Henry works in an analytical laboratory testing for lead contamination in soils.

Question

Henry works in an analytical laboratory testing for lead contamination in soils. The following details reflect one of the samples he analyzed. Correct for the indicated dilutions and determine the ppm Pb in the actual soil. In solutions ppm represents mg/L and in solid samples ppm represents mg/kg. Procedure. 0.1564 g of soil was placed in a microwave vessel and digested or dissolved with 10.00 mL of concentrated nitric acid followed by 2.00-mL of hydrogen peroxide. The digested sample(remaining liquid) was transferred to a 100-mL volumetric flask and diluted to volume with distilled, deionized water. From this 100-mL flask, a 5.00-mL aliquot was taken and diluted to 50-ml with water. The ICP-AES analysis indicated that the concentration in the 50-mL flask was 0.050 ppm Pb in the original soil sample?

Explanation / Answer

we had 50 ml of 0.05 ppm                    since ppM is mg/L   we consider vol in L hence50 ml = 0.05 L

which means Pb mass = (0.05 xmg/L) x 0.05 = 0.0025 mg

this is actually presnet in 5 ml aliquot taken

Hence for 100 ml aliquot we have Pb = ( 100/5) x 0.0025 = 0.05 mg

This is actually Pbmass in soil = 0.05 mg

soil mass = 0.1564 g = 0.1564 x 10^ -3 Kg

Conc in ppm = mass off Pb in mg / soil mass inKg   = ( 0.05 /0.1564x10^-3) = 319.7 ppm

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