38. Solving a chemistry problem

1. To determine lead in a sample, a calibration graph was constructed using the following data:
Concentration of standard Pb, µg/ml 2 4 6 8 10
Optical density at 283 nm 0.160 0.320 0.480 0.640 0.800
A sample weighing 0.5 g was dissolved and transferred into a 250.0 ml volumetric flask. The resulting solution was diluted 20 times and the optical density was measured, which was 0.220. Determine the mass fraction of lead in the sample as a percentage.