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46-414: A process for electrochemical production of titanium through the reduction of titanium oxide in a calcium chloride solution was first described in a 1904 German patent, and in 1954 U.S. patent 2845386A was awarded to Carl Marcus Olson for the production of metals like titanium by reduction of the metal oxide by a molten salt reducing agent in a specific gravity apparatus. The FFC Cambridge process

92-426: A hydride ion . 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 electrons relatively readily. Hydride transfer reagents , such as NaBH 4 and LiAlH 4 , reduce by atom transfer: they transfer the equivalent of hydride or H . These reagents are widely used in

138-504: A cathode (the oxide being reduced) in a solution of molten CaCl 2 . Depending on the nature of the oxide it will exist at a particular potential relative to the anode, which is dependent on the quantity of CaO present in CaCl 2 . The electrocalciothermic reduction mechanism may be represented by the following sequence of reactions, where "M" represents a metal to be reduced (typically titanium). When this reaction takes place on its own, it

184-411: A gas. Later, scientists realized that the metal atom gains electrons in this process. The meaning of reduction then became generalized to include all processes involving a gain of electrons. Reducing equivalent refers to chemical species which transfer the equivalent of one electron in redox reactions. The term is common in biochemistry . A reducing equivalent can be an electron or a hydrogen atom as

230-459: A more easily corroded " sacrificial anode " to act as the anode . The sacrificial metal, instead of the protected metal, then corrodes. A common application of cathodic protection is in galvanized steel, in which a sacrificial zinc coating on steel parts protects them from rust. Oxidation is used in a wide variety of industries, such as in the production of cleaning products and oxidizing ammonia to produce nitric acid . Redox reactions are

276-413: A redox reaction that takes place in a cell, the potential difference is: However, the potential of the reaction at the anode is sometimes expressed as an oxidation potential : 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 is written with a plus sign In

322-411: A substrate. In this context, the oxidizing agent can be called an oxygenation reagent or oxygen-atom transfer (OAT) agent. Examples include MnO 4 ( permanganate ), CrO 4 ( chromate ), OsO 4 ( osmium tetroxide ), and especially ClO 4 ( perchlorate ). Notice that these species are all oxides . In some cases, these oxides can also serve as electron acceptors, as illustrated by

368-408: A whole reaction. In electrochemical reactions the oxidation and reduction processes do occur simultaneously but are separated in space. Oxidation originally implied a reaction with oxygen to form an oxide. Later, the term was expanded to encompass substances that accomplished chemical reactions similar to those of oxygen. Ultimately, the meaning was generalized to include all processes involving

414-415: Is potassium dichromate , which does not pass the dangerous goods test of an oxidizing agent. The U.S. Department of Transportation defines oxidizing agents specifically. There are two definitions for oxidizing agents governed under DOT regulations. These two are Class 5 ; Division 5.1(a)1 and Class 5; Division 5.1(a)2. Division 5.1 "means a material that may, generally by yielding oxygen, cause or enhance

460-410: Is a substance in a redox chemical reaction that gains or " accepts "/"receives" an electron from a reducing agent (called the reductant , reducer , or electron donor ). In other words, an oxidizer is any substance that oxidizes another substance. The oxidation state , which describes the degree of loss of electrons , of the oxidizer decreases while that of the reductant increases; this

506-408: Is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a decrease in the oxidation state. The oxidation and reduction processes occur simultaneously in the chemical reaction. There are two classes of redox reactions: "Redox" is a portmanteau of

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552-429: Is also called an electron acceptor . Oxidants are usually chemical substances with elements in high oxidation states (e.g., N 2 O 4 , MnO 4 , CrO 3 , Cr 2 O 7 , OsO 4 ), or else highly electronegative elements (e.g. O 2 , F 2 , Cl 2 , Br 2 , I 2 ) that can gain extra electrons by oxidizing another substance. Oxidizers are oxidants, but

598-447: Is also known as its reduction potential ( E red ), 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 → 1 ⁄ 2 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., −0.763V for Zn ). For

644-469: Is dependent on these ratios. Redox mechanisms also control some cellular processes. Redox proteins and their genes must be co-located for redox regulation according to the CoRR hypothesis for the function of DNA in mitochondria and chloroplasts . Wide varieties of aromatic compounds are enzymatically reduced to form free radicals that contain one more electron than their parent compounds. In general,

690-428: Is expressed by saying that oxidizers "undergo reduction" and "are reduced" while reducers "undergo oxidation" and "are oxidized". Common oxidizing agents are oxygen , hydrogen peroxide , and the halogens . In one sense, an oxidizing agent is a chemical species that undergoes a chemical reaction in which it gains one or more electrons. In that sense, it is one component in an oxidation–reduction (redox) reaction. In

736-421: Is important because this molten salt can dissolve and transport the "O" ions to the anode to be discharged. The anode reaction depends on the material of the anode. Depending on the system it is possible to produce either CO or CO 2 or a mixture at the carbon anode: However, if an inert anode is used, such as that of high density SnO 2 , the discharge of the O ions leads to the evolution of oxygen gas. However

782-432: Is mined as its magnetite (Fe 3 O 4 ). Titanium is mined as its dioxide, usually in the form of rutile (TiO 2 ). These oxides must be reduced to obtain the corresponding metals, often achieved by heating these oxides with carbon or carbon monoxide as reducing agents. Blast furnaces are the reactors where iron oxides and coke (a form of carbon) are combined to produce molten iron. The main chemical reaction producing

828-505: Is not the reverse of the redox reaction in cellular respiration: Biological energy is frequently stored and released using redox reactions. Photosynthesis involves the reduction of carbon dioxide into sugars and the oxidation of water into molecular oxygen. The reverse reaction, respiration, oxidizes sugars to produce carbon dioxide and water. As intermediate steps, the reduced carbon compounds are used to reduce nicotinamide adenine dinucleotide (NAD ) to NADH, which then contributes to

874-441: Is oxidized, and the oxidant or oxidizing agent gains electrons and is reduced. The pair of an oxidizing and reducing agent that is involved in a particular reaction is called a redox pair. A redox couple is a reducing species and its corresponding oxidizing form, e.g., Fe / Fe .The oxidation alone and the reduction alone are each called a half-reaction because two half-reactions always occur together to form

920-430: Is referred to as the " calciothermic reduction" (or, more generally, an example of metallothermic reduction). For example, if the cathode was primarily made from TiO then calciothermic reduction would appear as: Whilst the cathode reaction can be written as above it is in fact a gradual removal of oxygen from the oxide. For example, it has been shown that TiO 2 does not simply reduce to Ti. It, in fact, reduces through

966-492: Is the ferrocenium ion Fe(C 5 H 5 ) 2 , which accepts an electron to form Fe(C 5 H 5 ) 2 . One of the strongest acceptors commercially available is " Magic blue ", the radical cation derived from N(C 6 H 4 -4-Br) 3 . Extensive tabulations of ranking the electron accepting properties of various reagents (redox potentials) are available, see Standard electrode potential (data page) . In more common usage, an oxidizing agent transfers oxygen atoms to

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1012-510: The combustion of other materials." Division 5.(a)1 of the DOT code applies to solid oxidizers "if, when tested in accordance with the UN Manual of Tests and Criteria (IBR, see § 171.7 of this subchapter), its mean burning time is less than or equal to the burning time of a 3:7 potassium bromate/cellulose mixture." 5.1(a)2 of the DOT code applies to liquid oxidizers "if, when tested in accordance with

1058-402: The conversion of MnO 4 to MnO 4 ,ie permanganate to manganate . The dangerous goods definition of an oxidizing agent is a substance that can cause or contribute to the combustion of other material. By this definition some materials that are classified as oxidizing agents by analytical chemists are not classified as oxidizing agents in a dangerous materials sense. An example

1104-443: The copper sulfate solution, thus liberating free copper metal. The reaction is spontaneous and releases 213 kJ per 65 g of zinc. The ionic equation for this reaction is: As two half-reactions , it is seen that the zinc is oxidized: And the copper is reduced: A disproportionation reaction is one in which a single substance is both oxidized and reduced. For example, thiosulfate ion with sulfur in oxidation state +2 can react in

1150-479: The creation of a proton gradient , which drives the synthesis of adenosine triphosphate (ATP) and is maintained by the reduction of oxygen. In animal cells, mitochondria perform similar functions. Free radical reactions are redox reactions that occur as part of homeostasis and killing microorganisms . In these reactions, an electron detaches from a molecule and then re-attaches almost instantly. Free radicals are part of redox molecules and can become harmful to

1196-476: The electron donor is any of a wide variety of flavoenzymes and their coenzymes . Once formed, these anion free radicals reduce molecular oxygen to superoxide and regenerate the unchanged parent compound. The net reaction is the oxidation of the flavoenzyme's coenzymes and the reduction of molecular oxygen to form superoxide. This catalytic behavior has been described as a futile cycle or redox cycling. Minerals are generally oxidized derivatives of metals. Iron

1242-415: The electrons cancel: The protons and fluoride combine to form hydrogen fluoride in a non-redox reaction: The overall reaction is: In this type of reaction, a metal atom in a compound or solution is replaced by an atom of another metal. For example, copper is deposited when zinc metal is placed in a copper(II) sulfate solution: In the above reaction, zinc metal displaces the copper(II) ion from

1288-446: The environment. Cellular respiration , for instance, is the oxidation of glucose (C 6 H 12 O 6 ) to CO 2 and the reduction of oxygen to water . The summary equation for cellular respiration is: The process of cellular 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

1334-660: The foundation of electrochemical cells, which can generate electrical energy or support electrosynthesis . Metal ores often contain metals in oxidized states, such as oxides or sulfides, from which the pure metals are extracted by smelting at high temperatures in the presence of a reducing agent. The process of electroplating uses redox reactions to coat objects with a thin layer of a material, as in chrome-plated automotive parts, silver plating cutlery , galvanization and gold-plated jewelry . Many essential biological processes involve redox reactions. Before some of these processes can begin, iron must be assimilated from

1380-413: The human body if they do not reattach to the redox molecule or an antioxidant . 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 and acetoacetate ), whose interconversion

1426-413: The loss of electrons or the increase in the oxidation state of a chemical species. Substances that have the ability to oxidize other substances (cause them to lose electrons) are said to be oxidative or oxidizing, and are known as oxidizing agents , oxidants, or oxidizers. The oxidant removes electrons from another substance, and is thus itself reduced. Because it "accepts" electrons, the oxidizing agent

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1472-401: The lower oxides (Ti 3 O 5 , Ti 2 O 3 , TiO etc.) to Ti. The calcium oxide produced is then electrolyzed: and Reaction (2b) describes the production of Ca metal from Ca ions within the salt, at the cathode. The Ca would then proceed to reduce the cathode. The net result of reactions (1) and (2) is simply the reduction of the oxide into metal plus oxygen: The use of molten CaCl 2

1518-492: The molten iron is: Electron transfer reactions are central to myriad processes and properties in soils, and redox potential , quantified as Eh (platinum electrode potential ( voltage ) relative to the standard hydrogen electrode) or pe (analogous to pH as -log electron activity), is a master variable, along with pH, that controls and is governed by chemical reactions and biological processes. Early theoretical research with applications to flooded soils and paddy rice production

1564-404: The presence of acid to form elemental sulfur (oxidation state 0) and sulfur dioxide (oxidation state +4). Thus one sulfur atom is reduced from +2 to 0, while the other is oxidized from +2 to +4. Cathodic protection is a technique used to control the corrosion of a metal surface by making it the cathode of an electrochemical cell . A simple method of protection connects protected metal to

1610-544: The reaction between hydrogen and fluorine , hydrogen is being oxidized and fluorine is being reduced: This spontaneous reaction releases 542 kJ per 2 g of hydrogen because the H-F bond is much stronger than the F-F bond. This reaction can be analyzed as two half-reactions . The oxidation reaction converts hydrogen to protons : The reduction reaction converts fluorine to the fluoride anion: The half-reactions are combined so that

1656-521: The redox status of soils. The key terms involved in redox can be confusing. For example, a reagent that is oxidized loses electrons; however, that reagent is referred to as the reducing agent. Likewise, a reagent that is reduced gains electrons and is referred to as the oxidizing agent. These mnemonics are commonly used by students to help memorise the terminology: Oxidizing agent An oxidizing agent (also known as an oxidant , oxidizer , electron recipient , or electron acceptor )

1702-410: The reducing agent is also called an electron donor . Electron donors can also form charge transfer complexes with electron acceptors. The word reduction originally referred to the loss in weight upon heating a metallic ore such as a metal oxide to extract the metal. In other words, ore was "reduced" to metal. Antoine Lavoisier demonstrated that this loss of weight was due to the loss of oxygen as

1748-494: The reduction of carbonyl compounds to alcohols . A related method of reduction involves the use of hydrogen gas (H 2 ) as sources of H atoms. The electrochemist John Bockris proposed the words electronation and de-electronation to describe reduction and oxidation processes, respectively, when they occur at electrodes . These words are analogous to protonation and deprotonation . They have not been widely adopted by chemists worldwide, although IUPAC has recognized

1794-441: The second sense, an oxidizing agent is a chemical species that transfers electronegative atoms, usually oxygen, to a substrate. Combustion , many explosives, and organic redox reactions involve atom-transfer reactions. Electron acceptors participate in electron-transfer reactions . In this context, the oxidizing agent is called an electron acceptor and the reducing agent is called an electron donor . A classic oxidizing agent

1840-437: The term is mainly reserved for sources of oxygen, particularly in the context of explosions. Nitric acid is a strong oxidizer. Substances that have the ability to reduce other substances (cause them to gain electrons) are said to be reductive or reducing and are known as reducing agents , reductants, or reducers. The reductant transfers electrons to another substance and is thus itself oxidized. Because it donates electrons,

1886-658: The terms electronation and de-electronation. Redox reactions can occur slowly, as in the formation of rust , or rapidly, as in the case of burning fuel . Electron transfer reactions are generally fast, occurring within the time of mixing. The mechanisms of atom-transfer reactions are highly variable because many kinds of atoms can be transferred. Such reactions can also be quite complex, involving many steps. The mechanisms of electron-transfer reactions occur by two distinct pathways, inner sphere electron transfer and outer sphere electron transfer . Analysis of bond energies and ionization energies in water allows calculation of

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1932-446: The thermodynamic aspects of redox reactions. Each half-reaction has a standard electrode potential ( E cell ), which is equal to the potential difference or voltage 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 where hydrogen is oxidized: The electrode potential of each half-reaction

1978-501: The use of an inert anode has disadvantages. Firstly, when the concentration of CaO is low, Cl 2 evolution at the anode becomes more favourable. In addition, when compared to a carbon anode, more energy is required to achieve the same reduced phase at the cathode. Inert anodes suffer from stability issues. Reduction (chemistry) Redox ( / ˈ r ɛ d ɒ k s / RED -oks , / ˈ r iː d ɒ k s / REE -doks , reduction–oxidation or oxidation–reduction )

2024-448: The words "REDuction" and "OXidation." The term "redox" was first used in 1928. Oxidation is a process in which a substance loses electrons. Reduction is a process in which a substance gains electrons. The processes of oxidation and reduction occur simultaneously and cannot occur independently. In redox processes, the reductant transfers electrons to the oxidant. Thus, in the reaction, the reductant or reducing agent loses electrons and

2070-467: Was developed by George Chen , Derek Fray , and Thomas Farthing between 1996 and 1997 at the University of Cambridge . (The name FFC derives from the first letters of the last names of the inventors). The intellectual property relating to the technology has been acquired by Metalysis, (Sheffield, UK). The process typically takes place between 900 and 1100 °C, with an anode (typically carbon) and

2116-433: Was seminal for subsequent work on thermodynamic aspects of redox and plant root growth in soils. Later work built on this foundation, and expanded it for understanding redox reactions related to heavy metal oxidation state changes, pedogenesis and morphology, organic compound degradation and formation, free radical chemistry, wetland delineation, soil remediation , and various methodological approaches for characterizing

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