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

Abstract

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⁺+SO ²⁻ ₄ ⇌M²⁺·SO ²⁻ ₄ (M=Ca, Co, Zn, and Cd) were calculated from the temperature dependence of the ion-association constants. The values obtained are as follows: ΔG ^o ₂₉₈ =−12.42 kJ-mole⁻¹, ΔH ^o=6.11 kJ-mole⁻¹, and ΔS ^o ₂₉₈ =62.1 J-^o K⁻¹-mole⁻¹ for Ca²⁺·SO ²⁻ ₄ ; ΔG ^o ₂₉₈ =−12.84 kJ-mole⁻¹, ΔH ^o=5.00 kJ-mole⁻¹, and ΔS ^o ₂₉₈ =59.8 J-^o K⁻¹-mole⁻¹ for Co²⁺·SO ²⁻ ₄ ; ΔG ^o ₂₉₈ =−12.65 kJ-mole⁻¹, ΔH ^o=8.65 kJ-mole⁻¹, and ΔS ^o ₂₉₈ =71.4 J-^o K⁻¹-mole⁻¹ for Zn²⁺·SO ²⁻ ₄ ; ΔG ^o ₂₉₈ =−13.28 kJ-mole⁻¹, ΔH ^o=8.39 kJ-mole⁻¹, and ΔS ^o ₂₉₈ =72.7 J-^o K⁻¹-mole⁻¹ for Cd²⁺·SO ²⁻ ₄ .