Nickel redox reactions

Complexes o/M". The absence of any other oxidation state of comparable stability for nickel implies that compounds of Ni" are largely immune to normal redox reactions. Ni" forms salts with virtually every anion and has an extensive aqueous chemistry based on the green [Ni(H20)6] + ion which is always present in the absence of strongly complexing ligands. 

In normal battery operation several electrochemical reactions occur on the nickel hydroxide electrode. These are the redox reactions of the active material, oxygen evolution, and in the case of nickel-hydrogen and nickel-metal hydride batteries, hydrogen oxidation. In addition there are parasitic reactions such as the corrosion of nickel current collector materials and the oxidation of organic materials from separators. The initial reaction in the corrosion process is the conversion of Ni to Ni(OH)2. 

CODH/ACS is an extremely oxygen-sensitive protein that has been found in anaerobic microbes. It also is one of the three known nickel iron-sulfur proteins. Some authors would consider that there are only two, since the CODH and ACS activities are tightly linked in many organisms. However, there is strong evidence that the ACS and CODH activities are associated with different protein subunits and the reactions that the two enzymes catalyze are quite different. CODH catalyzes a redox reaction and ACS catalyzes the nonredox condensation of a methyl group, a carbonyl group, and an organic thiol (coenzyme A). 

C04-0039. Predict whether or not a reaction will occur, and if a reaction does take place, write the half-reactions and the balanced redox reaction (a) a strip of nickel wire is dipped in 6.0 M HCl (b) aluminum foil is dipped in aqueous CaCl2 (c) a lead rod is dipped in a beaker of water (d) an iron wire is immersed in a solution of silver nitrate. 

The relatively simple chemistry of this redox reaction is one reason why nickel-cadmium batteries are rechargeable. As we show later in this chapter, applying an external voltage can reverse this reaction. 

There is then a redox reaction with the nickel and the formaldehyde ... 

The base was being prepared by distilling a mixture of hydroxylamine hydrochloride and sodium hydroxide in methanol under reduced pressure, and a violent explosion occurred towards the end of distillation [1], probably owing to an increase in pressure above 53 mbar. It explodes when heated under atmospheric pressure [2], Traces of hydroxylamine remaining after reaction with acetonitrile to form acetamide oxime caused an explosion during evaporation of solvent. Traces can be removed by treatment with diacetyl monoxime and ammoniacal nickel sulfate, forming nickel dimethylglyoxime [3], An account of an extremely violent explosion towards the end of vacuum distillation had been published previously [4], Anhydrous hydroxylamine is usually stored at 10°C to prevent internal oxidation-reduction reactions which occur at ambient temperature [5], See other REDOX REACTIONS... 

The presence of iron in nickel oxyhydroxide electrodes has been found to reduce considerably the overpotential for oxygen evolution in alkaline media associated with the otherwise iron free material.(10) An in situ Mossbauer study of a composite Ni/Fe oxyhydroxide was undertaken in order to gain insight into the nature of the species responsible for the electrocatalytic activity.(IT) This specific system appeared particularly interesting as it offered a unique opportunity for determining whether redox reactions involving the host lattice sites can alter the structural and/or electronic characteristics of other species present in the material. 

The anion [Fe3Co(CO)12] has recently been reported to be prepared by Chini from the redox reaction of Fe3(CO)12 with Co(CO)infrared spectra indicate a Co4(CO)i2 structure with nickel in the basal plane (234). 

Few comparative studies have been made on the reductive dissolution of different mineral phases. In one such study, the order of reaction with seven organic and transition metal reductants was found to be the same hematite (a-Fe203)>magnetite (FejO,/,)>nickel ferrite (NiFe204) (43). Magnetite is an interesting case, since both Fe(III) and Fe(II) are present in the lattice prior to reaction. Evidence indicates that Fe(IIl) sites reduced to Fe(II) sites by redox reaction dissolve more quickly than Fe(II) sites originally present in the mineral lattice (6). 

Nickel and copper are two metals that are important to the Ontario economy, particnlarly in the Sndhnry area. Nickel and copper ores usually contain the metals as snlfides, snch as NiS and Cn2S. Do the extractions of these pure elemental metals from their ores involve redox reactions Explain your reasoning. 

O In Section 10.3, you learned about a redox reaction used in the production of compact discs. In another step of this production process, nickel is electroplated onto the silver-coated master disc. 

O Nickel and copper are both very important to the Ontario economy. Before they can be refined by electrolysis, they must be extracted from their ores. Both metals can be extracted from a sulfide ore, NiS or CU2S. The sulfide is roasted to form an oxide, and then the oxide is reduced to the metal. Research the extraction processes for both nickel and copper, and write balanced equations for the redox reactions involved. One product of each extraction process is sulfur dioxide. Research the environmental effects of this compound. Describe any steps taken to decrease these effects. 

All oxidation reactions are coupled to reduction reactions. In many cases redox reactions can also involve or be affected by changes in the surrounding environment, such as changes in the pH or temperature (i.e., endothermic or exothermic reactions). Many elements in the subsurface can exist in various oxidation states, some examples include elements like carbon, nitrogen, oxygen, sulfur, iron, cobalt, vanadium, and nickel. 

We can now make sensible guesses as to the order of rate constant for water replacement from coordination complexes of the metals tabulated. (With the formation of fused rings these relationships may no longer apply. Consider, for example, the slow reactions of metal ions with porphyrine derivatives (20) or with tetrasulfonated phthalocyanine, where the rate determining step in the incorporation of metal ion is the dissociation of the pyrrole N-H bond (164).) The reason for many earlier (mostly qualitative) observations on the behavior of complex ions can now be understood. The relative reaction rates of cations with the anion of thenoyltrifluoroacetone (113) and metal-aqua water exchange data from NMR studies (69) are much as expected. The rapid exchange of CN " with Hg(CN)4 2 or Zn(CN)4-2 or the very slow Hg(CN)+, Hg+2 isotopic exchange can be understood, when the dissociative rate constants are estimated. Reactions of the type M+a + L b = ML+(a "b) can be justifiably assumed rapid in the proposed mechanisms for the redox reactions of iron(III) with iodide (47) or thiosulfate (93) ions or when copper(II) reacts with cyanide ions (9). Finally relations between kinetic and thermodynamic parameters are shown by a variety of complex ions since the dissociation rate constant dominates the thermodynamic stability constant of the complex (127). A recently observed linear relation between the rate constant for dissociation of nickel complexes with a variety of pyridine bases and the acidity constant of the base arises from the constancy of the formation rate constant for these complexes (87). 

Nickel(II) complexes with a variety of tetraaza macrocycles have been found to undergo facile one-electron redox reactions. Such reactions have been accomplished by means of both chemical and electrochemical procedures. The kinetic inertness and thermodynamic stability of the tetraaza macrocyclic complexes of nickel(II) make them particularly suitable systems for the study of redox processes. A very extensive summary of the potentials for the redox reactions of nickel(II) complexes with a variety of macrocycles is given in ref. 2622. 

Solution studies on the adducts formed by various heterocyclic bases with some nickel porphyrins have been reported.2899-2902 From these studies one can conclude that pyridine and substituted pyridines form predominantly 1 1 adducts while piperidine, imidazole and substituted imidazoles also form 1 2 complexes or a mixture of both 1 1 and 1 2 complexes. Electrochemical redox reactions of nickel porphyrins have been investigated.2903,2904... 

Redox reactions involving the nickel(IV) complex are also subject to divalent metal ion catalysis (170, 171). Oxidations of the two-electron reductant ascorbate (40) and the one-electron reductant [Fe(CN)6]4-(172) have been examined in some detail. Both reactions have as the rate-determining step the transfer of one electron from the reductant to nickel(IV) in an outer-sphere process to give an undetected nickel(III) transient. Spectroscopic properties of the nickel(III) species have been determined by pulse radiolysis (41). 

The possibility of using surface modification of cheap metals to make them effective electrode materials has been mentioned (Section 57.3.2.3(1)). A further example employs cyanoferrates and cyanoruthenates as the redox centres.76 Complexes such as [M(CN)5L]" (M = Fe, Ru L = CN, H20, NO, L-histidine) may be immobilized on a partially corroded nickel surface. The surfaces have good stability and diffuse reflectance IR spectroscopy shows the presence of bridging cyano groups, implying the presence of a binuclear (Ni, M) species in the surface. A general equation for the redox reaction is ... 

In conclusion, the [NiS] mediated formation of thioesters from alkyl, CO, and thiol groups lends support to an acetyl-CoA formation pathway that comprises CO insertion into a Ni Me and an intramolecular S -C bond formation between nickel-bound acyl groups and thiolate ligands. These reactions are favored at square-planar nickel complexes that enable two-electron redox reactions and readily add fifth ligands. 

Two clusters in CO dehydrogenase are required for oxidation of CO or reduction of CO 2 (Figure 1). The catalytic site is a nickel iron sulfur cluster called Cluster C. The two electrons involved in this redox reaction are transferred to or from a ferredoxin-like [4Fe64S] cluster called Cluster B. Cluster C is a NiFeS center whereas. Cluster B is most certainly a typical [4Fe64S] cluster (Ragsdale et ah, 1982 Lindahl et al., 1990 Lindahl et ah, 1990). 

The drawbacks of a simplified relative fo approach become apparent in the case of the relative volumetric properties of EeO and Ec203 in sihcate melts even at relatively low pressures (Kress and Carmichael, 1991). There are two problems first, the pressure dependence of EeO-Ec203 equilibria is different from the pressure dependence of the nickel-nickel oxide (NNO) buffer such that use of NNO as a normalization for relative/oj can be misleading. The volume change of the FMQ buffer (0.17 log/o units per GPa) is much closer to the redox state of a silicate melt than is that of the NNO buffer (0.51 log/o units per GPa). Second, the compressibilities of FeO and Fe203 are much different, so that even pressures of 1-2 GPa will have a large effect on their partial molar volumes. Any calculation of relative /o should include an assessment of the volumetric properties of both the buffer phases, and the phases involved in the redox reaction. 

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