Question

Hydrogen peroxide acts both as an oxidising and as well as a reducing agent depending upon the nature of the reacting species, In which of the following cases $H_{2}O_{2}$ can act as a reducing agent in an acidic medium?

• A. $KI$
• B. $Cr_{2}O_{7}^{2 -}$
• C. $SO_{3}^{2 -}$
• D. $MnO_{4}^{-}$

Answer 1

Answer: (D)

$\text{MnO}_{4}^{-} + 8 \text{H}^{+} + 5 \text{e}^{-} \rightarrow \text{Mn}^{2 +} + 4 \text{H}_{2} \text{O}$
$\text{H}_{2} \text{O}_{2} \rightarrow \text{O}_{2} + 2 \text{H}^{+} + 2 \text{e}^{-}$
$H_{2}O_{2}$ acts as a reducing agent get oxidised
$4H_{2}O_{2}+K_{2}Cr_{2}O_{7}+H_{2}SO_{4} \rightarrow 2CrO_{5}+K_{2}SO_{4}+5H_{2}O$
$CrO_{5}$ formation possibility is there, so $K_{2}Cr_{2}O_{7}$ not selected as choice but $KMnO_{4}$ selected.