Map d Sapling Learning An environmental chemist working for the Environmental Pr

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 clam

Explanation / 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

Related Questions

Navigate

• Browse (All)
• Browse M
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.