81. Solving a chemistry problem

10. A weighing of 0.30 g of a standard aluminum alloy containing 12.5% ​​Si was dissolved in a 500 ml flask. To construct a calibration graph, aliquots of this solution were placed in volumetric flasks of 100 ml, reagents were added - ammonium molybdate and iron (II) sulfate, and the volume was brought to the mark. Measurement of optical density relative to the first solution is shown in the table.
Vst, ml 5.2 5.4 5.6 5.8 6.0
Arel 0.105 0.215 0.330 0.440 0.550
Calculate the mass fraction (%) of silicon in the sample if 0.25 g of the alloy is dissolved in 500 ml. Then a 5.0 ml sample was placed in a 100 ml volumetric flask, reagents were added, and the optical density was measured as in the case of building a calibration. Ah rel was 0.47.