Standard Molar Enthalpy of Formation of Hydrated Sodium Cupric Arsenate [NaCuAsO4×1.5H2O(s)]

A new compound (NaCuAsO4×1.5H2O) was synthesized, and its composition was determined by means of the methods of ignition loss-in-weight and chemical analysis. The standard molar enthalpies of dissolution of the mixtures {Na3AsO4×12H2O(s) + CuSO4×5H2O(s)} and {NaCuAsO4×1.5H2O(s) + Na2SO4(s)} in 1.498 mol×dm–3 HCl so lu - tion at 298.15 K have been determined to be respectively Ds m. H 1 0 = (64322 š 63) J×mol–1 and Ds m. H 2 0 = –(20558 š 25) J×mol–1 using an isoperibol solution-reaction calorimetry. From these values and other thermodynamic data, the standard molar enthalpy of formation of NaCuAsO4×1.5H2O(s) has been de rived: Df m H0 (NaCuAsO4×1.5H2O, s, 298.15 K) = –(1469.33 š 0.65) kJ×mol –1. In addition, UV/Vis spectra and refractive in dexes of solution A and solution A’ were measured to examine the reliability of the designed thermodynamic cycle.