To spectrophotometrically determine the mass percent of cobalt in an ore containing cobalt and some — Spectrophotometry Chemistry Question

To spectrophotometrically determine the mass percent of cobalt in an ore containing cobalt and some inert materials, solutions with known [Co²⁺] are prepared and the absorbance of each of the solutions is measured at the wavelength of optimum absorbance. The data are used to create a calibration plot, shown below.

[VISUAL]

A 0.630 g sample of the ore is completely dissolved in concentrated HNO₃(aq). The mixture is diluted with water to a final volume of 50.00 mL. Assume that all the cobalt in the ore sample is converted to Co²⁺(aq).