To measure Ca in breakfast cereal, 0.521 6 g of crushed Cheerios was ashed in a

Question

To measure Ca in breakfast cereal, 0.521 6 g of crushed Cheerios was ashed in a crucible at in air for 2 h.22 The residue was dissolved in 6 M HCl, quantitatively transferred to a volumetric flask, and diluted to 100.0 mL. Then 5.00-mL aliquots were transferred to 50-mL volumetric flasks. Each was treated with standard (containing ), diluted to volume with , and analyzed by flame atomic absorption. Construct a standard addition graph and use the method of least squares to find the x-intercept and its uncertainty. Find wt% Ca in Cheerios and its uncertainty.

Ca2+ Standard Absorbance (mL) 0 0.151 1 0.185 3 247 5 0.3 8 0.388 10 0.445 15 0.572 20 0.723

Explanation / Answer

Concentration of standard:
((20mg/L) x (1L/1000mL))/(6mL x(1L/1000mL))= 0.0033333 mg/mL (standard

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