Samples containing iron(II) ion can be titrated with solutions containing dichro

Question

Samples containing iron(II) ion can be titrated with solutions containing dichromate ion under acidic conditions. Cr_2O_7^2- + 6Fe^2+ + 14H^+ rightarrow 2Cr^3+ + 6Fe^3+ 7H_2O (a) Which ion is oxidized in this reaction? (b) Which ion is the reducing agent in this reaction ? (C) If a 1.818 g sample containing iron(II) sulfate is dissolved and requires 33.1 mL of 0.0100 M K_2Cr_2O_7 solution to titrate it, what is the percent iron(II) sultate in the sample? What volume of a 0.0225 M solution of potassium permanganate are required to titrate 0.461 g of sample that is 70.6% sodium oxalate?

Explanation / Answer

(1) The species that is oxidised is Fe2+

(2) The species that is reduced is Cr2O72-

(3) Moles of K2Cr2O7 = 0.0100 * 33.1 / 1000 = 0.000331 mol

from the balanced equation,

1 mol of Cr2O72- needs 6 mol of Fe2+

Then, 0.000331 mol of Cr2O72- needs 6 * 0.000331 = 0.00197 mol of Fe2+

Mass of Iron(II) Sulphate = 0.00197 * 151.908 = 0.299 g.

Mass percentge of Iron(II)sulphate = (0.299/1.818)*100 = 16.4 %

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