Oxidation-Reduction/unit-8

Oxidation:

Oxidation is a process in which there is a loss of one or more electrons by an atom or groups of atoms. For examples,

• Na     ——> Na⁺  + e^–
• Fe⁺²  ——> Fe⁺³  + e^–
• Sn⁺²  ——> Sn⁺⁴  + 2e^–

Reduction:

Reduction is a process in which there is a gain of one or more electrons by an atom or groups of atoms. For examples,

• MnO₄^–    + e^–  ——>  MnO₄^-2
• Fe⁺³ + e^–   ——> Fe⁺²
• Sn⁺⁴  + 2e^–  ——> Sn⁺²

Oxidising agent or Oxidant:

An oxidizing agent is a substance which can accept one or more electrons readily. For examples, KMnO₄, K₂Cr₂O₇, Fe⁺³-ions, Sn⁺⁴-ion, etc.

• Fe⁺³ + e^– ——>  Fe⁺²
• Sn⁺⁴  + 2e^– ——> Sn⁺²

Reducing agent or Reductant: A reducing agent or reductant is a substance which can donate or loose one or more electrons. For example, Fe⁺²– ion, Sn⁺²-ion, etc.

Redox Reaction:

Since oxidation involves loss of electrons and reduction involves gain of electrons, it is evident that if one substance loses electrons, another substance at the same time must gain electrons because electrons cannot be the products in any chemical change. This means that in any process, oxidation can occur only if reduction is also taking place side by side and vice versa. Thus, neither oxidation, nor reduction can occur alone. The reaction which involves the simultaneous oxidation and reduction called redox reactions.  A complete redox reaction can be written in terms of oxidation half and reduction half. For example, consider a reaction between zinc and copper ions.

In this reaction zinc atoms lose electrons and are oxidised to zinc ions (Zn⁺²) whereas cupric ions (Cu⁺²) gain electrons and are reduced to copper atoms. Thus, cupric ions act as oxidising agent and zinc atoms act as reducing agent. In fact, the oxidising agent gets reduced while reducing agent gets oxidised during the redox reactions.

Oxidation and Reduction Half Reactions:

Every redox reaction can be split up into two half reactions, one representing loss of electrons i.e., oxidation half reaction while the other representing gain of electrons, i.e., reduction half reaction. For examples,

The reaction: Zn   +  Cu⁺² ——>  Zn⁺²   + Cu, can be split up into two half reaction as

Zn  —–>  Zn⁺²  + 2e^–       (Oxidation half reaction)

Cu⁺²  +  2e^– ——> Cu       (Reducing half reaction)

Note:

Oxidation: Process involving loss of one or more electrons.
Reduction: Process involving gain of one or more electrons.
Oxidising agents: Species which gain one or more electrons.
Reducing agents: Species which lose one or more electrons.