20-21. Standard addition. To measure Ca in breakfast cereal, 0.521 6 g of crushed Cheerios was ashed in a crucible at 600C in air for 2 h.32 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 Ca+ (containing 20.0 g/mL), diluted to volume with HO, 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. Ca+ standard (mL) 0 1.00 3.00 5.00 Absorbance 0.151 0.185 0.247 0.300 Ca+ standard (mL) 8.00 10.00 15.00 20.00 Absorbance 0.388 0.445 0.572 0.723