145. Solving a chemistry problem

48 (2). To build a calibration curve in the coordinates Aorn-C Mn, 11.00 12.00 13.00 14.00 15.00 ml of a standard solution containing 1.25 mg / ml Mn was placed in measuring flasks with a capacity of 250.0 ml and oxidized to permanganate . The optical density was measured relative to a solution containing 12.5 mg of Mn in 250.0 ml and received:
Vst, ml 11.00 12.00 13.00 14.00 15.00
Aoth 0,200, 0,400, 0,600 0,800 1,010
A portion of the ore weighing 0.5000 g was dissolved and the solution was diluted to 1000 ml. Manganese was oxidized to 50.0 ml of the filtrate to permanganate and diluted to 250.0 ml. Measured relative optical density, as in the construction of the calibration curve. Calculate the mass fraction of manganese in the ore samples if the values ​​Anx = 0.420 are obtained for them