5. Quantitative analysis by atomic spectroscopy. To measure Ca in breakfast cere

Question

5. Quantitative analysis by atomic spectroscopy. To measure Ca in breakfast cereal, 0.521 6 g of crushed Cheerios was ashed in a crucible at 600'C in air for 2 hours. The residue was dissolved in 6 M HCI, quantitatively transferred to a volumetric flask, and diluted to 100.0 mL. Then 5.00-m aliquots were transferred to 50-ml volumetric flasks. Each was treated with standard Ca (containing 20.0 ug/mL), diluted to volume with H 0, and analyzed by flame atomic absorption (FAAS). Construct a standard addition graph and use the method of least squares to find thex- intercept. Ca2 standard Ca standard (mL) Absorbance 0.151 0.185 0.247 0.300 Absorbance 0.388 0.445 0.572 0.723 m. 8.00 1.00 3.00 5.00 10.00 15.00 20.00 Find wt% Ca in Cheerios, and its uncertainty (bonus).

Explanation / Answer

Concentration of standard:
((20mg/L) x (1L/1000mL))/(6mL x(1L/1000mL))= 0.0033333 mg/mL (standard’s Ca2+ concentration)

((0.0033333 mg/mL)(0.185 AU))/(0.151 AU)=0.0040839mg/mL (Sample’s Ca2+ concentration)

(0.0040839mg/mL)(100mL)=0.40839mg Ca2+ in 0.521g Sample

(0.40839mg (1g/1000mg))/(0.521g Cheerio) x 100= 0.0783858 Ca2+ %(w/w)

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