Etude par potentiometrie et par calorimetrie des equilibres de substitution par les ions bromures des atomes de chlore des complexes de l'or trivalent en milieux aqueux a 25°C

Abstract

In an aqueous solution bromide ions react with tetrachloroaurate(III) ions according to the successive substitution reactions ( j) AuCl 5− j Br − j−1 + Br − = AuCl 4− j Br − j + Cl − where j = 1–4. The apparent constants of the successive equilibria have been determined by potentiometry at 25°C in aqueous solutions, the ionic strength being set between 0.1 M and 0.15 M. The following values were obtained: K 1 = 378.5±5, K 2 = 118.9±3, K 3 = 54.5±1, K 4 = 35.2±1. The enthalpy variations for these reactions, under the same experimental conditions, were also measured using microcalorimetry. From these measurements, the molar enthalpy of successive substitution reactions, referred to 1 kg of solvent, could be determined. The following values (in J mole −1) were obtained; Δ H 1 = −15940±50, Δ H 2 = −15940±50, Δ H 3 = −13660±50, Δ H 4 = −13660±50.