Question

Consider the following redox reactions given below. Identify which of the following the example of a disproportionation reaction?

• A. $Cu+4HN{O}_3\to Cu(N{O}_3{)}_2+2N{O}_2+2H_{2}O$
• B. $3I_2+6O{H}^{-}\to I{O}_3^{-}+5I^{-}+3H_{2}O$
• C. $2ICl\to C{l}_2+I_2$
• D. $Zn+2HCl\to ZnC{l}_2+H_2$

Answer 1

The correct option is B $3I_2+6O{H}^{-}\to I{O}_3^{-}+5I^{-}+3H_{2}O$

Disproportionation reactions
The redox reaction in which an element from the same oxidation state changes to two different oxidation states (one lower and other higher)

(a) $\stackrel{0}{C}u+4H\stackrel{+5}{N}{O}_3\to \stackrel{+2}{C}u(N{O}_3{)}_2+2\stackrel{+4}{N}{O}_2+2H_{2}O$
$Cu$ is undergoing oxidation while $HN{O}_3$ is undergoing reduction, hence it is an intermolecular redox reaction.

(b)
$3I_2+6O{H}^{-}\to I{O}_3^{-}+5I^{-}+3H_{2}O$

$3{\stackrel{0}{I}}_2\to \stackrel{+5}{I}{O}_3^{-}$ oxidation
$3{\stackrel{0}{I}}_2\to \stackrel{-1}{I}{}^{-}$ reduction
here $I_2$ is undergoing oxidation as well as reduction.
So, this is a disproportionation reaction.

c) $2\stackrel{+1}{I}\stackrel{-1}{C}l\to \stackrel{0}{C}{l}_2+{\stackrel{0}{I}}_2$
$I_2$ is undergoing oxidation while $C{l}_2$ is undergoing reduction.In this case, oxidation and reduction takes place through a single molecule so it is a intramolecular redox reaction.

d) $\stackrel{0}{Z}n+2\stackrel{-1}{H}Cl\to \stackrel{+2}{Z}nC{l}_2+{\stackrel{0}{H}}_2$
$Zn$ is undergoing oxidation while $HCl$ is undergoing reduction, hence it is an intermolecular redox reaction.