Conductometric and Spectrophotometric Determination of Ion-association Constants of Hexaamminechromium(III) and Tris(ethylenediamine)chromium(III) with Iodide and Perchlorate Ions

Abstract

Thermodynamic ion-association constants of hexaamminechromium(III) and tris(ethylenediamine)chromium(III) with iodide and perchlorate ions in aqueous solutions were determined by the conductometric and spectrophotometric methods. The values obtained by the conductometric method (Kcon) and the those by the spectrophotometric method (Ksp) at 25.0°C are as follows: Although no change was observed in the absorption spectra in ultra-violet region of these complexes in the presence of perchlorate ions at higher concentration, the ion-association constants of complex ions with perchlorate ions could be indirectly calculated from the apparent ion-association constants of complex ions with iodide ions determined in the solutions containing both iodide and perchlorate ions ; Ksp = 16 ± 4 for [Cr(en)3]3+-ClO4- and 10 ± 8 for [Cr(NH3)6]3+ - ClO4-. Though detailed comparison of constants determined by different methods was limited, it would be concluded that the ion-association constants obtained by conductometric method were in a relatively good agreement with those by spectrophotometric method. The ion-association constants for [Cr(NH3)6]3+ - X- (X = I, ClO4) would slightly be less than those for [Co(NH3)6]3+ - X- which have been reported. © 1974, The Chemical Society of Japan. All rights reserved.