1. To construct a calibration curve, 5.0 was placed in flasks with a capacity of 50 ml; 8.0; 10.0 ml of ferric ammonium alum solution with TFe = 0.000050, added hydrochloric acid and potassium thiocyanate, brought to the mark with water and measured the optical density at 496 nm:

Volume of standard solution, ml 5.0 8.0 10.0
Optical density 0.365 0.595 0.750

The test solution containing iron and nickel was diluted in a 100.0 ml flask, and two 20.0 ml aliquots were taken into 50.0 ml flasks. One sample was diluted to the mark with water, HCl and KSCN were added to the second sample and also diluted to the mark with water. The optical density of the first sample at 496 nm is equal to АNi=0.080. Optical density of the second sample = 0.46.
Calculate the mass of iron, mg, in solution.

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