A 0.500 g iron ore sample is dissolved and all iron is converted to Fe^2+, which needs 21.5 mL of 0.0200 M K2Cr2O7. Taking the molar mass of Fe2O3 as 160 g mol^-1, the mass percent of Fe2O3 is

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JEE Advanced levelSingle correct optionDifficulty 3 of 3eq071

A $0.500 g$ iron ore sample is dissolved and all iron is converted to $Fe X^{2 +}$ , which needs $21.5 mL$ of $0.0200 M$ $K X_{2} Cr X_{2} O X_{7}$ . Taking the molar mass of $Fe X_{2} O X_{3}$ as $160 g mo l^{- 1}$ , the mass percent of $Fe X_{2} O X_{3}$ is

A82.6%
B41.3%
C20.6%
D28.9%

Answer: B

mol Fe2+ = 6 x (0.0215 x 0.0200) = 2.580e-03. Each Fe2O3 gives 2 Fe, so mol Fe2O3 = 1.290e-03, mass = 0.2064 g. Percent = 0.2064/0.500 x 100 = 41.28%.

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A $0.500 g$ iron ore sample is dissolved and all iron is converted to $Fe X^{2 +}$ , which needs $21.5 mL$ of $0.0200 M$ $K X_{2} Cr X_{2} O X_{7}$ . Taking the molar mass of $Fe X_{2} O X_{3}$ as $160 g mo l^{- 1}$ , the mass percent of $Fe X_{2} O X_{3}$ is