefficients of KNO3, the osmotic coefficients, and the excess Gibbs free energies for the whole series of the studied mixed electrolyte system.

► Thermodynamic study has been performed on the mixed electrolyte in mixed solvent system.
► The self made electrodes have been used to the activity coefficient measurements.
► The Pitzer model has been used to calculate of thermodynamic properties.