Mean activity coefficients measurement of sodium chloride and thermodynamic modeling of sodium chloride and polysodium acrylate aqueous mixtures at T = (298.2 and 303.2) K

• The mean activity coefficient of NaCl in (NaCl + NaPA + H2O) system was determined.
• This work was carried out based on potentiometric method with self-made electrodes.
• The new modified Pitzer model was proposed to study the thermodynamic properties.
• The interaction parameters were evaluated for the studied ternary system.
• The values of thermodynamic properties were calculated using new model.

In this work, thermodynamic properties of the ternary (sodium chloride + polysodium acrylate) aqueous system was investigated using the potentiometric method at T = (298.2 and 303.2) K. Potentiometric measurements were carried out on the galvanic cell with ion-selective electrodes containing a solvent polymeric (PVC) Na-ISE and Ag–AgCl over total molality from 0.0010 to 2.9997 mol kg−1 for various series of molal ratios (r = mNaCl/mNaPA = 50, 40, 30, 20, and/or 15) and NaCl single electrolyte. Modeling of this ternary system was made based on proposed model and mixing interaction parameters (θClPA,ψNaClPAθClPA,ψNaClPA) were evaluated for the studied ternary system according to Pitzer graphical method. These parameters were used to calculate the values of the mean activity coefficients of NaPA, the osmotic coefficients, solvent activity and excess Gibbs free energies of the whole series for under investigation system.