Acid/Base Titration of an Eggshell

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 bird life. 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:

Standardization of NaOH：Clean and label a 150-ml beaker. Procure an egg from the teacher. 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 burette. Fill the burette with NaOH. Run out enough NaOH from the bottom to remove any air bubbles from the tip of the burette. Refill the burette to the mark close to 0.00 ml and record this amount onto the data table.

Clean a 250 ml conical flask and pipette exactly 10 ml of 0.2000 M HCl into this conical flask. Add approximately 50 ml of distilled water and 2 to 3 drops of phenolphthalein. Mix well.

Slowly add the NaOH into the conical flask until a slight pink color remains throughout the beaker. Record the amount of NaOH added. Determine the Molarity of the NaOH.

Determination of percent calcium carbonate in the eggshell：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 powder and place it into a clean dry 250 ml conical flask. Pipette 25 ml of 0.2000 M HCl and

add this to the conical flask. Boil the mixture for 15 minutes and then allow to cool down. Add a few drops of indicator and titrate this mixture with the NaOH. Determine the number of moles of HCl left in solution. Repeat the above procedures several times to obtain a more accurate reading. 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 for discussion:1. What is the use of pipette?2. What is the use of burette?3. What is STANDARD solution?4. What is the use of Primary standard?5. What is the use of Trial titration (usually the first titration)?6. What is strong acid?7. What is strong base?8. What is the end point of a titration?9. What is/are the purpose of using indicator during titration?10. Suggest any other method to replace the role of indicator in this experiment.

Materials are reference from http://chem.lapeer.org/Chem1Docs/EggshellTitration.html with email approval from Warren B. Brewer on May 2001.

Waste treatment:

Pls collect the excess HCL & NaOH and then collected

into waste bottle which is placed in fume cupboard.