Calamine, which is used for relief of skin irritations, is a mixture of zinc and

Question

Calamine, which is used for relief of skin irritations, is a mixture of zinc and iron oxides. A 1.0220 g sample of dried calamine was dissolved in acid and diluted to 250.0 mL. Potassium fluoride was added to a 10.00 mL aliquot of the diluted solution to mask the iron; after suitable adjustment of the pH, Zn^2+ consumed 38.71 mL of 0.01294 M EDTA. A second, 50.00 mL aliquot was suitably buffered and titrated with 2.40 mL of 0.002727 M ZnY^2- solution: Fe^3+ + ZnY^2- rightarrow FeY^- + Zn^2+. Calculate the percentages of ZnO and Fe2O3 in the sample.

Explanation / Answer

% of ZnO= (V x M x Mw. of ZnO x 100)/ wt.of sample x1000

% of ZnO= (38.71 x 0.01294 x 81.408 x 100)/ 1.022 x1000

% of ZnO= 3.99%

% of Fe2O3= (V x M x Mw. of Fe2O3 x 100)/ wt.of sample x1000

% of Fe2O3= (2.40 x 0.002727 x 159.69 x 100)/ 1.022 x1000

% of Fe2O3= 0.1022 %

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