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Determination of Calcium Carbonate in Eggshells by Acid/Base Titration

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Introduction

DETERMINATION OF CALCIUM CARBONATE IN EGGSHELLS BY ACID/BASE TITRATION OBJECTIVE To determine the mass percent of calcium carbonate (CaCO3) in an eggshell. INTRODUCTION During this lab, the percentage of CaCO3 in an eggshell is determined by reacting the eggshell with hydrochloric acid. The equation for this reaction is: 2HCl (aq) + CaCO3(s) ? Ca2+ (aq) + CO2(g) + H2O(l) + 2Cl- (aq) This reaction cannot be used directly to titrate the CaCO3. Instead, an excess of hydrochloric acid is added to dissolve the eggshell, and the remaining acid is titrated with NaOH solution to determine the amount of acid that did not react with the eggshell. The equation used to determine the amount of leftover acid is: HCl(aq) + NaOH(aq) ? H2O(l) + Na+(aq) + Cl- (aq) In order to help the hydrochloric acid dissolve the CaCO3, ethyl alcohol is added to the eggshell as a wetting agent. ...read more.

Middle

Hydrochloric acid Extremely corrosive. Inhalation of vapor can cause serious injury. Ingestion may be fatal. Liquid can cause severe damage to skin and eyes. Sodium hydroxide Very corrosive. Causes severe burns. May cause serious permanent eye damage. Very harmful by ingestion. Harmful by skin contact or by inhalation of dust. Wear suitable gloves (Neoprene or PVC). Products Calcium chloride (anhydrous) Irritating to eyes. Do not breathe dust and avoid contact with skin. Carbon dioxide In high concentration acts as an asphyxiant. Respiratory stimulant. If working with carbon dioxide in confined spaces where the concentration of gas may build up, ensure adequate ventilation. Sodium chloride May cause skin, eye or respiratory irritation. Not believed to present a significant hazard to health. Others Ethyl alcohol Causes skin, eye and respiratory system irritation. Ingestion can cause nausea, vomiting and inebriation; chronic use can cause serious liver damage. Highly flammable. Keep container tightly closed. ...read more.

Conclusion

Any membrane remnants would have reacted with the NaOH titrant; therefore, not all of the titrant would have reacted directly with the hydrochloric acid. One would have to consider that the volumes of the titrant measured would also include the amount of titrant reacted with the membranes. * Incomplete Dissolution of the Eggshell It is important that all of the ground eggshell dissolves because it contains the CaCO3 that is being analyzed in the experiment. The reaction between the CaCO3 and the hydrochloric acid might not have been completed if the flasks were removed from hotplates too early, since the higher temperature is beneficial in increasing the rate of said reaction. If that is the case, there would have been a greater volume of hydrochloric acid remaining in the flasks before the titrations. Therefore, the calculated mass percent CaCO3 in the eggshell would be lower than it would have been had all of the CaCO3 dissolved. 1 Brewer, Warren B. http://chem.lapeer.org/Chem1Docs/EggshellTitration.html 2 Butcher, Dr. Gary D. and Miles, Dr. Richard D. Concepts of Eggshell Quality. http://www.afn.org/~poultry/flkman4.htm ?? ?? ?? ?? ...read more.

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