Question

The number of moles of $KMn{O}_4$ 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. $0.1$

Answer 1

The correct option is B $0.6$

1)$0.6$

2)$KMn{O}_4$ 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$KMn{O}_4$should provide those $3$electrons as in acidic medium $KMn{O}_4$ gets reduced to $M{n}_2^{+}$ ions so one mole of$KMn{O}_4$ gains$5$ electrons

4)Hence,$3/5ie-0.6$ mole of$KMn{O}_4$is needed to react completely(oxidise completely) one mole of ferrous oxalate.