Some Basic Concepts of Chemistry - Result Question 4
4. In order to oxidise a mixture of one mole of each of $\mathrm{FeC}_2 \mathrm{O}_4$, $\mathrm{Fe}_2\left(\mathrm{C}_2 \mathrm{O}_4\right)_3, \mathrm{FeSO}_4$ and $\mathrm{Fe}_2\left(\mathrm{SO}_4\right)_3$ in acidic medium, the number of moles of $\mathrm{KMnO}_4$ required is
(2019 Main, 8 April I)
(a) 2
(b) 1
(c) 3
(d) 1.5
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Answer:
Correct Answer: 4. (a)
Solution: The oxidation of a mixture of one mole of each of $\mathrm{FeC}_2 \mathrm{O}_4, \mathrm{Fe}_2\left(\mathrm{C}_2 \mathrm{O}_4\right)_3 \mathrm{FeSO}_4$ and
$\mathrm{Fe}_2\left(\mathrm{SO}_4\right)_3$ in acidic medium with $\mathrm{KMnO}_4$ is as follows :
$ \begin{aligned} & \mathrm{FeC}_2 \mathrm{O}_4+\mathrm{KMnO}_4 \longrightarrow \mathrm{Fe}^{3+}+\mathrm{CO}_2+\mathrm{Mn}^{2+}……(i) \\ & \mathrm{Fe}_2\left(\mathrm{C}_2 \mathrm{O}_4\right)_3+\mathrm{KMnO}_4 \longrightarrow \mathrm{Fe}^{3+}+\mathrm{CO}_2+\mathrm{Mn}^{2+}……(ii) \\ & \mathrm{FeSO}_4+\mathrm{KMnO}_4 \longrightarrow \mathrm{Fe}^{3+}+\mathrm{SO}_4^{2-}+\mathrm{Mn}^{2+}……(iii) \end{aligned} $
Change in oxidation number of Mn is 5 . Change in oxidation number of Fe in (i), (ii) and (iii) are $+3,+6,+1$, respectively.
$ \begin{aligned} n_{\mathrm{eq}} \mathrm{KMnO}4 & =n{\mathrm{eq}}\left[\mathrm{FeC}_2 \mathrm{O}_4+\mathrm{Fe}_2\left(\mathrm{C}_2 \mathrm{O}_4\right)_3+\mathrm{FeSO}_4\right] \\ n \times 5 & =1 \times 3+1 \times 6+1 \times 1 \\ \therefore \quad n & =2 \end{aligned} $
BETA
