1. Determine the calcium carbonate content of a sample of an egg shell
08-09 Chemistry Report
Determine the calcium carbonate content of a sample of an egg shell
Members : Ho chi nam Tong wing kwan Chan siu sing Chan sing yeung Lee cheung fat

2. Introduction
The pesticide DDT has caused significant damage to the environment and its wildlife.
Birds are especially affected because the DDT weakens the shells of their eggs which would break before hatching.
This caused certain bird species to become endangered (i.e. the American bald eagle).
One method of monitoring the strength of the egg is by determining the percentage of calcium carbonate in eggshell

3. Principle
During this experiment,the percentage of CaCO3 in an eggshell is determined by reacting the eggshell with hydrochloric acid.
2HCl(aq)+CaCO3(s)→Ca2+(aq)+CO2(g)+H2O(l)+2Cl-(aq)

4. Back titration
This reaction cannot be used directly to titrate the CaCO3 because it is dissolved in water .Thus ,we must use back titration.
Back titration is an analytical chemistry technique that allows the user to find the concentration of a reactant of unknown concentration by reacting it with an excess volume of another reactant of known concentration.

5. The resulting mixture is then titrated back, taking into account the molarity of the excess that was added.
Through to find out the molarity of resulting mixture,we can calculate the abundant of an unknown sample

6. In this experiment,excess of standard hydrochloric acid is added to dissolve the eggshell.
Ethyl alcohol is added to eggshell as a wetting agent to help the hydrochloric acid dissolve the CaCO3.
Wetting agents are chemicals that increase the spreading and penetrating properties of a liquid by lowering its surface tension – that is, the tendency of its molecules to adhere to each other.

7. The remaining acid is titrated with NaOH solution.
determine the amount of acid that did not react with the eggshell HCl(aq)+NaOH(aq)→H2O(l)+Na+(aq)+Cl-(aq)
Through to find out the amount of acid ,we can calculate the abundant of CaCO3.

8. Experimental apparatus
Wash bottle x1
Conical flask x4
Mortar and Pestle x1
Filter funnel x1
Electronic balance x1
50.00ml Burette x1
White tile x1
25.00ml pipette
250.00ml beaker x2
Oven x1
Bunsen burner x2
Tripod x2
250.00ml volumetric flask x2

9. Experimental Chemical
Phenolphthalein
M NaOH
0.2175M HCl
Enthanol
Distilled water
Paper towel
Egg shell x2 (import form USA and Malaysia respectively)

10. Preparing fine egg shell powder:
Procedure
Preparing fine egg shell powder:
Eggs were put into boiling water for 5 minutes.
Eggshells of 2 eggs were washed with distilled water.
Eggshells of 2 eggs were obtained by break the eggs shell.

11. The inside membrane was removed.
The eggshell of 2 eggs was put into oven for 15 minutes.
The eggshell powder of 2 eggs were ground by using mortar and pestle.

12. Preparation
0.20g of dried eggshells powder was weighed into each of 4 conical flask accurately.
25.00cm3 of M HCl solution was pipetted into each flask.
5.00cm3 of ethanol was added to each flask.
The flasks were swirled to wet all of the solid . Any excess HCl should be disposed in the sink by diluting with water.

13. The solutions in the flasks were heated until they began to boil and allow to cool .The walls of the flasks were rinsed with distilled water from the wash bottle.
3 drops of phenolphthalein was added to each flask.

14. 7. A funnel was used to partly fill a clean burette with NaOH solution to rinse it.
8. The burette was filled with NaOH solution by using a funnel, and some solution were run out to remove all bubbles from the tip.
9. The initial volume was recorded.

15. 10. Titrate the first sample to get a reference.
11. Titrate other three samples and record the results.
12. Calculate the percentage of calcium carbonate in each sample and the mean value.
13. Calculate the average deviation from the mean.

16. Results Table showing the titration result of Malaysia egg shell :
Trial 1 2 3
Aveage
Volume
Final burette reading
26.1
26.6
25.2
27.2
Initial burette reading
1.5
0.5
2.8
3.4
Volume of NaOH used
24.6
22.4
23.8
24.1
Table showing the titration result of U.S.A egg shell :
Titration
Trial 1 2 3
Aveage
Volume
Final burette reading
28.6
29.2
30.2
47.8
Initial burette reading
0.1
0.4
17.7
Volume of NaOH used
29.1
29.8
30.1

17. Calculations the initial moles of HCl = 0.2175M x 25cm3/1000cm3
= x 10-3 mol
HCl (aq) + NaOH (aq)→NaCL (aq) + H2O (l)
1 mole of HCl (aq) react with 1 mole of NaOH (aq)
the moles of HCl react with NaOH = the moles of NaOH used
= x 24.1cm3/1000cm3
= x 10-3 mol

18. The moles of HCL react with CaCO3 = the Initial moles of HCl – the moles of HCl reacted with NaOH
= x 10-3mol – x 10-3mol
= x 10-3mol

19. CaCO3 (s) + 2HCl (aq) →CaCl (aq) + H2O (l) + CO2 (g)
1 mole of CaCO3 react with 2 moles HCl
The moles of CaCO3 = x 10-3mol / 2
= x 10-3 mol
Percentage of CaCO3 in eggshell = x 10-3mol x( x3)g-mol/0.2g x 100
= 75.05%

20. the initial moles of HCl = 0.2175M x 25cm3/1000cm3
= x 10-3 mol
HCl (aq) + NaOH (aq)→NaCL (aq) + H2O (l)
1 mole of HCl (aq) react with 1 mole of NaOH (aq)
the moles of HCl react with NaOH = the moles of NaOH used
= x 29.8cm3/1000cm3
= x 10-3 mol

21. The moles of HCL react with CaCO3 = the Initial moles of HCl – the moles of HCl reacted with NaOH = x 10-3 x 10-3mol – x 10-3mol
= x 10-3mol

22. CaCO3 (s) + 2HCl (aq) →CaCl (aq) + H2O (l) + CO2 (g)
1 mole of CaCO3 react with 2 moles HCl
The moles of CaCO3 = x 10-3mol / = x 10-3 mol
Percentage of CaCO3 in eggshell = x 10-3 mol x( x3)g-mol/0.2g x 100
=60.61%

23. Observations
Bubbles appeared when dissolving egg shell powder by HCl(aq).
Eggshell powder could not completely dissolve in HCl.
The sodium hydroxide solution was colourless.
When the sodium hydroxide solution was added to the mixture of eggshell and hydrochloride, the mixture turned pink.

24. Remarks
Ethanol must be added before the boiling of mixture of eggshell and hydrochloride.
The ethanol should be stored in a closed vessel and was pipette only when it was used.
When the mixture heated to 80oC,the titration was started immediately.
Shark flask continuously during the titration.
Make sure that the eggshell powder was dry.
The conical flask should be heated by air bath because the mixture contain ethanol which is flammable.

25. Source of error Variation in visual judgement at the end point.
Eggshell powder could not dissolve completely in HCl.
The inside membrane was not completely removed.
The mixture was not heated enough.
Although after through rinsing,not all the eggshell powder is transferred to the volumetric flask.

26. Precautions
The hydrochloride acid and Sodium hydroxide solution are corrosiveness.
During the heating, the safety goggles must be weared.
Label the containers of each solution because they are colorless solution.
We should wash our hands after the experiment.

27. It reflect that the pollution of DDT is more serious in U.S.A
Conclusion
Though the experiment,the egg of Malaysia was found that the percentage of CaCO3 was 75.05%. The egg of U.S.A. was found that the percentage of CaCO3 was 60.61%. The egg of Malaysia contain more CaCO3 than the egg of U.S.A.
It reflect that the pollution of DDT is more serious in U.S.A