Lead Amalgam Electrodes Research Articles

Behavior of glutathione as ligand of lead (II).

The presence and mobilization of toxic metal cations represents under many aspects a current and important problem in the environmental field. In this research, as cation lead (II) ion was studied. The formation of complexes between glutathione and lead (II) was studied at 25°C and in 1.00M NaCl as ionic medium by means of measurements of electromotive force (e.m.f.) of cells containing glass and lead amalgam electrodes. In the same experimental conditions, the protonation constants of glutathione were determined potentiometrically, using a cell containing the glass electrode. In the same experimental conditions, by considering glutathione (GSH) completely deprotonated, four protonation constants were determined. Potentiometric data could be explained by assuming the formation of 1:1 complexes between GSH and Pb2+ and with the participation of hydrogen ions. The stability constants of the assumed complexes were determined. The 1:1 ratio between GSH and lead (II) was confirmed by spectrophotometric investigations. Measurements by Infrared Rays (IR) and protonic Nuclear Magnetic Resonance (1H NMR) provide information on the structure of the found complexes.

Composition of Sodium Cholate Micellar Solutions

To study the composition of sodium cholate solutions, an investigation was carried out at 25 degrees C and in N(CH3)4Cl, as a constant ionic medium, at three different concentrations (W = 0.100; 0.500 and 0.800 mol dm(-3)). Electromotive force measurements of three different galvanic cells, the first involving a glass electrode for hydrogen ions, the second an electrode for sodium ions and the third a lead amalgam electrode, were performed. Independently, lead (II) cholate solubility measurements in the presence of sodium ions were performed, as well. The experimental results obtained from both approaches were explained by assuming the formation of aggregates in cholate and sodium of different composition depending on W and on the cholate concentration. The maximum aggregation found number for cholate was 24 and even aggregation numbers were markedly predominant. Only two species with odd aggregation number were found, but at a low percentage. The assumed species and the relative constants were compared with those found for the other sodium salt of cholanic acids.

On the standard potential of the mercury:Mercurous sulfate electrode at 25�C in aqueous solution

The standard potential of the mercury:mercurous sulfate electrode in aqueous solution at 25°C is determined in terms of the Weston saturated and Clark saturated standard cells. Eight electrode combinations involving cadmium-amalgam or zinc-amalgam electrodes and one lead-amalgam electrode are employed with the emf of the standard cells. A best value of 0.61544 V was obtained that agrees within 0.09 mV with the value previously reported by Harned and Hamer.

The induction time in the electrocrystallization of lead chloride and lead sulphate on an amalgamated lead electrode

The induction time in the electrocrystallization of lead chloride and lead sulphate on a lead amalgam electrode, determined from the observation of the light scattered by the electrode surface, has been treated according to the well known nucleation models. The analysis shows that the atomistic model is more realistic than the classical model. The critical nuclei size ranges between 0 and 1 growth unit.

The anodic growth of lead chloride and lead sulphate on a saturated lead amalgam electrode: A combined study by electrochemical and light scattering methods

The electrocrystallization of lead chloride and lead sulphate on a lead amalgam electrode has been studied. The instant at which the nuclei start to grow shows up most clearly in the light scattering signal, while in potential sweep and potential step experiments that instant is less identifiable or almost undetectable in the current transient. The light scattering patterns also show the changes in surface roughness during the process.

Anodic phase formation on lead amalgam electrodes in sodium sulfide solution

The anodic electrochemistry of the lead amalgam electrode in alkaline sulfide solutions was studied by cyclic voltammetry, chronoamperometry and chronopotentiometry. The first anodic peak in cyclic voltammetry is attributed to formation of three monolayers of PbS. This amount of PbS also formed in potential step transients, which showed a non-zero initial current which rose to a maximum and then decayed. The transients showed evidence of a nucleation and growth mechanism at low overpotentials, but at higher overpotentials the shapes were in good agreement with a multilayer adsorption model. Subsequent film thickening occurs to a thickness of about ten monolayers, and then film breakdown occurs with production of a soluble lead species.

Complex Formation Between Lead(II) and Bromide Ions

Abstract Activity coefficient effects represent the main source of uncertainty in the interpretation of equilibrium data in the Pb(II)-Br- system. This is presumably the reason for a number of contrasting reports on the stoichiometry and formation constants of PbBrn 2-n complexes. Specific Interaction Theory is employed in the present paper to select experimental conditions under which minimal activity coefficient variations are produced as well as to interpret the data. Emf measurements (lead amalgam electrode) based on junctionless cell (sodium ion-sensitive glass electrode, internal reference) show that in the range of bromide concentration 0.03–5.0 m all species PbBrn 2-n (1 ≤ n ≤ 6) are formed. The corresponding formation constants, expressed on the 5.0 m (= 4.1 M) NaC104 activity scale, are reported.

A new approach to measurement of the donor strength and co-ordination chemistry of various solvents by oxidation of metal amalgam electrodes in dichloromethane

Electrochemical oxidation of thallium, lead, and cadmium amalgam electrodes in dichloromethane containing 0.2 mol dm–3[NBu4][PF6] produces highly activated metal cations. The cations generated in this non-co-ordinating medium react rapidly with added donor solvents (solv) such as dimethyl sulphoxide, dimethylformamide, tetrahydrofuran, methanol, ethanol, and acetonitrile but not benzene to produce solvated metal ions. The kinetics of solvation are more rapid than precipitation of the metal salts which occurs in longer-time-scale bulk electrolysis experiments. The co-ordination number and equilibrium constants have been calculated for many of the solvated metal complexes, and the equilibrium constants compared with the solvent donor strengths. In the case of the dropping thallium amalgam electrode, the oxidation process is a well defined, strictly reversible one-electron step. From the data obtained for the thallium oxidation process, the value of the equilibrium constant, β1, may be calculated for the reaction TI++ solv [graphic omitted] [TI(solv)]+ and correlated with the Gutmann donor number. Measurement of β1 values calculated in this way is proposed as a simple method of estimating the donor strengths of co-ordinating solvents.

ChemInform Abstract: Two‐Dimensional Electrocrystallization of PbCO3 and Pb3(CO3)2(OH)2 on Lead Amalgam Electrodes in Sodium Carbonate and Bicarbonate Solutions.

AbstractThe results of XRD and electrochemical measurements show that a layer of PbCO3 forms on lead amalgam electrodes in NaHCO3 solutions, and a layer of Pb3(CO3)2(OH)2 in Na2CO3.

Two-dimensional electrocrystallisation oif PbCO 3 and Pb 3(CO 3) 2(OH) 2 on lead amalgam electrodes in sodium carbonate and bicarbonate solutions

The formation of anodic monlayers on lead amalgam electrodes in aqueous carbonate or bi-carbonate solutions was investigated by potentiostatic step and linear sweep voltammetric methods. Powder X-ray diffraction and the electrochemical measurements show that in bicarboante solutions (pH = 8.3) the layer formed was PbCO 3 and in carbonate containing solutions (pH ⩾ 10.0) the layer was Pb 3(CO 3) 2(OH) 2. At low current densities, monolayer formation via a 2D nucleation and growth mechanism was rate controlling with a potential dependence of about 4 mV/decade. The potential step transients at all higher overpotentials possessed truncated peaks. It was shown that this could be explained by preferential nucleation occurring around the inner lip of the electrode capillary. Large dissolution currents were observed and are attributed to the dissolution of lead as a complex ion, possibly as Pb(CO 3) 2− 2.

LEAD(II) COMPLEXES WITH SOMEN-SUBSTITUTED IMINODIACETIC ACIDS

Abstract Complex formation between lead(II) ions and some N-substituted iminodiacetic acids has been studied at 25° in aqueous sodium perchlorate with ionic strength 0.50 M. Measurements have been carried out with glass and lead amalgam electrodes. For all the ligands 1:1 mononuclear complexes form, one of which monoprotonated. The stability constants have been evaluated.

The influence of ammonium lignosulphonate as an expander on the formation of PbSO4 on lead amalgam electrodes

Linear potential sweeps and potentiostatic pulse perturbations have been employed to investigate the influence of the expander ammonium lignosulphonate, on the anodic formation of PbSO4 on lead amalgam electrodes in sulphuric acid solutions at 24 °C. It was found that the expander strongly adsorbs onto the clean amalgam surface thus affecting the formation of the PbSO4 film. The expander increased the charge necessary for passivation, inhibited the cathodic reduction of the film, and produced a more porous film. Evidence is given for the presence of an optimum concentration of expander. Some speculations concerning the mode of action of the expander onto the amalgam surface are presented.

Potentiometric investigation of complexes between lead(II) and ethylenedithiodiacetic acid

Complex formation between lead(II) and ethylenedithio diacetic acid (H2L) has been studied at 25°C in aqueous 0.5M sodium perchlorate medium. Measurements have been carried out with a glass electrode and with a lead amalgam electrode. In acidic medium and in the investigated concentration range experimental data can be explained by assuming the following equilibria: $$\begin{gathered} Pb^{2 + } + L^{2 - } \rightleftharpoons PbL log\beta _{101} = 3.62 \pm 0.03 \hfill \\ Pb^{2 + } + H^ + + L^{2 - } \rightleftharpoons PbHL^ - log\beta _{111} = 6.30 \pm 0.07 \hfill \\ \end{gathered} $$

Anodic behaviour of a dropping lead amalgam electrode in halide medium in the presence of EDTA

The behaviour of the dropping lead amalgam electrode has been studied. Calculated and experimental current—voltage curves have been compared and an explanation has been given for the observed differences. Selective determination of metal ions appears to be possible in the presence of saturated chloride, 1 M bromide and 10 −2 M iodide by means of amperometric complex-formation titrations using normal pulse polarography with the dropping lead amalgam electrode.

The anodic behaviour of lead amalgam electrodes in HCl solution

The anodic behaviour of lead amalgam electrodes in HCl solution

The anodic behaviour of lead amalgam electrodes in HCl solution

The anodic behaviour of the lead amalgam electrode has been investigated in aqueous hydrochloric acid solutions. Both voltammetric and potential pulse results are described. The mechanism of passivation is shown to be the nucleation and growth of three-dimensional nuclei of PbCl 2 which progressively block the electrode. The nuclei are considered to be right circular cones, distributed at random on the electrode surface. As in the case of solid lead electrodes, a simultaneous dissolution of PbCl n 2− n complexes is observed, which diffuse away from the electrode under mass transport control. Evidence is also presented that the first stage in the growth of the anodic film is the two-dimensional nucleation and growth of a monolayer of PhCl 2. Unfortunately, this process is partially obscured by the dissolution reaction. A reaction scheme is proposed.

Lead(II) complexes with thiodiacetic, oxydiacetic and iminodiacetic acids

Complexes of lead with thiodiacetic, oxydiacetic, and iminodiacetic acids were studied in aqueous solution and in the solid state. In solution, in an acidic medium, only 1:1 complexes were found in all cases. Mixed complexes with hydrogen ion are also formed. The relative formation constants were evaluated at 25°C in 0.5 M NaClO 4 by the potentiometric method using a lead amalgam electrode. In the solid state the 1:1 compounds were isolated and characterized. Their probable structure is discussed.

On the complex formation between lead(II) and citrate ions in alkaline solution

The complex formation between lead(II) and citrate ions ( L) in alkaline solution has been investigated by means of potentiometric measurements by employing a lead amalgam electrode at 25°C and in 2 M Na(ClO 4). The experimental data can be explained by assuming the following equilibria: Pb(II)+L→ Pb(II)l+ OH − logβ 1.−1.1=−0.94±0.05 where Pb(II) indicates the plumbite ion.

On the complex formation between lead(II) and citrate ions in acid solution

Complex formation between lead(II) and citrate ions ( L) has been investigated potentiometrically at 25°C and in 2 M Na(ClO 4) by using a lead amalgam electrode and a glass electrode. The experimental data can be explained by assuming the following equilibria: Pb 2++ L→ PbL log β 1, 0, 1= 4·08±0·10 Pb 2++H ++ L→ PbHL log β 1, 1, 1= 8·15±0·05 Pb 2++2H ++ L→ PbH 2L log β 1, 2, 1=10·85±0·10 Pb 2++2 L→ PbL 2 log β 1, 0, 2=6·06±0·20 Pb 2++2H ++2 L→ PbH 2L 2 log β 1, 2, 2=14·95±0·15 Pb 2++4H ++2 L→ PbH 4L 2 log β 1, 4, 2=21·68±0·15 Symbols: L = citrate ion = C 6H 5O 7 3− B = total concentration of Pb 2+ b = free concentration of Pb 2+ A = total concentration of citrate ions a = free concentration of citrate ions H = total concentration of hydrogen ions h = free concentration of hydrogen ions K n = formation constants of citric acid, defined as follows: K n = [H nL] h[H n−1L] where n=1,2,3 β q, p, r = stability constants of a species Pb q H p L r , defined as follows: β q,p,r = [Pb qH pLr] b qh pa r Charges are generally omitted.

On the complex formation between lead(II) and tartrate ions in alkaline solution

The complex formation between lead(II) and tartrate ions( L) has been investigated potentiometrically, at 25°C and in 1M Na +(ClO 4 −), in the range 0·050M ⩽ [OH −] ⩽ 0·200M, by using a lead amalgam electrode. The experimental data can be explained by assuming the following equilibria: Pb(II) + L ⇌ Pb L + OH − log β 1, −1,1 = 1·10±0·12Pb(II) + 2 L ⇌ Pb 2 L 2 + 2 OH − log β 2, −2,2 = 5·48±0·12Pb(II) + 3 L ⇌ Pb 2 L 3 + 3 OH − log β 2, −3,3 = 4·65±0·15 where Pb(II) indicates the plumbite ion. Symbols: B = total concentration of Pb(II) b = free concentration of Pb(II) not complexed with tartrate ions A = total concentration of tartrate a = free concentration of tartrate H = total concentration of H + h = free concentration of H + OH = concentration of OH − η = log B b β q,− p, r = stability constant of a species Pb q L r defined by the following [Pb q L r ] = β q, p− r b q a r OH p where q ⩾ 1, p ⋛ 0 and r ⩾ 1. K n = stability constant of the species [H n L] = K n h[H n−1 L] where n = 1, 2. Charges are generally omitted; the tartrate ion is indicated by L.