Thermodynamic properties of aqueous solutions of bivalent sulphates

Abstract

Osmotic coefficients, galvanic cell potentials, and heat of dilution data from 0 to 25°C for the sulphates of bivalent Cu, Zn, Cd, Ni, Co, Mn, Ca, Mg, and Be in aqueous solution have been analyzed in terms of association equilibria to form MX ion pairs and M₂X²⁺ and MX^2– ₂ ion triplets together with Debye-Hückel ion interaction effects. Good agreement is obtained up to 0.3–0.5 M, and the results provide a basis for placing the activity coefficients at higher concentrations on an absolute basis. The temperature effects are significant between 0 and 25°C and yield rough values for the enthalpy of the ion association reactions. The change of heat capacity for ion association into pairs is large but not accurately known. The equilibrium constants for ion-pair dissociation do not vary much and are presumably dominated by electrostatic factors. The constants for formation of ion triplets show greater variation and reflect the known tendency of some of these metallic ions to form covalent complexes.