The reduction It is all that chemical reaction where the atoms of one of the reactants end up gaining electrons; What can also be seen this way: your vacancy or electronic "discomfort" is reduced. An atom gains electrons when a species donates them; that is, it rusts.
This type of reaction cannot happen by itself: if one species accepts the electrons, another must necessarily give them up. Otherwise, matter would be being created from nothing, reducing the atoms after gaining electrons from the vacuum. Therefore it is a redox half reaction (reduction / oxidation).
An illustrative example of the reduction that can be shown in classrooms is the reaction between a metallic surface of copper, and an aqueous solution of silver nitrate, AgNO3.
In solution, silver is found as cations Ag+, positively charged. These, by interacting with the surface of the copper, shaped like a Christmas tree, snatch the electrons from the copper atoms. When this occurs, copper replaces silver in the nitrate salt; and as a result, copper nitrate, Cu (NO3)two.
Cu cationstwo+ next to NO3- turn the solution bluish; and silver, whitens the Christmas tree as if it covered it with snow.
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In reduction it has already been said that a species gains electrons. How can this be verified in a chemical equation? For example, in the equation for the reaction between Cu and AgNO3, How to know when the reduction occurs? To verify it, it is necessary to determine the number or oxidation state.
The elements in their natural states, have by definition an oxidation state equal to zero, since it is assumed that they have neither lost nor gained electrons. Thus, solid metals have zero oxidation state. Thus, the silver goes from +1 (Ag+) to 0 (Ag). The charge of a metal ion is equal to its oxidation state.
On the other hand, the electrons came from copper: going from 0 (Cu) to +2 (Cutwo+). Nitrate anion, NO3- remains unchanged while both metals exchange electrons; therefore, the equation can be written as:
2Ag+ + Cu => 2Ag + Cutwo+
Notice that both charges and atoms are balanced..
This is what chemical reduction consists of: in the gain of electrons that make the oxidation states of the atoms less positive than that of the electrons..
Oxygens are very electronegative and oxidizing atoms, so when an atom forms compounds with them (like oxides), they have positive oxidation states. The greater the number of oxygens interacting with the atom, the more positive its oxidation state will be; or what is the same, it is more rusty.
Therefore, when a compound has fewer oxygen atoms, it is said to be less oxidized; that is, the atom loses fewer electrons.
A classic example can be seen in carbon monoxide and carbon dioxide. For CO, carbon has an oxidation state of +2; while for the COtwo, its oxidation state is +4.
So, if in a reaction the COtwo it transforms to CO, a reduction is said to be occurring; since, carbon now interacts with one oxygen and not two. For the opposite reaction, CO transforming into COtwo, there is talk of an oxidation of carbon.
This applies to all atoms, especially metals in their metal oxides; for example, CrOtwo (Cr4+) and CrO3 (Cr6+).
In chemical equations where one species loses oxygen while the other species gains it, an oxygen transfer is said to occur.
You can always determine if there was a reduction by changing the oxidation state to a less positive value. As just explained, a quick way to notice without even doing the math is by observing if there is a decrease in oxygen atoms in a compound..
The same can happen with any other atom that is more electronegative than the atom that gains or loses electrons.
For example, if the CF4 reacts in such a way that it becomes CH4, a reduction is then said to have occurred; since fluorine is much more electronegative than the hydrogen atom. As a result, the carbon is less oxidized in the CH4 that in the CF4, which is equal to saying that it has been reduced.
The CF example4 and CH4 it reflects what happens in organic reactions, where the reduction of the partial charge of an atom is considered as an electronic gain. This applies a lot when considering the reduction of oxygenated functional groups..
For example, consider the groups ROH, RCHO, and COOH. The first corresponds to alcohols, where carbon bonds with oxygen (C-OH); the second is the aldehyde group, where carbon forms a double bond with oxygen and is also bonded to hydrogen (C = O-H); and the third is the carboxyl group.
In the carboxyl group, carbon forms a double bond with one O, and a single bond with another O (HO-C = O).
Therefore, a reduction occurs if a carboxylic acid is transformed into an alcohol:
RCOOH => ROH
Chemical reduction is extremely important in the processes of extracting metals from their minerals. Some of the reactions are:
HgS + Otwo => Hg + SOtwo
Mercury sulfide is reduced to metallic mercury.
CutwoS + Otwo => 2Cu + SOtwo
Copper sulfide is reduced to metallic copper.
2ZnS + 3Otwo => 2ZnO + 2SOtwo
ZnO + C => Zn + CO (note the transfer of O)
Zinc sulfide is first reduced to its monoxide and then to its metallic form.
FaithtwoOR3 + 3CO => 2Fe + 3COtwo
Ferric oxide is reduced to metallic iron.
WO3 + 3Htwo => W + 3HtwoOR
And tungsten trioxide is reduced to metallic tungsten.
As an exercise, the oxidation number of the metal can be determined before it is reduced.
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