1011. Solving a chemistry problem

4. The mass fraction (%) of MoO3 in the mineral sample was determined by photocolorimetry using a calibration curve. . For this purpose, a standard solution was prepared from a reference substance - ammonium molybdate reagent, qualification x. including dissolving 1.0000 g of reagent containing 99.8% of the main component in 500 cm3 of distilled water. To construct a calibration graph, calibration solutions have been prepared. In this chemical analysis, they are used to measure the light absorption intensity of the colored reaction product of molybdenum ions with dithiol in optical density (A) values as a set of reference samples with an accurately known mass concentration of molybdenum in solution to cover the possible range of molybdenum contents in mineral samples.
Calibration solutions were prepared in the following way. Aliquots of a standard solution of ammonium molybdate (Va) were quantitatively transferred into 50 cm3 volumetric flasks, the required amount of the photometric reagent dithiol was added to each flask, and the solutions were brought to the mark with distilled water. For each calibration solution, the optical density A, rel., was measured. units in a cuvette with an absorbing layer thickness of 1 cm relative to a reference solution that does not contain molybdenum ions. The measurement data is summarized in the table:
Va, cm3 0.5 1.0 1.5 2.0
A, rel. units 0.231 0.465 0.690 0.940

Calculate the mass fraction of molybdenum in terms of MoO3 (%) in a mineral sample if a 0.2400 g sample of the mineral taken for analysis is dissolved in 100 cm3. The same reagent was added to an aliquot equal to 10 cm3, placed in a 50 cm3 volumetric flask, and the volume was adjusted to the mark with distilled water. The measured optical density of such a solution is 0.510 rel. units