in 1. From a sample of ore weighing m (g) containing niobium, after appropriate processing, 100.0 ml of solution was obtained. Place 2.00 in volumetric flasks with a capacity of 25.00 ml; 3.00 and 3.00 ml of the resulting solution and 1.00 ml of a standard solution containing 10.0 µg/ml niobium was added to the third flask. EDTA, tartaric and sulfuric acids, lumogallion IREA were poured into each flask, heated to accelerate the complexation reaction, cooled and brought to the mark. The optical densities of the second (Aotn.2) and third (Aotn.3) solutions were measured relative to the solution in the first flask. Calculate the mass fraction (%) of niobium in the ore for the following options:
option 1 2 3
m, g 0.1000 0.1500 0.2500
Aotn,2 0.325 0.310 0.245
Aotn,3 0.510 0.495 0.430

Answer: 1) 1.76%; 2) 1.12%; 3) 0.53%.

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