Eggshell Lab Report

Purpose: The aim of this experiment is to determine the percentage by mass of Calcium Carbonate present in a sample of white eggshells using the back titration method. Introduction: By definition, an eggshell is the thin and hard outer covering of an egg and its other forms with soft outer coats. In the preceding years, insecticides such as dichlorodiphenyltrichloroethane (DDT) have been used expansively. Its harmful effects have affected the living systems we come to know of. One example would be the wearying or diminishing eggshell strength of certain wild birds. The consequence of such action has resulted to the breakage of the eggshells, even before it is given the chance to hatch itself. Needless to say, the strength of an eggshell

This practical makes use of a technique known as back titration. A known excess of acid is added to the sample ensuring that the reaction goes to completion. The excess acid is then diluted with water, made up to a known volume and then titrated against a standard solution of sodium hydroxide. The amount of acid that reacted with the sample can then be deduced. The equation used to deduce the amount of remaining acid is: HCL (aq) (leftover) + NaOH (aq)à NaCl(aq) +

Put on safety goggles and a lab apron.

2. 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 a pre-massed beaker, and dry the shell in the drying oven at 110°C for about 15 min.

3. While waiting for eggshell, prepare the burette for the NaOH solution using cleaning and rinsing protocol learned in previous titrations.

4. Prepare a burette to use for the HCl in the same manner as above.

5. Remove the eggshell and beaker from the oven. Cool them in a desiccator, if available.

6. Record the mass of the entire eggshell in table 1. Place half the shell in a clean mortar, and grind it to a very fine powder. This will save time when dissolving the eggshell. (If time permits, dry the crushed eggshell again, and cool it in the desiccator.)

7. Measure the mass of a piece of weighing paper or boat. Transfer about 0.5 g of ground eggshell to a piece of weighing paper, and measure the eggshell’s mass as accurately as possible. Record the mass in table 1. Place this eggshell sample in a clean 125 or 200 mL bottle or Erlenmeyer flask. A flask will make it easier to swirl the mixture when