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. $C{r}_2{O}_7^{2-}$
• C. $S{O}_3^{2-}$
• D. $Mn{O}_4^{-}$

Answer 1

Answer: (D)

${\text{MnO}}_4^{-}+8{\text{H}}^{+}+5{\text{e}}^{-}\to {\text{Mn}}^{2+}+4{\text{H}}_2\text{O}$
${\text{H}}_2{\text{O}}_2\to {\text{O}}_2+2{\text{H}}^{+}+2{\text{e}}^{-}$
$H_2{O}_2$ acts as a reducing agent get oxidised
$4H_2{O}_2+K_{2}C{r}_2{O}_7+H_{2}S{O}_4\to 2Cr{O}_5+K_{2}S{O}_4+5H_{2}O$
$Cr{O}_5$ formation possibility is there, so $K_{2}C{r}_2{O}_7$ not selected as choice but $KMn{O}_4$ selected.