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Answer to Question #18128 in Other Chemistry for Ani

Question #18128
1) Dichromate and ferrous ions react in acidic solution to form chromic and ferric ions, respectively. If 1.285 grams of iron(II) bisulfate dissolved in sulfuric acid solution requires 35.78 mL of sodium dichromate solution for complete titration, what is the molarity of the sodium dichromate solution? Show the balanced net ionic and complete chemical equations for this reaction.

2) The sodium dichromate solution from Problem 1 was used to titrate a solution made by dissolving 3.500 g of a pure ferrous salt in sulfuric acid. The titration required 47.22 mL of the sodium dichromate solution. Calculate the percent by mass of iron in the pure salt. The net ionic equation here is the same as in Problem 1. You will not be able to write a balanced molecular equation for this because the anion in the ferrous salt was not specified in this problem.
Expert's answer
1) 6Fe2+ + Cr2O72- + 14H+ → 5Fe3+ + 2Cr3+ + 7H2O

Fe2+ - 1e- → Fe3+ reductant

Cr2O72+ + 14H+ + 6e- → 2Cr3+ + 7H2O oxidant

n(FeSO4) = 1.285 / 152 = 0.00845 mol
n(Na2Cr2O7) = 0.00140899122 mol
Cm(Na2Cr2O7) = 0.00140899122 / 0.03578 = 0.0339 M

2) n(Na2Cr2O7) = 0.04722 * 0.0339 = 0.0016 mol
n(FeSO4) = 0.0016 * 6 = 0.0096 mol
m(Fe) = M(Fe) / M(FeSO4) * m
m(Fe) = 56/152 * 3.5 = 1.288 g
%(Fe) = 1.288 / 3.5 * 100 % = 36.8 %

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