4. For the turbidimetric determination of lead, a calibration curve was built:

From a weighed portion of 6.400 g of the analyzed sample, a solution was prepared in a volumetric flask with a capacity of 100 ml. From 10 ml of this solution in a volumetric flask with a capacity of 50 ml, a suspension of PbSO4 was obtained, the optical density was equal to 0.32. Determine the mass fraction of lead in the analyzed sample.

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