1. Chemistry Project 06 - 07 Lau Ching Fai(8) Tze Chi Ho(21)
Kwan Siu Hong(5) Lee Chun Tak(10)

2. Title:
To determine the percentage of calcium carbonate in eggshell

3. Principle
The major component of eggshells is calcium carbonate (CaCO3). Calcium carbonate (limestone) is very insoluble in pure water but will readily dissolve in acid according to the equation :
 2HCl (aq) + CaCO3(s) ----> Ca2+(aq) + CO2(g) + H2O(l) + 2Cl- (aq)
By adding an excess of acid to dissolve all of the CaCO3 and then titrating the remaining H3O+ with NaOH solution to determine the amount of acid which has not reacted with the calcium carbonate.
The difference between amount of the acid (HCl) initially added and the amount left over after the reaction is equal to the amount used by the CaCO3. The reaction used to determine the leftover acid is according the equation:
   HCl (aq) + NaOH (aq) ----> H2O(l) + Na+(aq) + Cl-(aq)

4. Chemicals: Sample A (Brown Eggs) x 1g Sample B (Leghorn Eggs) x 1g
Hydrochloric acid(1M) x 50ml
Distilled water x 100ml
Sodium hydroxide (0.2M) X 200ml
Ethanol x 30ml
Phenolphthalein (a few)

5. Experimental procedures:
Eggs were boiled
Removed the eggshell that the protein membrane was left behind
The eggshells was ground into fine powder
Placed the ground powder in a drying oven for about 10 minutes
Weighed accurately about 0.1 gram of each sample into a conical flask

6. Added 5ml ethanol into the flask (This acts as a wetting agent and helps the HCl dissolve the CaCO3)
Added 10ml hydrochloric acid(1M) into the flask
Heated the solutions in the flasks until they begin to boil and allow to cool

7. Add 3-4 drops of phenolphthalein to each flask
Filled the burette with the NaOH(0.2M) solution
Recorded the initial volume and titrate the sample with NaOH to persistent pink color
Read and recorded the final volume
Repeated the titration with other samples

8. Mass of eggshell dissolved
Experimental results:
Sample A : Brown Eggs
Sample B : Leghorn Eggs
Table to show the result of weighing
Trial 1
Trial 2
Trial 3(only sample B)
Sample A B
Bottle + eggshell
8.02g
8.49g
8.10g
8.55g
8.03g
Bottle + residue
7.92g
8.36g
7.97g
8.43g
7.90g
Mass of eggshell dissolved
0.1g
0.13g
0.12g

9. Initial burette reading
Table to show the result of titration
Sample A
Sample B
Trial 1
Trial 2
Trial 3
Final burette reading
43.2 cm3
44.3 cm3
41.9 cm3
43 cm3
39.9 cm3
Initial burette reading
1.2 cm3
4.8 cm3
1.9 cm3
2.1 cm3
1.0 cm3
Volume of NaOH used
42 cm3
39.5 cm3
40 cm3
40.9 cm3
38.9 cm3
Average : 40.8 cm3
Average : 39.9 cm3

10. Calculations:
Calculate the number of moles of HCl added to each shell sample
Calculate the moles of HCl left in each sample after the reaction with CaCO3
For each sample determine the number of moles of HCl that has reacted with CaCO3 by taking the difference between the moles of HCl added and the moles of HCl remaining after the reaction is complete
The moles of CaCO3 in each sample
Calculate the percent CaCO3 in each sample

11. For Sample A (Brown Eggs)
Trial 1
Trial 2
Mass of eggshell
0.10 g
0.13 g
Volume of HCl
10ml
Volume of NaOH
42 cm3
39.5 cm3
Moles of HCl
(10/1000)(1) = 0.01 mol
Moles of NaOH to neutralize the excess moles of HCl
(42/1000)(0.2)
= mol
(39.5/1000)(0.2)
= mol
mol of HCL reacted = mol of HCL - mol of NaOH
0.01 –
= mol
0.01 –
= mol
mol of CaCO3(1/2mol of HCL reacted)
mol
mol
Molar mass of CaCO3
100.1 g mol-1
percentage of CaCO3
Trial 1 (0.0008)(100.1)(100%)/0.1=80.08%
Trial 2 ( *100.1*100)/0.13=80.85%
Average : ( )/2=80.465%

12. Sample B (Leghorn Eggs)
Trial 1
Trial 2
Trial 3
Mass of eggshell
0.13 g
0.12 g
Volume of HCl
10ml
Volume of NaOH
40 cm3
40.9 cm3
38.9 cm3
Moles of HCl
(10/1000)(1) = 0.01 mol
Moles of NaOH to neutralize the excess moles of HCl
(40/1000)(0.2)
=0.008 mol
(40.9/1000)(0.2)
= mol
(38.9/1000)(0.2)
= mol
mol of HCL reacted = mol of HCL - mol of NaOH
0.01 – 0.008
=0.002 mol
0.01 –
= mol
0.01 –
= mol
mol of CaCO3(1/2mol of HCL reacted)
mol
mol
mol
Molar mass of CaCO3
100.1 g mol-1
percentage of CaCO3
Trial 1 (0.001*100.1*100%)/0.13=77%
Trial 2 ( *100.1*100)/0.12=75.9%
Trial 3 ( *100.1*100)/0.13=85.47%
Average: ( )/3=79.157%

13. Remarks:
Safety goggles should be put on during heating
Be careful when using Bunsen burner
Take great care of 1M HCl because it is corrosive
Dilute the acid by pouring it into sink with slowly running water
Sources of errors:
The eggshell powder did not dissolve completely.
Some ethanol may evaporated.
The eggshells may contained impurities.
Variation in visual judgment at the end point.

14. Conclusion:
As the percentage of CaCO3 in Brown Eggs and Leghorn Eggs are
80.465% and % respectively, these show that the main component
of eggshells is CaCO3. This result is less than our expectation because of
the presence of DDT. How does DDT affect the thinness of eggshell?
Let’s get an answer……..

15. Further study - The side effects of DDT
DDT is a colourless crystalline substance which is practically insoluble in water but highly soluble in fats and most organic solvents.
It kills insects by opening sodium ion channels in neurons, causing the neuron to fire spontaneously
Side effects:
DDT cause cancer
Killing higher level organisms like the birds.
Harm bird reproduction by weakening and thinning eggshells since eggshells mainly contain CaCO3
Therefore DDT should be banned
The molecular structure of DDT

16. THANK YOU !