7. Lead was precipitated from 3.2060 g of the alloy in the form of PbCrO4. By the action of acid and potassium iodide on the precipitate, iodine was isolated, for the titration of which 9.15 ml of a 0.1028 M solution of Na2S2O3 was used. Calculate the mass fraction of lead in the alloy. Write reaction equations.

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