Some Basic Concepts of Chemistry - Result Question 12
####12. Number of moles of $MnO_4^{-}$required to oxidize one mole of ferrous oxalate completely in acidic medium will be :
(a) 0.6 moles
(b) 0.4 moles
(c) 7.5 moles
(d) 0.2 moles
[2008]
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Solution:
- (b)
From above equation 2 moles of $MnO_4$ required to oxidise 5 moles of oxalate.
Thus number of moles of $MnO_4^{-}$required to oxidise one mole of oxalate $=2 \times 2 / 5=0.4$ moles
In $KMnO_4$ the oxidation state of $Mn$ is +7 . In acidic medium Mn takes up five electrons and making it an oxidizing agent. In strongly alkaline solution it takes up only 1 electrons and making it much weaker oxidising agent. In neutral medium it gives up 3 electrons to form $MnO_2$ Acidic medium:
$ MnO_4^{-}+8 H^{+}+5 e^{-} \to Mn^{2+}+4 H_2 O $
Alkaline medium: $MnO_4^{-}+e^{-} \to MnO_4^{2-}$
Neutral medium:
$ MnO_4^{-}+4 H^{+}+3 e^{-} \to MnO_2+2 H_2 O $
