Determination a 25°c des proprietes thermodynamiques des complexes chlores du plomb divalent a partir de mesures de solubilite dans des solutions aqueuses de force ionique inferieure a 1 mol kg −1

Abstract

The solubility of divalent lead chloride is measured at 25°C in aqueous solutions {H 2O + HClO 4 + HCl} and {H 2O + HClO 4 + Pb(ClO 4) 2} as a function of the initial ionic strength X (0 ⩽ X ⩽ 1 mol kg −1). The apparent solubility product of lead chloride, K s, and the apparent constants β i of the equilibria (i) have been determined at different values of the equilibrium ionic strength, I Pb 2+ (aq) + i Cl − (aq) = PbCl (i−2)− i(aq) (i) The experimental values are well interpreted by the existence of Pb 2+, PbCl +, PbCl 2 and PbCl − 3. The results permitted an empirical representation of K s and β i values as functions of I which may be extrapolated to infinite dilution. The thermodynamic solubility product and the thermodynamic constants of the equilibria (i) were determined at 25°C K 0 s = (1.696±0.004)×10 −5 K 0 1 = 40.3±0.2 K 0 2 = 47.2±3 K 0 3 = 420±10 From these values, we have calculated the standard Gibbs energy function of formation of the different lead complexes at 25°C Δ f G 0(PbCl +) = −164820 J mol −1 Δ f G 0(PbCl 2) = −296440 J mol −1 Δ f G 0(PbCl − 3) = −433084 J mol −1