94. Solving a chemistry problem

63. A weighing of 0.5056 g of sulfanol was dissolved in a volumetric flask with a capacity of 250 ml and brought to the mark. Then, 5 ml of this solution was transferred into a 100 ml volumetric flask, a suspension of BaSO4 was prepared in it, and the mixture was made up to the mark with water. The apparent optical density of this solution was found to be 0.82. To construct a calibration curve, 25 ml of H2SO4 solution with a titer of 0.215 mg SO3/ml was placed in a 100 ml volumetric flask. Then in 100 ml volumetric flasks containing 20.0; 14.0; 12.0; 5.0; 2.5 ml of this solution, prepared a suspension of BaSO4 and measured their apparent optical densities, which were respectively equal to 0.48; 0.70; 0.80; 1.02; 1.16. Determine the mass fraction of Na2SO4 in sulfanol.