OXIDATION & REDUCTION

Classical Idea of oxidation and Reduction

Oxidation:

Definition 1: Addition of oxygen or an electronegative element to a substance.

Example:

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.

Example:

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)

Reduction:

Definition 1: Removal of oxygen or some electronegative element from a substance.

Example:

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.

Example:

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^–  S^2–

Oxidation and reduction can be represented in a general way as follows

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 + 2e^–A

To make electrons lost and gained equal, we multiply first reaction by 2 and second reaction by 3 and we get overall reaction as

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.

Example:

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^–

OXIDATION & REDUCTION