44. Solving a chemistry problem

391. To construct a calibration graph for the nephelometric determination of the sulfate ion, 25.00 cm3 of an H2SO4 solution containing 0.215 mg/cm3 of SO3 was placed in a 100.00 cm3 volumetric flask. Then in 100 cm3 volumetric flasks containing 20.00; 15.00; 10.00; 6.00 and 2.00 cm3 of this solution were prepared in suspension and their apparent optical densities were measured. According to the data (Table 18), a calibration graph was built.
The analyzed solution of 50.00 cm3 was diluted in a volumetric flask by 100.00 cm3. Then 20.00 cm3 of this solution was transferred to a volumetric flask with a capacity of 100.00 cm3, a suspension of BaSO4 was prepared in it and brought to the mark with water, the apparent optical density was measured (Table 18)
Determine the content of SO3 in the analyzed solution in mg/dm3.
Table 18
Task No. Standard solution Test solution
Apparent optical density DX
I II III IV V
391 0.51 0.62 0.80 0.98 1.22 0.72