Concept of Oxidation and Reduction





Electronic Concept of Oxidation and Reduction (Modern Concept)

The process in which any substance (atom, ion or molecule) loses one or more electrons is called oxidation. Thus, it is a deelectronation process. The substance which loses electrons is said to be oxidised.

E. g.

Zn \to Zn^2 + 2e^- \\ Fe^{2+} \to Fe^{3+} + e^- \\ 2Cl^- \to Cl_2 + 2e^-

 

The above reactions are known as oxidation half-reactions. In these reactions Zn, Fe^{2+} \text{and}Cl^- are oxidised to, Zn^{2+}, Fe^{3+} \text{and} Cl_2, respectively.

The process in which any substance (atom, ion or molecule) gains one or more electrons is called reduction. Thus it is an electronation process. The substance which gains electrons is said to be reduced.

E. g.

Cu^{2+} + e^- \to Cu^+ \\ 2H^+ + 2e^- \to H_2 \\ Cl + e^- \to Cl^-

 

The above reactions are known as reduction: half-reactions. In these reactions and Cu^{2+}, H^+ \text{and} Cl  are reduced to Cu^+, H_2 \text{and} Cl^- , respectively.

In brief, oxidation involves following things.

(i)  Addition of oxygen or other electro negative element.

2Mg + O_2 \to MgO [Mg is oxidised here]

(ii) Removal of H_2 or other electro positive element.

oxidation (iii) Increase of oxidation no.

(iv)  Loss of electrons. 2Fe^{+2}- e^- \to 2Fe^{3+}

  • During oxidation acidic nature increases.
  • Burning of coal, rusting of iron and combustion reactions involve oxidation.
  • Just reverse process occurs during reduction.

Oxidising and Reducing agents

A substance which oxidises others but itself undergoes reduction is known as oxidising agent or oxidant. Thus we can say that oxidising agent is an electron acceptor. A substance which undergoes oxidation but reduces others is known as reducing agent or reductant. In other words a reducing agent is an electron loser.

Some important oxidising agents are O_2, O_3, H_2O_2, Cl_2, HNO_3, KMnO_4, K_2Cr_2O_7 etc.

Some important reducing agents areH_2, C, H_2S, SO_2, SnCl_2, Al etc.



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