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

Highlights: • 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. - Abstract: 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 = m_NaCl/m_Na2HCit = 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