125. Solving a chemistry problem

When determining Fe3, a hematogen weighing 0.0100 g after ashing was dissolved in HCl, transferred to a volumetric flask with a capacity of 50.00 ml, diluted with distilled water to the mark. The resulting solution with a volume of 10 ml was placed in a volumetric flask with a capacity of 25 ml, NH4SCN was added, and diluted with water to the mark. The optical density of the solution is 0.50 (I=1.0 cm, λ=496 nm). The calibration graph, built on FeCl3 standard solutions under identical conditions, is described by the equation A=7.5*104*C, where C is the mass concentration of iron, mg/ml. Calculate the mass fraction of Fe3 in the analyzed hematogen.