Complexation of Pb(II) by Chloride Ions in Aqueous Solutions

Lead chloride formation constants at 25°C were derived from analysis of previous spectrophotometrically generated observations of lead speciation in a variety of aqueous solutions (HClO ₄ –HCl and NaCl–NaClO ₄ mixtures, and solutions of MgCl ₂ and CaCl ₂ ). Specific interaction theory analysis of these formation constants produced coherent estimates of (a) PbCl ⁺ , PbCl ₂ ⁰ , and PbCl ⁻ ₃ formation constants at zero ionic strength, and (b) well-defined depictions of the dependence of these formation constants on ionic strength. Accompanying examination of a recent IUPAC critical assessment of lead formation constants, in conjunction with the spectrophotometrically generated formation constants presented in this study, revealed significant differences among various subsets of the IUPAC critically selected data. It was found that these differences could be substantially reduced through reanalysis of the formation constant data of one of the subsets. The resulting revised lead chloride formation constants are in good agreement with the formation constants derived from the earlier spectrophotometrically generated data. Combining these data sets provides an improved characterization of lead chloride complexation over a wide range of ionic strengths.