Portugaliae
Electrochimica Acta

The procedure for the voltammetric determination of palladium(II) involves an adsorptive accumulation of palladium(II)-DMG complex on a stationary mercury electrode, followed by a stripping voltammetric measurement of reduction current of adsorbed palladium(II) chelate complex. The optimum conditions for the analysis of palladium(II) included pH (3.5 - 4) and an accumulation potential between 0 and - 0.3 V (vs. Ag/AgCl). The peak current is proportional to the Pd-DMG concentration and increases linearly with a preconcentration time.

Electrochemical oxidation of 3,5 dimethylpyrazole-pentacyanoferrate (II) complexes at glassy carbon electrode has been determined from analyses of voltamperometric curves at different pH values. The complex species formed are dependent on the pH media. Voltammograms display only a well-defined wave but the peak potentials shift to less positive values as the pH medium increases. The possible mechanisms of the reaction have been discussed.

Mutual differential diffusion coefficients of lithium chloride in moderately concentrated (0.1 to 1.0 mol dm-3) aqueous solutions were measured at 25 °C using an improved open-ended conductimetric capillary cell method. A critical examination of the response of the technique to such improvements is done on the basis of the analysis of different experimental parameters as well as from the reproducibility of the diffusion coefficients. The imprecision of the diffusion coefficients, generally < 1 %, is not affected by the improvements. The reported LiCl mutual diffusion coefficients agree with those obtained previously by Gouy interferometry, and Rayleigh interferometry within lower deviations than 2-3 %. Agar's semi-empirical equation for the concentration dependence of electrolyte diffusion coefficients is in good agreement with the experimental data.

Ni(II) and Zn(II) complexes of a macrocyclic diimine crown ether, 2,3,11,12-dibenzo-5,9-diaza-4,9(l0)-cisdiimino-l,13-dioxacyclopentadecane (O-en-N-tn), were prepared and their electrochemical behaviours were reported. Reduction of the complexes was studied in ethyl alcohol-water mixture (1:5 v/v) using sampled current polarographic, differential pulse polarographic, cyclic voltammetric, chronoamperometric and chronocoulometric techniques. A mechanism for the electrode reaction was proposed. Heterogeneous rate constant and the transfer coefficient of the electrode reaction were determined. Adsorptional characteristics of the complexes on mercury electrode were studied and adsorbed amounts of the complexes were found to be 10-11 mol/cm2 and 10-12 mol/cm2 order of magnitude in acidic and basic media respectively.

When experimental data for activity coefficients are analyzed,one typical feature of the variation of logarithm of mean ionic activity coefficient with ionic strength is the presence of a minimum in the curve. The presence of this minimum gives rise to a new point at which lnγ± takes a value of zero in spite of the ionic strength being different from zero. In this paper the position of both points has been determined for 151 electrolytes using Pitzer equations to describe the dependence of lnγ± on ionic strength.

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