145. Solving a chemistry problem

41. To determine the acetone concentrate in wastewater, it is used to condense it with furfural, which results in the formation of an acid-colored compound in a violet-red color, the absorption maximum of which is located at 520–540 nm. 200.00 ml of water were taken for analysis, 2/3 of the volume was distilled off from it, the distillate was diluted in a 250.00 ml volumetric flask. 2.50 ml samples were taken for analysis. According to the calibration schedule, they found that the aliquot contains 2.5 mg of acetone. Determine the concentration (mg / dm3) of acetone in water.