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An inorganic bromide impurity in a sample is precipitated as silver bromide. \( 2.00 g \) of the sample required \( 6.4 mL \) of \( 0.20 M AgNO { }_{3} \) to completely precipitate the impurity. The mass percentage of impurity is 

(A) \( 5.11 \) (B) \( 2.56 \) (C) \( 9.15 \) (D) \( 1.28 \)

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Correct option is (1) 5.11 

\(\underset{Inorganic \\\,\,sample} {AB_r} + AgNO_3 \longrightarrow AgBr(s) + ANO_3\)

∵ 1 mole of Br- ion precipitated by 1 mole of AgNO3 to form 1 mol AgBr.

∵ 6 - 4 ml at 0.2 M AgNO3 is required to complete precipitate the impurity (Br-).

∴ Number of moles of AgNO3 required = 0.0064 x 0.2 = 0.00128 mol.

∴ Number of moles of AgBr formed = 0.00128 mol.

∴ Number of moles of Br- in sample = 0.00128 mol.

∴ Mass of Br- in sample = 0.00128 x 80 = 0.1024 g

∴ Mass percentage of impurity (Br-) = \(\frac{0.1024}{2.00} \times 100 \) = 5.12 %

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