Solid-liquid equilibria for the ternary systems of RbX + CdX2 + H2O (X = Cl, Br) at T=298.15 K and the thermodynamic properties of the new solid compounds

Solid-liquid equilibria in the ternary systems RbX + CdX2 + H2O (X = Cl, Br) at T = 298.15 K and under 101.3 kPa were investigated by the method of isothermal solution saturation, and the corresponding phase diagrams were constructed. It was found that there were five crystallization regions corresponding to CdCl2 center dot 2.5H(2)O, RbCd(2)Cl5 center dot H2O, RbCdCl3, Rb4CdCl6 and RbCl in the system (RbCl + CdCl2 + H2O). Four crystallization regions corresponding to CdBr2 center dot 4H(2)O, RbCdBr3, Rb4CdBr6 and RbBr were found in the system (RbBr + CdBr2 + H2O). The new solid compounds RbCdCl3, RbCdBr3 and Rb4CdBr6 were congruently soluble in water, and new double salts RbCd2Cl5 center dot H2O and Rb4CdCl6 were incongruently soluble in water. The new solid-phase compounds RbCd2Cl5 center dot H2O, RbCdCl3, Rb4CdCl6, RbCdBr3 and Rb4CdBr6 were characterized by chemical analysis, XRD and TG-DTG techniques. The standard molar enthalpies of solution of RbCd2Cl5 center dot H2O, RbCdCl3, Rb4CdCl6, RbCdBr3 and Rb4CdBr6 in water were measured to be (20.74 +/- 0.16) k J.mol(-1), (28.00 +/- 0.39) kJ.mol(-1), (96.56 +/- 0.50) kJ.mol(-1), (35.38 +/- 0.33) kJ.mol(-1) and (110.64 +/- 0.62) kJ. mol(-1) by microcalorimetry in the condition of infinite dilution, and their standard molar enthalpies of formation were determined to be-(1545.3 +/- 0.6) kJ.mol(-1),-(856.5 +/- 0.7) kJ.mol(-1),-(2180.1 +/- 1.3) kJ.mol(-1),-(727.1 +/- 0.7) kJ.mol(-1) and-(1920.5 +/- 1.3) kJ.mol(-1), respectively. (c) 2020 Elsevier Ltd.