Portugaliae
Electrochimica Acta

Scatchard, Buffle and van den Berg/Ruzic graphical methods for the analysis of complexation reactions of metal ions by soil and water organic matter (SWOM) samples using a simple 1:1 model, were assessed. Simulated and experimental (SWOM sample: Laurentian fulvic acid, FA) data sets were analysed. Simulated data shows that the presence of ligand heterogeneity results in deviations from linearity of the Scatchard and Buffle plots, while van den Berg/Ruzic plots remains linear. Average conditional equilibrium constants (K) and ligand concentration (LT) can be estimated from van den Berg/Ruzic plots. The graphical analysis of experimental data for the system FA plus Cu(TJ), obtained with a Cu(II) ion selective electrode, shows that the sample is characterised by ligand heterogeneity. The equilibrium parameters obtained from van den Berg/Ruzic plots are the following (standard deviation in parentheses): Log K = 5.56(1); LT = 44(2) M [{L}= 1.76(8) mmol/gFA].

Proton ligand dissociation and metal ligand stability constants of acrylonitrile (AN) with some transition metal ions in 0.1 M KC1 and 50% (v/v) methanol-water mixture were determined potentiometrically. In the presence of 2,2'-azobisisobutyronirrile as initiator of the proton-polymeric ligand dissociation of the metal polymeric ligand stability constants were also evaluated. The influences of temperature on the dissociation of AN and the stability of its metal complexes in the monomelic and polymeric forms were critically studied. Based on the thermodynamic functions, the dissociation process of AN was found non-spontaneous, endothennic and entropically unfavourable. The metal complexes formed exhibit spontaneous, endothermic and entropically favourable behavior. Key words: acrylonitrile, dissociation constants, stability constants, thermodynamics . Recently considerable interest has been focused on aqueous organometallic chemistry due to environmental and toxicological importance [1], In solution, polymer-metal complexes form microheterogeneous regions occupied by polymer backbone [2,3]. Polymeric ligands are used to select a specific metal ion from a mixture, thus to isolate important metals from wastewater [4]. Therefore, the aim of the present work was focused on studying the dissociation constants of AN and the stability constants for its metal complexes with Pb2+ , Cd2+ , Hg2+ , U022'1' and Th4+ in monomelic and polymeric forms employing potentiometric and thermodynamic measurements.

The effect of l-benzoyl-4-phenyl-3-thiosemicarbazide derivatives as inhibitors for the corrosion of copper in 3M HNO3 acid has been studied using weight loss, galvanostatic polarization and C.V. techniques. The inhibition efficiency calculated from the three measurements are in good agreement and depends on the type and concentration of inhibitor. Application of Hammett equation supported the obtained results. The effect of temperature was studied over a temperature range 30-60°C using weight loss technique. The inhibitors appear to function through general adsorption following the Langmuir adsorption isotherm. Quantum calculations were performed to give a more general picture of the nature of corrosion inhibition.

Electrochemical deposition and dissolution of zinc in acidic zinc plating bath solutions containing formaldehyde (FA), benzaldehyde (BA) or furfuraldehyde (FUA) has been studied by cyclicvoltammetric technique. Shapes of voltammograms, peak potentials and Tafel slopes are not affected by the presence of aldehydes in the plating bath solution. Aldehydes decreased the peak currents and the extent of decrease is in the order: FUA>BA>FA. This is accounted by Langmuir type of adsorption of aldehydes on zinc-solution interface and the electron density of oxygen atoms in aldehydes. SEM photographs of zinc deposits indicated the gradual decrease of grain size from FA to BA and FUA. Negative values of S°a and G°a suggested the considerable interaction of aldehydes on zinc surface with rigid adsorbed species.