Oxidation and Reduction

Oxidation:

Term oxidation was used to describe the addition of oxygen to an element or a compound. Because of the presence of dioxygen in the atmosphere many elements combine with it and this is the principal reason why they commonly occur on the earth in the form of their oxides. The following reactions represent oxidation processes according to the limited definition of oxidation:

2 Mg (s) + O2 (g) → 2 MgO (s)

S (s) + O2 (g) → SO2 (g)

In these two reaction magnesium and sulphur are oxidised on account of addition of oxygen to them.

Reduction:

Reduction was considered as removal of oxygen from a compound. The following are the examples of reduction processes:

2HgO (s) → 2Hg (l) + O2 (g)

(removal of oxygen from mercuric oxide)

There are some rules which will define the oxidation and reduction reaction process.

1.     Addition of oxygen in a species is called oxidation of that species and removal of oxygen from a species is called reduction.

2.     Removal of hydrogen from an element is called oxidation and addition of hydrogen is called reduction.

3.     Oxygen is electronegative species. So, if an electronegative species add from an element then it is called oxidation and opposite if an electronegative species removes from an element then it is called reduction.

4.     Similarly, hydrogen is electropositive species. So if an electropositive species is removed from an element then the reaction is called oxidation and if an electropositive species is added then it is called reduction.

5.     If an element loss their electron then the reaction is called oxidation, and if an element gains some electron then the reaction is called reduction.

In short manner, if we want to say:

Oxidation

Reduction

1.     Addition of oxygen

      1. Removal of oxygen

2.     Removal of hydrogen

2. Addition of hydrogen

3.     Addition of an electronegative element

3. Removal of an      electronegative element

4.     Removal of an electropositive element

4. Addition of an electropositive element

5.     Loss of electron

5. Gain of electron

Here we are giving some example of oxidation and reduction on basis of above five bullet points.

Example: -

CH4 (g) + 2O2 (g) → CO2 (g) + 2H2O (l)

2 H2S(g) + O2 (g) → 2 S (s) + 2 H2O (l)

Mg (s) + F2 (g) → MgF2 (s)

Mg (s) + Cl2 (g) → MgCl2 (s)

Mg (s) + S (s) → MgS (s)

2K4 [Fe(CN)6 ](aq) + H2O2 (aq) →2K3 [Fe(CN)6 ](aq) + 2 KOH (aq)

2 FeCl3 (aq) + H2 (g) →2 FeCl2 (aq) + 2 HCl(aq)

(removal of electronegative element, chlorine from ferric chloride)

CH2 = CH2 (g) + H2 (g) → H3C – CH3 (g)

(addition of hydrogen)

2HgCl2 (aq) + SnCl2 (aq) → Hg2Cl2 (s) + SnCl4 (aq)

(addition of mercury to mercuric chloride)