Some Basic Concepts of Chemistry 2 Question 4
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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)
======= ####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)
3e0f7ab6f6a50373c3f2dbda6ca2533482a77bed (a) 2
(b) 1
(c) 3
(d) 1.5
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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 :
$$ \begin{aligned} \mathrm{FeC}{2} \mathrm{O}{4}+\mathrm{KMnO}{4} & \longrightarrow \mathrm{Fe}^{3+}+\mathrm{CO}{2}+\mathrm{Mn}^{2+} \ \mathrm{Fe}{2}\left(\mathrm{C}{2} \mathrm{O}{4}\right){3}+\mathrm{KMnO}{4} & \longrightarrow \mathrm{Fe}^{3+}+\mathrm{CO}{2}+\mathrm{Mn}^{2+} \ \mathrm{FeSO}{4}+\mathrm{KMnO}{4} & \longrightarrow \mathrm{Fe}^{3+}+\mathrm{SO}_{4}^{2-}+\mathrm{Mn}^{2+} \end{aligned} $$
Change in oxidation number of $\mathrm{Mn}$ is 5 . Change in oxidation number of $\mathrm{Fe}$ in (i), (ii) and (iii) are $+3,+6,+1$, respectively.
$$ \begin{aligned} n_{\mathrm{eq}} \mathrm{KMnO}{4} & =n{\mathrm{eq}}\left[\mathrm{FeC}{2} \mathrm{O}{4}+\mathrm{Fe}{2}\left(\mathrm{C}{2} \mathrm{O}{4}\right){3}+\mathrm{FeSO}_{4}\right] \ \therefore \quad n \times 5 & =1 \times 3+1 \times 6+1 \times 1 \ \therefore \quad n & =2 \end{aligned} $$
