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← JEE Advanced 2021 · Paper 2
ChemistryNumerical+2Question 31 of 57

JEE Advanced 2021 · Paper 2, Chemistry question 12

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Question Stem for Question Nos. 11 and 12

A sample (5.6 g) containing iron is completely dissolved in cold dilute HCl to prepare a 250 mL of solution. Titration of 25.0 mL of this solution requires 12.5 mL of 0.03 M KMnOX4\ce{KMnO4} solution to reach the end point. Number of moles of FeX2+\ce{Fe^{2+}} present in 250 mL solution is x×10−2\mathbf x \times 10^{-2} (consider complete dissolution of FeClX2\ce{FeCl2}). The amount of iron present in the sample is y\mathbf y% by weight.

(Assume: KMnOX4\ce{KMnO4} reacts only with FeX2+\ce{Fe^{2+}} in the solution

Use: Molar mass of iron as 56 g mol−1^{-1})

The value of y\mathbf y is ____.

Answer and worked solution

Official answer: 18.7

From the previous part, the sample contains 1.875×10−21.875\times10^{-2} mol of iron:
1.875×10−2×56=1.05 g.1.875\times10^{-2}\times56=1.05\text{ g}.

Percentage. 1.055.6×100=18.75%\frac{1.05}{5.6}\times100=18.75\%, so y=18.75y=18.75.