Polarographic prewaves of electroreduction of nickel(II) in solutions of organic and inorganic complexing agents were observed by a number of workers. Especially the papers of Mark et al. ~, Tur'yan and coworkers 2, and Ikeda and Itabashi 3 should be mentioned.
These prewaves in the case of a linear dependence between their heights and nickel(II) or ligand concentration are used in the analytical determinations.
Also in the presence of azides in water solutions which are specifically adsorbed on mercury electrodes 4-°, Ni(II) exhibits a prewave lb' v at potentials considerably more positive than the wave of reduction of nickel(II) in perchlorate solutions s.
In dilute solutions of azides this prewave has a kinetic character, at higher concentrations an irreversible wave controlled by transport is recorded.
It is known that nickel(II) forms complexes with azides 9-12.
In this paper we present the results of studies on the chemical reaction preceding the charge transfer and also on the mechanism of the electrode reaction of the nickel(II)-azide system.
In addition to electroanalytical investigations optical and ion-exchange measurements were carried out in order to determine the composition of nickel(II~ azide complexes existing in the bulk of solution at various azide concentrations.
Since, before the electrochemical studies, the knowledge of the complex equilibria in the solution was essential, spectrophotometric and ion,exchange meas.urements were performed initially and they are described at the beginning of the experimental part of this work.
EXPERIMENTAL
Reagents
Ni(C104) 2 and Ca(C104) 2 were prepared by neutralizing their respective carbonates (p.a.) with HC104 (p.a.) and later recrystallized from thrice distilled water. Also NaC104 (p.a.) was recrystallized from thrice distilled water. Pure NaN3 was recrystallized from ethanol 13 and dried in vacuum at 70°C.
The concentration of nickel(II) in stock solution was determined by titration with EDTA and azides by using silver nitrate. The solutions investigated were prepared from stock solutions by a proper dilution. All solutions were prepared