1) Potassium permanganate solutions used in oxidation-reduction titrations are often standardized against sodium oxalate, Na₂C₂O₄, used as a primary standard. The reaction involved is 5C₂O₄²⁻(aq) + 2MnO₄⁻(aq) + 16 H⁺(aq) → 2Mn²⁺(aq) + 8H₂O(l) + 10CO₂(g) A 0.2452 g sample of sodium oxalate is dissolved in 100 mL of acid solution, and the permanganate solution is added slowly from a buret. The endpoint is reached when 15.85 mL of the permanganate solution has been added. The molar mass of sodium oxalate is 134.00 g/mol. Calculate [MnO₄⁻], the molar concentration of the permanganate solution.
1) Potassium permanganate solutions used in oxidation-reduction titrations are often standardized against sodium oxalate, Na₂C₂O₄, used as a primary standard. The reaction involved is 5C₂O₄²⁻(aq) + 2MnO₄⁻(aq) + 16 H⁺(aq) → 2Mn²⁺(aq) + 8H₂O(l) + 10CO₂(g) A 0.2452 g sample of sodium oxalate is dissolved in 100 mL of acid solution, and the permanganate solution is added slowly from a buret. The endpoint is reached when 15.85 mL of the permanganate solution has been added. The molar mass of sodium oxalate is 134.00 g/mol. Calculate [MnO₄⁻], the molar concentration of the permanganate solution.
2) Potassium permanganate solutions used in oxidation-reduction titrations are sometimes standardized against Fe²⁺ ion. The reaction involved is 8H⁺(aq) + MnO₄⁻(aq) + 5Fe²⁺(aq) → 5Fe³⁺(aq) + Mn²⁺(aq) + 4H₂O(l) .A convenient source for Fe²⁺ ion is ammonium iron(II) sulfate, (NH₄)₂Fe(SO₄)₂(H₂O)₆ (FW = 392.14), also known as Mohr's salt, which is readily crystallized, and the crystals resist oxidation by air. A 0.6735 g sample of Mohr's salt is dissolved in 100 mL of acid solution, and the permanganate solution is added slowly from a buret. The endpoint is reached when 17.86 mL of the permanganate solution has been added. Calculate [MnO₄⁻], the molar concentration of the permanganate solution.
3) The iron content of iron ore can be determined by titration with KMnO₄ according to the equation 8H⁺(aq) + MnO₄⁻(aq) + 5Fe²⁺(aq) → 5Fe³⁺(aq) + Mn²⁺(aq) + 4H₂O(l) A sample of iron ore with a mass of 1.535 g was dissolved with HCl and then treated with a reducing agent to convert any Fe³⁺ in the ore to Fe²⁺. Titration with 0.0455 M KMnO₄ solution required 59.15 mL of the solution to reach the endpoint where the purple MnO₄⁻ ion was no longer being consumed. The molar mass of Fe is 55.85 g/mol. Determine the mass percent iron in the ore
4) The iron content of iron ore can be determined by titration with K₂Cr₂O₇ according to the equation 14H⁺(aq) + Cr₂O₇²⁻(aq) + 6Fe²⁺(aq) → 6Fe³⁺(aq) + 2Cr³⁺(aq) + 7H₂O(l) Diphenyl
5) Vitamin C (ascorbic acid, C₆H₈O₆, 176.12 g/mol) can be measured by redox titration with iodine solution. Iodine is reduced to iodide ion, while ascorbic acid is oxidized to dehydroascorbic acid (C₆H₆O₆). The iodine solution is usually made in the presence of iodide ion, forming the more stable triiodide ion, I₃⁻, giving the following overall reaction C₆H₈O₆(aq) + I₃⁻(aq) + H₂O(l) → C₆H₆O₆(aq) + 3I⁻(aq) + 2H⁺(aq) The titration is carried out in the presence of starch, which forms a dark blue complex with the excess iodine when the endpoint is reached. You are testing a new multivitamin pill for its vitamin C content. One pill weighing 0.763 g is dissolved in dilute acid and titrated with 0.0236 M I₃⁻ solution, requiring 28.3 mL to reach the endpoint. Calculate the percent by mass of vitamin C in the pill.
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