Mean Activity Coefficients and Phase Equilibria of the NaBr–Na2SO4–H2O Ternary System at 278.2 and 288.2 K

In this paper, the cell potential method is used to determine the activity coefficients of the NaBr–Na₂SO₄–H₂O ternary system at 278.2 and 288.2 K. The cell potentials of NaBr–H₂O solutions are measured using a cell without a liquid junction composed of ion-selective electrodes. According to the measured cell potentials of NaBr-H₂O solutions, the response curve can be obtained by combining the Nernst equation. The measured cell potentials of NaBr–Na₂SO₄–H₂O mixed solutions are combined with the Nernst equation to determine the activity coefficients, and the mixed ion interaction parameters θ_Br,SO4 and ψ_Na,Br,SO4 of the Pitzer model are obtained by applying the activity coefficients and the programming solver. Then, other thermodynamic parameters are calculated using Pitzer equations, such as the activity coefficient of Na₂SO₄ (γ_Na2SO4), the osmotic coefficient ($\mathrm{\Phi }$), water activity (a_w), and excess Gibbs free energy (G^E). In addition, the phase equilibria of the NaBr–Na₂SO₄–H₂O ternary system at 288.2 K were investigated using the isothermal dissolution equilibrium method, and phase equilibrium predictions were made for the NaBr–Na₂SO₄–H₂O ternary system at 278.2 and 288.2 K. The experimental values of the system at 288.2 K are in good accordance with the predictions, and therefore, the fitted parameters have good applicability.