66. Solving a chemistry problem

9. In the photometric determination of iron (ΙΙΙ) in the form of a colored complex with sulfosalicylic acid, 1.0, 2.0, 3.0, 4.0 and 5.0 ml of the initial solution with an iron content of 10 mg/ml, an excess of sulfosalicylic acid was added and made up to the mark with water. The measured values of the optical density of the prepared standard solutions were 0.12, 0.24, 0.36, 0.48 and 0.60, respectively. Build a calibration graph and determine the concentration of iron ions in the analyzed solution if the optical density of this solution is 0.30. Calculate the mass of iron in 250 ml of the analyzed solution.