Question
What is meant by ‘disproportionation’? Give two examples of disproportionation reaction in aqueous solution.
✓
Answer
A reaction in which the same species is simultaneously oxidised as well as reduced is called a disproportionation reaction.
Thus we can say taht disproportionation reaction is a special type of redox reaction. In which an element in one oxidation state simutaneously undergoes both oxidation and reduction. For example, Cr(V) and Mn(VI) species undergo disproportionation reaction in acidic medium as follows:
$3\text{CrO}^{3-}_4+8\text{H}^+\rightarrow2\text{CrO}^{2-}_4+\text{Cr}^{3+}+4\text{H}_2\text{O}$
(Cr in +5 o. s) (Cr in +6 o. s)
$3\text{MnO}^{3-}_4+4\text{H}^+\rightarrow2\text{MnO}^{2-}_4+\text{MnO}_2+2\text{H}_2\text{O}$
Mn in +6 o.s +7 o.s 4 o. s
Here, we can say that Cr in + 5 oxidation state undergo disproportionation into its +6 and +3 states. Similarly, Mn in +6 oxidation state undergo disproportionation into +7 and +4 oxidation states.
Thus we can say taht disproportionation reaction is a special type of redox reaction. In which an element in one oxidation state simutaneously undergoes both oxidation and reduction. For example, Cr(V) and Mn(VI) species undergo disproportionation reaction in acidic medium as follows:
$3\text{CrO}^{3-}_4+8\text{H}^+\rightarrow2\text{CrO}^{2-}_4+\text{Cr}^{3+}+4\text{H}_2\text{O}$
(Cr in +5 o. s) (Cr in +6 o. s)
$3\text{MnO}^{3-}_4+4\text{H}^+\rightarrow2\text{MnO}^{2-}_4+\text{MnO}_2+2\text{H}_2\text{O}$
Mn in +6 o.s +7 o.s 4 o. s
Here, we can say that Cr in + 5 oxidation state undergo disproportionation into its +6 and +3 states. Similarly, Mn in +6 oxidation state undergo disproportionation into +7 and +4 oxidation states.
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