1,10-Phenanthroline forms a bright red complex with iron(III). The complex has an analytical wavelength of 510 nm and has a high molar absorptivity. Hydroxylamine hydrochloride is added to keep the iron in a reduced +2 state, and the pH is controlled using an acetate buffer. A series of iron(III) phenanthroline solutions were made by adding various amounts of 4.300 × 10-4 M Fe 2+ (stock solution) to 5 mL each of the hydroxylamine hydrochloride, acetate buffer, and 1,10-phenanthroline. Distilled water was added to make the total volume of each solution 50.00 mL. The percent transmittance of each solution was read, using a blank that contains all of the same components as the sample solutions except for the iron(II) solution.

How would you figure the concentration of [Fe(ph)3]2+? They are asking us to find the concentration for several different volumes of it, such as 1.00mL, 2.00mL, etc.