Oxidation and Reduction

Oxidation and reduction are complementary chemical processes that involve a loss of electrons (oxidation) by one reactant and a corresponding gain (reduction) by another. Both processes must occur simultaneously and in equivalent amounts. The most familiar oxidative processes utilize oxygen from the atmosphere; these include the rusting of iron, combustion, and respiration in each case oxygen is reduced. Reductive processes include the recovery of metals from their ores, the photosynthetic production of carbohydrates, and the hydrogenation of fats.

Oxidizing Agents
The substance that acquires electrons during an oxidation-reduction reaction is an oxidizing agent. In the course of the reaction, the oxidizing agent react and become weak reducing agent. Of the chemical elements, the most electronegative elements have the greatest tendency to participate in reactions as oxidizing agents, because they form negative ions very readily. Fluorine, with with the most highly electronegative atoms, is the most active oxidizing agent among the elements. It reacts to form the fluoride ion (oF), the weakest reducing agent. Oxygen (O2) is highly active, particularly so as ozone (O3). All of the halogen elements can as strong oxidation agents.

Certain oxygen containing compounds readily give up oxygen to another reactant, becoming reduced in the process. Some examples are hydrogen peroxide, nitric acid, concentrated sulfuric acid, potassium nitrate, and the permanganate, dichromate, chlorate, and hypochlorite ions.

Reducing Agent
Elements that readily form positive ions are reducing agents and, as expected from their low electronegatives, the most active are the alkali metals followed by the alkaline earth metals. Useful reducing agent of the elements. Useful reducing agents in organic chemistry include hydrogen lithium aluminum hydride, and sodium borohydride.

In general, the strength of a reactant in an oxidation-reduction process depends on the reaction conditions. In oxidize or reduce certain functional groups on a complex molecule but leave other unaffected, a chemist must carefully select the appropriate agent, catalyst, concentrations, temperature, and pressure.

Biological Oxidation and Reduction
The vase majority of living organisms rely on oxygen to generate oxidative power. The actual mechanism is not a direct chemical reaction but a series of electron transfers through a number of intermediate compounds that readily accept and release electrons, alternating between an oxidized and reduced form. This route is called the electron transport chain and is similar in all organism. As the strongest oxidizing agent of the chain, oxygen is the final electron acceptor. Its vital role in living organisms is essentially as a substance on which to "dump" electrons. Many organism are anaerobic; that is they do not required oxygenfor survival, such sulfur and some of its compounds, as oxidizing agents.

All micro-organism gnerate reducing power through the reversible biochemical reaction of substances such as nicotinamide adenine dinucleotide (NAD), flavin, and cytochromes, which can exist in an oxidized or reduced form. By participating in the electron transport chain, the reduced form is continually regenerated from the oxidized form.

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