Solubility of cadmium chloride and the standard potential of the cadmium electrode in formamide

The e.m.f. of the cell, Cd : Hg(2-phase amalgam)/CdCl₂(m)/AgCl/Ag, where m is the number of moles of anhydrous CdCl₂ per kg of formamide and lies in the range 0 < m < 0.02 has been measured at 298.15 K. The measurements are analyzed in terms of complex formation in solution to yield a value of the molal standard potential of the Cd²⁺/Cd electrode of –0.412 V at 298.15 K. By combining this value with the standard potential of the Cd/CdCl₂(s)/Cl^– electrode,¹ where CdCl₂(s) denotes a solid solvate of composition CdCl₂· 2½HCONH₂, the solubility product of cadmium chloride in formamide is calculated to be 2 × 10^–7(mol kg^–1)³. The solubility of anhydrous cadmium chloride in formamide has also been measured at 288.15 K, 298.15 K and 308.15 K using a radiochemical technique. The results suggest extensive complex formation in formamide, the dominant species being the CdCl^2–₄ ion.