Classical Idea of oxidation and Reduction


Definition 1: Addition of oxygen or an electronegative element to a substance.
2Mg (s) + O2 (g) 2MgO (s) (oxidation of Mg)
S + O2 SO2 (oxidation of S)
Fe + S FeS (oxidation of Fe)
Mg + F2 MgF2 (oxidation of Mg)
Definition 2: Removal of hydrogen or some electropositive element from a substance.
H2S + Cl2 2HCl + S (oxidation of H2S)
4HI + O2 2H2O + 2I2 (oxidation of HI)
H2O2 + 2KI 2KOH + I2 (oxidation of KI)
2KI + Cl2 2KCl + I2 (oxidation of KI)


Definition 1: Removal of oxygen or some electronegative element from a substance.
2HgO 2Hg + O2
2HgCl2 + SnCl2 Hg2Cl2 + SnCl4
(Reduction of HgCl2)
2FeCl3 + H2 2FeCl2 + 2HCl
(Reduction of FeCl3)
Definition 2: Addition of hydrogen or some electropositive element to a substance.
Cl2 + H2 2HCl (Reduction of Cl2)
C2H4 + H2 C2H6 (Reduction of C2H4)
HgCl2 + Hg Hg2Cl2 (Reduction of Hg Cl2)
CuCl2 + Cu Cu2Cl2 (Reduction of CuCl2)

Modern Concept of oxidation and Reduction

According to the modern concept, loss of electrons (de-electronation) is oxidation whereas gain of electrons is reduction. (Electronation).
Example of oxidation reactions are:
Na Na+ + e
Zn Zn+2 + 2e
Examples of reduction reactions are:
Cl2 + 2e 2Cl
S + 2e S2–
Oxidation and reduction can be represented in a general way as follows
Picture 8
oxidation and reduction
All oxidation and reduction reactions are complementary to one another and occur simultaneously, one cannot take place without the other. The simultaneous oxidation and reduction reactions are termed as redox reactions.
Since reduction and oxidation reactions go hand in hand, no. of electrons gained must be equal to no. of electrons lost.
Oxidation: B B+3 + 3e
Reduction: A+2 + 2eA
To make electrons lost and gained equal, we multiply first reaction by 2 and second reaction by 3 and we get overall reaction as
Picture 1
Redox Reaction

Oxidising Agent and Reducing Agent

Oxidising Agent or Oxidant:
A substance which brings oxidation is known as oxidising agent.
It is a substance which can accept electrons from other substances.
Reducing Agent or Reductant:
A substance which brings reduction is known as reducing agent.
It is a substance which can lose electrons to other substances.
Write the half reactions and identify the oxidising and reducing agents.
2Fe+3 (aq) + 2I (aq) 2Fe+2 (aq) + I2 (aq)
Solution: Oxidation Half Reaction: 2I I2 + 2e
Reduction Half Reaction: 2Fe+3 + 2e 2Fe+2
Oxidising agent: Fe+3
Reducing agent: I

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