Redox reactions oxidation states

A reaction in which the oxidation number of an element is increased. Examples (1, 2, 3) 2 Mg(s) + 02(g) - 2 MgO(s) (2, 3) Mg(s) - Mg2+(s) + 2e". oxidation number The effective charge on an atom in a compound, calculated according to a set of rules (Toolbox K.l). An increase in oxidation number corresponds to oxidation, and a decrease, to reduction, oxidation-reduction reaction See redox reaction. oxidation state The actual condition of a species with a specified oxidation number. 

The following equations represent examples of redox reactions. Oxidation states are shown above the formulas, and oxidizing and reducing agents are indicated ... 

Interactivity Redox Reactions—Oxidation States for Nitrogen (19.1)... 

Redox reactions Oxidation states Reduction potentials Nernst equation Disproportionation Potential diagrams Frost-Ebsworth diagrams... 

Although the redox reaction mechanisms of iridium oxide are still not clear, most researchers believe that the proton exchange associated with oxidation states of metal oxides is one of the possible pH sensing mechanisms [41, 87, 100, 105], During electrochemical reactions, oxidation state changes in the hydrated iridium oxide layer are... 

The first step in this system is to assign an oxidation number to each atom in the reaction equation. As you become better acquainted with the procedure, you will gain a better understanding of what the numbers signify, but for now, just think of them as tools for keeping track of the flow of electrons in redox reactions. Oxidation numbers are also called oxidation states. 

Identifying Redox Reactions, Oxidizing Agents, and Reducing Agents Using Oxidation States (4.9) Example 4.17, 4.18 For Practice 4.17, 4.18 For More Practice 4.17 Exercises 95, 96 ... 

By working out the relevant oxidation numbers, specify which of the following are redox reactions and state which element is oxidized, and which is reduced. 

Step 3 A series of redox reactions converts chromium from the 4+ oxidation state m HCr03 to the 3 + oxidation state... 

In a complexation reaction, a Lewis base donates a pair of electrons to a Lewis acid. In an oxidation-reduction reaction, also known as a redox reaction, electrons are not shared, but are transferred from one reactant to another. As a result of this electron transfer, some of the elements involved in the reaction undergo a change in oxidation state. Those species experiencing an increase in their oxidation state are oxidized, while those experiencing a decrease in their oxidation state are reduced, for example, in the following redox reaction between fe + and oxalic acid, H2C2O4, iron is reduced since its oxidation state changes from -1-3 to +2. 

You will recall from Chapter 6 that the Nernst equation relates the electrochemical potential to the concentrations of reactants and products participating in a redox reaction. Consider, for example, a titration in which the analyte in a reduced state, Ared) is titrated with a titrant in an oxidized state, Tox- The titration reaction is... 

In this titration the analyte is oxidized from Fe + to Fe +, and the titrant is reduced from CryOy to Cr +. Oxidation of Fe + requires only a single electron. Reducing CryOy, in which chromium is in the +6 oxidation state, requires a total of six electrons. Conservation of electrons for the redox reaction, therefore, requires that... 

Redox Electrodes Electrodes of the first and second kind develop a potential as the result of a redox reaction in which the metallic electrode undergoes a change in its oxidation state. Metallic electrodes also can serve simply as a source of, or a sink for, electrons in other redox reactions. Such electrodes are called redox electrodes. The Pt cathode in Example 11.1 is an example of a redox electrode because its potential is determined by the concentrations of Ee + and Ee + in the indicator half-cell. Note that the potential of a redox electrode generally responds to the concentration of more than one ion, limiting their usefulness for direct potentiometry. 

In some cases two polarographic waves are seen as the redox reaction occurs in steps. Half-wave potentials are given for each wave, with the corresponding change in oxidation states shown in parentheses. 

The action of redox metal promoters with MEKP appears to be highly specific. Cobalt salts appear to be a unique component of commercial redox systems, although vanadium appears to provide similar activity with MEKP. Cobalt activity can be supplemented by potassium and 2inc naphthenates in systems requiring low cured resin color lithium and lead naphthenates also act in a similar role. Quaternary ammonium salts (14) and tertiary amines accelerate the reaction rate of redox catalyst systems. The tertiary amines form beneficial complexes with the cobalt promoters, faciUtating the transition to the lower oxidation state. Copper naphthenate exerts a unique influence over cure rate in redox systems and is used widely to delay cure and reduce exotherm development during the cross-linking reaction. 

Oxidation—Reduction. Redox or oxidation—reduction reactions are often governed by the hard—soft base rule. For example, a metal in a low oxidation state (relatively soft) can be oxidized more easily if surrounded by hard ligands or a hard solvent. Metals tend toward hard-acid behavior on oxidation. Redox rates are often limited by substitution rates of the reactant so that direct electron transfer can occur (16). If substitution is very slow, an outer sphere or tunneling reaction may occur. One-electron transfers are normally favored over multielectron processes, especially when three or more species must aggregate prior to reaction. However, oxidative addition... 

The main by-products of the Ullmaim condensation are l-aniinoanthraquinone-2-sulfonic acid and l-amino-4-hydroxyanthraquinone-2-sulfonic acid. The choice of copper catalyst affects the selectivity of these by-products. Generally, metal copper powder or copper(I) salt catalyst has a greater reactivity than copper(Il) salts. However, they are likely to yield the reduced product (l-aniinoanthraquinone-2-sulfonic acid). The reaction mechanism has not been estabUshed. It is very difficult to clarify which oxidation state of copper functions as catalyst, since this reaction involves fast redox equiUbria where anthraquinone derivatives and copper compounds are concerned. Some evidence indicates that the catalyst is probably a copper(I) compound (28,29). 

More detailed consideration of these various equilibria and other redox reactions of the halogen oxoacids will be found under the separate headings below. As expected, the rates of redox reactions of the halogen oxyanions will depend, sometimes crucially, on the precise conditions used. However, as a very broad generalization, they tend to become progressively faster as the oxidation state of the halogen decreases, i.e. ... 

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. 

Soluble sulfides (i.e., H S, HS" and S ", with sulfur at minus two oxidation state) are chemically very reactive. The two general types of soluble-sulfide reactions may be identified as precipitation reaction (type A) and redox reaction (type B). 

Type B (redox) reactions are more complex. Sulfide in this reaction is converted into some other oxidation state of sulfur. For example, sulfides can be converted to a zero oxidation state of elemental sulfur by oxygen ... 

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