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A primary standard grade As2O3 (m.m. = 197.84) weighing 0.2068 g is dissolved in NaOH and then acidified with HCl. The resulting solution is then titrated with 42.45 ml of the KMnO4 solution. MnO4 + 8h + 5e H:AsO3 + H2O Mn2+ + 4h2o H:AsO4 + 2h* + 2e Calculate the molarity of the KMnO4 solution. a a. 0.09850 b b. 0.04925 c c. 0.01970 d d. 0.03254
Accepted Answer
The molarity of the KMnO4 solution is 0.01970 M (option C). Here's how to calculate it:
1. Balance the Redox Reaction:
- The balanced redox reaction is:
2MnO4- + 5H3AsO3 + 6H+ → 2Mn2+ + 5H3AsO4 + 3H2O
2. Calculate moles of As2O3:
- Moles of As2O3 = mass / molar mass = 0.2068 g / 197.84 g/mol = 0.001045 mol
3. Relate moles of As2O3 to moles of KMnO4:
- From the balanced equation, 2 moles of MnO4- react with 5 moles of H3AsO3.
- Moles of KMnO4 = (0.001045 mol As2O3)
(2 mol MnO4-) / (5 mol H3AsO3) = 0.000418 mol
4. Calculate molarity of KMnO4:
- Molarity = moles / volume = 0.000418 mol / 0.04245 L = 0.009850 M
Important Note: The answer choices provided in the question are incorrect. The correct molarity is 0.009850 M, which is not listed. It's possible there's a typo in the answer choices or in the problem setup.
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