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Name: 9. (15 points) A 5.00 g soil sample was analyzed for biologically available Pb2+ by suspending 50.00 grams of sample in 500.00 mL of 2.4% (w/w) acetic acid. The sample is shaken in a mechanical wrist action shaker for 24 hours. The sample is then centrifuged, and the liquid phase is removed and filtered through a 0.5um filter. The sample is analyzed by anodic stripping voltammetry. A 10.00 mL aliquot of the sample is placed into a 25.00 mL volumetric flask then 0 to 200 uL of a 10 ppm Pb standard was added, followed by 100 uL of 16 M HNO3. The sample is then diluted to volume. The sample is quantitatively transferred to the electrolysis cell. The sample is analyzed on a static mercury drop electrode. Lead deposition occurs by applying a -700mV potential to the mercury drop for 4 minutes. The deposited lead is then stripped from the Hg drop using a square wave voltammetry (-700 V to -100 V). The current peak is recorded. The results from a series of analysis are presented below. What is the concentration of Pb in the sample in ppb and mol/L? What is the concentration of Pb in the soil (use ppm units or mg/Kg)? Note that the units of standard addition are uL. Pb by ASV 4.000E-07 3.500E-07 y = 1.43E-09x + 5.98E-08 R2 = 9.98E-01 3.000E-07 2.500E-07 Signal (UA) 2.000E-07 1.500E-07 1.000E-07 5.000E-08 0.000E+00 0 50 100 150 200 250 uL of 10 ppm std