The purpose of this experiment is to determine the percentage by mass of calcium carbonate in eggshells. Introduction To avoid the breakage of eggs before reaching market, the eggshells needs to be as strong as possible. The strength of eggshells is mainly determined by the percentage of calcium carbonate in it. In order to monitor the quality of eggshells, the following experiment has to be done to determine the percentage of calcium carbonate in eggshells. In this experiment, back titration is used.
First, excess acid is reacted with the calcium carbonate in eggshells: 2HCl(aq) + CaCO3(s) > CaCl2(aq) + H2O(l)+ CO2(g) Later, if we can find out the number of mole of unreacted acid, number of mole of calcium carbonate can then be found out. The number of mole of unreacted acid can be found by titration with the following reaction: HCl(aq) + NaOH(aq) > H2O(l) + NaCl(aq) Percentage by mass of calcium carbonate in eggshell can then be calculated by the following formula: % by mass of CaCO3 = Requirements eggshell burette, 50 cm3, and stand pipette, 25 cm3 pipette filler methyl orange indicator M NaOH solution, standardized 1 M hydrochloric acid, standardized ethanol wash-bottle with de-ionized water mortar and pestle forceps safety spectacles 2 beakers, 100 cm3 volumetric flask, 250 cm3 filter funnel, small magnetic stirrer pH meter electronic balance Procedures 1. The attached membrane of the eggshell was removed carefully by forceps and the remaining eggshell was ground into a fine powder with mortar and pestle. 2. 2 g of powder was weighed accurately by the difference on an electronic balance and put into a beaker on a magnetic stirrer.