68. Solving a chemistry problem

87. To determine silicon in steels in water of the silicon-molybdenum complex, a calibration curve was built for pure silicon dioxide. In this case, the following values of the optical density of solutions were obtained:
Dioxide content
silicon, mg/ml 0.02 0.40 0.60 0.80 1.00 1.20
Optical density 0.015 0.29 0.43 0.61 0.74 0.90
A weighing of 0.253 g of steel was dissolved in acid and, after appropriate treatment, 100 ml of a colored solution of silicomolybdic acid was obtained, the optical density of which was 0.56.