Lecture 5 – RedOx Reactions

Redox reactions:

Redox reactions are those reactions in which both REDuction and OXidation takes place.

Figure 6:

 

Examples:

i.                    Rusting of Iron:

Before reaction:

Oxidation state of Fe in Fe= 0

Oxidation state of O in O₂ = 0

After rusting:

Oxidation state of Fe in Fe₂O₃ = +3

Oxidation state of O in Fe₂O₃ = -2

Oxidation state of Iron increases from 0 to +3. (Oxidation)

Oxidation state of Oxygen decreases from 0 to -2. (Reduction)

ii.                  Displacement reaction in metals:

Before reaction:

Oxidation state of Zn in Zn= 0

Oxidation state of Cu in CuSO₄ = +2

Oxidation state of SO₄ in CuSO₄ = -2

After reaction:

Oxidation state of Zn in ZnSO₄ = +2

Oxidation state of Cu in Cu = 0

Oxidation state of SO₄ in CuSO₄ = -2

Oxidation state of Zinc increases from 0 to +2. (Oxidation)

Oxidation state of Copper decreases from +2 to 0. (Reduction)

iii.                Replacement reaction in halogens:

Before reaction:

Oxidation state of Cl in Cl₂= 0

Oxidation state of I in KI = -1

Oxidation state of K in KI = +1

After reaction:

Oxidation state of Cl in KCl= -1

Oxidation state of I in I₂ = 0

Oxidation state of K in KCl = +1

Oxidation state of Iodine increases from -1 to 0. (Oxidation)

Oxidation state of Chlorine decreases from 0 to -1. (Reduction)

Note: the oxidation state that remain unchanged during the reaction like Sulphate’s and Potassium’s in example ii and iii, respectively are not mentioned.