Löslichkeitsprodukte von Metall‐Oxyden und ‐Hydroxyden. 4. Mitteilung. Löslichkeitsprodukt und Freie Bildungsenthalpie des Cadmiumhydroxydes

The solubility equilibrium of cadmium hydroxide at 25° has been investigated by determining [Cd 2+ ] and [H+] in solution in contact with the solid phase. [H + ] has been measured by EMF‐method at the constant ionic strength 3 M while [Cd 2+ ] has been calculated from analytical data regarding the hydrolysis. The precipitation and the dissolving reaction take considerable time. The steady state of both reactions can be expressed by the equation\documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{l} {\rm Cd}{}^{{\rm 2 + }}{\rm 2 H}_{\rm 2} {\rm O = Cd(OH)}_{\rm 2} {\rm + 2 H}^{\rm + } \\ {\rm with}\,\,\,\,\,\,{\rm log *K}_{\rm s} {\rm o = } - {\rm 14}{\rm .03 } \pm {\rm 0}{\rm .04} \\ \end{array} $$\end{document} Since in 3 M NaClO 4\documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{l} \log {\rm K}_{\rm w} {\rm = log [H}^{\rm + } {\rm] + log [OH}^ -]{\rm = } - 14.22 \pm 0.02, \\ \,\log {\rm K}_{\rm s} {\rm o = log [Cd}^{{\rm 2 + }}]{\rm } \cdot {\rm }[{\rm OH}^ -]^2 {\rm = } - 14.41 \pm 0.05. \\ \end{array} $$\end{document} From * K s o, the free enthalpy of the reaction\documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm Cd + H}_{\rm 2} {\rm + O}_{\rm 2} {\rm = Cd(OH)}_{\rm 2} $$\end{document} has been calculated by means of a simple cycle:\documentclass{article}\pagestyle{empty}\begin{document}$$ \Delta {\rm G = } - {\rm 113}{\rm .37 } \pm {\rm 0}{\rm .07 kcal (25}^{{\circ}} {\rm)}{\rm .} $$\end{document}