In order to oxidize a mixture of one mole of each of $\mathrm{FeC}_{2} \mathrm{O}_{4}, \mathrm{Fe}_{2}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{3}, \mathrm{FeSO}_{4}$ and $\mathrm{Fe}_{2}\left(\mathrm{SO}_{4}\right)_{3}$ in acidic medium, the number of moles of $\mathrm{KMnO}_{4}$ required is:

JEE Main · 2019 · 08 Apr 2019 · Shift 1 · Redox Reactions and Electrochemistry

In order to oxidize a mixture of one mole of each of

FeC_{2} O_{4}, Fe_{2} (C_{2} O_{4})_{3}, FeSO_{4}

and

Fe_{2} (SO_{4})_{3}

in acidic medium, the number of moles of

KMnO_{4}

required is:

Answer: (C)

In acidic medium permanganate is reduced from

Mn^{7 +}

Mn^{2 +}

, an

n

-factor of

5

, so match the total electrons the mixture can give up. One mole of

FeS O_{4}

supplies

1

electron as

Fe^{2 +} \to Fe^{3 +}

; one mole of

Fe C_{2} O_{4}

supplies

3

, one from iron and two from oxalate going to

C O_{2}

; one mole of

F e_{2} (C_{2} O_{4})_{3}

supplies

6

from its three oxalates, its iron already being

Fe^{3 +}

; and

F e_{2} (S O_{4})_{3}

supplies none. The electrons total

1 + 3 + 6 + 0 = 10

, so the permanganate required is

\frac{10}{5} = 2

moles.

JEE Main · 2019 · 08 Apr 2019 · Shift 1 · Single correct option