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Sep 6, 2018

Oxidation and reduction

Oxidation and reduction:

Oxidation and reduction reaction according to old concept:

Oxidation:

Oxidation has been classically defined as the combination of oxygen or any other electronegative element with another element or compound or as the removal of hydrogen or any other electro-positive element from chemical compound.

Oxidation Reduction Reactions with Examples
Process of Oxidation
Example:
1. Addition of Oxygen:

(a) When carbon burns in oxygen to produce carbon dioxide. Here oxygen is added with carbon to produce Carbon dioxide and carbon is considered to have been oxidised.
C O    CO
Oxidation Reduction Reactions with Examples
Oxidation of Carbon

(b) The magnesium metal reacts with chlorine to produce magnesium chloride. In this reaction magnesium is considered to have been oxidised.
Mg + O₂ MgO
(c) When Ferrous Oxide heated in oxygen to produce Ferric Oxide. Here Ferrous oxide is considered to have oxidised. 
4FeO + O₂ 2Fe₂O₃
2. Addition of electronegative element:
(a) When Chlorine gas passes through the colorless ferrous chloride solution it form yellow Ferric chloride. Here ferrous chloride oxidised by the addition of electronegative element chlorine.
2FeCl₂ + Cl₂ 2FeCl₃
3. Removal of Hydrogen:
(a) Manganese dioxide reacts with conc. Hydrochloric acid to produce greenish yellow chlorine gas.
Oxidation Reduction Reactions with Examples
Oxidation Reaction
Here hydrogen can remove from HCl to form chlorine gas, hence removal of hydrogen from HCl indicated that HCl can oxidised.
(b) Hydrogen Sulphide reacts with chlorine to produce Sulphur.
H₂S + Cl₂  2HCl + S
In the above reaction hydrogen can remove from hydrogen sulphide. Thus hydrogen sulphide oxidised to form sulphur. 
4. Removal of electro-positive elements:
Potassium iodide reacts with Hydrogen peroxide to produce iodine.
2KI + H₂O₂ 2KOH + I₂
In the above reaction electro-positive metal K can removes from KI to from iodine. Thus KI can oxidised.

Reduction:

Reduction has been classically defined as the combination of hydrogen or any other electro-positive element with another element or compound or as the removal of oxygen or any other electronegative element from chemical compound.
Oxidation Reduction Reactions with Examples
Process of Reduction
1. Addition of Hydrogen:
(a) Bromine can reacts with hydrogen to produce HBr.
Oxidation Reduction Reactions with Examples
Reduction of Bromine
In the above reaction Bromine can combination with hydrogen to produce hydrogen bromide. Thus bromine can reduced.
(b)Hydrogen Sulphide reacts with chlorine to produce Hydrogen chloride and Sulphur.
Oxidation Reduction Reactions with Examples
Oxidation Reduction Reaction
In the above reaction chlorine can combine with hydrogen. Thus chlorine can reduced.
2. Addition of electro-positive elements:
2K₃[Fe(CN)₆ + 2KOH + H₂O₂  2K₄[Fe(CN)₆] + 2H₂O + O₂
In the above reaction Potassium fericyanide combination with electro-positive element K to produce potassium freocyanide. Thus potassium fericyanide can reduced.
3. Removal of Oxygen:
When hydrogen can passes through black color heated CuO, Oxygen can removes from CuO to form red color Cu. Thus CuO can reduced.
CuO + H₂ Cu +H₂O
4. Removal of electro-negative elements:
Sulphur dioxide gas passes through yellow ferric sulfate solution it turns greenish ferus sulfate solution.
Fe₂(SO₄)₃ + 2SO₂ + H₂O 2FeSO₄ + 2H₂SO₄
In the above reaction ferric sulfate removes sulfate to form ferus sulfate. Thus ferric sulfate reduced to form ferus sulfate.

Electronic Concept of Oxidation and Reduction:

Oxidation:

According to Electronic concept, Oxidation is a process which results in the loss of one or more electrons by atoms or ions. Therefore an oxidizing agent is one that gains electrons and is then reduces to a lower valence.
Oxidation Reduction Reactions with Examples
Process of Oxidation 

1. Loss of Electron by Atom: 
Na, K, Ca, Al etc. can losses one or more electrons to from their respective cation.
Na Na⁺ + e
K K⁺ + e
Ca Ca⁺² + 2e
Al Al⁺³ + 3e 
All the above reaction the atoms can loses one or more electrons to form respective cations. Thus all the above reaction is oxidation reaction and all these atoms are oxidized.
2. Loss of Electron by Cation:

Fe⁺²(Ferrous), Cu⁺(Cuprous), Sn⁺²(Stannous) ion converted Fe⁺³(Ferric), Cu⁺²(cupric), Sn⁺⁴(Satanic) ion by losses one or more electrons. Thus these cations can oxidised.
Fe⁺² Fe⁺³ + e
Cu⁺ Cu⁺² + e
Sn⁺² Sn⁺⁴ + e
3. Loss of Electron by Anion:
Cl⁻(Chloride), Br⁻(Bromide), I⁻(Iodide), S⁻²(Sulphide) anion can losses one or more electrons to from respective elements. In these reaction these anion can oxidised. 
2Cl⁻ Cl₂ + e
2Br⁻ Br₂ + e
2I⁻ I₂ + e
S⁻² S + 2e 
From the above Examples we understand that oxidation is,
(i) Oxidation is a process for conversation of metal atom to cation.
(ii) Oxidation is a process for conversation lower valence cation to higher valence cation. 
(iii) Oxidation is a process for conversation of anion to neutral atom.

Reduction: 

According to Electronic concept, Reduction is a process which results in the gain of one or more electrons by atoms or ions. Therefore reducing agent is one that loses electrons and is oxidized to a higher valence.
Oxidation Reduction Reactions with Examples
Process of Reduction

1. Gain of Electron by Cation:
Na⁺, Cu⁺², Fe⁺², Fe⁺³ cations can gain one or more electrons to form respective metals.
Na⁺ + e Na
Cu⁺² + 2e Cu
Ca⁺² + 2e Ca
Al⁺³ + 3e Al 
2. Formation of Lower Valence cation from Higher Valence Cation:
Fe⁺³(Ferric), Cu⁺²(cupric), Sn⁺⁴(Satanic) ion gaining one or more electrons to form Fe⁺²(Ferrous), Cu⁺(Cuprous), Sn⁺²(Stannous) ion. Thus these cation can reduced.
Fe⁺³ + e Fe⁺²
Cu⁺² + e Cu⁺
Sn⁺⁴ + e Sn⁺² 
3. Accept of electrons by atom: 
Chlorine, Bromine, sulphur Oxygen can accept electron to from respective anion. In these reaction these anion can reduced.
Cl₂ + 2e Cl⁻
S + 2e S⁻²
O₂ +4e O⁻² 
From the above discussion it is clear that reduction reaction is reverse reaction of oxidation.