Map d Sapling Learning An environmental chemist working for the Environmental Pr
ID: 1088255 • Letter: M
Question
Map d Sapling Learning An environmental chemist working for the Environmental Protection Agency (EPA) was directed to collect razor clams from a heavily-contaminated river superfund site and analyze them for their Cd content using graphite furnace atomic absorption spectrometry (GFAAS). The chemíst dried the clams at 95 C overnight and ground them in a scientific blender, resulting in approximately 50 g of homogenized dry weight. A representative 88.91 mg sample was taken from the approximately 50 g of dry material and dissolved in 100.0 mL of 0.1 M HCI to create a sample solution. Using the method of standard additions, the chemist prepared five standard solutions in 100.0-mL volumetric flasks, each containing 5.00-mL aliquots of the sample solution. Varying amounts of a 78.0 ppb (/L) Cd2+ standard were added to each of the flasks, which were then brought to volume with 0.1 M HCI. The Cd2 content of the solutions was then analyzed using GFAAS, resulting in the following absorbance data. Sample Vol. (mL) Cd Standard Vol. (mL) Absorbance 5.00 5.00 5.00 5.00 5.00 0.00 2.50 5.00 7.50 10.00 0.080 0.119 0.163 0.200 0.241 Determine the amount of Cd2 per gram of dry clam. Express your final result as milligrams of Co? per gram of dry clam Number mg cd* /g clamExplanation / Answer
Analysis of clam for Cd2+ content
standard addition method
from first two reading in the table
concentration of standard in 100 ml solution [2.50 ml] = 78 ug/L x 2.50 ml/100 ml = 1.95 ug/L (let this be Cs)
let concentration of Cd2+ in this diluted solution = Cx
absorbance for solution without standard (Ax) = 0.080
absorbance for solution with 2.50 ml standard (A) = 0.119
Using,
Cx/(Cx + Cs) = Ax/A
feeding values,
Cx/(Cx + 1.95) = 0.080/0.119
Cx = 4 ug/L
concentration of Cd2+ in diluted solution = 4 ug/L x 0.1 L = 0.4 ug
this is in 5 ml solution
so, concentration Cd2+ in original 100 ml solution (88.91 mg) = 0.4 ug x 100/5 = 8 ug
concentration Cd2+ in original 50 g sample = 8 ug x 50/0.08891 = 4499 ug = 4.5 mg
Hence,
amount of Cd2+ per gram of dry clam = 4.5 mg/50 g = 0.09 mg Cd2+/g dry clam