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Q.
The number of moles of $KMnO_4$ that will be needed to react
completely with one mole of ferrous oxalate in acidic
medium is
IIT JEEIIT JEE 1997Some Basic Concepts of Chemistry
Solution:
The number of moles of $KMnO _{4}$ that will be needed to react completely with one mole of ferrous oxalate in acidic solution is $\frac{3}{5}$.
Potassium permangante is a very strong oxidizing agent. It oxidizes iron(II) ion as well as the oxalate ion.
Oxalate oxidation: $2 MnO _{4}-+16 H ^{+}+5 C _{2} O _{4}^{2-} \rightarrow 2 Mn ^{2+}+8 H _{2} O +10 CO _{2}$
Iron(II) oxidation: $MnO _{4}^{-}+8 H ^{+}+5 Fe ^{2+} \rightarrow Mn ^{2+}+4 H _{2} O +5 Fe ^{3+}$
Hence, moles of $KMnO _{4}$ that will be needed to react completely with one mole of ferrour oxalate $Fe \left( C _{2} O _{4}\right)$ is $\frac{3}{5}$ ($2$ moles for oxalate and $1$ mole for iron (II)).