21. Solving a chemistry problem

2. The analysis of hydrogen peroxide is based on the oxidation of iron (II) by 1,10-phenanthroline. To build a calibration graph, 1.00 was placed in volumetric flasks with a capacity of 50 ml; 1.10; 1.20; 1.30; 1.40; 1.50 ml of a standard solution of hydrogen peroxide with a concentration of 1.0 * 10-4 mol / l. Perchloric acid, sodium acetate, iron (II), 1,10-phenanthroline were added to each flask and diluted with water to the mark. We measured optical densities relative to the last standard and got:
VCT, ml 1.00 1.10 1.20 1.30 1.40
Arel 0.340 0.270 0.205 0.135 0.070
Calculate the concentration (mol/l) of H2O2, if 20 ml of the analyzed solution was placed in a volumetric flask with a capacity of 500 ml, the above reagents were added, photometrically, as in the construction of a calibration graph, and the results were obtained: Аotn, x = 0.120.