The Calcium Carbonate Content of White to Brown Eggshells

Essay by ievadruHigh School, 12th grade February 2010

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ABSTRACTDuring my experiment, I have been investigating my research question: ‘To what extent do white and brown eggshells differ in respect to percentage by mass of calcium carbonate content?’Calcium carbonate is a substance found in the eggshells giving them hardness and strength. It is essential to the commercial egg industry that the biggest possible amount of eggs reaches the market. Hence, as calcium carbonate reacts steadily with hydrochloric acid to produce carbon dioxide as well as two other substances, I investigated which type of an eggshell contains more calcium carbonate. This reaction cannot be used directly to titrate the calcium carbonate because it is very slow when the reaction is close to the endpoint. Hence, I carried out ‘back titration’ by adding an excess of hydrochloric acid to dissolve all of the calcium carbonate and then titrating the remaining H3O+ with sodium hydroxide solution. This way I could determine the amount of acid which has reacted with the calcium carbonate, hence, the calcium carbonate content of a sample of an eggshell.

The results of the investigation proved my hypothesis that brown eggshells contain more calcium carbonate than white eggshells do. This trend comes from the difference in the hens dietary. The average mass percent of calcium carbonate in brown eggshell is 91% while in the white eggshell it is 87.6 %. The difference between these means and the theoretical value of 95% might have come from such methodological flaws as the calcium carbonate that failed to dissolve or the remnants of the organic inner membrane of an egg. Further suggestions for the experiment might include broader eggshells sampling and investigation into more features of an eggshell, not only the mineral content.

1 INTRODUCTIONCalcium carbonate, CaCO3, is found in the nature giving hardness and strength to things such...