redox 101 - wikipedia, the free encyclopedia

8/10/2019 Redox 101 - Wikipedia, The Free Encyclopedia

1/12

17/10/2014 Redox - Wikipedia, the free encyclopedia

http://en.wikipedia.org/wiki/Redox 1/12

Sodium and fluorine bonding ionically to formsodium fluoride. Sodium loses its outer electron togive it a stable electron configuration, and thiselectron enters the fluorine atom exothermically.The oppositely charged ions are then attracted toeach other. The sodium is oxidized, and the fluorineis reduced.

RedoxFrom Wikipedia, the free encyclopedia

Redox (portmanteau of reduction and oxidation )reactions include all chemical reactions in whichatoms have their oxidation state changed; in general,redox reactions involve the transfer of electrons

between species.

This can be either a simple redox process, such asthe oxidation of carbon to yield carbon dioxide

(CO 2) or the reduction of carbon by hydrogen toield methane (CH 4), or a complex process such as

the oxidation of glucose (C 6H12O6) in the human

body through a series of c omplex electron transfer processes.

The term "redox" comes from two concepts involvedwith electron transfer: reduction and oxidation. [1] Itcan be explained in simple terms:

Oxidation is the loss of electrons or an increase in oxidation state by a molecule, atom, or ion.

Reduction is the gain of electrons or a decrease in oxidation state by a molecule, atom, or ion.

Although oxidation reactions are common ly associated with the formation of oxides from oxygenmolecules, these are only specific examples of a more general concept of reactions involving electrontransfer.

Red ox reactions, or oxidation-reduction rea ctions, have a number of simil arities to ac idbase reactions.Like acid base reactions, redox reactions are a matched set, t hat is, there can not be an oxidation reactionwithout a reduction reaction happ ening si multaneo usly. The o xidation alone an d the reduction alone areeach called a half -react ion , be cause two h alf-reactions always occur together to form a whole reaction.When writing half-reactions, the gained or lost ele ctrons are typically included explicitly in order thatthe half-reaction be balanced with respect to electr ic charge.

Though sufficient for many pu rposes, these descri ptions are not precisely correct. Oxida tion andreduction properly re fer to a change in oxidation s tate the actual transfer of electrons may never occur. Thu s, oxidatio n is better defined as an increase in oxidation state , and reduction as a decrease inoxidation state . In practice, the transfer of electrons will always cause a change in oxidation state, butthere are many reactions that are classed as "redox" even though no electron transfer occurs (such asthose involving covalent bonds).
http://en.wikipedia.org/wiki/Half-reactionhttp://en.wikipedia.org/wiki/Human_bodyhttp://en.wikipedia.org/wiki/Exothermichttp://en.wikipedia.org/wiki/Methanehttp://en.wikipedia.org/wiki/Electron_configurationhttp://en.wikipedia.org/wiki/Hydrogenhttp://en.wikipedia.org/wiki/Sodium_fluoridehttp://en.wikipedia.org/wiki/Electronhttp://en.wikipedia.org/wiki/Carbonhttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/File:NaF.gifhttp://en.wikipedia.org/wiki/File:NaF.gifhttp://en.wikipedia.org/wiki/Oxidation_statehttp://en.wikipedia.org/wiki/File:NaF.gifhttp://en.wikipedia.org/wiki/Chemical_reactionhttp://en.wikipedia.org/wiki/Chemical_reactionhttp://en.wikipedia.org/wiki/File:NaF.gifhttp://en.wikipedia.org/wiki/File:NaF.gifhttp://en.wikipedia.org/wiki/Portmanteauhttp://en.wikipedia.org/wiki/Covalenthttp://en.wikipedia.org/wiki/Oxidation_statehttp://en.wikipedia.org/wiki/Balanced_reactionhttp://en.wikipedia.org/wiki/Half-reactionhttp://en.wikipedia.org/wiki/Acid%E2%80%93base_reactionhttp://en.wikipedia.org/wiki/Ionhttp://en.wikipedia.org/wiki/Atomhttp://en.wikipedia.org/wiki/Moleculehttp://en.wikipedia.org/wiki/Electronhttp://en.wikipedia.org/wiki/Electron_transferhttp://en.wikipedia.org/wiki/Human_bodyhttp://en.wikipedia.org/wiki/Glucosehttp://en.wikipedia.org/wiki/Methanehttp://en.wikipedia.org/wiki/Hydrogenhttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Carbonhttp://en.wikipedia.org/wiki/Chemical_specieshttp://en.wikipedia.org/wiki/Electronhttp://en.wikipedia.org/wiki/Oxidation_statehttp://en.wikipedia.org/wiki/Chemical_reactionhttp://en.wikipedia.org/wiki/Portmanteauhttp://en.wikipedia.org/wiki/Exothermichttp://en.wikipedia.org/wiki/Electron_configurationhttp://en.wikipedia.org/wiki/Electronhttp://en.wikipedia.org/wiki/Sodium_fluoridehttp://en.wikipedia.org/wiki/Fluorinehttp://en.wikipedia.org/wiki/Sodiumhttp://en.wikipedia.org/wiki/File:NaF.gif


2/12



The two parts of a redox reaction

Rusting iron

A bonfire

Contents

1 Etymology

2 Oxidizing and reducing agents

2.1 Oxidizers

2.2 Reducers

3 Standard electrode potentials (reduction potentials)

4 Examples of redox reactions

4.1 Metal displacement

4.2 Other examples

4.2.1 Corrosion and rusting
http://en.wikipedia.org/wiki/Firehttp://en.wikipedia.org/wiki/File:Large_bonfire.jpghttp://en.wikipedia.org/wiki/Rusthttp://en.wikipedia.org/wiki/File:RustyChainEdit1.jpghttp://en.wikipedia.org/wiki/File:Redox_Halves.png


3/12



5 Redox reactions in industry

6 Redox reactions in biology

6.1 Redox cycling

7 Redox reactions in geology

8 Balancing redox reactions

8.1 Acidic media

8.2 Basic media

9 Memory aids

10 See also

11 References

12 External links

Etymology"Redox" is a portmanteau of "reduction" and "oxidation".

The word oxidation originally implied reaction with oxygen to form an oxide, since dioxygen (O 2 (g))

was historically the first recognized oxidizing agent. Later, the term was expanded to encompassoxygen-like substances that accomplished parallel chemical reactions. Ultimately, the meaning wasgeneralized to include all processes involving loss of electrons.

The word reduction originally referred to the loss in weight upon heating a metallic ore such as a metaloxide to extract the metal. In other words, ore was "reduced" to metal. Antoine Lavoisier (1743-1794)showed that this loss of weight was due to the loss of oxygen as a gas. Later, scientists realized that themetal atom gains electrons in this process. The meaning of reduction then became generalized to includeall processes involving gain of electrons. Even though "reduction" seems counter-intuitive whenspeaking of the gain of electrons, it might help to think of reduction as the loss of oxygen, which was itshistorical meaning.

The electrochemist John Bockris has used the words electronation and deelectronation to describereduction and oxidation processes respectively when they occur at electrodes. [2] These words areanalogous to protonation and deprotonation, but they have not been widely adopted by chemists.

The term "hydrogenation" could be used instead of reduction, since hydrogen is the reducing agent in alarge number of reactions, especially in organic chemistry and biochemistry. But, unlike oxidation,which has been generalized beyond its root element, hydrogenation has maintained its specificconnection to reactions that add hydrogen to another substance (e.g., the hydrogenation of unsaturatedfats in saturated fats, R-CH=CH-R + H 2 R-CH 2-CH 2-R).

Oxidizing and reducing agents

In redox processes, the reductant transfers electrons to the oxidant. Thus, in the reaction, the reductant or reducing agent loses electrons and is oxidized, and the oxidant or oxidizing agent gains electrons and isreduced. The pair of an oxidizing and reducing agent that are involved in a particular reaction is called aredox pair . A redox couple is a reducing species and its corresponding oxidized form, e.g., Fe 2+/Fe3+.
http://en.wikipedia.org/wiki/Deprotonationhttp://en.wikipedia.org/wiki/Protonationhttp://en.wikipedia.org/wiki/Electrodehttp://en.wikipedia.org/wiki/John_Bockrishttp://en.wikipedia.org/wiki/Antoine_Lavoisierhttp://en.wikipedia.org/wiki/Metal_oxidehttp://en.wikipedia.org/wiki/Orehttp://en.wikipedia.org/wiki/Portmanteau


4/12



Oxidizers

Substances that have the ability to oxidize other substances (cause them to lose electrons) are said to beoxidative or oxidizing and are known as oxidizing agents, oxidants, or oxidizers. That is, the oxidant(oxidizing agent) removes electrons from another substance, and is thus itself reduced. And, because it"accepts" electrons, the oxidizing agent is also called an electron acceptor, hence the name. Oxygen isthe quintessential oxidizer.

Oxidants are usually chemical substances with elements in high oxidation states (e.g., H 2O2, MnO4 ,

CrO 3, Cr 2O27 , OsO 4), or else highly electronegative elements (O 2, F2, Cl 2, Br 2) that can gain extra

electrons by oxidizing another substance.

Reducers

Substances that have the ability to reduce other substances (cause them to gain electrons) are said to bereductive or reducing and are known as reducing agents, reductants, or reducers. The reductant

(reducing agent) transfers electrons to another substance, and is thus itself oxidized. And, because it"donates" electrons, the reducing agent is also called an electron donor. Electron donors can also formcharge transfer complexes with electron acceptors.

Reductants in chemistry are very diverse. Electropositive elemental metals, such as lithium, sodium,magnesium, iron, zinc, and aluminium, are good reducing agents. These metals donate or give awayelectrons readily. Hydride transfer reagents , such as NaBH 4 and LiAlH 4, are widely used in organic

chemistry, [3][4] primarily in the reduction of carbonyl compounds to alcohols. Another method of reduction involves the use of hydrogen gas (H 2) with a palladium, platinum, or nickel catalyst. These

catalytic reductions are used primarily in the reduction of carbon-carbon double or triple bonds.

Standard electrode potentials (reduction potentials)

Each half-reaction has a standard electrode potential (E0cell ), which is equal to the potential difference

(or voltage) (E 0cell ) at equilibrium under standard conditions of an electrochemical cell in which the

cathode reaction is the half-reaction considered, and the anode is a standard hydrogen electrode wherehydrogen is oxidized: H 2 H

+ + e -.

The electrode potential of each half-reaction is also known as its reduction potential E0red, or potential

when the half-reaction takes place at a cathode. The reduction potential is a measure of the tendency of the oxidizing agent to be reduced. Its value is zero for H + + e H 2 by definition, positive for

oxidizing agents stronger than H + (e.g., +2.866 V for F 2) and negative for oxidizing agents that are

weaker than H + (e.g., 0.763 V for Zn 2+).[5]

For a redox reaction that takes place in a cell, the potential difference E 0cell = E0

cathode E0

anode

However, the potential of the reaction at the anode was sometimes expressed as an oxidation potential ,E0ox = E

0. The oxidation potential is a measure of the tendency of the reducing agent to be oxidized,

but does not represent the physical potential at an electrode. With this notation, the cell voltage equation
http://en.wikipedia.org/wiki/Standard_hydrogen_electrodehttp://en.wikipedia.org/wiki/Anodehttp://en.wikipedia.org/wiki/Half-reactionhttp://en.wikipedia.org/wiki/Cathodehttp://en.wikipedia.org/wiki/Electrochemical_cellhttp://en.wikipedia.org/wiki/Standard_statehttp://en.wikipedia.org/wiki/Voltagehttp://en.wikipedia.org/wiki/Electrode_potentialhttp://en.wikipedia.org/wiki/Catalysthttp://en.wikipedia.org/wiki/Nickelhttp://en.wikipedia.org/wiki/Platinumhttp://en.wikipedia.org/wiki/Palladiumhttp://en.wikipedia.org/wiki/Alcoholshttp://en.wikipedia.org/wiki/Carbonylhttp://en.wikipedia.org/wiki/Organic_chemistryhttp://en.wikipedia.org/wiki/Lithium_aluminium_hydridehttp://en.wikipedia.org/wiki/Sodium_borohydridehttp://en.wikipedia.org/wiki/Aluminiumhttp://en.wikipedia.org/wiki/Zinchttp://en.wikipedia.org/wiki/Ironhttp://en.wikipedia.org/wiki/Magnesiumhttp://en.wikipedia.org/wiki/Sodiumhttp://en.wikipedia.org/wiki/Lithiumhttp://en.wikipedia.org/wiki/Metalhttp://en.wikipedia.org/wiki/Electropositivehttp://en.wikipedia.org/wiki/Charge_transfer_complexhttp://en.wikipedia.org/wiki/Electron_donorhttp://en.wikipedia.org/wiki/Reducing_agenthttp://en.wikipedia.org/wiki/Brominehttp://en.wikipedia.org/wiki/Chlorinehttp://en.wikipedia.org/wiki/Fluorinehttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Electronegativityhttp://en.wikipedia.org/wiki/Osmium(VIII)_oxidehttp://en.wikipedia.org/wiki/Dichromatehttp://en.wikipedia.org/wiki/Chromium_trioxidehttp://en.wikipedia.org/wiki/Permanganatehttp://en.wikipedia.org/wiki/Hydrogen_peroxidehttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Electron_acceptorhttp://en.wikipedia.org/wiki/Oxidizing_agent


5/12



Illustration of a redox reaction

is written with a plus sign E 0cell = E0

cathode + E0

ox (anode)

Examples of redox reactions

A good example is the reaction between hydrogenand fluorine in which hydrogen is being oxidized

and fluorine is being reduced:

H2 + F 2 2 HF

We can write this overall reaction as two half-reactions:

the oxidation reaction:

H2 2 H+ + 2 e

and the reduction reaction:

F2 + 2 e 2 F

Analyzing each half-reaction in isolation can often make the overall chemical process clearer. Becausethere is no net change in charge during a redox reaction, the number of electrons in excess in theoxidation reaction must equal the number consumed by the reduction reaction (as shown above).

Elements, even in molecular form, always have an oxidation state of zero. In the first half-reaction,hydrogen is oxidized from an oxidation state of zero to an oxidation state of +1. In the second half-reaction, fluorine is reduced from an oxidation state of zero to an oxidation state of 1.

When adding the reactions together the electrons are canceled:

H2 2 H+ + 2 e

F2 + 2 e 2 F

H2 + F 2 2 H+ + 2 F

And the ions combine to form hydrogen fluoride:

2 H + + 2 F 2 HF

The overall reaction is:

H2 + F 2 2 HF

Metal displacement
http://en.wikipedia.org/wiki/Hydrofluoric_acidhttp://en.wikipedia.org/wiki/Fluoridehttp://en.wikipedia.org/wiki/Electronhttp://en.wikipedia.org/wiki/Hydrogen_ionhttp://en.wikipedia.org/wiki/Half-reactionhttp://en.wikipedia.org/wiki/Fluorinehttp://en.wikipedia.org/wiki/Hydrogenhttp://en.wikipedia.org/wiki/File:Redox_reaction.png


6/12



A redox reaction is the force behind an electrochemical celllike the Galvanic cell pictured. The battery is made out of azinc electrode in a ZnSO 4 solution connected with a wire

and a porous disk to a copper electrode in a CuSO 4 solution.

In this type of reaction, a metal atom in a compound (or in a solution) is replaced by an atom of another metal. For example, copper is depositedwhen zinc metal is placed in a copper(II)sulfate solution:

Zn(s)+ CuSO 4(aq) ZnSO 4(aq) + Cu(s)

In the above reaction, zinc metal displacesthe copper(II) ion from copper sulfatesolution and thus liberates free copper metal.

The ionic equation for this reaction is:

Zn + Cu 2+ Zn 2+ + Cu

As two half-reactions, it is seen that the zincis oxidized:

Zn Zn 2+ + 2 e

And the copper is reduced:

Cu 2+ + 2 e

Cu

Other examples

The reduction of nitrate to nitrogen in the presence of an acid (denitrification):

2 NO 3 + 10 e + 12 H + N 2 + 6 H 2O

The combustion of hydrocarbons, such as in an internal combustion engine, which produces water,

carbon dioxide, some partially oxidized forms such as carbon monoxide, and heat energy.

Complete oxidation of materials containing carbon produces carbon dioxide.

In organic chemistry, the stepwise oxidation of a hydrocarbon by oxygen produces water and,

successively, an alcohol, an aldehyde or a ketone, a carboxylic acid, and then a peroxide.

Corrosion and rusting

The term corrosion refers to the electrochemical oxidation of metals in reaction with an oxidant

such as oxygen. Rusting, the formation of iron oxides, is a well-known example of

electrochemical corrosion; it forms as a result of the oxidation of iron metal. Common rust often

refers to iron(III) oxide, formed in the following chemical reaction:

4Fe + 3O 2 2Fe 2O3

The oxidation of iron(II) to iron(III) by hydrogen peroxide in the presence of an acid:
http://en.wikipedia.org/wiki/Hydrogen_peroxidehttp://en.wikipedia.org/wiki/Iron(III)_oxidehttp://en.wikipedia.org/wiki/Ironhttp://en.wikipedia.org/wiki/Iron_oxidehttp://en.wikipedia.org/wiki/Rusthttp://en.wikipedia.org/wiki/Corrosionhttp://en.wikipedia.org/wiki/Peroxidehttp://en.wikipedia.org/wiki/Carboxylic_acidhttp://en.wikipedia.org/wiki/Ketonehttp://en.wikipedia.org/wiki/Aldehydehttp://en.wikipedia.org/wiki/Alcoholhttp://en.wikipedia.org/wiki/Organic_chemistryhttp://en.wikipedia.org/wiki/Carbonhttp://en.wikipedia.org/wiki/Energyhttp://en.wikipedia.org/wiki/Carbon_monoxidehttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Internal_combustion_enginehttp://en.wikipedia.org/wiki/Hydrocarbonhttp://en.wikipedia.org/wiki/Combustionhttp://en.wikipedia.org/wiki/Denitrificationhttp://en.wikipedia.org/wiki/Nitrogenhttp://en.wikipedia.org/wiki/Nitratehttp://en.wikipedia.org/wiki/Half-reactionhttp://en.wikipedia.org/wiki/Copper(II)_sulfatehttp://en.wikipedia.org/wiki/Zinchttp://en.wikipedia.org/wiki/Copperhttp://en.wikipedia.org/wiki/Galvanic_cellhttp://en.wikipedia.org/wiki/Electrochemical_cellhttp://en.wikipedia.org/wiki/File:Galvanic_cell_with_no_cation_flow.png


7/12



Oxides, such as iron(III) oxide or rust, which consists of hydratediron(III) oxides Fe 2O3 nH2O and

iron(III) oxide-hydroxide (FeO(OH),Fe(OH) 3), form when oxygen

combines with other elements

Iron rusting in pyrite cubes

Fe2+ Fe 3+ + e

H2O2 + 2 e 2 OH

Overall equation:

2 Fe 2+ + H 2O2 + 2 H+ 2 Fe 3+ + 2 H 2O

Redox reactions in industry

Cathodic protection is a technique used to control the corrosionof a metal surface by making it the cathode of an electrochemicalcell. A simple method of protection connects protected metal to amore easily corroded "sacrificial anode" to act as the anode. Thesacrificial metal instead of the protected metal, then, corrodes. Acommon application of cathodic protection is in galvanized steel,

in which a sacrificial coating of zinc on steel parts protects themfrom rust.

The primary process of reducing ore at high temperature to produce metals is known as smelting.

Oxidation is used in a wide variety of industries such as in the production of cleaning products and oxidizing ammonia to produce nitric acid, which is used in most fertilizers.

Redox reactions are the foundation of electrochemical cells.

The process of electroplating uses redox reactions to coat objectswith a thin layer of a material, as in chrome-plated automotive parts, silver plating cutlery, and gold-

plated jewelry.

The production of compact discs depends on a redox reaction, which coats the disc with a thin layer of metal film.

Redox reactions in biology

Many important biological processes involve redox reactions.

Cellular respiration, for instance, is the oxidation of glucose (C 6H12O6) to CO 2 and the reduction of

oxygen to water. The summary equation for cell respiration is:

C6H12O6 + 6 O 2 6 CO 2 + 6 H 2O

The process of cell respiration also depends heavily on the reduction of NAD + to NADH and the reverse

reaction (the oxidation of NADH to NAD +). Photosynthesis and cellular respiration are complementary, but photosynthesis is not the reverse of the redox reaction in cell respiration:

6 CO 2 + 6 H 2O + light energy C 6H12O6 + 6 O 2
http://en.wikipedia.org/wiki/Photonhttp://en.wikipedia.org/wiki/Photosynthesishttp://en.wikipedia.org/wiki/NAD%2Bhttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Glucosehttp://en.wikipedia.org/wiki/Cellular_respirationhttp://en.wikipedia.org/wiki/Biologyhttp://en.wikipedia.org/wiki/Compact_discshttp://en.wikipedia.org/wiki/Jewelryhttp://en.wikipedia.org/wiki/Gold-platedhttp://en.wikipedia.org/wiki/Cutleryhttp://en.wikipedia.org/wiki/Plating#Silver_platinghttp://en.wikipedia.org/wiki/Automotivehttp://en.wikipedia.org/wiki/Chrome_platinghttp://en.wikipedia.org/wiki/Electroplatinghttp://en.wikipedia.org/wiki/Electrochemical_cellhttp://en.wikipedia.org/wiki/Fertilizershttp://en.wikipedia.org/wiki/Nitric_acidhttp://en.wikipedia.org/wiki/Ammoniahttp://en.wikipedia.org/wiki/Category:Cleaning_productshttp://en.wikipedia.org/wiki/Smeltinghttp://en.wikipedia.org/wiki/Metalshttp://en.wikipedia.org/wiki/Galvanizationhttp://en.wikipedia.org/wiki/Sacrificial_anodehttp://en.wikipedia.org/wiki/Cathodic_protectionhttp://en.wikipedia.org/wiki/Pyritehttp://en.wikipedia.org/wiki/File:PyOx.JPGhttp://en.wikipedia.org/wiki/Iron(III)_oxide-hydroxidehttp://en.wikipedia.org/wiki/Iron(III)_oxidehttp://en.wikipedia.org/wiki/Rusthttp://en.wikipedia.org/wiki/Iron(III)_oxidehttp://en.wikipedia.org/wiki/File:Rust_screw.jpg


8/12



Top: ascorbic acid (reduced

form of Vitamin C)

Bottom: dehydroascorbic

acid (oxidized form of

Vitamin C)

Biological energy is frequently stored and released by means of redoxreactions. Photosynthesis involves the reduction of carbon dioxide intosugars and the oxidation of water into molecular oxygen. The reversereaction, respiration, oxidizes sugars to produce carbon dioxide and water.As intermediate steps, the reduced carbon compounds are used to reducenicotinamide adenine dinucleotide (NAD +), which then contributes to thecreation of a proton gradient, which drives the synthesis of adenosine

triphosphate (ATP) and is maintained by the reduction of oxygen. In animalcells, mitochondria perform similar functions. See the Membrane potential article.

Free radical reactions are redox reactions that occur as a part of homeostasisand killing microorganisms, where an electron detaches from a moleculeand then reattaches almost instantaneously. Free radicals are a part of redoxmolecules and can become harmful to the human body if they do notreattach to the redox molecule or an antioxidant. Unsatisfied free radicalscan spur the mutation of cells they encounter and are, thus, causes of cancer.

The term redox state is often used to describe the balance of GSH/GSSG, NAD +/NADH and NADP +/NADPH in a biological system such as a cell or organ. The redox state is reflected in the balance of several sets of metabolites (e.g., lactate and pyruvate, beta-hydroxybutyrate, andacetoacetate), whose interconversion is dependent on these ratios. Anabnormal redox state can develop in a variety of deleterious situations, suchas hypoxia, shock, and sepsis. Redox mechanism also control some cellular

processes. Redox proteins and their genes must be co-located for redoxregulation according to the CoRR hypothesis for the function of DNA inmitochondria and chloroplasts.

Redox cycling

A wide variety of aromatic compounds are enzymatically reduced to form free radicals that contain onemore electron than their parent compounds. In general, the electron donor is any of a wide variety of flavoenzymes and their coenzymes. Once formed, these anion free radicals reduce molecular oxygen tosuperoxide, and regenerate the unchanged parent compound. The net reaction is the oxidation of theflavoenzyme's coenzymes and the reduction of molecular oxygen to form superoxide. This catalytic

behavior has been described as futile cycle or redox cycling.

Examples of redox cycling-inducing molecules are the herbicide paraquat and other viologens andquinones such as menadione. [6]

Redox reactions in geology

In geology, redox is important to both the formation of minerals and the mobilization of minerals, and isalso important in some depositional environments. In general, the redox state of most rocks can be seenin the color of the rock. The rock forms in oxidizing conditions, giving it a red color. It is then"bleached" to a greenor sometimes whiteform when a reducing fluid passes through the rock. Thereduced fluid can also carry uranium-bearing minerals. Famous examples of redox conditions affectinggeological processes include uranium deposits and Moqui marbles.
http://en.wikipedia.org/wiki/Navajo_Sandstone#Iron_oxide_concretions_.28Moqui_marbles.29http://en.wikipedia.org/wiki/Uranium_mininghttp://en.wikipedia.org/wiki/Uranium_ore_deposits#Uranium_mineralshttp://en.wikipedia.org/wiki/Depositional_environmentshttp://en.wikipedia.org/wiki/Geologyhttp://en.wikipedia.org/wiki/Menadionehttp://en.wikipedia.org/wiki/Quinonehttp://en.wikipedia.org/wiki/Viologenhttp://en.wikipedia.org/wiki/Paraquathttp://en.wikipedia.org/wiki/Herbicidehttp://en.wikipedia.org/wiki/Superoxidehttp://en.wikipedia.org/wiki/Coenzymehttp://en.wikipedia.org/wiki/Radical_(chemistry)http://en.wikipedia.org/wiki/Enzymehttp://en.wikipedia.org/wiki/Aromaticityhttp://en.wikipedia.org/wiki/CoRR_hypothesishttp://en.wikipedia.org/wiki/Sepsishttp://en.wikipedia.org/wiki/Shock_(circulatory)http://en.wikipedia.org/wiki/Hypoxia_(medical)http://en.wikipedia.org/wiki/Acetoacetatehttp://en.wikipedia.org/wiki/Beta-hydroxybutyratehttp://en.wikipedia.org/wiki/Pyruvatehttp://en.wikipedia.org/wiki/Lactic_acidhttp://en.wikipedia.org/wiki/Nicotinamide_adenine_dinucleotide_phosphatehttp://en.wikipedia.org/wiki/Glutathionehttp://en.wikipedia.org/wiki/Antioxidanthttp://en.wikipedia.org/wiki/Homeostasishttp://en.wikipedia.org/wiki/Free_radicalhttp://en.wikipedia.org/wiki/Membrane_potentialhttp://en.wikipedia.org/wiki/Mitochondriahttp://en.wikipedia.org/wiki/Adenosine_triphosphatehttp://en.wikipedia.org/wiki/Proton_gradienthttp://en.wikipedia.org/wiki/Nicotinamide_adenine_dinucleotidehttp://en.wikipedia.org/wiki/Water_(molecule)http://en.wikipedia.org/wiki/Sugarhttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Vitamin_Chttp://en.wikipedia.org/wiki/Oxidizing_agenthttp://en.wikipedia.org/wiki/Dehydroascorbic_acidhttp://en.wikipedia.org/wiki/Vitamin_Chttp://en.wikipedia.org/wiki/Reducing_agenthttp://en.wikipedia.org/wiki/Ascorbic_acidhttp://en.wikipedia.org/wiki/File:Dehydroascorbic_acid.pnghttp://en.wikipedia.org/wiki/File:Ascorbic_acid_structure.png


9/12



Mi Vida uranium mine, near Moab,Utah. The alternating red andwhite/green bands of sandstonecorrespond to oxidized and reducedconditions in groundwater redoxchemistry.

Balancing redox reactions

Describing the overall electrochemical reaction for a redox process requires a balancing of thecomponent half-reactions for oxidation and reduction. In general, for reactions in aqueous solution, thisinvolves adding H +, OH , H 2O, and electrons to compensate for the oxidation changes.

Acidic media

In acidic media, H+

ions and water are added to half-reactions to balance the overall reaction.

For instance, when manganese(II) reacts with sodium bismuthate:

Unbalanced

reaction:

Mn2+

(aq) + NaBiO 3(s) Bi3+

(aq) +

MnO 4 (aq)

Oxidation:4 H 2O(l) + Mn

2+(aq) MnO

4 (aq) + 8

H+

(aq) + 5 e

Reduction:2 e

+ 6 H

+ + BiO

3 (s) Bi

3+(aq) + 3

H2O(l)

The reaction is balanced by scaling the two half-cell reactions to involve the same number of electrons

(multiplying the oxidation reaction by the number of electrons in the reduction step and vice versa):

8 H 2O(l) + 2 Mn2+

(aq) 2 MnO4 (aq) + 16 H

+(aq) + 10 e

10 e

+ 30 H+

+ 5 BiO3 (s) 5 Bi

3+(aq) + 15 H 2O(l)

Adding these two reactions eliminates the electrons terms and yields the balanced reaction:

14 H+

(aq) + 2 Mn2+

(aq) + 5 NaBiO 3(s) 7 H 2O(l) + 2 MnO4 (aq) + 5 Bi

3+(aq) + 5 Na

+(aq)

Basic media

In basic media, OH ions and water are added to half reactions to balance the overall reaction.

For example, in the reaction between potassium permanganate and sodium sulfite:

Unbalanced reaction: KMnO 4 + Na 2SO3 + H 2O MnO 2 + Na 2SO4 + KOH

Reduction: 3 e

+ 2 H 2O + MnO 4 MnO 2 + 4 OH

Oxidation: 2 OH + SO 32 SO 4

2 + H 2O + 2 e

Balancing the number of electrons in the two half-cell reactions gives:
http://en.wikipedia.org/wiki/Sodium_sulfitehttp://en.wikipedia.org/wiki/Potassium_permanganatehttp://en.wikipedia.org/wiki/Hydroxidehttp://en.wikipedia.org/wiki/Sodium_bismuthatehttp://en.wikipedia.org/wiki/Manganesehttp://en.wikipedia.org/wiki/Water_(molecule)http://en.wikipedia.org/wiki/Hydroxidehttp://en.wikipedia.org/wiki/Protonhttp://en.wikipedia.org/wiki/Half-reactionhttp://en.wikipedia.org/wiki/Oxidizedhttp://en.wikipedia.org/wiki/Sandstonehttp://en.wikipedia.org/wiki/Moab,_Utahhttp://en.wikipedia.org/wiki/Charles_Steen#Mi_Vidahttp://en.wikipedia.org/wiki/File:UraniumMineUtah.JPG


10/12



6 e

+ 4 H 2O + 2 MnO 4 2 MnO 2 + 8 OH

6 OH + 3 SO 32 3 SO 4

2 + 3 H 2O + 6 e

Adding these two half-cell reactions together gives the balanced equation:

2 KMnO 4 + 3 Na 2SO3 + H 2O 2 MnO 2 + 3 Na 2SO4 + 2 KOH

Memory aids

The key terms involved in redox are often confusing to students. [7][8] For example, an element that isoxidized loses electrons; however, that element is referred to as the reducing agent. Likewise, an elementthat is reduced gains electrons and is referred to as the oxidizing agent. [9] Acronyms or mnemonics arecommonly used [10] to help remember what is happening:

"OIL RIG" O xidation Is L oss of electrons, R eduction Is G ain of electrons. [7][8][9][10]

"LEO the lion says GER" Loss of E lectrons is O xidation, G ain of E lectrons is

R eduction. [7][8][9][10]

"LEORA says GEROA" Loss of E lectrons is O xidation ( R educing Agent), G ain of E lectrons

is R eduction ( O xidizing Agent). [9]

"RED CAT" and "AN OX", or "AnOx RedCat" ("an ox-red cat"), Red uction occurs at the

Cat hode and the An ode is for Ox idation.

"RED CAT gains what AN OX loses" - Red uction occurs at the Cat hode gains (electrons) what

An ode Ox idation loses (electrons).

See also

Bessemer process

BioremediationCalvin cycle

Chemical equation

Chemical looping combustion

Citric acid cycle

Electrochemical series

Electrochemistry

ElectrolysisElectron equivalent

Electron transport chain

Electrosynthesis
http://en.wikipedia.org/wiki/Electrosynthesishttp://en.wikipedia.org/wiki/Electron_transport_chainhttp://en.wikipedia.org/wiki/Electron_equivalenthttp://en.wikipedia.org/wiki/Electrolysishttp://en.wikipedia.org/wiki/Electrochemistryhttp://en.wikipedia.org/wiki/Electrochemical_serieshttp://en.wikipedia.org/wiki/Citric_acid_cyclehttp://en.wikipedia.org/wiki/Chemical_looping_combustionhttp://en.wikipedia.org/wiki/Chemical_equationhttp://en.wikipedia.org/wiki/Calvin_cyclehttp://en.wikipedia.org/wiki/Bioremediationhttp://en.wikipedia.org/wiki/Bessemer_process


11/12


http://en.wi kipedia.org/wiki/Redox 11/12

Refer ences

1. ^ "R edox Reactions" (http://www.wiley.com/college/boyer/0470003790/reviews/redox/redox.htm). wiley.com .

2. ^ John O'M. Bockris and Amulya K. N. Reddy (1970). Modern Electrochemistry . Plenum Press. pp. 3523.

3. ^ Hudlick, Milo (1996). Reductions in Organic Chemistry . Washington, D.C.: American Chemical Society.

p. 4 29. ISBN 0-8412-3344-6.

4. ^ Hudlick, Milo (1990). Oxidations in Organic Chemistry . Washington, D.C.: American Chemical Society.

p. 4 56. ISBN 0-8412-1780-7.

5. ^ E lectrode potential values from R.H.Petrucci, W.S.Harwood and F.G.Herring (2002). General Chemistry

(8th ed.). Prentice-Hall. p. 832.

6. ^ "gutier.doc" (http://www.bioscience.org/2000/v5/d/gutier/gutier.pdf). Retrieved 2008-06-30. PDF (2.76 MiB)

7. ^ a b c Robertson, William (2010). More Chemistry Basics (http://books.google.com/books?

id=hIzuarlXtH4C&pg=PA82&dq=confusing). National Science Teachers Association. p. 82. ISBN 978-1-

936137-74-9.

8. ^ a b c Phillips, John; Strozak, Victor; Wistrom, Cheryl (2000). Chemistry: Concepts and Applications .

Glencoe McGraw-Hill. p. 558. ISBN 978-0-02-828210-7. "Students often are confused when associating

reduction with the gain of electrons."

9. ^ a b c d Rodgers, Glen (2012). Descriptive Inorganic, Coordination, and Solid-State Chemistry

(htt p://books.google.com/books?id=g_ybia0hGw8C&pg=PA330). Brooks/Cole, Cengage Learning. p. 330.

ISBN 978-0-8400-6846-0.

10. ^ a b c Zumdahl, Steven; Zumdahl, Susan (2009). Chemistry (http://books.google.com/books?

id=IdhYqXy37KIC&pg=PA160). Houghton Mifflin. p. 160. ISBN 978-0-547-05405-6.

Schr ing, J., Schulz, H. D., Fischer, W. R., Bttcher, J., Duijnisveld, W. H. (editors)(1999). Redox:

Fundamentals, Processes and Applications, Springer-Verlag, Heidelberg, 246 pp. ISBN 978-3-540-66528-1

Gal vanic cell

Hydr ogenation

Me m brane potential

Nu cleophilic abstraction

Organic redox reaction

Oxidative addition and reductive elimination

Oxidative phosphorylation

Par tial oxidation

Pro-oxidant

Reduced gas

Reducing agent

Reducing atmosphere

Reduction potential

Ther mic reactionTra nsmetalation
http://en.wikipedia.org/wiki/Transmetalationhttp://en.wikipedia.org/wiki/Thermic_reactionhttp://en.wikipedia.org/wiki/Reduction_potentialhttp://en.wikipedia.org/wiki/Reducing_atmospherehttp://en.wikipedia.org/wiki/Reducing_agenthttp://en.wikipedia.org/wiki/Reduced_gashttp://en.wikipedia.org/wiki/Pro-oxidanthttp://en.wikipedia.org/wiki/Partial_oxidationhttp://en.wikipedia.org/wiki/Oxidative_phosphorylationhttp://en.wikipedia.org/wiki/Oxidative_additionhttp://en.wikipedia.org/wiki/Organic_redox_reactionhttp://en.wikipedia.org/wiki/Nucleophilic_abstractionhttp://en.wikipedia.org/wiki/Membrane_potentialhttp://en.wikipedia.org/wiki/Hydrogenationhttp://en.wikipedia.org/wiki/Galvanic_cellhttp://en.wikipedia.org/wiki/Special:BookSources/9783540665281http://en.wikipedia.org/wiki/Special:BookSources/978-0-547-05405-6http://en.wikipedia.org/wiki/International_Standard_Book_Numberhttp://books.google.com/books?id=IdhYqXy37KIC&pg=PA160http://en.wikipedia.org/wiki/Special:BookSources/978-0-8400-6846-0http://en.wikipedia.org/wiki/International_Standard_Book_Numberhttp://books.google.com/books?id=g_ybia0hGw8C&pg=PA330http://en.wikipedia.org/wiki/Special:BookSources/978-0-02-828210-7http://en.wikipedia.org/wiki/International_Standard_Book_Numberhttp://en.wikipedia.org/wiki/Special:BookSources/978-1-936137-74-9http://en.wikipedia.org/wiki/International_Standard_Book_Numberhttp://books.google.com/books?id=hIzuarlXtH4C&pg=PA82&dq=confusinghttp://en.wikipedia.org/wiki/Mebibytehttp://www.bioscience.org/2000/v5/d/gutier/gutier.pdfhttp://en.wikipedia.org/wiki/Special:BookSources/0-8412-1780-7http://en.wikipedia.org/wiki/International_Standard_Book_Numberhttp://en.wikipedia.org/wiki/Special:BookSources/0-8412-3344-6http://en.wikipedia.org/wiki/International_Standard_Book_Numberhttp://www.wiley.com/college/boyer/0470003790/reviews/redox/redox.htm


12/12


Wikimedia Commons hasmedia related to Redox reactions .

(pdf 3,6 MB) (http://hdl.handle.net/10013/epic.31694.d001)

Tratnyek, Paul G.; Grundl, Timothy J.; Haderlein, Stefan B., eds. (2011). Aquatic Redox Chemistry . ACS

Symposium Series 1071 . doi:10.1021/bk-2011-1071 (http://dx.doi.org/10.1021%2Fbk-2011-1071).

ISBN 9780841226524.

External links

Chemical Equation Balancer

(http://www.berkeleychurchill.com/software/chembal.php)

- An open source chemical equation balancer that handles

redox reactions.

Video - Synthesis of Copper(II) Acetate (http://www.youtube.com/watch?v=rF1ls-v7puQ) 20 Feb.

2009

Redox reactions calculator (http://www.shodor.org/UNChem/advanced/redox/redoxcalc.html)

Redox reactions at Chemguide

(http://www.chemguide.co.uk/inorganic/redox/definitions.html#top)

Online redox reaction equation balancer, balances equations of any half-cell and full reactions

(http://www.webqc.org/balance.php)

Retrieved from "http://en.wikipedia.org/w/index.php?title=Redox&oldid=627443322"

Categories: Soil chemistry Chemical reactions

This page was last modified on 28 September 2014 at 18:23.Text is available under the Creative Commons Attribution-ShareAlike License; additional termsmay apply. By using this site, you agree to the Terms of Use and Privacy Policy. Wikipedia is aregistered trademark of the Wikimedia Foundation, Inc., a non-profit organization.
http://www.wikimediafoundation.org/http://wikimediafoundation.org/wiki/Privacy_policyhttp://wikimediafoundation.org/wiki/Terms_of_Usehttp://en.wikipedia.org/wiki/Wikipedia:Text_of_Creative_Commons_Attribution-ShareAlike_3.0_Unported_Licensehttp://en.wikipedia.org/wiki/Help:Categoryhttp://en.wikipedia.org/w/index.php?title=Redox&oldid=627443322http://www.webqc.org/balance.phphttp://www.chemguide.co.uk/inorganic/redox/definitions.html#tophttp://www.shodor.org/UNChem/advanced/redox/redoxcalc.htmlhttp://www.youtube.com/watch?v=rF1ls-v7puQhttp://www.berkeleychurchill.com/software/chembal.phphttp://en.wikipedia.org/wiki/Special:BookSources/9780841226524http://en.wikipedia.org/wiki/International_Standard_Book_Numberhttp://dx.doi.org/10.1021%2Fbk-2011-1071http://en.wikipedia.org/wiki/Digital_object_identifierhttp://hdl.handle.net/10013/epic.31694.d001http://en.wikipedia.org/wiki/Category:Chemical_reactionshttp://en.wikipedia.org/wiki/Category:Soil_chemistryhttp://commons.wikimedia.org/wiki/Category:Redox_reactions

redox 101 - wikipedia, the free encyclopedia

Documents