Chemical Thermodynamics and Calculation of Parameters of Ionic Equilibria of Indium(III) in Perchlorate, Chloride and Sulphate Aqueous Solutions
The problem of activity coefficients dependence of indium(III)-containing complex species and of corresponding concentration formation constants from qualitative and quantitative composition of aqueous solutions is discussed. The Brønsted-Guggenheim-Scatchard's model (Specific ion Interaction Theory, SIT), basing on extended semi-empirical Debye-Hückel equation in third approximation is supplied. The checking of data for formation constants of complexes on comparability and consistency, including for different background electrolytes can be done using this model. The survey of basic specific interaction coefficients (SIC) is done. The constancy of this coefficients is permissible in the definite ionic strengths ranges, or it's necessary using twoparameters coefficients fitting. The classical SIT model is modified by the introduction of mixing parameters (SIC of same charge ion). On the basis of the numerical critical analysis of the available literature experimental data, with employment of the SIT, thermodynamic formation (stability) constants of chloro-, sulfato-aqua-complexes and hydrolysis constants of indium(III) and related specific interaction coefficients (“non-ideality” parameters) in acidic aqueous solutions (pH < 5.5) at ambient temperature (20-25 °C) are calculated. The quotients of cationic and anionic complexes parts in SIC are separated according to empiric Ciavatta's approach. Discrepancies of published «thermodynamic» constants may be caused by evidencing methodological and calculated errors (essential change of activity factors in series of experiments or various competing ion equilibria are neglected), as well as inaccuracies of extrapolation methods and choice of conditional standard state or erroneous evaluation of formal and standard potentials, but with the exception of alternative Baes-Mesmer's nonlinear regression procedure. The job's results could be used for modeling of the indium(III) state in some aqueous solutions and for study of indium and other metal ions complexation or prediction of their electrochemical and geochemical behaviour.