A. Arévalo

On the adsorption of cadmium(II) ions on a HMDE from KF + thiourea aqueous solutions: A chronocoulometric study

Abstract The adsorption of cadmium(II) ions from thiourea aqueous solutions has been studied by double potential step chronocoulometry (DPSSC). The adsorption is strong on mercury electrodes and it has been studied as a function of thiourea concentration, cadmium(II) concentration and potential. A discrepancy between the double-layer charge values from either blank solutions or solutions containing reactant obtained by this technique has been found.

Potential-dependent competitive processes on platinum in acid solution in the presence of propargyl alcohol

Abstract The electroadsorption interactions between dilute propargyl alcohol and smooth platinum in 0.5 M H 2 SO 4 at 25° C have been investigated at different potentials. When the platinum electrode is covered by H atoms the hydrogenation of propargyl alcohol takes place. Otherwise, when the platinum electrode is held at a potential located in the double-layer region, the electroadsorption of propargyl alcohol involves a disruptive electro-oxidation yielding strongly bound adsorbed residues. The latter can be electrodesorbed presumably as carbon dioxide and protons. This process occurs within the O-electroadsorption potential range. The complete residue electrodesorption requires several voltammetric cycles. Competition between the hydrogenation reaction and the disruptive electroadsorption process can be observed at potentials where the platinum surface is partially covered by H atoms.

Voltammetric approach to multicomponent electrochemical systems at platinum electrode surfaces

Abstract Adsorption interactions of different systems on electrodispersed and smooth platinum electrodes were explored through anodic stripping voltammetry using a conventional flow cell technique at 25°C. A first adsorbate was formed at the platinum electrode in contact with the solution containing the adsorbable species I, and subsequently the platinum—adsorbate I system was put into contact with a solution containing the adsorbable species II, where I  CO, CH 3 OH and reduced CO 2 , and II C 2 H 4 , C 2 H 2 and CO, and vice versa. The anodic stripping voltammograms revealed either a total or partial displacement of adsorbate I by adsorbate II, or chemical interactions among adsorbed residues I and Il. The following decreasing platinum—adsorbate interaction sequence was established C 2 H 2 -2 > CO > C 2 H 4 > CH 3 OH ≈ CO 2 .

On the real significance of the complex constants obtained from a polarographic method by adjusting the ionic strength with weakly complexing electrolytes

Abstract It is theoretically and experimentally demonstrated that the constants obtained by applying the method of DeFord and Hume to metal—ligand studies in which the ionic strength has been adjusted by weakly complexed electrolytes do not have the characteristics of stability constants. Instead, they are shown to correspond to specific groupings of stability constants of the simple and mixed coordinate species found in the medium.

Anion-induced adsorption of bismuth(III) on mercury from chloride medium

Abstract The adsorption of bismuth(III) on a mercury electrode in chloride perchloric acid medium has been measured by double-step chronocoulemetry. The amount of adsorption of Bi(III) increases with the concentration of chloride, a maximum value being reached around c C 1 = 80 m M , to diminish at greater concentrations of the halide. The adsorption of Bi(III) also shows maximum values when the electrode charge varies. The results allow the existence of several coordinated Bi-Cl − species to be postulated, which would be responsible for the adsorption process and the subsequent reduction of Bi(III).

Polarographic studies of complexes of cadmium with chloride and thiocyanate ions in aqueous medium

Abstract This is a polarographic study of the system Cd(II)−NaCl−NaSCN in aqueous medium of a constant ionic strength of μ =1.0 M with NaClO 4 . Reduction takes place through a reversible bielectronic process. The diffusion magnitudes I d and D have been determined, and the formation of the mixed complexes CdClSCN, [CdCl 2 SCN] − and [CdCl(SCN) 2 ] − , with stability constants of β 11 =106±101 2 mol −2 , β 21 =156±101 3 mol −3 and β 12 =484±801 3 mol −3 , respectively, has been demonstrated. The values of these constants are discussed in the light of statistical aspects and Watters equations.

A polarographic study of the mixed complexes of Pb(II) with oxalate and malonate ions

Abstract The coordinated mixed Pb(II)-oxalate-malonate system has been polarographically studied in aqueous medium. The ionic strength has been maintained constant at μ = 1.0 by using NaClO 4 . Application of the Schaap and McMasters method detected only the existence of the [Pb-ox-mal] 2− complex, the overall stability constant of which was β 11 = 4.1 x 10 5 . The various coordination equilibria are discussed on the basis of statistical aspects.

Adsorption of Tl(I) on mercury in azide media

Abstract The Tl(I) surface excess in azide media on the HMDE has been determined by using the double-potential step chronocoulometric technique. The absorption of Tl(I) increases as the electronic charge on mercury becomes more negative. These results are not in agreement with the adsorption behaviour of ions of white metals following an anion bridge mechanism. Actually the absorption process does not change the charge on the electrode. This is related to the assumption that the neutral species TIN 3 , which is the only complex species existing in the solution, is responsible for the adsorption process.

Adsorption of 2-mercaptoethanol and In(III)-2-mercaptoethanol on mercury electrodes in HClO4 + NaClO4 medium

Abstract The surface excess of In(III)-(C2H6OS)x in HClO4+NaClO4 media on the HMDE has been determined by using the double potential step chronocoulometric technique. The adsorption of In(III) increases as the electric charge on the mercury becomes more negative. The adsorption of C2H6OS has also been determined using the method of Anson et al. The plot of the adsorption of In(III)-(C2H6OS)x vs. the adsorption of C2H6OS is in agreement with the behaviour of white metal ions, following the anion bridge mechanism. The species involved in the adsorption mechanism have been determined. The results show that all the complex species intervene in the adsorption process.

Polarographic study of the coordinated Cd(II)−leucinate system

Abstract The coordinated Cd(II)-leucinate system has been studied polarographically in an aqueous medium and at constant ionic strength (μ = 1.0) (adjusted with NaClO4). The stabilization of the coordinated species [CdL2] and [CdL3]− has been established, with stability constants β2 = 3.0 × 107 l2 mol−2 and β3 = 8.2 × 1010 l3 mol−3, respectively.