Oxidation and reduction reactions

What is the oxidation and reduction reactions?

Oxidation and reduction reactions are always found to go hand in hand during redox reactions. Whenever an element or compound oxidized, another element or compound must be simultaneously reduced. Thus oxidizing agents reduced but reducing agents oxidized.

Definition of the oxidation-reduction reactions

oxidation reduction reactions
oxidation and reduction

Classically oxidation has defined as the combination of oxygen or electronegative element with another element or compound or as the removal of hydrogen or electropositive element from a chemical compound.

In the same way, the reduction has defined as the combination of hydrogen or electropositive element with another element or compound or as the removal of oxygen or electronegative element from a chemical compound.

The electronic structure of elements gives the quantitative relations between classical and electronic concept oxidation-reduction.

2Mg + O2 ⇆ 2MgO

On the above reaction magnesium metal burns in oxygen to produce magnesium oxide with the addition of oxygen. Thus the balanced chemical equations of the above reaction

2Mg → 2Mg+2 + 4e
O2 + 4e → 2O-2

In this reaction, oxygen led to the removal of two electrons from zerovalent magnesium metal by forming magnesium(II) ion. On the other hand, the lost electrons accept oxygen by forming oxide ion.

Thus shows that the classical definition of oxidation-reduction has an intimate connection with the electronics concept.

Examples of oxidation reactions

Combination of oxygen

  • Carbon burns in oxygen to produce carbon dioxide. Here oxygen forming chemical bonds with carbon to produce carbon dioxide. Thus carbon can be oxidized.

C + O2 ⇆ CO2

  • Magnesium metal reacts with chlorine to produce magnesium chloride. In this reaction, magnesium combines with oxygen to produced magnesium oxide. Thus magnesium can be oxidized.

Mg + Cl2 ⇆ MgCl2

  • When ferrous oxide heated in oxygen to produce ferric oxide. Here ferrous oxide oxidized.

4FeO + O2 ⇆ 2Fe2O3

Combination of electronegative element

When Cl2 passes through the colorless FeCl2 solution, it turns red FeCl3. This is the example of oxidation, by the addition of the electronegative elements.

2FeCl2 + Cl2 ⇆ 2FeCl3

Removal of hydrogen example

  • When MnO2 reacts with concentrated HCl, it produces greenish-red Cl2 gas. Here hydrogen can be removed from HCl to form Cl2, hence the removal of hydrogen means oxidation. Thus HCl can be oxidized.

4HCl + MnO2 ⇆ MnCl2 + Cl2 + H2O

  • H2S reacts with Cl2 to produce sulfur. In this reaction, remove hydrogen from H2S. Thus H2S oxidized to form sulfur.

H2S + Cl2 ⇆ 2HCl + S↓

Removal of electro-positive elements

When KI reacts with H2O2, it produces iodine. Here electro-positive potassium removes from KI to form iodine. Thus KI can be oxidized.

2KI + H2O2 ⇆ 2KOH + I2

Examples of reduction reactions

Addition of hydrogen

  • When bromine reacts with hydrogen,  it produces hydrogen bromide. Here bromine combines with hydrogen to produce hydrogen bromide.

H2 + Br2 ⇆ 2HBr

  • When H2S reacts with chlorine to produce hydrogen chloride and sulfur. Here chlorine combines with hydrogen and reduced.

H2S + Cl2 ⇆ HCl + S↓

Addition of electro-positive elements


In the above reaction potassium ferricyanide combine with electro-positive element potassium to produce potassium ferrocyanide. Thus potassium ferricyanide reduced.

Removal of oxygen reduction

When hydrogen passes through black heated CuO, oxygen removes from CuO to form red copper. Thus CuO is reduced.

CuO + H2 ⇆ Cu +H2O

Removal of electro-negative elements

When SO2 passes through a red ferric sulfate solution, it turns into a greenish ferrous sulfate solution.

Fe₂(SO₄)₃ + 2SO₂ + H₂O ⇆ 2FeSO₄ + 2H₂SO₄

In the above reaction, electronegative sulfate removes form ferric sulfate. Thus ferric sulfate reduced to form ferrous sulfate.