A study of the prewave of the Ni2+ - nicotine system was carried out under the experimental conditions when the influence of electroreduction of nicotine is negligible. The kinetics of Ni(II) reduction in nicotine media on the dropping mercury electrode were studied by direct current Tast polarography (DCTP) via the determination of the Koutecky's parameter, χ and the influence of different variables was analyzed. An electrochemical study of the prewave was also made by using various polarographic techniques. Values of χ depend on the nicotine concentration, pH, ionic strength (ψ-effect), and on the nature of the supporting electrolyte. The αn product (χ = transfer coefficient, n = number of electrons) and the stoichometric number,v, were determined. The prewave is interpreted as a surface reaction, the main features of the mechanism being its catalytic nature. The discharge is a two electron step and reaction between species of opposite charge is rate-determining.Key words: catalytic, prewave, polarography, nickel(II), nicotine.
A study of two prewaves of the Ni(II)-SCN- system was carried out under the experimental conditions when the influence of electroreduction of SCN- is negligible. Kinetics of Ni(II) reduction in thiocyanate media on the dropping mercury electrode was studied by DC Tast Polarography (DCTP) via determination of Koutecký's parameter χ; the influence of different variables was analyzed. The study of prewaves was performed using various polarographic techniques. Values of χ depend on the SCN- concentration, pH, ionic strength (Ψ-effect) and on the nature of the supporting electrolyte. The number of electrons n, the transfer coefficient α, the stoichiometric number ν, ∆H≠, and ∆S≠ were determined (compensation effect). The first prewave has character of a reaction in the solution, the second prewave is a surface process. Main features of both mechanisms are common: catalytic nature, one-electron step discharge and the rate-determining process between species of opposite charges.
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