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Abstract: Two pure zinc borates, Zn2B6O11·7H2O and Zn3B10O18·14H2O have been synthesized and characterized by XRD, FT-IR, DTA–TG techniques and chemical analysis. The molar enthalpies of solution of Zn2B6O11·7H2O(s) and Zn3B10O18·14H2O(s) in 1moldm−3 HCl(aq) were measured to be 15.42±0.03kJmol−1 and 57.78±0.11kJmol−1, respectively. The molar enthalpy of solution of ZnO(s) in (HCl+H3BO3)(aq) was determined to be −80.01±0.15kJmol−1. With incorporation of the previously determined enthalpy of solution of H3BO3(s) in 1moldm−3 HCl(aq), and the standard molar enthalpies of formation for ZnO(s), H3BO3(s), and H2O(l), the standard molar enthalpies of formation of −6738.1±4.8kJmol−1 for Zn2B6O11·7H2O and −11,786.4±8.0kJmol−1 for Zn3B10O18·14H2O were obtained. [Copyright &y& Elsevier]

Abstract: Hydrated strontium borate, SrB4O7·3H2O, has been synthesized and characterized by XRD, FT-IR, DTA-TG and chemical analysis. The molar enthalpy of solution of SrB4O7·3H2O in 1moldm−3 HCl(aq) was measured to be (21.15±0.29)kJmol−1. With incorporation of the previously determined enthalpies of solution of Sr(OH)2·8H2O(s) in [HCl(aq)+H3BO3(aq)] and H3BO3 in HCl(aq), and the enthalpies of formation of H2O(l), Sr(OH)2·8H2O(s) and H3BO3(s), the enthalpy of formation of SrB4O7·3H2O was found to be −(4286.7±3.3)kJmol−1. [Copyright &y& Elsevier]