Question

A calibration curve was created using a solution made up of 0.08 g Pb(NO₃)₂ diluted in a 500 mL volumetric flask with 0.28% HNO₃ solution. Dilutions were made at 2.5, 5.0, 7.5, and 10.0 ppm to generate the curve. A 0.5 g brass sample was prepared by adding 5 mL HNO₃ and 5 mL HCl, then diluted with 0.28% HNO₃ solution in a 100 mL volumetric flask. A 3:200, 2:100, and 5:200 dilute solution was made (using 0.28% HNO₃) from the unknown sample and placed in a 100 mL volumetric flask. From the data below, what is the % Pb in the unknown brass sample?

Concentration (mg/L)	Absorbance
2.5	0.05
5.0	0.9
7.5	0.13
10.0	0.17
4.8	0.08	3:200
6.7	0.1	2:100
8.9	0.15	5:200