Thermodynamic investigation of the ternary mixed electrolyte (NaCl + Na2HCit + H2O) system using potentiometric measurements at T = (298.2 and 308.2) K

• Mean activity coefficients of NaCl in (NaCl + Na2HCit + H2O) system were determined.
• This work was performed based on potentiometric method with self made electrodes.
• The mixing parameters were obtained with and without higher-order effects.
• The values of thermodynamic properties were calculated using Pitzer model.

In this work, the mean activity coefficients of NaCl in the (NaCl + Na2HCit + H2O) ternary mixed electrolyte system were determined using the potentiometric method. The potentiometric measurements were carried out on the galvanic cell without liquid junction of the type: Na-ISE/NaCl (m1), Na2HCit (m2), H2O/Ag–AgCl over total ionic strengths from (0.01 to 4.000) mol · kg−1. Different series of the salt molal ratios r (r = mNaCl/mNa2HCitmNa2HCit = 0.1, 1, 2.5, 5.0, 7.5, 10.0) and pure NaCl were used for the measurement at T = (298.2 and 308.2) K and P = 0.1 MPa. The results were interpreted by using Pitzer ion-interaction model with and without higher-order electrostatic effects. The mixing parameters obtained were used to calculate the values of the mean activity coefficients of Na2HCit, the osmotic coefficients, solvent activity and the excess Gibbs free energies for the whole series of the studied mixed electrolyte system.