The Calcium Carbonate Content of White to Brown Eggshells

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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 as seashells, rocks, and eggshells . Much information has been learned about eggshell quality during the past fifty years. During this period of time, the genetics of the chicken diets, house design and management practices have changed dramatically. In the future it is very likely that additional changes will have to be made by the commercial egg industry. In my investigation I am particularly focused in determining the amount of calcium carbonate present in white (chicken) eggshells and brown eggshells. The reason for choosing this topic is that no matter what changes occur, the eggshell needs to be as strong as possible to maximize the number of eggs reaching the market, thus, this topic might be treated as a really relevant issue nowadays.

As hard as calcium carbonate substance is , it reacts readily with hydrochloric acid to yield carbon dioxide gas (and two other products). During the experiment I will investigate the reaction between 1 M hydrochloric acid solution and calcium carbonate in eggshells in order to compare the calcium carbonate composition of white to brown eggshells.

RESEARCH QUESTIONTo what extent do white and brown eggshells differ in respect to percentage by mass of calcium carbonate content?2 BACKGROUND INFORMATION2.1 The concepts of eggshell qualityA good quality eggshell should contain, on average, 2.2 grams of calcium in the form of calcium carbonate. Approximately 95% of a dry eggshell is calcium carbonate and has a typical mass of 5.5 grams, although these values can differ depending on sources. The remaining mass is composed largely of phosphorus and magnesium, and trace amounts of sodium, potassium, zinc, manganese, iron, and copper.

If the calcium from the shell is removed, the organic matrix material is left behind. This organic material has calcium binding properties and its organization during shell formation influences the strength of the shell. The organic material must be deposited so that the size and organization of the crystalline components (calcium carbonate mostly) are ideal, thus leading to a strong shell. The majority of the true...
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