In our daily life we come across processes like rusting of iron articles, fading of the colour of the clothes, burning of the combustible substances such as cooking gas, wood, coal, etc. All these processes fall in the category of redox reactions. A large number’ of industrial processes like, electroplating, extraction of metals like aluminium and sodium, bleaching of wood pulp, manufacture of caustic soda, etc., are also based upon the redox reactions: Redox reactions also form the basis of electrochemical and electrolytic cells. In the present unit we shall understand the meaning of oxidation, reduction, oxidising agents and reducing agents.
CLASSICAL CONCEPT OF OXIDATION AND REDUCTION
According to classical concept following definitions were proposed to explain the process of oxidation and reduction.
Oxidation: It is a process of chemical addition of oxygen or any electronegative radical or removal of hydrogen or any electropositive radical.
Reduction: It is a process of chemical addition of hydrogen or any electropositive radical or removal of oxygen or any electronegative radical.
Some examples of oxidation and reduction reactions are given below:
(i) Peaction of PbO and carbon
Here, oxygen is being removed from lead oxide (PbO) and is being added to carbon (C). Thus, PbO is reduced while C is oxidised.
(ii) Reaction of H2S and Cl2
Here, hydrogen is being removed from hydrogen sulphide (H2S) and is being added to chlorine (C2S). Thus, H2S is oxidised and Cl2 is reduced.
(iii) Reaction between Mg and F2
Here, electronegative radicals fluoride ion (p) is added to magnesium while electropositive radical Mg2+ is added to fluorine. Hence, Mg is oxidised and F2 is reduced.
Looking at all the reactions given above we observe that oxidation and reduction occurs simultaneously, hence the word “redox” was coined for this class of chemical reactions.