Oxidation & Reduction
Antoine Lavoisier first discovered the process of oxidation in 1772 A.D. His observation of combustion prompted definition of oxidation as any reaction between elements or compounds and oxygen as oxidation. Further, in 20th century it was explained as a process of loss of electrons is called oxidation as (shown in fig 1). Paradoxically, both oxidation and reduction reaction occurs simultaneously. By definition the process of gaining of electron by element or compound during a reaction is called reduction. Moreover, the process of transfer of hydrogen is also classified as reduction reaction. And collectively these reactions are also called as redox reactions.
Figure 1a: Oxidation reaction of magnesium-to-magnesium dioxide; figure 1b: Ionic representation for reduction reaction and figure 1b: oxidation of phosphorus-to-phosphorus oxide.
2Mg+O2 2MgO ——— — (1a)
[2Mg+O2 2[Mg+2] [O2-] —— — (1b)
P4+ 5O2 P4O10 ———— (1c)
Moreover, it was further observed that there was no change in the valence electrons on any atom when carbon dioxide reacts with hydrogen gas to form carbon monoxide and water (as shown in fig 2).
CO2+H2 CO+H2O ———— (2a)
O=C=O + H-H O + H-O-H ———— (2b)
Hence, a concept of oxidation number came into existence. Here, oxidation was process was defined as process of increasing the oxidation number of an atom.Whereas the process of reduction of oxidation number of an atom is called reduction. Oxidation number of an atom is defined, as the charge of an atom would have if the compound were in its ionic state. Oxidation state of a neutral compound is zero. Change in oxidation state of compounds during a reaction
determines the oxidized or reduced state of compounds.
These reactions are the most fundamental processes, which has both commercial and vital importance sustaining life on earth. Oxidation of ethanol is one the metabolic pathways responsible for elimination of alcohol from body. Oxidizing agents can be classified as weak and stronger oxidizer depending upon their ability to provide oxygen during the reaction. Materials like hydrogen peroxide (H2O2), acid chromates (HClO4-), hypocholorus acid (HClO), and potassium permanganate are strong oxidizing agents. Moreover, halogens are also considered to be the oxidizing agents as shown from the reactions where there is change in the oxidation states. As mentioned previously hydrogen reactions are also called as reduction reaction.