Results of calorimetric determinations of heats of solution and of ionization of sulfamic acid, sulfanilic acid, and taurine are presented and used in subsequent thermodynamic calculations. For ionization of the aqueous acids we find AH°= 0.25, 4.2, and 9.99 kcal. mole-1 and AS°= -3.8, -0.7, and -7.95 cal. (deg. mole)-1 for sulfamic acid, sulfanilic acid, and taurine, respectively. These small negative values for entropies of ionization provide supporting evidence that the aqueous acids exist in the zwitterion form. We calculate S2°= 56.4 and 48.4 cal. (deg. mole)-1 for the standard partial molal entropies of aqueous taurine and the aqueous anion derived from taurine, respectively.
We have combined results of earlier measurements leading to equilibrium constants for formation and reaction of aluminum–citrate complexes in aqueous solution at 298.15 K with results of our calorimetric measurements at this same temperature to obtain ΔH values for reactions of Al3+(aq) with citrate ions. Results of some of these calorimetric measurements also lead to a value of ΔH for the reaction Al3+(aq) + 4 OH`(aq) = Al(OH)4−(aq). Keywords: aluminum hydroxide, Al(OH)4−(aq), thermodynamics; aluminium–citrate complexes, thermodynamics; citrate–aluminum complexes, thermodynamics; aluminum (3+, aq), thermodynamics.
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