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JEE MainChemistryRedox Reactions

Which of the following reagents is a valid primary standard for redox titrations, and what is its equivalent weight in an acidic medium? (Let M be the molar mass of the reagent)

Options

  1. AKMnO ₄ , M 5
  2. BNa ₂ Cr ₂ O ₇ , M 6
  3. CK ₂ Cr ₂ O ₇ , M 6
  4. DK ₂ Cr ₂ O ₇ , M 3

Correct answer

C. K ₂ Cr ₂ O ₇ , M 6

Step-by-step solution

For a reagent to be used as a primary standard, it must be highly pure, stable, and non-hygroscopic/non-deliquescent. KMnO ₄ is a secondary standard because it is unstable and decomposes in the presence of light or traces of organic matter. Na ₂ Cr ₂ O ₇ is deliquescent and absorbs moisture, making it unsuitable for accurate weighing. FeSO ₄ 7 H ₂ O is easily oxidized by atmospheric oxygen. K ₂ Cr ₂ O ₇ is highly pure, stable, and not hygroscopic, making it an excellent primary standard. In an acidic medium, the di

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