An investigation of the nature of certain complex gold compounds in aqueous solution

Abstract

An investigation of the nature of Chlorauric acid and its potassium salt, has been carried out, with the object of ascertaining certain properties of the complex ions present in aqueous solutions of these compounds. 1. The normal potential was determined at 25°C.by measuring the potential of gold electrodes in solutions containing a known concentration of the complex compound, in the presence of a measured excess of chloride ions. The values of the normal potential were calculated from the equation, where the symbols have their usual meaning. The mean values of were found to be 1.0066 volts and 1.0055 volts at 25°, from measurement of the acid and salt respectively. The value of this constant previously determined by Bjerrum and Kirschner Is 1.001 volts at 17°0.2. The formulae of the complex ions existing in solutions containing different concentrations of the complex compound, in the presence of varying excess of chloride ions, were calculated by the method of Bodlander. The results obtained indicate that the complex AuCl is the stable ion in solutions containing 0.1, 0.02 and 0.01 M chlorauric acid, in the presence of 0.1 N hydrochloric acid. With greater concentration of the latter, the higher complex AuCl is produced, whilst in dilute solutions containing a small proportion of free chloride ions, hydrolysis occurs. The ion AuCl preponderates In solutions of 0.02 Mpotassium chloraurate containing 0.02 and 0.04 M potassium chloride: no evidence was obtained, for the existence of higher complexes in solutions of this compound. 5. The stability constant of the aurichloride ion, was determined from E.M. F. measurements, from the results of which the concentration of auric ions was calculated, in solutions containing known concentrations of both the complex compound and free chloride Ions. The mean values obtained were 1.83 x 10 and 2.085 x 10, from measurements of solutions of Chlorauric acid and Potassium chloraurate respectively. These values, together with the figures obtained for the normal potential Au AuCl4, shew that the complex ion is somewhat less stable in the presence of hydrogen ions than in the presence of potassium ions of equivalent concentration.