97. Solving a chemistry problem

3. To conduct a spectrophotometric determination of the total iron content in a solution, prepare a series of standard solutions of Fe2 (C = 0.07 mg/ml). To do this, add 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ml of a standard solution into 6 volumetric flasks with a capacity of 50 ml. Take 10.0 ml from the task flask, transfer it to a 50 ml volumetric flask and dilute with distilled water to the mark. Take 1.0 ml from the resulting solution and transfer it to a 50 ml volumetric flask. The obtained optical density values ​​are given in the table.
Experiment number Volume of standard Fe2 solution, ml Absolute photometry Differential photometry
Optical density of the standard solution Optical density of the test solution Optical density of the standard solution Optical density of the test solution
1 1.0 0.080 0.507
0.506
0.505 -0.135 0.292
0.294
0.294
2 2.0 0.208 0
3 3.0 0.322 0.092
4 4.0 0.422 0.207
5 5.0 0.507 0.292
6 6.0 0.590 0.375

Calculate the mass of iron in the sample.