Prediction of hydrogen ion activity in the ZnSO4–Na2SO4–H2SO4–NaOH–H2O system at 25 °C

For the ZnSO4–Na2SO4–H2SO4–NaOH–H2O system, a chemical model was developed to predict the hydrogen ion activity at 25 °C. This chemical model consisted of chemical equilibria, and mass and charge balance equations. The activity coefficients of solutes and the activity of water were calculated by using the Pitzer equation. The distribution of sulfate species as a function of the electrolyte concentration was obtained from the model. In the range of 0.5–4.3 m ionic strength of the solution, the experimental pH values were in good agreement with the predicted pH values. The mean activity coefficients of NaOH calculated by the Pitzer equation agreed well with the experimental values obtained from the literature.