Aim
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…show more content… Therefore, 1.34 × 10-3 mole of HCl was used in the reaction.
However, the solution was diluted by 10 times.
Therefore, number of mole of HCl left after the reaction with CaCO3 = 1.34 × 10-3 × 10 = 0.0134 mol
Number of mole of HCl added = 50/1000 dm3 × 1.003 M = 0.05015 mol
Number of mole of HCl used to react with CaCO3 in eggshells
= 0.05015 – 0.0134 =0.03675 mol
According to the equation:
2HCl(aq) + CaCO3(s) → CaCl2(aq) + H2O(l)+ CO2(g)
2 mole of HCl will react with 1 mole of CaCO3. Therefore, 0.018375 mole of CaCO3 was used in the reaction.
Mass of CaCO3 used = 0.018375 × (40.1 + 12 + 16 × 3) = 1.855875g
Therefore, percentage by mass of CaCO3 in eggshells = 1.855875g/2.00g × 100 % = 92.8 %
Conclusion
The percentage by mass of calcium carbonate in eggshells is determined to be 92.8 %.
Discussion
1. Calcium carbonate may not react with acid with a very fast rate. Therefore, enough acid should be added overnight or the eggshell should be ground into a very fine powder to ensure that all calcium carbonate can be reacted.
2. After the reaction of calcium carbonate with hydrochloric acid, carbon dioxide is formed. The carbon dioxide may affect the experiment. It is because the bubbles of carbon dioxide may cause trouble while diluting the solution into 250 cm3. Moreover, some carbon dioxide may dissolve into the solution and may affect the result. To get rid of carbon dioxide, boiling of
