# JEE Main & Advanced Chemistry Redox Reactions Oxidation-Reduction And Redox Reactions

Oxidation-Reduction And Redox Reactions

Category : JEE Main & Advanced

(1) Oxidation : Oxidation is a process which involves; addition of oxygen, removal of hydrogen, addition of non-metal, removal of metal, Increase in +ve valency, loss of electrons and increase in oxidation number.

(i)  Addition of oxygen : 2Mg + O2 $\to$2MgO

(ii) Removal of hydrogen : H2S+Cl2$\to$2HCl + S

(iii) Addition of Non-metal : Fe + S $\to$ FeS

(iv) Removal of metal : 2KI+H2O2$\to$2KOH+I2

(v) Increase in +ve valency : $F{{e}^{2+}}\,\to \,F{{e}^{3+}}+{{e}^{-}}$

(vi) Loss of electrons (also known as de-electronation)

(a) ${{H}^{0}}\to {{H}^{+}}+{{e}^{-}}$            (Formation of proton)

(b) $MnO_{4}^{2-}\to MnO_{4}^{-}+{{e}^{-}}$      (De-electronation of $MnO_{4}^{2-}$)

(c) $2F{{e}^{0}}\to 2Fe_{{}}^{3+}+6{{e}^{-}}$      (De-electronation of iron)

(vii) Increase in oxidation number

(a) $M{{g}^{0}}\to M{{g}^{2+}}$                         (From 0 to +2)

(b) ${{\left[ F{{e}^{+2}}{{(CN)}_{6}} \right]}^{4-}}\to {{\left[ F{{e}^{+3}}{{(CN)}_{6}} \right]}^{3-}}$   (From +2 to +3)

(c) $2C{{l}^{-}}\to Cl_{2}^{0}$                             (From –1 to 0)

(2) Reduction : Reduction is just reverse of oxidation. Reduction is a process which involves; removal of oxygen, addition of hydrogen, removal of non-metal, addition of metal, decrease in +ve valency, gain of electrons and decrease in oxidation number.

(i) Removal of oxygen : $CuO+C\to Cu+CO$

(ii) Addition of hydrogen : $C{{l}_{2}}+{{H}_{2}}\to 2HCl$

(iii) Removal of non-metal

$2HgC{{l}_{2}}+SnC{{l}_{2}}\to H{{g}_{2}}C{{l}_{2}}+SnC{{l}_{4}}$

(iv) Addition of metal : $HgC{{l}_{2}}+Hg\to H{{g}_{2}}C{{l}_{2}}$

(v) Decrease in +ve valency

(a) $F{{e}^{3+}}\,\to \,F{{e}^{2+}}$     (+ve valency decreases)

(b) ${{[Fe\,{{(CN)}_{6}}]}^{3-}}\to {{[Fe{{(CN)}_{6}}]}^{4-}}$ (–ve valency increases)

(vi) Gain of electrons (also known as electronation)

(a) $Z{{n}^{2+}}(aq)+2{{e}^{-}}\to Zn(S)$ (Electronation of $Z{{n}^{2+}}$)

(b) $P{{b}^{2+}}+2{{e}^{-}}\to P{{b}^{0}}$ (Electronation of $P{{b}^{2+}}$)

(c) ${{[Fe{{(CN)}_{6}}]}^{3-}}+{{e}^{-}}\to {{[Fe{{(CN)}_{6}}]}^{4-}}$

(Electronation of ${{[Fe{{(CN)}_{6}}]}^{3-}}$)

(vii) Decrease in oxidation number

(a) $M{{g}^{2+}}\to M{{g}^{0}}$                         (From +2 to 0)

(b) ${{\left[ Fe{{(CN)}_{6}} \right]}^{3-}}\to {{\left[ Fe{{(CN)}_{6}} \right]}^{4-}}$               (From +3 to +2)

(c) $Cl_{2}^{0}\to 2C{{l}^{-}}$                             (From 0 to –1)

(3) Redox-reactions

(i) An overall reaction in which oxidation and reduction takes place simultaneously is called redox or oxidation-reduction reaction. These reactions involve transfer of electrons from one atom to another. Thus every redox reaction is made up of two half reactions; One half reaction represents the oxidation and the other half reaction represents the reduction.

(ii) Types of redox reaction

(a) Direct redox reaction : The reactions in which oxidation and reduction takes place in the same vessel are called direct redox reactions.

(b) Indirect redox reaction : The reactions in which oxidation and reduction takes place in different vessels are called indirect redox reactions. Indirect redox reactions are the basis of electro-chemical cells.

(c) Intermolecular redox reactions : In which one substance is oxidised while the other is reduced.

For example, $2\,Al+F{{e}_{2}}{{O}_{3}}\to A{{l}_{2}}{{O}_{3}}+2Fe$

Here, Al is oxidised to $A{{l}_{2}}{{O}_{3}}$ while $F{{e}_{2}}{{O}_{3}}$is reduced to Fe.

(d) Intramolecular redox reactions : In which one element of a compound is oxidised while the other is reduced.

For example, $2\,KCl{{O}_{3}}\xrightarrow{\Delta }2\,KCl+3\,{{O}_{2}}$

Here, $C{{l}^{+5}}$ in $KCl{{O}_{3}}$ is reduced to $C{{l}^{-1}}$ in KCl while ${{O}^{2-}}$ in $KCl{{O}_{3}}$ is oxidised to $O_{2}^{0}$.

##### Notes - Oxidation Reduction

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