INTRODUCTION:
During the 1960's and 70's the United States used a pesticide called DDT extensively. Unfortunately, the run-off from this pesticide entered our waterways and eventually into many of our wild birdlife. DDT affected the population by weakening the eggshells which would break before hatching. An example of this devastation was the American Bald Eagle whose population was as low as 400 mating pairs in the lower 48 states.
The pesticide has been banned in the United States and the Bald Eagle is no longer on the endangered species list. One method of monitoring the strength of the egg is by determining the percent calcium carbonate in the eggshell. This can be accomplished through an acid/base titration method.
PROCEDURE:
Clean and label a 150 ml beaker. Weigh the clean, dry beaker and record this amount onto your data table. Procure an egg from me. Remove the white and the yolk from the egg and dispose of them down the drain. Wash the shell with distilled water and carefully peel all the membranes from the inside of the shell. Discard the membranes. Place ALL of the shell in the preweighed beaker and dry the shell in the oven overnight.
Acquire a buret. Fill the buret with NaOH. Run out enough NaOH from the bottom to remove any air bubbles from the tip of the buret. Refill the buret to the 0.00 ml mark and record this amount onto the data table.
Clean a 250 ml beaker and pipet exactly 25 ml of 1.0 M HCl into this beaker. Add approximately 50 ml of distilled water and 2 to 3 drops of phenolphthalein. Mix well.
slowly add the NaOH into the beaker until a slight pink color remains throughout the beaker. Record the amount of NaOH added. Determine the Molarity of the NaOH.
Take out the eggshell from the oven and cool to room temperature. Reweigh the beaker with the eggshell and record this weight onto the data table. Determine the weight of the eggshell.
Place the eggshell in a mortar and grind it into a powder with the pestle. Weigh out 0.2 grams of the eggshell and place it into a clean dry 250 ml beaker. Pipet 50 ml of HCl and add this to the beaker. Stir for 5 minutes. Titrate this mixture with the NaOH. Determine the number of moles of HCl left in solution. Determine the moles of Calcium Carbonate in the mixture. Determine the percent calcium carbonate in the entire eggshell. The reactions taking place are:
2 HCl + CaCO3 -------------> CaCl2 + H2O + CO2
HCl + NaOH _________> H2O + NaCl
Questions? Comments??
Warren B. Brewer