JEE Main 2021 · Chemistry · Redox Reactions and Titrations · medium

20 mL of 0.50 M FeC2O4 (ferrous oxalate) is titrated in acidic medium with 0.10 M KMnO4. The volume of KMnO4 required for complete oxidation is

Single correct option

20\ \mathrm{mL}

0.50\ \mathrm{M}

\mathrm{FeC_2O_4}

(ferrous oxalate) is titrated in acidic medium with

0.10\ \mathrm{M}

\mathrm{KMnO_4}

. The volume of

\mathrm{KMnO_4}

required for complete oxidation is

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Answer: (C) $60\ \mathrm{mL}$

Both

\mathrm{Fe^{2+}}

and oxalate are oxidised. Per formula unit:

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

gives

1\,e^-

and

\mathrm{C_2O_4^{2-}}\to2\mathrm{CO_2}

gives

2\,e^-

, so the n-factor of

\mathrm{FeC_2O_4}

3

. For

\mathrm{MnO_4^-}\to\mathrm{Mn^{2+}}

the n-factor is

5

. Millimoles of

\mathrm{FeC_2O_4}=20\times0.5=10

. Equivalents:

10\times3=30

meq

=V\times0.10\times5

, so

V=60\ \mathrm{mL}

. Counting only

\mathrm{Fe^{2+}}

gives

20\ \mathrm{mL}

and counting only oxalate gives

40\ \mathrm{mL}

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