Phase Equilibrium System of HoCl₃−CdCl₂−HCl(7.52 %)−H₂O at 298.15 K and Standard Molar Enthalpy of Formation of Cd₄HoCl₁₁·14H₂O

Abstract

The equilibrium solubility of the quaternary system HoCl 3 -CdCl 2 -HCl-H 2 O was determined at 298.15 K, and the corresponding equilibrium diagram was constructed. The quaternary system is complicated with three equilibrium solid phases, CdCl 2 • H 2 O, Cd 4 HoCl 11 • 14H 2 O (4:1 type), and HoCl 3 • 6H 2 O, of which the new compound Cd 4 HoCl 11 • 14H 2 O was found to be congruently soluble in the system. The new compound obtained was identified and characterized by the methods of X-ray diffraction, thermogravimetry, and differential thermogravimetry. The standard molar enthalpy of solution of Cd 4 HoCl 11 • 14H 2 O in deionized water was measured to be (15.74 ( 0.18) kJ • mol -1 by heat conduction microcalorimetry. Its standard molar enthalpy of formation was calculated to be (-6864.7 ( 1.3) kJ • mol -1 . The standard molar enthalpy of formation, the solubility data, and the phase diagram of the quaternary system could provide the fundamental basis and serve as a guide for the preparation of Cd 4 HoCl 11 • 14H 2 O.