Question

Calculate the no.of moles of $KMn{O}_4$ required for the oxidation of 1 mol of $Fe{C}_2{O}_4$ in an acetic medium.

• A. $1$
• B. $\frac{5}{3}$
• C. $\frac{3}{5}$
• D. $\frac{1}{5}$

Answer 1

Answer: (C)

$\frac{3}{5}$

1)$3/5$

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.