Stoichiometry oxidation-reduction reactions

Material balances can be written for moieties which are conserved during the reaction, such as the atoms of a particular element or the total charge, or for reactant or product species if the stoichiometry is unambiguous. Oxidation-reduction reactions may be particularly troublesome. In the following situation, for example, one cannot write a material balance relating protons to water molecules. Consider the oxidation of O2 to H2O and the equilibrium dissociation of I O. 

The catalytic effect of metal ions such as Mg2+ and Zn2+ on the reduction of carbonyl compounds has extensively been studied in connection with the involvement of metal ions in the oxidation-reduction reactions of nicotinamide coenzymes [144-149]. Acceleration effects of Mg2+ on hydride transfer from NADH model compounds to carbonyl compounds have been shown to be ascribed to the catalysis on the initial electron transfer process, which is the rate-determining step of the overall hydride transfer reactions [16,87,149]. The Mg2+ ion has also been shown to accelerate electron transfer from cis-dialkylcobalt(III) complexes to p-ben-zoquinone derivatives [150,151]. In this context, a remarkable catalytic effect of Mg2+ was also found on photoinduced electron transfer reactions from various electron donors to flavin analogs in 1984 [152], The Mg2+ (or Zn2+) ion forms complexes with a flavin analog la and 5-deazaflavins 2a-c with a 1 1 stoichiometry in dry MeCN at 298 K [153] ... 

Chemical reactions are frequently carried out in solution, and their description requires modifications to the rules of stoichiometry described in Chapter 2. We illustrate these modified rules by the important analytical techniques of titration in acid-base and oxidation-reduction reactions. 

In this chapter we will examine oxidation-reduction stoichiometry, equilibria, and the graphical representation of simple and complex equilibria, and the rate of oxidation-reduction reactions. The applications of redox reactions to natural waters will be presented in the context of a discussion of iron chemistry the subject of corrosion will provide a vehicle for a discussion of the application of electrochemical processes a presentation of chlorine chemistry will include a discussion of the kinetics of redox reactions and the reactions of chlorine with organic matter finally, the application of redox reactions to various measurement methods will be discussed using electrochemical instruments as examples. 

Stoichiometry of a Precipitation Reaction, an Oxidation-Reduction Reaction, and a Compiexation Reaction... 

Oxidation-reduction reactions have been classified in two general ways the first, historically, is by stoichiometry and the second is by mechanism. 

The synthesis of 2,5-disubstituted oxazoles from methyl ketones and benzylamines in a metal and peroxide-free environment is achieved using l2-promoted domino oxidative cyclization involving C-H bond cleavage and the formation of C-N and C-0 bonds. Slow oxidation of A-acetyl homocysteine thiolactone by iodate to A-acetyl homocysteine thiolacone sulfoxide occurs in a reaction S1 having 1 3 stoichiometry (oxidant reductant). The stoichiometric ratio in excess of 103 (reaction S2) is 2 5 because excess 103 oxidizes the r ion, generated in reaction SI, to I2. The stoichiometry ratio for the I2 oxidation (reaction S3) is 1 1. Complex kinetics are observed because reactions SI, S2 and S3 occur simultaneously with comparable rates. 

An increasing number of chemists use electrochemistry as a characterization technique in a fashion analogous to their use of infrared, UV-visible, NMR, and ESR spectroscopy. Some of the chemical questions that are amenable to treatment by electrochemistry include (1) the standard potentials (E°) of the compound s oxidation-reduction reactions, (2) evaluation of the solution thermodynamics of the compound, (3) determination of the electron stoichiometry of the compound s oxidation-reduction reactions, (4) preparation and study of unstable intermediates, (5) evaluation of the valence of the metal in new compounds, (6) determination of the formulas and stability constants of metal complexes, (7) evaluation of M-X, H-X, and O-Y covalent-bond-formation energies (-AGbf), and (8) studies of the effects of solvent, supporting electrolyte, and solution acidity upon oxidation-reduction reactions. 

Distinguish between an electrolyte and a nonelectrolyte, and provide examples of each. 5.2 Use the solubility guidelines tor common ionic solids to determine whether 5-4 Oxidation-Reduction Reactions Some General Principles 5-7 Stoichiometry of Reactions in Aqueous Solutions Titrations... 

Barium metal is produced commercially by the reduction of barium oxide with a less reactive, nonvolatile element, usually aluminum (16—22). Depending on initial stoichiometry, two overall reactions occur in the BaO reduction ... 

Study, the students are taught the basic concepts of chemistry such as the kinetic theory of matter, atomic stmcture, chemical bonding, stoichiometry and chemical calculations, kinetics, energetics, oxidation-reduction, electrochemistry, as well as introductory inorgarric and organic chemistry. They also acquire basic laboratory skills as they carry out simple experiments on rates of reaction and heat of reaction, as well as volrrmetric analysis and qualitative analysis in their laboratory sessions. 

The Incentive to modify our existing continuous-flow microunit to incorporate the square pulse capability was provided by our work on perovskite-type oxides as oxidation-reduction catalysts. In earlier work, it had been inferred that oxygen vacancies in the perovskite structure played an important role in catalytic activity (3). Pursuing this idea with perovskites of the type Lai-xSrxFeg 51 10 503, our experiments were hampered by hysteresis effects which we assumed to be due to the response of the catalyst s oxygen stoichiometry to the reaction conditions. 

To establish the stoichiometry of the sulfide formation, Equation (6.3) must be combined with the oxidation process for the organic matter that is the actual electron donor for the heterotrophic sulfate-reducing bacteria. The procedure for the combination of the oxidation and the reduction process steps is the same as outlined in Section 2.1.3. If organic matter is considered simply as CH20, the combination of the oxidation process as depicted in Example 2.2 and the reduction reaction for sulfate shown in Equation (6.3) result in the following redox process ... 

Radical mechanisms account for the stoichiometry for reduction of triketohydrindane by N(5)-ethyldihydroflavin and reduction of triphenylmethyl carbonium ion species by dihydroflavin, (24). One-electron reduction of quinone by N(5)-ethyldihydroflavin also has been shown. These results are not surprising since the substrates and flavin support reasonably stable radical states. Radical species also can be established as intermediates in the oxidation of 9-hydroxyfluorene and methyl mandelate by Flox (Equations 28 and 29, respectively). The reactions of Equations 28 and 29 are facile when carried out in... 

The procedure for the preparation of the platinum compounds is an extension of the method described by Kharasch and Ashford.5 A glacial acetic acid solution of chloroplatinic acid is mixed with the appropriate olefin, and in the ensuing reaction the platinum is reduced from the 4+ oxidation state to the 2 + state. The overall stoichiometry of these reactions is not known however, the reduction of the platinum is1 accompanied by the partial oxidation of the olefin. 

Several high-temperature procedures have been described in the literature for the preparation of the transition-metal dioxides. Direct oxidation of the metals, lower oxides, chlorides, or nitrate precursors provides a convenient route to the dioxides of several metals Ti, Mn, Ru, Rh, Os, Ir, and Pt.1,3-5 (Syntheses of the rutile forms of rhodium and platinum dioxides by direct oxidation requires application of high pressures.5) Reduction of higher oxides is the most common method of synthesis for these dioxides V02, Nb02, Mo02, W02, and /3-Re02.4,6-8 Stoichiometry in these reactions is most readily controlled by use of the respective metal or a lower oxide as reductant. Chromium dioxide is normally synthesized by hydrothermal reduction of the trioxide.9... 

Reaction Stoichiometry in Solutions Oxidation-Reduction Titrations... 

So far, we have only reported oxidation type reactions. However, reduction type reactions have also been reported in the case of TCNQ-based materials associated with organometallic species.24,25 Moreover, in these examples, it was shown that different stoichiometries were reached and were controlled by the electrochemical conditions. 

Titrations are widely used in analytical chemistry to determine acids, bases, oxidants, reductants, metal ions, proteins, and many other species. Titrations are based on a reaction between the analyte and a standard reagent known as the titrant. The reaction is of known and reproducible stoichiometry. The volume, or the mass, of the titrant needed to react essentially completely with the analyte is determined and used to obtain the quantity of analyte. A volume-based titration is shown in this figure, in which the standard solution is added from a buret, and the reaction occurs in the Erlenmeyer flask. In some titrations, known as coulometric titrations, the quantity of charge needed to completely consume the analyte is obtained. In any titration, the point of chemical equivalence, experimentally called the end point, is signaled by an indicator color change or a change in an instrumental response. 

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