Question

a) Compute oxidation number of underlined elements in the following
${Na}_2{S}_2{O}_7$ ${KI}_3$
b) What is disproportionation reaction? ${ClO}_3^{-}$ does shows disproportionation but ${ClO}_4^{-}$ does not, explain.

Answer 1

(a) $N{a}_2{S}_2{O}_7$

Let oxidation state of $S$ be $x$

$\therefore 2(+1)+2\left(x\right)+7(-2)=0$

$\Rightarrow 2x-12=0$

$\Rightarrow x=+6$

$K{I}_3$

Let oxidation state of $I$ be $x$

$\therefore 1(+1)+3\left(x\right)=0$

$\Rightarrow 1+3x=0$

$\Rightarrow x=-1/3$

(b) Disproportionation is a redox reaction in which a compound of intermediate oxidation state gets converted into $2$ different compounds one of higher & one of lower oxidation states.

In $Cl{O}_4^{-}$ oxidation state of $Cl$ is already the highest i.e. $+7$ & hence cannot be further oxidized. But in $Cl{O}_3^{-}$ it is $+5$ & can be further oxidized.