Jadwiga Saba

The influence of thiourea on the electroreduction of Zn2+ ions in various supporting electrolytes in respect to the cap-pair effect

Abstract The mechanism of the cap-pair effect was examined with respect to its acceleration of the electro-reduction of Zn 2+ ions in NaCIO 4 , NaCl and NaBr. It was found that the presence of thiourea in the solution increased the rate of the electrode process; a role is played in the acceleration by the composition of zinc complexes formed in the bulk of the solution.

The Influence of Thiourea on the Two-Step Electroreduction of Zn(II) Ions

Summary. The two-step reduction of Zn(II) ions at a dropping mercury electrode in 1 M NaClO4/0.001 M HClO4 in the presence of thiourea was examined in wide potential and frequency ranges using the impedance method. The catalytic activity of thiourea concerns both electron transfer steps. It was found that the acceleration of the electroreduction process depends on the surface concentration of thiourea.Zusammenfassung. Die zweistufige Reduktion von Zn(II)-Ionen an einer Quecksilbertropfelektrode in 1 M NaClO4/0.001 M HClO4 in Gegenwart von Thioharnstoff wurde in einem breiten Potential- und Frequenzbereich mittels der Impedanzmethode untersucht. Die katalytische Aktivität von Thioharnstoff betrifft beide Elektronenübertragungsschritte. Es wurde beobachtet, daß die Beschleunigung der Elektroreduktion von der Oberflächenkonzentration des Thioharnstoffs abhängt.

Studies of the mixed n-butanol—thiourea adsorption layer on the mercury electrode

Abstract Properties of the mixed adsorption layer of n-butanol—thiourea on the mercury/1 M NaClO 4 solution interface were described using their adsorption parameters as well as kinetic ones for the piloting process of Zn(II)ion reduction. Butanol is an inhibitor of this process but thiourea accelerates it according to the cap-pair rule. Additivity of thiourea and butanol adsorption was found. For the concentration ratio of butanol: thiourea ≈ 12 the compensation of inhibiting and accelerating effects in a wide range of concentrations was observed. Formation of mixed adsorption layers was experimentally confirmed.

Mixed adsorption layers of 0.1 M tert-butanol-tetramethylthiourea at the interface of Hg/aqueous perchlorate solutions.

The electrosorption behavior of tetramethylthiourea (TMTU) on a mercury electrode from 1.0, 0.5, and 0.1 M NaClO(4) solutions containing 0.1 M tert-butanol (TB) is described by means of adsorption isotherm constants. The adsorption parameters for the double layer were calculated from a double-layer differential capacity measurement extrapolated to zero frequency. The values of the relative surface excess increase along with the concentration of NaClO(4). It seems that the adsorption of TMTU is determined by an interaction between adsorbed molecules. The presence of TB in the adsorption layer distinctly influences the parameters of the inner layer.

Description of the mixed polyethyleneglycoles-thiourea adsorption layer on a mercury electrode and its effect on the electroreduction of zinc (II)

Abstract Adsorption of the mixture of thiourea-polyethylene glycols of molecular weights 400 and 10 000 on a mercury electrode in 1 M NaClO 4 was described. The experimental data were obtained from the measurements of differential capacity and kinetic parameters of Zn(II) ion reduction as a piloting ion. It was stated that the Zn(II) ions reduction could be accelerated, inhibited or the effect of compensation of these phenomena could take place depending on the ratio of molar concentrations of the studied substances. The adsorption parameters of thiourea in the presence of various concentrations of polyethylene glycols as well as electrostatic parameters of the internal layer were given.

Application of the cap-pair effect in reducing the inhibition of electrode processes. The determination of zinc in the presence of tween-80

Abstract The “cap-pair” effect, which accelerates electrode processes, is shown to be useful in decreasing the effects of inhibitors on reduction processes. The determination of zinc in the presence of Tween-80 is used as an example. In the square-wave polarography of zinc at the 10 -5 M level, addition of thiourea (10 g l -1 ) eliminates or greatly reduces the inhibitory action of Tween-80, thus allowing precise determinations.