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1.
The title subject has been studied using single pulse and chronopotentiometric polarization measurements on the Zn(Hg)/Zn(II) electrode and equilibrium measurements on the same and the Zn/Zn(II) electrode, mainly in 2 M NH4Cl with 0–0.3 M NH3. At low ammonia concentrations, the Zn(Hg)/Zn(II) reactions are found to occur in two consecutive charge-transfer steps with Zn(I) as intermediate, and with little or no participation of ammonia. At higher ammonia concentrations, however, nearly symmetric transfer by divalent zinc ion (α=0.5 and n=2) to and from diammine species appears to be the predominant charge-transfer step.  相似文献   

2.
Combined thermodynamic and kinetic studies have yielded convenient single-ion activity coefficients for manganese(II), alkaline-earth, and chloride ions and standard exchange currents for the two steps of the Mn(Hg)/Mn(II) electrode in 0.005 M MnCl2+0.495 M MeCl2 (for Me=Mg, Ca, Sr, Ba, and Mn) at 25°C. The results indicate that the fall in mean ionic activity coefficient for the alkaline-earth chlorides along the sequence from magnesium to barium is carried to a larger extent by the cation than by the anion, that also the activity coefficient for the minority cation Mn(II) falls along this sequence, and that other than activity-coefficient effects on the Mn(Hg)/Mn(II) reactions appear only with barium ions, which retard the reactions additionally. The results are discussed with emphasis on ionic interactions and double-layer effects.  相似文献   

3.
The title subject has been studied by galvanostatic single-pulse, chronopotentiometric and equilibrium measurements on the Mn(Hg)/Mn(II) electrode (mainly saturated managanese amalgams) in one molar alkali chloride (LiCl, KCl and CsCl) and potassium iodide and thiocyanate solutions of pH 4 to 5 at 25°C. The Mn(Hg)/Mn(II) reactions are found to occur in two consecutive steps with monovalent ions as intermediate in all these solutions. The rates of both the ion-transfer step Mn(Hg)/Mn(I) and the electron-transfer step Mn(I)/Mn(II) appear independent of the cations Li+ and K+ and of the anions Cl?, I? and SCN?, when differences in bulk activities of electroactive species are corrected for. The Cs+ ion, however, seems to retard the reactions more than expected from bulk activity changes, and this can be explained by Cs+ specific adsorption or by variations in the properties of the inner layer with the cation.  相似文献   

4.
The title subject has been studied using stationary, single-pulse, and chronopotentiometric polarization measurements on the Zn/Zn(II) electrode and equilibrium measurements on the same and the Ag/AgCl electrode in 0.5–4 M chloride solutions at 25°C. The Zn/Zn(II) electrode reactions are found to occur in two consecutive charge-transfer steps with Zn(I) as intermediate. The ion-transfer step Zn/Zn(I) is too fast to exhibit its kinetics. The electron-transfer step Zn(I)/Zn(II) mostly occurs by the couple ZnCl2(H2O)y/ZnCl2(H2O)y, but species with one or no chloride ligand take over as the main electroactive ones at chloride (or salt) concentrations below 1 M. The value of y is not clearly revealed by the data. Some sluggishness in complex equilibration and some, double-layer effects are observed. A convenient scale for single-ion activities is described, used, and recommended.  相似文献   

5.
The title subject has been studied by galvanostatic single-pulse, chronopotentiometric and equilibrium measurements on the Zn(Hg)/Zn(II) electrode in x M KI+(1?x) M KCl (x from 0 to 1), 1 M KBr and 1 M MeCl (Me=Li, Na, K and Cs) solutions of pH 3 at 25°C. Quantitative information about the effect of specifically adsorbed halides on the rates of the Zn(II)/Zn(I) and the Zn(I)/Zn(Hg) steps is obtained separately (for the latter step mainly at potentials near ?1.0 V(SCE)), and the latter step seems to be more influenced than the former by the adsorption. An attempt is made to correlate the adsorption effect on the rate of the Zn(II)/Zn(I) step to double-layer parameters according to recent models for such effects. The extra current observed at potentials where the halides are adsorbed, seems to vary with the surface activity of the specifically adsorbed ion. The lack of any observed kinetic effect of Cs+, which is specifically adsorbed at these potentials, is possibly due to the Cs+ specific adsorption enhancing the Cl? specific adsorption and vice versa, so that the decelerating and accelerating effects by these ions may cancel each other.  相似文献   

6.
Combined thermodynamic and kinetic studies have revealed amalgam properties, solution activities, and diffusion data besides charge-transfer parameters and exchange rates for either step of the Cu(Hg)/Cu(II) electrode in aqueous solutions of xM CuSO4+(0.5?x) M MgSO4+H2SO4 (to pH about 2.5) at 25°C. The studies allow separation of mean ionic activities into convenient single-ion ones. The kinetic results demonstrate the consecutive two-step mechanism involved. Comparison is made to the solid Cu/Cu(II) electrode, and double-layer effects are discussed.  相似文献   

7.
The electrode reaction Hg(II)/Hg in complex chloride solutions with dimethyl sulfoxide as solvent has been investigated at the equilibrium potential by the faradaic impedance method and a cyclic current-step method. The ionic strength was 1 M with ammonium perchlorate as supporting electrolyte, and the temperature was 25°C. Double-layer data have been determined by electrocapillary measurements. From the results of the kinetic measurements at ligand numbers ≤1.1 or ≥2.3 it is concluded that the overall charge transfer proceeds step-wise. The solvated Hg2+ and Hg22+ as well as the complexes HgClj2?j and the dinuclear Hg2Cl3+ contribute to the exchange current density. The rate constant of the step HgClj2?j/ Hg(I) is found to increase with the number of Cl? coordinated. This increase can be correlated to a decrease in solvation and a lengthening of the Hg?Cl distance. For 1.1 << 2.3, impedance measurements indicate a rate-controlling adsorption step. It is suggested that the uncharged HgCl2 then forms an adsorbed network on the mercury surface.  相似文献   

8.
The title subject has been studied through equilibrium potential measurements on the Zn/Zn(II) and the Ag/AgCl electrode vs. SCE and galvanostatic single-step and chronopotentiometric polarization measurements on the former electrode, all in acidified (to pH about 3) solutions of 0.005 M ZnCl2+0.99 M MeCl (for Me=Li, Na, K, and Cs) at 25°C. It is found that the Zn(II) activity decreases together with the alkali-ion activity along the sequence LiCl>NaCl>KCl>CsCl, that the chloride-ion activity essentially is insensitive to mutual substitutions of alkali ions, and that the Zn/Zn(II) reactions exhibit no other than pure activity effects of such substitutions. The results support that the Zn/Zn(II) electrode reacts in two consecutive steps with Zn(I) as intermediate, and that some sluggishness appears in chemical reactions to and from electroactive Zn(II) species.  相似文献   

9.
A new method of determining electrochemical kinetic parameters by square-wave polarography was presented, in which the faradaic current at θ/2, θ being the half-period of superimposed square-wave voltage, was used for the analysis. The method gave the following kinetic parameters for the electrode reaction, Zn(II) + 2e(Hg), in aqueous solutions at 25° C: kcθ=0.0052 cm s?1 and αc=0.36 in 1 M KCl, kcθ=0.011 cm s?1 and αc=0.30 in 1 M KBr, and kcθ=0.020 cm s?1 and αc=0.52 in 1 M KNCS. Induced adsorption of Zn(II) on the dropping mercury electrode was suggested in solutions containing thiocyanate ions.  相似文献   

10.
The electrochemical Peltier effect was studied at a gold electrode in solutions containing some Fe(II)/Fe(III) redox couples by measuring the local temperature change in the electrode/solution interphase under controlled-potential and controlled-current polarization. Relative values of the electrochemical Peltier coefficient for the cathodic process at equilibrium potential, which is denoted by (Πc)I=0, were determined by analyzing the observed temperature change as a function of current. The values of (Πc)I=0 were found to be positive for the Fe(H2O)62+/Fe(H2O)63+ systems in HClO4 (1 M), HNO3 (1 M), H2SO4 (0.5 M), and HCl (1 M), their magnitudes being very similar in the first three acid solutions, but smaller in the HCl solution. On the other hand, a negative value of (Πc)I=0 was obtained in the case of a Fe(CN)64?/Fe(CN)63? couple in a H2SO4 (0.5 M) solution. Such a difference in the Peltier coefficient is considered to be due to the difference in the ionic species of iron involved in the electrode reaction.  相似文献   

11.
The electrode reaction of the Ni(II)/Ni(Hg) system occurring in 4–13.7 mol kg?1 solutions of Ca(ClO4)2 in the temperature range 20–185°C was studied by means of pulse polarography and cyclic voltammetry. From analysis of the formal potentials with respect to the ferricinium ionferrocene electrode as a function of the logarithm of the water activity, the hydration numbers of Ni(II) were found. They decrease as both the molality of Ca(ClO4)2 and the temperature increase. Limiting values of hydration numbers at both high temperature and concentration of Ca(ClO4)2 were near to 6. The electrode reaction proceeds in a step-wise manner with the Ni(I)/Ni(Hg) system controlling the rate of the overall process.The rate constants at formal potentials under different conditions are presented.The electrode reaction orders are determined with respect to the water point to the participation of Ni(H2O)4+ in the rate-determining step.  相似文献   

12.
铂电极上醋酸-醋酐溶液中Mn(III)/Mn(II)电对研究   总被引:2,自引:0,他引:2  
平衡电极电势实验确定了25 ℃, 1.5 mol•L-1醋酸钾+醋酸-醋酐(3:1体积比)溶液中Mn(III)/Mn(II)的条件电极电势为0.719 V(vs SCE);采用电势扫描和旋转圆盘电极技术研究了醋酸-醋酐溶液中铂电极上Mn(III)/Mn(II)电对的阳极氧化动力学. 结果表明:Mn(II)阳极氧化成Mn(III)的电极反应控制步骤属电荷传递过程, 阳极传递系数β=0.347,交换电流密度i0=5.84×10-6 A•cm-2,阳极标准反应速率常数ka=1.35×10-8 m•s-1, Mn(II)和OAc-的反应级数均为一级.  相似文献   

13.
The reduction and reoxidation processes of the Fe(II)/Fe(Hg) system in thiocyanate solutions at stationary mercury electrodes have been investigated by cyclic voltammetric, anodic stripping and controlled potential electrolysis methods. In 0.1 M NaSCN and 0.4 M NaClO4 solution containing 1×10?3M Fe(II), the voltammogram on the first cycle at. 0.05 V s?1 gives two consecutive cathodic peaks near ?1.2 and ?1.39 V with a hysteresis on the reversal, and an anodic wave with two large peaks near ?0.58 and ?0.05 V and two small peaks near ?0.52 and ?0.43 V, respectively. The multicyclic voltammogram under the same conditions in the potential region between 0.00 and ?1.50 V gives a cathodic wave with a principal peak near ?1.02 V and two small peaks near ?0.02 and ?0.53 V, respectively, and an anodic wave with a principal peak near ?0.72 V, three small peaks near ?0.64, ?0.52 and ?0.40 V, and with a shoulder near ?0.05 V, respectively. The variation of the shape of the voltammogram on the second and subsequent runs is due to the formation of S2? and CN? during the process of electroreduction of Fe(II). A mechanism is proposed which involves an initial reduction of Fe(II)?SCN? produced in an activation step at a mercury electrode, followed by the chemical redox reaction of a part of Fe(0)?SCN? in the species giving FeS and CN?, and takes into account the influence of FeS and CN? on the further reduction and reoxidation of iron. Both FeS and CN? stimulate further reduction, and reoxidation of iron. The hysteresis of the cathodic wave on the first cycle arises from the fact that Fe(II) is reduced more easily at the mercury electrode covered with FeS than at a pure mercury electrode.  相似文献   

14.
Abstract

The stepwise complex formation between 2-amino-2-hydroxymethyl-1,3-propanediol (TRIS) with Co(II) and Mn(II) was studied by potentiometry at constant ionic strength 2.0 M (NaClO4) and T = (25.0 ± 0.1)°C, from pH measurements. Data of average ligand number (Bjerrum's function) were obtained from such measurements followed by integration to obtain Leden's function, F 0(L). Graphical treatment and matrix solution of simultaneous equations have shown two overall stability constants of mononuclear stepwise complexes for the Mn(II)/TRIS system (β1 = (5.04 ± 0.02) M?1 and β2 = (5.4 ± 0.5) M?2) and three for the Co(II)/TRIS system (β1 = (1.67 ± 0.02) × 102 M?1, β2 = (7.01 ± 0.05) × 103 M?2 and β3 = (2.4 ± 0.4) × 104 M?3). Slow spontaneous oxidation of Co(II) solutions by dissolved oxygen, accelerated by S(IV), occurs in a buffer solution TRIS/HTRIS+ 0.010/0.030 M, with a synergistic effect of Mn(II).  相似文献   

15.
The electrode reaction Cu(I)/Cu(Hg) in complex chloride, bromide and iodide solutions with DMSO as solvent has been studied at the equilibrium potential by the faradiac impedance method and a cyclic current-step method. The kinetic data refer to the ionic strength 1 M with ammonium perchlorate as supporting electrolyte and to the temperature 25°C. Double-layer data have been obtained from electrocapillary measurements. From the results for the chloride system at [Cl?]>15 mM it is concluded that the charge transfer is catalysed by ligand bridging at the amalgam and the following parallel reactions predominate: Clads?-Cu++e?(am)Clads?+Cu(am) Clads?-Cu2Clj2?j+e?(am)Clads?+Cu(am)+CuClj1?j At lower [Cl?] and in the whole ligand concentration range available in the bromide and iodide systems the impedance measurements indicate a rate-controlling adsorption step. It is suggested that uncharged complex CuL (L?=halide ion) then forms an adsorbed two-dimensional network on the amalgam surface.  相似文献   

16.
Some metal complexes of DL–methionine were prepared in aqueous medium and characterized by different physico-chemical methods. Methionine forms 1:2 complexes with metal, M(II). The general empirical formula of the complexes is proposed as [(C5H10NO2S)2MII]; where MII = Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II). All the complexes are extremely stable in light and air and optically inactive. Magnetic susceptibility data of the complexes demonstrate that they are high spin paramagnetic complex except Zn(II), Cd(II) and Hg(II) complexes. The bonding pattern in the complexes are similar to each other as indicated by electronic absorption spectra and FTIR spectral analysis. The current potential data, peak separation (AE) and the peak current ratio (ipa/ipc) of the (Mn, Cu and Cd) complexes indicate that the charge transfer processes are irreversible, the systems are diffusion controlled and also adsorptive controlled. The charge transfer rate constant of metals in their complexes are less than those in their metal salts at identical experimental conditions due to the coordination of metal with methionine.  相似文献   

17.
Two novel heterobimetallic coordination polymers with Hg(SCN)42− as a linker have been synthesized and characterised by means of IR, EPR, magnetic measurements and single crystal X-ray. The compounds [Mn(bpzm)Hg(SCN)4]n (1) and [Mn(bdmpzm)2Hg(SCN)4]n (2) form supramolecular framework structures. The compound 1 creates a three-dimensional coordination polymer and compound 2 has one-dimensional chain structure extending along the crystallographic direction [1 0 0]. Variable-temperature magnetic susceptibility measurements show very weak antiferromagnetic interactions between the paramagnetic Mn(II) centres of structures 1 and 2.  相似文献   

18.
The title subject is studied by electrode-kinetic measurements in acetate buffered potassium chloride and magnesium sulphate solutions of varied concentration at 25°C, using literature data for activity and double-layer properties. The results indicate that the Fe(II)/Fe(Hg) reaction occurs by an essentially symmetric (α near 1/2) ferrous-ion transfer (n=2), that this transfer is second order in water-activity dependence, and that it exhibits a smaller than classically expected double-layer effect. No specific interaction appears for any of the ions of the supporting salts. An e.c. reaction scheme is proposed for the Fe(Hg)/Fe(II) electrode in non-complexing aqueous solution.  相似文献   

19.
The reaction of Mn(OAc)2·4H2O with isatin-hydrazone-S-benzyldithiocarbazate (HIsa-SBn) results in the formation of a bis-ligand complex [Mn(Isa-SBn)2]·2DMF. Its single crystal is obtained and the structure is determined by X-ray diffraction. It belongs to a monoclinic space group C2/c with the cell parameters: a = 23.290(4) Å, b = 11.4980(18) Å, c = 18.483(5) Å, V = 4087.6(14) Å3. The Mn(II) atom is six-coordinated with two amide O atoms, two azomethine N atoms, and two thiolate S atoms, resulting in a distorted octahedral geometry.  相似文献   

20.
Thermodynamic and kinetic studies have revealed conventional mean-ion and convenient single-ion activity coefficients for copper(II), magnesium and sulphate ions and standard exchange rates for either step of the liquid Cu(Hg)/Cu(II) electrode and of the solid Cu/Cu(II) electrode, all in 0.005 mol kg?1 CuSO4+0.005 mol kg?1 H2SO4+(x?0.01) mol kg?1MgSO4 (for x=0.2 to 3) at 25°C. With increasing x, the sulphate activity coefficient steadily falls, the copper(II) and magnesium activity coefficients go through a minimum near x=1, and the standard rates fall. The kinetic changes with x reveal some information on double-layer and ligand effects.  相似文献   

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