Question

Standard electrode potential data are useful for understanding the suitability of an oxidant in a redox titration. Some half-cell reactions and their standard potentials are given below :
$Mn{O}_4^{-}(aq)+8H^{+}(aq)+5e^{-}⟶M{n}^{2+}(aq)+4H_{2}O(l),E^{\circ }=1.51V$
$C{r}_2{O}_7^{2-}(aq)+14H^{+}(aq)+6e^{-}⟶2C{r}^{3+}(aq)+7H_{2}O(l),E^{\circ }=1.38V$
$F{e}^{3+}(aq)+e^{-}⟶Fe{r}^{2+}(aq)E^{\circ }=0.77V$
$C{l}_2(g)+2e^{-}⟶2C{l}^{-}(aq)E^{\circ }=1.40V$
Identify the incorrect statement regarding the quantitative estimation of aqueous $Fe(N{O}_3{)}_2$

• A. $Mn{O}_4^{-}$ can be used in aqueous $HCl$
• B. $C{r}_2{O}_7^{2-}$ can be used in aqueous $HCl$
• C. $Mn{O}_4^{-}$ can be used in aqueous $H_{2}S{O}_4$
• D. $C{r}_2{O}_7^{2-}$ can be used in aqueous $H_{2}S{O}_4$

Answer 1

Answer: (A)

$Mn{O}_4^{-}$ cannot be used for oxidation of $F{e}^{2+}$ in $HCl$ medium because the following reaction is spontaneous :
$Mn{O}_4^{-}+C{l}^{-}⟶M{n}^{2+}+C{l}_2;E^{\circ }=1.51-1.40=0.11V$
In all other cases, the redox process between oxidising agent and medium $(HCl$ or $H_{2}S{O}_4)$ are non-spontaneous, would not interfere oxidation of $F{e}^{2+}$.