Determine the %w/w of Ca in the original crushed eggshell sample.
Back titration: The major component of eggshells is calcium carbonate (CaCO3)(CaCO3) . To determine its calcium content, a back titration was done as described. 0.7520 g of dry, crushed eggshell was placed into an Erlenmeyer flask and dissolved with 25.00 mL of 1.026 M HCl according to the following reaction.
CaCO3(s)+2HCl(aq)→CaCl2(aq)+H2O(l)+CO2(g)CaCO3(s)+2HCl(aq)→CaCl2(aq)+H2O(l)+CO2(g)
To assist with the reaction between the HCl and CaCO3CaCO3 , the solution was heated to a boil, and then left to cool. Once no more CO2(g)CO2(g) was being produced (the bubbling had stopped), approximately 25 mL of deionized water was added to the flask, and its contents were quantitatively transferred to a 100.00 mL volumetric flask. The volumetric flask was filled to the mark with deionized water and mixed. A 25.00 mL aliquot of the diluted CaCO3CaCO3 sample was pipetted into a separate Erlenmeyer flask and titrated with 22.96 mL of standardized 0.1080 M NaOH to the phenolphthalein end point. Determine the %w/w of Ca in the original crushed eggshell sample.
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