Medium Composition Dependence of Lead(II) Complexation by Chloride Ion

Stepwise formation constants of PbCl (super +) , PbCl (super degrees ) 2 , and PbCl (super -) 3 in aqueous HCl-HClO 4 , NaCl-NaClO 4 , MgCl 2 , and CaCl 2 media exhibit systematic medium composition effects at constant ionic strength. Cationic composition of test media influences the affinity of chloride ions for trace metals in a quantitatively predictable manner. Medium composition effects for both Pb(II) and Cu(II) complexation can be described in terms of chloride activity coefficient variation at constant ionic strength. Lead chloride formation constant results at ionic strengths up to one molar are quantitatively examined in terms of chloride ion pairing.--Modified journal abstract