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Acid Base titration to determine the percentage by mass of calcium carbonate in an egg shell .

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Introduction

Gerald Veliz 11°C - IB Davy College Acid-base titration Investigation # 6 GERALD VELIZ 06/06/2012 ________________ Acid-base Titration Objectives: 1. To determine the percentage by mass of calcium carbonate in an egg shell . Results: The first product is composed by the reactants: 0.6 grams of a ¨impure¨ sample of calcium carbonate and 20cm3 of 1.00 mol/dm3 hydrochloric acid solution, and it forms the following equation: CaCO3 + 2HCl → CaCl2 + CO2 + H2O , which will be later use to complete the objective of the experiment. As having the acidic solution, sodium nitrate of 0.100 mol/dm3 was used to titrate the hydrochloric acid, and with the use of Vernier instruments, the exact volume of sodium nitrate needed to reach the equivalence point, would be obtained. ...read more.

Middle

The pH of the final solution is now alkaline because after the dissociation of the hydrogen ion of the acid which was dissolved in water, it then forms hydroxide ions, which makes the pH to be higher than seven. In the initial part of the curve, this is between 0-9ml of the base solution used, it is called the buffering region, in this region, the amount of strong base added is still not enough to neutralize completely the weak acid. The buffer solution achieves their resistance to pH change because of the presence of equilibrium between the acid (HCl) and its conjugate base (Cl-). The use of the phenolphthalein advertises when it reach an equivalence point, but it doesn´t give an exact quantity results, because when it turns into a purple color, the pH has already pass 7. ...read more.

Conclusion

In respect to the limitations, one of them is in the procedure, where the smash eggshell was mixed with the hydrochloric acid and then it was used directly for the titration. The problem with this was that in the solution, it formed some foam and there was some precipitation of some big pieces of the eggshell, so this it may cause some differences in the volume and concentration of the final solution after the titration. A way to solve this limitation is by making sure that the sample of the eggshell is smash completely, if necessary the use of a colander could be very useful, which will also help to have a more precise mass of the sample. The second part would be to filtrate the solution of the hydrochloric acid and the sample, to eliminate the foam and precipitation left, and then start the titration. ...read more.

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