Question

What is meant by disproportionation? Give two examples of disproportionation reactions in aqueous solutions.

Answer 1

Hint: A disproportionation reaction is a type of chemical reaction. It includes oxidation as well as reduction but it is slightly different than a redox reaction. Among the products formed in a disproportionation reaction, one is the oxidised product and the other is the reduced product of the same element.

Complete step by step answer:
We can define disproportionation reaction as a redox reaction where both oxidation as well as reduction takes place from the same element/species i.e. the same element is oxidised as well as reduced and forms two or more different products.
In simpler words, we can explain it as a reaction where the same element is both reduced and oxidised at the same time to give us a two different products or, we can say that if the compound forms two products, one as a result of oxidation and other as a result of reduction, we can say it undergoes disproportionation.
Now, let us discuss examples of disproportionation reactions in aqueous medium.
Copper (I) compounds are unstable in aqueous medium thus undergo disproportionation forming copper (II) as well as copper (solid). We can write the reaction as-
     \[2C{{u}^{+}}(aq.)\to C{{u}^{2+}}+Cu(s)\]

As we can see, the oxidation number of copper is +1 and it undergoes disproportion and the oxidation number changes into +2 and 0.
Gallium chloride in aqueous solution undergoes a disproportionation reaction and gives us gallium (solid) and gallium(II). The reaction is-
     \[2GaCl(aq.)\to GaC{{l}_{2}}+Ga(s)\]

Note: Every disproportionation reaction is a redox reaction but every redox reaction is not a disproportionation reaction. Thus, disproportionation is a special case of a redox reaction. Certain compounds undergo disproportionation in order to gain higher stability which results from oxidation or reduction. Also we should remember that gain of electron is reduction and loss of electron is oxidation.