Manganese standard electrode potential

Thermodynamic data (4) for selected manganese compounds is given ia Table 3 standard electrode potentials are given ia Table 4. A pH—potential diagram for aqueous manganese compounds at 25°C is shown ia Figure 1 (9). 

Manganese oxides, which have different structural and surface properties, vary in their ability to promote the precipitation and crystallization of Fe oxides and oxyhydroxides (Krishnamurti and Huang, 1988). The standard electrode potential (E°) of the redox pairs Fe -MnO2 and Fe -Mn3O4 can be described by the following equations (Bricker, 1965)... 

A Latimer diagram shows the standard electrode potentials associated with the different oxidation states of an element, as illustrated in Fig. 1 for manganese. Potentials not given explicitly can be calculated using Equation 1 and taking careful account of the number of electrons involved. Thus the... 

We can confirm this by calculating the standard electrode potential for manganese acting as the anode (oxidation) and nickel acting as the cathode (reduction). 

The Mn3+/Mn2+ couple is ostensibly pH independent, but we must bear in mind that manganese(III), in particular, will hydrolyze unless the acidity is very high, and both Mn(OH)3 and Mn(OH)2 will come out of solution in alkaline media. Small degrees of hydrolysis in solution have little impact on E°, but precipitation of hydroxides (and all metal hydroxides except those of the alkali metals and Ca, Sr, Ba, and Ra are poorly soluble in water) affects E° profoundly. Thus, in alkaline media, the electrode potentials (often called Eh by geologists, wherever [H+] is not the standard value) of Mn2+ and Mn3+ are controlled by the solubility products (Ksp) of Mn(OH)2 and Mn(OH)3, respectively. In practice, Mn(OH)3 tends to dehydrate to MnO(OH), so we consider the Mn2+(aq)/Mn(s) couple ... 

At standard conditions, the redox potential of the zinc electrode equals —0.76 V. The redox potential of the manganese dioxide electrode is about +1.1 V and the nominal voltage at normal usage is around 1.5-1.6 V. 

I. 4-methoxyacetophenone (30 //moles) was added as an internal standard. The reaction was stopped after 2 hours by partitioning the mixture between methylene chloride and saturated sodium bicarbonate solution. The aqueous layer was twice extracted with methylene chloride and the extracts combined. The products were analyzed by GC after acetylation with excess 1 1 acetic anhydride/pyridine for 24 hours at room temperature. The oxidations of anisyl alcohol, in the presence of veratryl alcohol or 1,4-dimethoxybenzene, were performed as indicated in Table III and IV in 6 ml of phosphate buffer (pH 3.0). Other conditions were the same as for the oxidation of veratryl alcohol described above. TDCSPPFeCl remaining after the reaction was estimated from its Soret band absorption before and after the reaction. For the decolorization of Poly B-411 (IV) by TDCSPPFeCl and mCPBA, 25 //moles of mCPBA were added to 25 ml 0.05% Poly B-411 containing 0.01 //moles TDCSPPFeCl, 25 //moles of manganese sulfate and 1.5 mmoles of lactic acid buffered at pH 4.5. The decolorization of Poly B-411 was followed by the decrease in absorption at 596 nm. For the electrochemical decolorization of Poly B-411 in the presence of veratryl alcohol, a two-compartment cell was used. A glassy carbon plate was used as the anode, a platinum plate as the auxiliary electrode, and a silver wire as the reference electrode. The potential was controlled at 0.900 V. Poly B-411 (50 ml, 0.005%) in pH 3 buffer was added to the anode compartment and pH 3 buffer was added to the cathode compartment to the same level. The decolorization of Poly B-411 was followed by the change in absorbance at 596 nm and the simultaneous oxidation of veratryl alcohol was followed at 310 nm. The same electrochemical apparatus was used for the decolorization of Poly B-411 adsorbed onto filter paper. Tetrabutylammonium perchlorate (TBAP) was used as supporting electrolyte when methylene chloride was the solvent. 

Precipitation of lead dioxide by anodic deposition on a platinum gauze electrode Is a standard method of separation and determination for lead (H3) In the standard procedure the presence of chloride Ion, mercury, arsenic, tellurium, selenium and phosphorus prevent the complete deposition of lead, while bismuth, tin, antimony, and manganese co-deposit. The use of controlled potential deposition and com-plexlng agents make this separation method much more selective (l4). The eleotroanalytical method has been Important for lead analysis and is discussed In detail In section IV-10,... 

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