Composition Of Calcium Carbonate In An Egg Shell

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Aim of the Experiment: To investigate volumetrically the percentage composition of calcium carbonate in an egg shell, using back titration and to analyze the sources of error to evaluate the results of the experiment. Equations: Part A. C6H4COOH.COOK + NaOH  C6H4COOK.COONa Part B. NaOH + HCl  NaCl + H2O Part C. CaCO3 + 2HCl  CaCl2 + CO2 + H2O Qualitative Observations: The egg shell was broken down into small piece in mortar and pestle, then it was added in hydrochloric acid, effervescence was observed this shows CO2 is released. And then Ethanol was added to the solution for the fizzing to stop raising up. And then phenolphthalein indicator was added to the solution after the fizzing has stopped, so that the…show more content…
Volume of total HCl acid = (60.00 ±0.05)/1000 = 0.06000 ± 0.00005 dm3 Volume of NaOH used to neutralize excess HCl acid = (63 ±0.05)/1000 = 0.06300 ± 0.00005 dm3 Number of moles of NaOH used to neutralize excess HCl acid: n = c × v = 0.733 × 0.06300 = 0.0462 moles Δn = n(Δv/v+Δc/c) = 0.0462×(0.00005/0.06300+0.010/0.733) = 0.0006 moles = 0.0462 ± 0.0006 moles Mole ratio of NaOH and excess HCl, initial number of moles of excess HCl: NaOH: HCl = 1: 1 (referred in equation 2 given) = 0.0462 ± 0.0006 moles Initial number of moles of HCl acid used : n = c × v = 1.57 × 0.06 = 0.094 moles Δn = n(Δv/v+Δc/c) = 0.094×(0.00005/0.06000+0.02/1.57) = 0.0012 n = 0.094 ± 0.001 moles Number of moles of HCl acid reacted with calcium carbonate: Initial number of moles of HCl acid – number of moles of excess HCl acid = (0.0940 ± 0.0010) - (0.0462 ± 0.0006) = 0.0478 moles Uncertainties = 0.0010 + 0.0006 = 0.0004 moles = 0.0478 ± 0.0004 moles Ratio of calcium carbonate and HCl acid, number of moles of calcium carbonate reacted: CaCO¬3: 2HCl = 1: 2 (referred in equation 3 given) = (0.0478 ±0.0004)/2 = 0.0239 ± 0.0002 moles Mass of calcium carbonate…show more content…
Then I found out the concentration of HCl by reacting HCl with NaOH and then used simple titration. This gives me a chance to calculate the mass of the calcium carbonate followed by the percentage of the calcium carbonate in the egg shell. The mass of the calcium carbonate which I have achieved is 2.39 ± 0.02g. The percentage purity of calcium carbonate in the egg shell I found is 48.5 ± 0.6%. All the results which I have achieved are all dependent on the shape, size, and mass of the egg as well as the source used, so there is no specific value to compare my percentage composition to. But many stats which I found online shows that the percentage composition of calcium carbonate is ranging from 70% to 95% (Source: "To Determine the Percentage of Calcium Carbonate in Eggshell." Docstoc.com. N.p., n.d. Web. 23 July 2014. <http://www.docstoc.com/docs/101809828/To-determine-the-percentage-of-calcium-carbonate-in-eggshell>. And "Calcium Carbonate." Calcium Carbonate. N.p., n.d. Web. 23 July 2014. <http://www.ukessays.com/essays/chemistry/calcium-carbonate.php>.) but the reason I am not getting the results in this range is
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