Conductimetric determination of ion-association constants for calcium,cobalt, zinc,and cadmium sulfates in aqueous solutions at various temperatures between 0°C and 45°C

Thermodynamic ion-association constants for calcium, cobalt, zinc, and cadmium sulfates in aqueous solutions were determined by means of conductivity measurements at various temperatures between 0°C and 45°C. The standard Gibbs energy, enthalpy, and entropy for the reaction M²⁺+SO₄^2–M²⁺·SO₄^2– (M=Ca, Co, Zn, and Cd) were calculated from the temperature dependence of the ion-association constants. The values obtained are as follows: G₂₉₈^o=–12.42 kJ-mole^–1, H^o=6.11 kJ-mole^–1, and S₂₉₈^o=62.1 J-^o K^–1-mole^–1 for Ca²⁺·SO₄^2–; G₂₉₈^o=–12.84 kJ-mole^–1, H^o=5.00 kJ-mole^–1, and S₂₉₈^o=59.8 J-^o K^–1-mole^–1 for Co²⁺·SO₄^2–; G₂₉₈^o=–12.65 kJ-mole^–1, H^o=8.65 kJ-mole^–1, and S₂₉₈^o=71.4 J-^o K^–1-mole^–1 for Zn²⁺·SO₄^2–; G₂₉₈^o=–13.28 kJ-mole^–1, H^o=8.39 kJ-mole^–1, and S₂₉₈^o=72.7 J-^o K^–1-mole^–1 for Cd²⁺·SO₄^2–.