Determination of Thermodynamic Complexity Constants and Speciation for Multicomplexing Electrolytes within the Mean Spherical Approximation Model
2018
Simonin, Jean-Pierre
It has been shown in previous work that the determination of speciation in aqueous solutions containing self-complexing electrolytes requires caution as regards the thermodynamic model used to estimate the activity coefficients of the solute species and the complexity constant values, which seem uncertain if not irrelevant in some cases. This topic was studied using a simple molecular model based on the mean spherical approximation (MSA) theory. In the present work, the case of aqueous ternary mixtures with common chloride anion is considered within the same framework. The mixtures are composed of a self-complexing 2-1 salt, MCl₂, and of a strong 1-1 or 2-1 salt containing chloride at 25 °C. The metal cation M²⁺ is Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, or Pb²⁺. Complexity constant values for the divalent cations were obtained by optimizing the representation of experimental osmotic or activity coefficients for binary and ternary electrolyte solutions and at the same time by imposing constraints on the speciation, when such experimental data are available. Solutions of ZnCl₂ were found to exhibit a peculiar behavior.
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