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Encyclopedia > Reducing agent

A reducing agent (also called a reductant or reducer) is the element or a compound in a redox (reduction-oxidation) reaction (see electrochemistry) that reduces another species. In doing so, it becomes oxidized, and is therefore the electron donor in the redox. For example consider the following reaction: Semi-accurate illustration of a redox reaction Redox reactions include all chemical processes in which atoms have their oxidation number (oxidation state) changed. ... English chemists John Daniell (left) and Michael Faraday (right), both credited to be founders of electrochemistry as known today. ... Chemical species is a common, general name for atoms, molecules, molecular fragments and ions as entities being subjected to a chemical process or to a measurement. ... An electron donor is a compound that gives up or donates an electron during cellular respiration, resulting in the release of energy. ...

2Mg(s) + O2 → 2Mg2+(s) + 2O2-

The reducing agent in this reaction is magnesium. Magnesium donated its two valence electrons, has become an ion, and allows itself as well as oxygen to become stable. General Name, Symbol, Number magnesium, Mg, 12 Chemical series alkaline earth metals Group, Period, Block 2, 3, s Appearance silvery white Atomic mass 24. ... In chemistry, valence, also known as valency or valency number, is a measure of the number of chemical bonds formed by the atoms of a given element. ... Multivalent redirects here. ... General Name, Symbol, Number oxygen, O, 8 Chemical series Nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance colorless (gas) very pale blue (liquid) Atomic mass 15. ...


Reducing agents need to be protected from air because they react with oxygen.

Contents

What makes a strong reducing agent?

Strong reducing agents easily lose (or donate) electrons. The atomic nucleus attracts its orbiting electrons. For elements whose atoms have relatively large atomic radii, the distance from the nucleus to the electrons is greater and its attraction for them weaker; these elements tend to be strong reducing agents. Also, elements that have a low electronegativity, “the ability of an atom or molecule to attract bonding electrons”1, and relatively small ionization energies serve as good reducing agents too. "The measure of a material to oxidize or lose electrons is known as its oxidation potential"2. The table below shows a few reduction potentials that could easily be changed to oxidation potential by simply changing the sign. Reducing agents can be ranked by increasing strength by ranking their oxidation potentials. The reducing agent will be the strongest when it has a more positive oxidation potential and will be a weak reducing agent whenever it has a negative oxidation potential. The following table provides the reduction potentials of the indicated reducing agent at 25° C. Also remember the useful mnemonic device, OILRIG which means, Oxidation Is Loss (of electrons) and Reduction Is Gain (of electrons). Electronegativity is a measure of the ability of an atom or molecule to attract electrons in the context of a chemical bond. ... The ionization energy (IE) of an atom or of a molecule is the energy required to strip it of an electron. ...

Oxidizing Agent Reducing Agent Reduction Potential (v)
Li+ + e- = Li -3.04
Na+ + e- = Na -2.71
Mg+2 + 2e- = Mg -2.38
Al+3 + 3e- = Al -1.66
2H2O(l) + 2e- = H2(g) + 2OH - -0.83
Cr+3 + 3e- = Cr -0.74
Fe+2 + 2e- = Fe -0.41
2H+ + e- = H2 0.00
Sn+4 + 2e- = Sn+2 +0.15
Cu+2 + e- = Cu+ +0.16
Ag+ + e- = Ag +0.80
Br2 + 2e- = 2Br- +1.07
Cl2 + 2e- = 2Cl- +1.36
MnO4-2 + 8H+ + 5e- = Mn+2 + 4H2O +1.49

In order to tell which is the strongest reducing agent, change the sign of its respective reduction potential in order to make it oxidation potential. The bigger the number the stronger a reducing agent it is.


For example if you were to list Cu, Cl-, Na and Cr in order, you get their reduction potential, change the sign to make it oxidation potential and list them from greatest to least. You will get Na, Cr, Cu and Cl-; Na being the strongest reducing agent and Cl- being the weakest one.


A few good common reducing agents include active metals such as potassium, calcium, barium, sodium and magnesium and also, compounds that contain the H- ion, those being NaH, LiAlH4 and CaH2.


Also, some elements and compounds can be both reducing or oxidizing agents. Hydrogen gas is a reducing agent when it reacts with non-metals and an oxidizing agent when it reacts with metals. European Union Chemical hazard symbol for oxidizing agents Dangerous goods label for oxidising agents An oxidizing agent (also called an oxidant or oxidizer) is referred to as A chemical compound that readily transfers oxygen atoms or A substance that gains electrons in a redox chemical reaction. ...


2Li(s) + H2(g) -->2LiH(s) hydrogen acts as an oxidizing agent because it accepts an electron donation from lithium, which causes Li to be oxidized.


Half Reactions 2Li(s)0 -->2Li(s)+1 + 2e-::::: H20(g) + 2e- --> 2H-1(g)


H2(g) + F2(g) --> 2HF(g) hydrogen acts as a reducing agent because it donates its electrons to fluorine, which allows fluorine to be reduced.


Half Reactions H20(g) --> 2H+1(g) + 2e-::::: F20(g) + 2e- --> 2F-1(g)


The Importance of Reducing and Oxidizing Agents

Reducing agents and Oxidizing agents are the ones responsible for corrosion, which is the “degradation of metals as a result of electrochemical activity”3. Corrosion requires an anode and cathode to take place. The anode is an element that loses electrons (reducing agent), thus oxidation always occurs in the anode, and the cathode is an element that gains electrons (oxidizing agent), thus reduction always occurs in the cathode. Corrosion occurs whenever there’s a difference in oxidation potential. When this is present, the anode metal will begin deteriorating given that there is an electrical connection and the presence of an electrolyte. Corrosion is deterioration of intrinsic properties in a material due to reactions with its environment. ... Diagram of a zinc anode in a galvanic cell. ... Diagram of a copper cathode in a Daniells cell. ... An electrolyte is a substance containing free ions which behaves as an electrically conductive medium. ...


Common reducing agents

Lithium aluminium hydride (LiAlH4), commonly abbreviated to LAH, is a powerful reducing agent used in organic chemistry. ... In chemistry, nascent hydrogen is non- ionised, monatomic hydrogen (H0) that exists transiently after the reduction of hydrogen ions. ... Potassium ferricyanide (K3[Fe(CN)6]) also known as red prussiate, Prussian red or potassium hexacyanoferrate(III), is a coordination compound that is stable at room temperature and pressure and forms ruby red crystals and powder. ... In chemistry, sodium amalgam is an amalgam, or alloy of mercury, with sodium metal. ... Sodium borohydride, also known as sodium tetrahydridoborate, has the chemical formula NaBH4 (CAS 16940-66-2). ... A space-filling model of the sulfite anion Sulfites (also sulphite) are compounds that contain the sulfite ion SO32−. They are often used as preservatives in wines (to prevent spoilage and oxidation), dried fruits, and dried potato products. ... Hydrazine is the chemical compound with formula N2H4. ... The Wolff-Kishner reduction is a chemical reaction that fully reduces a ketone (or aldehyde) to an alkane. ... The Clemmensen reduction is a chemical reaction aimed at reducing carbonyl groups of aldehydes and ketones to -CH2- groups. ... DIBAH (Diisobutylaluminum hydride) is a reducing agent, useful in reducing esters to aldehydes. ... A Lindlar catalyst is a palladium heterogeneous catalyst on calcium carbonate poisoned or deactivated or conditioned by lead acetate. ... Oxalic acid (IUPAC name: ethanedioic acid, formula C2H2O4) is a dicarboxylic acid with structure (HOOC)-(COOH). ...

Common reducing agents and their products

Agent Product
H2 Hydrogen H+, H2O
metals metal ions
C CO2 carbon dioxide
hydrocarbons CO2 carbon dioxide, H2O

This article is about the chemistry of hydrogen. ... == // IGOR ROCKS!!!!!!!!!!!!!!! == Carbon dioxide is a chemical compound composed of one carbon and two oxygen atoms. ... In chemistry, a hydrocarbon is a cleaning solution consisting only of carbon (C) and hydrogen (H). ... == // IGOR ROCKS!!!!!!!!!!!!!!! == Carbon dioxide is a chemical compound composed of one carbon and two oxygen atoms. ...

See also

European Union Chemical hazard symbol for oxidizing agents Dangerous goods label for oxidising agents An oxidizing agent (also called an oxidant or oxidizer) is referred to as A chemical compound that readily transfers oxygen atoms or A substance that gains electrons in a redox chemical reaction. ... Electronegativity is a measure of the ability of an atom or molecule to attract electrons in the context of a chemical bond. ... English chemists John Daniell (left) and Michael Faraday (right), both credited to be founders of electrochemistry as known today. ... Corrosion is deterioration of intrinsic properties in a material due to reactions with its environment. ... An electrolyte is a substance containing free ions which behaves as an electrically conductive medium. ...

External links

  • Table summarizing strength of reducing agents

Sources


 
 

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