Thermodynamic study of the quaternary electrolyte (NaCl + NaNO3 + HCONH2 + H2O) system using potentiometric measurements at T = (298.2 and 303.2) K

In this work, the thermodynamic properties of the quaternary electrolyte (NaCl + NaNO3 + HCONH2 + H2O) system, using the potentiometric method, are reported. The potentiometric measurements were carried out on the galvanic cells without liquid junction of the types:Ag–AgCl|NaCl (mA), (100-w%) H2O + w% HCONH2|Na–ISE,Ag–AgCl|NaCl (m1), NaNO3 (m2), (100-w%) H2O + w% HCONH2|Na–ISE andNO3–ISE|NaNO3 (mB), (100-w%) H2O + w% HCONH2|Na–ISEover total ionic strengths from 0.001 to 4.000 mol · kg−1. Different series of the salt molal ratios r   (r=mNaCl/mNaNO3r=mNaCl/mNaNO3 = 0.1, 1, 2.5, 5.0, 10.0) and pure NaCl in mixed solvent system containing 10% mass fraction of formamide were used for the measurements at T = (298.2 and 303.2) K. The modeling of this quaternary system was made based on the Pitzer ion-interaction model. In according to Pitzer graphical method, the mixed ionic interaction parameters (θClNO3,ψNaClNO3θClNO3,ψNaClNO3) were evaluated for each series of the studied system. Then, the obtained parameters were used to calculate the values of the mean activity coefficients of NaNO3, the osmotic coefficients, solvent activity and the excess Gibbs free energies for the whole series of the studied mixed electrolyte system at T = (298.2 and 303.2) K.

► 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.