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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3eq110

of pyrolusite ore is heated with of in dilute acid (). The unreacted oxalate needs of in acid. Taking the molar mass of as , which of the following are correct?

  1. AThe oxalate left over after reaction with the ore is mmol.
  2. BThe content of the ore is between and by mass.
  3. CThe oxalate consumed by the ore, and hence present, is mmol.
  4. DThe permanganate titration consumes mmol of oxalate.

Answer: A, B, C

Permanganate = 20.0 x 0.0400 = 0.80 mmol; oxalate left = 2.5 x 0.80 = 2.00 mmol. Oxalate taken = 5.00 mmol, so consumed (= MnO2) = 3.00 mmol. Mass MnO2 = 3.00 x 87 = 261 mg; percent = 261/400 x 100 = 65.25%. The permanganate step consumes only 2.00 mmol of oxalate, not 4.00.
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