Question

# The number of moles of $$KMnO_{4}$$ that will be needed to react with one mole of ferrous oxalate in acidic solution is ?

A
0.4
B
0.6
C
0.8
D
0.1

Solution

## The correct option is B $$0.6$$1)$$0.6$$2)$$KMnO_4$$ oxidises both ferrous ions to ferric ions and oxalate ions to carbon dioxide as we can see that the oxidation number of$$C$$ atom in oxalate ion(upper pic)is $$+3$$,while the oxidation state of $$C$$atom in carbon dioxide is $$+4$$(lower pic).3)So, one mole of oxalate ions loose$$2$$electrons(one electron for each$$C$$ atom)while one the other hand one mole of ferrous ion looses$$1$$ electron so one mole of ferrous oxalate molecule looses $$3$$electrons in  total so the required number of$$KMnO_4$$should provide those $$3$$electrons as in acidic medium $$KMnO_4$$ gets reduced to $$Mn_2^+$$ ions so one mole of$$KMnO_4$$ gains$$5$$ electrons4)Hence,$$3/5 ie-0.6$$ mole of$$KMnO_4$$is needed to react completely(oxidise completely) one mole of ferrous oxalate.Chemistry

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