JEE MAIN - Chemistry (2022 - 29th July Morning Shift - No. 7)
In neutral or faintly alkaline medium, $$\mathrm{KMnO}_{4}$$ being a powerful oxidant can oxidize, thiosulphate almost quantitatively, to sulphate. In this reaction overall change in oxidation state of manganese will be :
5
1
0
3
Explanation
In neutral or Faintly alkaline medium, thiosulphate is oxidised almost quantitatively to sulphate ion according to reaction given below,
$8 \mathrm{MnO}_{4}^{-}+3 \mathrm{~S}_{2} \mathrm{O}_{3}^{2-}+\mathrm{H}_{2} \mathrm{O} \rightarrow 8 \mathrm{MnO}_{2}+6 \mathrm{SO}_{4}^{2-}+2 \mathrm{OH}^{-}$
Here the $\mathrm{Mn}$ changes from $\mathrm{Mn}^{+7}$ to $\mathrm{Mn}^{+4}$
Thus overall change in its oxidation number would be of 3 .
$8 \mathrm{MnO}_{4}^{-}+3 \mathrm{~S}_{2} \mathrm{O}_{3}^{2-}+\mathrm{H}_{2} \mathrm{O} \rightarrow 8 \mathrm{MnO}_{2}+6 \mathrm{SO}_{4}^{2-}+2 \mathrm{OH}^{-}$
Here the $\mathrm{Mn}$ changes from $\mathrm{Mn}^{+7}$ to $\mathrm{Mn}^{+4}$
Thus overall change in its oxidation number would be of 3 .
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