Hydrogen ion activities and species distribution in mixed metal sulfate aqueous systems

The activity of the hydrogen ion (H + ) is estimated in sulfuric acid aqueous solutions of concentrations 0.25 to 2.0 mol.L −1 at temperatures 298 to 373 K (25 to 100°C). This is done by following an existing “extended Debye‐Hückel” equation, which was originally developed only for the case of pure H 2 SO 4 solutions at ambient temperature. The same equation is applied for the evaluation of the activity of H + in mixed metal sulfate solutions, particularly for the aqueous system H 2 SO 4 ‐ZnSO 4 ‐FeSO 4 ‐Fe 2 (SO 4 ) 3 . The estimation of the activity of H + by this method requires the knowledge of the molality of free H + ions and the true ionic strength (in molal scale). Consequently, an algorithm is advanced for the calculation of species concentrations in such mixed solutions. Estimated p H values agree very well with experimentally measured ones.