Reduction from oxidation number

The concept of oxidation has been expanded from a simple combination with oxygen to a process in which electrons are transferred. Oxidation cannot take place without reduction, and oxidation numbers can be used to summarize the transfer of electrons in redox reactions. These basic concepts can be applied to the principles of electrochemical cells, electrolysis, and applications of electrochemistry. 

If you electrolyse a solution of salt, NaCl, for example, there will be two positive ions present, hydrogen ions (H+) from the water and sodium ions (Na+) from the salt. Both of these travel to the cathode. Only the hydrogen ions are discharged, however, because it takes too much energy to force a sodium ion to accept an electron. Electron gain is also called reduction, the oxidation number has gone down from +1 to 0. 

Oxidation-Reduction Reactions Oxidation Numbers Balancing Oxidation-Reduction Equations Using Half-Reactions Electrical Energy from Oxidation-Reduction Reactions Oxidation-Reduction Reactions That Require Electrical Energy Oxidation of Alcohols Extended Topic... 

Oxidation-reduction reactions must be balanced if correct predictions are to be made. Just as in selecting a route for a trip from San Francisco to New York, there are several ways to reach the desired goal. Which route is best depends to some extent upon the likes and dislikes of the traveler. We will discuss two ways to balance oxidation-reduction reactions—first, using half-reactions and, next, using the oxidation numbers we have just introduced. 

The other procedure which is of value in the calculation of the equivalents of substances is the oxidation number method. This is a development of the view that oxidation and reduction are attended by changes in electronic charge and was originally developed from an examination of the formulae of the initial and final compounds in a reaction. The oxidation number (this will be abbreviated to O.N.) of an element is a number which, applied to that element in a particular compound, indicates the amount of oxidation or reduction which is required to convert one atom of the element from the free state to that in the compound. If oxidation is necessary to effect the change, the oxidation number is positive, and if reduction is necessary, the oxidation number is negative. 

The oxidation number of zinc changes from 0 to +2 (an oxidation), whereas that of copper decreases from +2 to 0 (a reduction). Therefore, because zinc is oxidized, zinc metal is the reducing agent in this reaction. Conversely, because copper is reduced, copper(II) ions are the oxidizing agent. 

Specimens were placed in a silica reactor that was equipped with two side tubes for XPS and ESR measurements and connected to a circulation apparatus, described elsewhere [25, 26]. The catalysts, dried at 383 K, were characterized as prepared (a.p.), after heating in dry oxygen at 773 K (s.o.), or after reduction with CO. In some experiments, as specified, samples were exposed to NO, NH3, or various mixtures NO-O2-NH3. Electrons per V atom (e/V) were determined from the CO consumed. The average oxidation number of vanadium was calculated as 5 - eA/. 

Thermal reduction at 623 K by means of CO is a common method of producing reduced and catalytically active chromium centers. In this case the induction period in the successive ethylene polymerization is replaced by a very short delay consistent with initial adsorption of ethylene on reduce chromium centers and formation of active precursors. In the CO-reduced catalyst, CO2 in the gas phase is the only product and chromium is found to have an average oxidation number just above 2 [4,7,44,65,66], comprised of mainly Cr(II) and very small amount of Cr(III) species (presumably as Q -Cr203 [66]). Fubini et al. [47] reported that reduction in CO at 623 K of a diluted Cr(VI)/Si02 sample (1 wt. % Cr) yields 98% of the silica-supported chromium in the +2 oxidation state, as determined from oxygen uptake measurements. The remaining 2 wt. % of the metal was proposed to be clustered in a-chromia-like particles. As the oxidation product (CO2) is not adsorbed on the surface and CO is fully desorbed from Cr(II) at 623 K (reduction temperature), the resulting catalyst acquires a model character in fact, the siliceous part of the surface is the same of pure silica treated at the same temperature and the anchored chromium is all in the divalent state. 

They are the basis of many products and processes, from batteries to photosynthesis and respiration. You know redox reactions involve an oxidation half-reaction in which electrons are lost and a reduction half-reaction in which electrons are gained. In order to use the chemistry of redox reactions, we need to know about the tendency of the ions involved in the half-reactions to gain electrons. This tendency is called the reduction potential. Tables of standard reduction potentials exist that provide quantitative information on electron movement in redox half-reactions. In this lab, you will use reduction potentials combined with gravimetric analysis to determine oxidation numbers of the involved substances. 

This process contrasts with the elemental-silicon processes sometimes used for alkyl silicates (8) and the elemental-silicon processes generally used for oligomeric and polymeric organosi-loxanes ( ,7) Since the silicon in these processes is obtained from quartz, these processes entail, in terms of bond cleavage, the destruction of four silicon-oxygen bonds per silicon and the subsequent reformation of the required number of such bonds. In terms of oxidation number, they entail the reduction of the silicon from four to zero and then its reoxidation back to four, Figures 2 and 3. 

In Sec. 13.2 we will learn to determine oxidation numbers from the formulas of compounds and ions. We will learn how to assign oxidation numbers from electron dot diagrams and more quickly from a short set of rules. We use these oxidation numbers for naming the compounds or ions (Chap. 6 and Sec. 13.4) and to balance equations for oxidation-reduction reactions (Sec. 13.5). In Sec. 13.3 we will learn to predict oxidation numbers for the elements from their positions in the periodic table in order to be able to predict formulas for their compounds and ions. 

In every reaction in which the oxidation number of an element in one reactant (or more than one) goes up, an element in some reactant (or more than one) must go down in oxidation number. An increase in oxidation number is called an oxidation. A decrease in oxidation number is called a reduction. The term redox (the first letters of reduction and oxidation) is often used as a synonym for oxidation-reduction. The total change in oxidation number (change in each atom times number of atoms) must be the same in the oxidation as in the reduction, because the number of electrons transferred from one species must be the same as the number transferred to the other. The species that causes another to be reduced is called the reducing agent in the process, it is oxidized. The species that causes the oxidation is called the oxidizing agent in the process, it is reduced. 

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