Critical evaluation of thermodynamic data for sulfate complexes in aqueous solution. Part 1. H ⁺ (IUPAC Technical Report)

Abstract This Report is the first of five proposed parts that will in total collect and evaluate the experimental equilibrium constants (and related thermodynamic parameters) for the association of cations with the sulfate ion in aqueous solution. In this Report, quantitative data for the equilibrium: SO 4 2− (aq) + H + (aq) <m:math xmlns:m="http://www.w3.org/1998/Math/MathML"> <m:mrow> <m:mo>⇌</m:mo> </m:mrow> </m:math> $\rightleftharpoons $ HSO 4 − (aq) were abstracted by a comprehensive review of the scientific and technological literature, including accessible databases. The equilibrium constants so obtained were accepted or rejected using an explicit set of criteria. The accepted results were then evaluated in closer detail, including comparison with related data. Where possible ‘best estimates’ under a given set of conditions were calculated as unweighted averages (means) and classified as Reliable, Provisional, or Indicative, depending on the level of agreement among independent measurements. Reliable values of the equilibrium constant and the accompanying enthalpy and entropy changes could be established over wide ranges of temperature, pressure, ionic strength, and electrolyte medium. Nevertheless, gaps in the database remain: in particular, few values for the isobaric heat capacity change are available under any conditions.