Ferrous-ferric

The mechanism and rate of hydrogen peroxide decomposition depend on many factors, including temperature, pH, presence or absence of a catalyst (7—10), such as metal ions, oxides, and hydroxides etc. Some common metal ions that actively support homogeneous catalysis of the decomposition include ferrous, ferric, cuprous, cupric, chromate, dichromate, molybdate, tungstate, and vanadate. For combinations, such as iron and... 

RA Kuharski, JS Bader, D Chandler, M Sprik, ML Klein, RW Impey. Molecular model for aqueous ferrous-ferric electron transfer. J Chem Phys 89 3248-3257, 1988. 

Smith BB, Halley JW. 1994. Simulation study of the ferrous ferric electron transfer at a metal-aqueous electrolyte interface. J Chem Phys 101 10915-10924. 

The last reaction cited above as shown is very effectively catalyzed by bacterial action but is very slow chemically by recycling the spent ferrous liquors and regenerating ferric iron bacterially, the amount of iron which must be derived from pyrite oxidation is limited to that needed to make up losses from the system, principally in the uranium product stream. This is important if the slow step in the overall process is the oxidation of pyrite. The situation is different in the case of bacterial leaching of copper sulfides where all the sulfide must be attacked to obtain copper with a high efficiency. A fourth reaction which may occur is the hydrolysis of ferric sulfate in solution, thus regenerating more sulfuric acid the ferrous-ferric oxidation consumes acid. 

Another method is that based on the ferrous/ferric thiocyanate determination of hydroperoxides [1]. This exploits the ion-catalysed decomposition as shown by... 

Ferrous ferric oxide showed a different concentration-time profile with change of pH in comparison to the two other materials - it was linear, while the decline in gold concentration was rather steep for FeOOH and AI2O3 within the first minutes of the experiment. This behavior was observed under all pH conditions. Furthermore, in the case of Fe304 it was seen that an increase in pH resulted in a gradual increase in speed of gold removal from solution, e.g., while it took 90 min to remove all gold present at pH=2 and 3 it took about 60 min at pH=4 and had finished after 5 min at pH=5 and 6, which can also be explained with the mentioned speciation effect in connection with the associated different complex stabilities. 

A platinum electrode is needed in some half-cells to provide a surface at which electrons can be exchanged. Such a surface is lacking where there is no solid metal as part of the half-reaction, such as with the ferrous-ferric half-reaction. 

After more than two decades of investigation, it is pertinent to ask to what extent the predictions of this type of theory, and its agreement with experiment, have changed. The system which has received most study is the aquo ferrous-ferric outer-sphere symmetrical exchange ... 

Figure 11. Determination of ferrous-ferric isotope exchange kinetics in dilute aqueous solutions using Fe-enriched tracer solutions. Measured 5 Fe values for ferrous (squares) and ferric (circles) Fe in solution versus time. Initial 5 Fe values for Fe(II), 0%o and Fe(III),q 331%o. The rapid convergence in Fe/ Fe ratios for the ferric and ferrous species indicates that isotopic equilibrium is attained within minutes. Adapted from Welch et al. (2003).

Suppose we add a small quantity of redox indicator to a relatively large volume of our redox titration mixture, e.g. aqueous ferrous and ferric ions. In addition, suppose that the starulard electrode potential of the indicator couple (we will call it E ) is greater than that of the ferrous-ferric... 

Roth CB, Jackson ML, Syers JK. 1969. Deferration effect on structural ferrous-ferric iron ration and CEC of vermiculites and soils. Clays and Clay Minerals 17 253-264. 

Paul A. and Douglas R. W. (1965a). Ferrous-ferric equilibrium in binary alkali silicate glasses. Phys. Chem. Glasses, 6 207-211. 

I. The oxidation pathway and inhibition of the ferrous-ferric oxidation. Reclamation and Revegetation Research, 4, 279-291. 

Tetrachloroethene in an Aqueous Ferrous/Ferric Iron Solution... 

Another example of the phenomenon is often observed in the chemical laboratory when a solution containing ferrous ion is precipitated with alkali. Ferrous hydroxide is white, and ferric hydroxide is brown. When a ferrous solution is precipitated, however, the initially white precipitate is immediately partially oxidized by atmospheric oxygen to form a ferrous ferric hydroxide, which is black in color (or deep green when finely divided). 

Grides Mauneiiie FeiOj Ferrous-ferric oxide... 

The cuprous-cupric electron transfer reaction is believed to be the rate-limiting step in the process of stress corrosion cracking in some engineering environments [60], Experimental studies of the temperature dependence of this rate at a copper electrode were carried out at Argonne. Two remarkable conclusions arise from the study reviewed here [69] (1) Unlike our previous study of the ferrous-ferric reaction [44], we find the cuprous-cupric electron transfer reaction to be adiabatic, and (2) the free energy barrier to the cuprous cupric reaction is dominated in our interpretation by the energy required to approach the electrode and not, as in the ferrous-ferric case, by solvent rearrangement. 

We first used the model described to estimate the equilibrium potential for the electron transfer reaction. We took considerable trouble, some of which is described here with more detail in Ref. 69, to assure that the equilibrium potential was reasonably well-described by the model, because if a simulation model does not correctly reproduce the electrode charge density at which the two ionic charge states are in equilibrium, then the simulation may proceed in a very unrealistic electrostatic environment. This can lead to qualitatively misleading results. Unlike the ferrous-ferric reaction, the cuprous-cupric... 

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