JEE Advanced · Chemistry · 9. Redox Reactions

A sample $(5.6 \mathrm{~g})$ containing iron is completely dissolved in cold dilute $\mathrm{HCl}$ to prepare a $250 \mathrm{~mL}$ of solution. Titration of $25.0 \mathrm{~mL}$ of this solution requires $12.5 \mathrm{~mL}$ of $0.03 \mathrm{M} \mathrm{KMnO}_{4}$ solution to reach the end point. Number of moles of $\mathrm{Fe}^{2+}$ present in $250 \mathrm{~mL}$ solution is $\mathbf{x} \times 10^{-2}$ (consider complete dissolution of $\mathrm{FeCl}_{2}$ ). The amount of iron present in the sample is $\mathbf{y} \%$ by weight.
(Assume: $\mathrm{KMnO}_{4}$ reacts only with $\mathrm{Fe}^{2+}$ in the solution Use: Molar mass of iron as $56 \mathrm{~g} \mathrm{~mol}^{-1}$ )
The value of $x$ is________ .

A 16.45
B 18.75
C 15.24
D 15.26

Verified Solution

Answer & Solution

Correct Answer

(B) 18.75

Step-by-step Solution

Detailed explanation

Moles of

{Fe}^{2 +}

present in

250 ml

solution

= x \times 10^{- 2}

Moles of

{Fe}^{2 +}

present in

25 ml

solution

= x \times 10^{- 3} mole

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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