An interface reaction of Hexavalent chromium: The polarographic behaviour of HCrO4- and CrO42-

1955 ◽  
Vol 8 (1) ◽  
pp. 51 ◽  
Author(s):  
JH Green ◽  
A Walkey
Keyword(s):  
Ph Value ◽  
Mercury Electrode ◽  
Interface Reaction ◽  
Proton Donor ◽  
Interface Reactions ◽  
Inorganic Systems ◽  
Trivalent State ◽  
Current Voltage ◽  
Dropping Mercury Electrode ◽  
Adsorption Desorption

Current-voltage relationships have been determined for the electroreduction of dilute chromate solutions in a range of bicarbonate-carbonate buffers at the dropping mercury electrode. Double waves are obtained whose relative heights are a function of the pH value. By analogy with the behaviour of pyruvic acid an interface reaction with some proton donor prior to the reduction to the trivalent state is suggested (CrO42- +HB- → HCrO4- + B-). The rate constants for the interface reaction are computed for different donors by the method of Koutecky and Brdicka (1947). Adsorption-desorption processes in the region of the electrocapillary zero may account for the shape of the current-voltage curves, and, if so, the explanation based simply on an interface reaction will require modification. The occurrence of interface reactions and of adsorption-desorption processes in other inorganic systems is discussed.

Oxidation of hydrogen peroxide at the dropping mercury electrode

1984 ◽  
Vol 49 (10) ◽  
pp. 2320-2331 ◽  
Author(s):  
Miroslav Březina ◽  
Martin Wedell
Keyword(s):  
Hydrogen Peroxide ◽  
Superoxide Anion ◽  
Ph Value ◽  
Mercury Electrode ◽  
Electrode Process ◽  
Electrochemical Processes ◽  
Dropping Mercury Electrode ◽  
Oxidation Of Hydrogen ◽  
Decreasing Ph ◽  
Rate Controlling Step

Reduction of oxygen and oxidation of hydrogen peroxide at the dropping mercury electrode are electrochemical processes strongly influenced both by the pH value and the anions in solution. With decreasing pH, both processes become irreversible, especially in the presence of anions with a negative φ2 potential of the diffusion part of the double layer. In the case of irreversible oxygen reduction, the concept that the rate-controlling step of the electrode process is the acceptance of the first electron with the formation of the superoxide anion, O2-, was substantiated. Oxidation of hydrogen peroxide becomes irreversible at a lower pH value than the reduction of oxygen. The slowest, i.e. rate-controlling step of the electrode process in borate buffers at pH 9-10 is the transfer of the second electron, i.e. oxidation of superoxide to oxygen.

Electrochemical Investigations of the Nickel(II)-Penicillamine System. 3. A Study of the Catalytic Hydrogen Prewave in Connection with Structure of Nickel(II)-Penicillamine Complexes

2000 ◽  
Vol 65 (6) ◽  
pp. 995-1013 ◽  
Author(s):  
Florinel G. Banica ◽  
Ana Ion
Keyword(s):  
Redox Reactions ◽  
Mercury Electrode ◽  
Proton Donor ◽  
Electrode Process ◽  
Nickel Ion ◽  
Acid Component ◽  
Hydronium Ion ◽  
Dropping Mercury Electrode ◽  
Catalytic Hydrogen ◽  
Catalytic Hydrogen Evolution

The catalytic hydrogen evolution on the dropping mercury electrode in the presence of Ni(II) and D-penicillamine (Pen) at pH around 6 yields a catalytic hydrogen prewave (CHP) with E1/2 = -1.21 V vs SCE. This wave is similar to the CHP produced by selenocysteine and cysteine described previously. The occurrence of the CHP depends on the formation of the mono(D-penicillamine-N,S)nickel(II) complex whereas bis(D-penicillamine-N,S)nickel(II) complex is inert and has no influence on the CHP electrode process. Although the analogous bis(cysteine) complex is labile, there is strong evidence that it does not take part directly in the CHP process in the Ni(II)-cysteine system. The actual proton donor in the CHP electrode process is the hydronium ion and not the acid component of the buffer. A tentative reaction mechanism was formulated with emphasis on the state of the intermediate hydrogen species. The characteristic pH, nickel ion involvement and the structure of the ligand make the CHP process an attractive model for hydrogen redox reactions catalyzed by [NiFe] hydrogenase.

Polarographic current-time curves and the Ilkovic Equation.

1958 ◽  
Vol 11 (3) ◽  
pp. 271 ◽  
Author(s):  
HA McKenzie
Keyword(s):  
Mercury Electrode ◽  
Potassium Nitrate ◽  
Current Time ◽  
Current Voltage ◽  
Modified Equations ◽  
Dropping Mercury Electrode ◽  
Instantaneous Current ◽  
Average Current ◽  
The One ◽  
Oxygen Measurements

The Ilkovic equation for the limiting diffusion current obtained with a dropping mercury electrode predicts that the instantaneous current grows during the life of the mercury drop as the one-sixth power of the time, and that the ratio of the instantaneous current at the end of the drop life (the maximum current) to the average current is 1.17. McKenzie (1948) showed in a preliminary study that these relations are not obeyed. The present paper is concerned with a more detailed study of current-time curves for cadmium(II), lead(II), and thallium(I) ions and oxygen. Measurements are made both in the presence and absence of maximum suppressor (gelatin) in two supporting electrolytes (potassium chloride and potassium nitrate). It is found that the rate of growth of the instantaneous current is not in accordance with the Ilkovic equation. Also, it does not accurately follow the modified equations, such as the Lingane-Loveridge equation, particularly during the early stages of drop life. The ratio of maximum to average current varies for the different electroactive substances, but in all cases examined 1.23<imax./iav.<1.30. An interesting observation is also made on the current-time curves for cadmium(II) in potassium nitrate in the presence of gelatin. At pH values appreciably below the isoelectric point (?pH 5) the current-time curves and the current-voltage curves are distorted. The implications of these results in the measurement of polarographic waves, both in theoretical and analytical applications, are discussed.

Polarography of some coordination compounds of Platinum. III. Ions of the tetrammineplatinum(II) type

1956 ◽  
Vol 9 (1) ◽  
pp. 14 ◽  
Author(s):  
JR Hall ◽  
RA Plowman
Keyword(s):  
Trans Isomer ◽  
Coordination Compounds ◽  
Supporting Electrolyte ◽  
Mercury Electrode ◽  
Trans Isomers ◽  
Cis And Trans Isomers ◽  
Current Voltage ◽  
Dropping Mercury Electrode ◽  
Divalent Platinum ◽  
Cis And Trans

A number of tetrammine ions of divalent platinum, in which the ligands were ammonia, methylamine, dimethylamine, ethylenediamine, pyridine, aniline, and combinations of some of these, were studied at the dropping mercury electrode. Some of the ions showed maxima in their current-voltage curves (c-v curves). The formation of hydrogen interfered with the c-v curves of other ions, so that limiting currents were not obtainable. A method was devised for the measurement of a voltage by means of which the ease of reduction of the ions could be compared. Using a supporting electrolyte of 0.1M KCl and 0.01% gelatin, the order of increasing ease of reduction was found to be [Pt{(CH3)2NH)4]2+ = [Pt(NH3)4]2+ = [Pt(NH3)3(C5H5N)]2+ = [Pt{C2H4(NH2)2}2]2+ < cis-[Pt(NH3)2(C5H5N)2]2+ < trans-[Pt(NH3)2C5H5N)2]2+ < [Pt(CH3NH2)4]2+ = [Pt(NH3)(C5H5N)3]2+ <[Pt(C6H5N)4]2+ < cis-[Pt(NH3)2(C6H5NH2)2]2+ < trans-[Pt(NH3)2(C6H5NH2)2]2+. When the ammonia groups of [Pt(NHS),l2+ were successively replaced by pyridine groups, the resulting e-v curves shifted progressively to more positive voltages. It was also found that cis- and trans-isomers of [PtA,B,I2+ reduced at different voltages. The trans-isomer reduced more readily.

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