Conductometric and Spectrophotometric Determination of Ion-association Constants of Hexaamminechromium(III) and Tris(ethylenediamine)chromium(III) with lodide 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 25.00C are as follows:
Kcon=19 4, Ksp= 22 7for[Cr(NH3)6]3+-I- Kcon=26 6,
Ksp=21 4 for[Cr(en)3]3+-I-, Kcon=15 3 for[Cr(NH3)6]3+-CI04-,
Kcon=11 4 for[Cr(en)3]3+-CIO4-
Although no change was observed in the absorption spectra in ultra-violet region of these complexes in thepresence of perchlorate ions at higher concentration, the ion-asseciation constants of complex ions with perchlorate ions could be indirectly calculated from theapparent ion-association constants of cemplex ions with iodide ions determined in the solutions containing both iodide and perchlorate ions Ksp=16 4 for[Cr(en)8]3+-CIO4- and 10 8 for[Cr(NH3)6]3+- CI04-.
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-associationconstants for [Cr(NHs)G]3+-X- X=I, CIO4 would slightly be less than those for [Co(NH3)6]3+- X- which have been reported.