Polarographic studies of indium(III) in aqueous medium of sodium azide

Abstract

In this paper, some aspects of the polarography of indium(III) in azide/hydrazoic acid buffer are presented. The electrode process is mostly governed by diffusion in the complexing medium. Nevertheless, for controlled-potential coulometry (involving a large time window) a catalytic process was observed, ascribed to the reaction of the hydrazoic acid and indium amalgam. The stability of azide complexes of In(III) was studied polarographically, and the formation of four mononuclear species was confirmed by computational analysis of data obtained from polarograms of In(III) in different azide concentrations. The values of the global constants obtained are: β1 = 3.7 × 103 M−1, β2 = 8.6 × 105 M−2, β3 = 5.0 × 107 M−3, β4 = 2.1 × 109 M−4, in a constant ionic strength medium held at 2.0 M with NaClO4. These data are in good agreement with those obtained by potentiometry. The value found for E0′ of the In(III)/In couple was −512.2 mV vs. calomel electrode (3 M NaCl), the mean diffusion coefficient of the complex being (6.1 ± 0.2) × 10−6 cm2 s−1 in perchlorate medium (T = 25 °C). Keywords: polarography, indium(III), azide, stability constants, catalytic wave.