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Thermochemistry of the Coordination Compounds of Zinc Nitrate with Several L-alfa-Amino Acids

Di Y. Y.

Polish Journal of Chemistry

2008

Vol. 82, nr 3

599-606

Molar enthalpies of dissolution of {ZnSO4×7H2O(s) + 2NaNO3(s) + L-AA(s)} (in which AA stand for phenylalanine, histidine and methionine) in 100 cm3 of 2 mol×dm-3 HCl at T = (298.15 š 0.001) K have been measured to be deltaHm,1 o = (69.417 š 0.051) kJ×mol-1, (79.830 š 0.058) kJ×mol-1, and (56.929 š 0.051) kJ×mol-1, respectively, by means of an isoperibol solution-reaction calorimeter. Molar enthalpies of dissolution of {Zn(AA)(NO3)2×xH2O(s) + Na2SO4(s)} (in which x = 1 for phenylalanine, x = 1/2 for histidine and methionine) under the same conditions have been determined to be deltaHm,2 o = (48.137 š 0.038) kJ×mol-1, (51.146 š 0.041) kJ×mol-1, and (37.337 š 0.029) kJ×mol-1, respectively, using the calorimeter. The standard molar enthalpies of formation of these complexes Zn(AA)(NO3)2×xH2O(s) have been derived to be delta fHm o [Zn(Phe)(NO3)2×H2O, s, 298.15 K] = -(1367.07 š 3.52) kJ×mol-1, delta fm o [Zn(His)(NO3)2×1/2H2O, s, 298.15 K] = -(1207.19 š 2.82) kJ×mol-1, and delta fHm o [Zn(Met)(NO3)2×1/2H2O, s, 298.15 K] = -(1327.08 š 0.75) kJ×mol-1, respectively, by the combination of the experimental values of enthalpies of dissolution with some auxiliary thermodynamic data through a designed Hess thermochemical cycle on the basis of a supposed chemical reaction.

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

Di Y. Y., Chen J. T., Tan Z. C.

Polish Journal of Chemistry

2007

Vol. 81, nr 9

1535-1540

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.