123. Solving a chemistry problem

10. To determine the content of lead in the ore, a sample of ore weighing 5,000 g was taken. After dissolving it in acid, the Pb2+ ion was precipitated in the form of PbCrO4, the precipitate was filtered, washed and dissolved in a mixture of HCl and KI. The iodine released during this reaction was titrated with 42.0 ml of a sodium thiosulfate solution with a concentration c(Na2S2O3) = 0.5000 mol/l. Write down the equations of the reactions that take place during the determination, calculate the equivalent mass of lead using the law of equivalents, and the lead thiosulfate titer T(Na2S2O3/Pb). Calculate the mass fraction (%, wt.) of lead in the ore.