A study of the properties of bismuth (III) iodide complexes in aqueous solution

Abstract

Freezing point depression, conductometric, and spectrophotometric studies have been made on bismuth triiodide in aqueous hydriodic acid solution at 25 degrees centigrade. These data indicate that the Bil₆⁻³ ion is the predominant complex species present in this solution for all concentrations of bismuth triiodide up to 0.2 molality. Thermometric titration data indicate the formation of the Bil₆⁻³ ion in this solution from the solid bismuth triiodide is a rapid process with no indication of intermediate complexes being present. The heat of formation of the BiI₆⁻³ has been determined and found to be a function of the amount of bismuth triiodide used. A value for the standard heat of formation of bismuth triiodide has been determined. Preliminary studies have been performed on the heats of precipitation of the complex bismuth ions with amine salts. The data available indicate the heats of precipitation of these salts are a function of the amount of precipitating reagent used, but further study is needed to confirm this premise. The heat of formation of the tris-trimethylammonium-nonaiodobismuthate (III) salt was calculated from measured and previously published thermodynamic data. The entropy for the process of formation Bi₆⁻³ ion in aqueous hydriodic acid from solid bismuth triiodide has been calculated and is in agreement with current theories regarding entropies for complex ion formation.