a. A total of 21.15 ml of K2Cr2O7 is required for the titration of a 0.1414 gram

Question

a. A total of 21.15 ml of K2Cr2O7 is required for the titration of a 0.1414 gram sample of FeSO4, that is 88.88% pure. If the products are Cr +3 and Fe +2, what is the molarity of the k2cr2o7?

b. You take a sample of iron ore, dry it, and then weigh it at 0.9757 grams. After dissolving it and reducing the natural Fe +3 to Fe +2, this sample was titrated with KMnO4. This sample required 10.55 ml of 0.03233 M KMnO4 to reach the equivalence point, where the permanganate was reduced to Mn +2. Calculate the % Fe in the original ore.

c. how else might you analyze this solution for % Fe? which is easier?

Explanation / Answer

a. moles of FeSO4 = 0.1414 g/151.908 g/mol = 9.31 x 10^-4 mols

molarity of K2Cr2O7 = 9.31 x 10^4/6 x 0.02115 L = 7.33 mM

b. moles of KMnO4 used = 0.03233 M x 10.55 ml = 0.3411 mmol

mass of Fe in sample = 0.3411 mmol x 5 x 55.845 g/1000 = 0.0952 g

%Fe in iron ore = (0.0952/0.9757) x 100 = 9.76%

c. We may also analyse iron ore for Fe by dichlromate oxidation. 1 mole of dichromate reacts with 6 moles of Fe.

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