JEE Main 2019 · Chemistry · Redox Reactions and Titrations · medium

A 25 mL sample of an acidified Fe^2+ solution requires 20 mL of 0.020 M KMnO4 for complete oxidation. The volume of 0.010 M K2Cr2O7 (in acidic…

Single correct option

25\ \mathrm{mL}

sample of an acidified

\mathrm{Fe^{2+}}

solution requires

20\ \mathrm{mL}

0.020\ \mathrm{M}

\mathrm{KMnO_4}

for complete oxidation. The volume of

0.010\ \mathrm{M}

\mathrm{K_2Cr_2O_7}

(in acidic medium) needed to oxidise another

25\ \mathrm{mL}

of the same

\mathrm{Fe^{2+}}

solution is

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Answer: (A) $33.3\ \mathrm{mL}$

\mathrm{MnO_4^-}

gains

5e^-

n(\mathrm{Fe^{2+}}) = 5\times(20\times0.020) = 2.0

mmol in

25\ \mathrm{mL}

\mathrm{Cr_2O_7^{2-}} \to 2\mathrm{Cr^{3+}}

takes

6e^-

per formula unit, so each mL of

0.010\ \mathrm{M}

dichromate oxidises

6\times0.010 = 0.060

mmol

\mathrm{Fe^{2+}}

. Volume

=2.0/0.060 = 33.3\ \mathrm{mL}

. Using

3

electrons for dichromate would give

66.7

Original question written in the JEE Main 2019 pattern and checked twice for the correct answer. Not an official question paper. How we write and check questions · Corrections policy · Report a mistake