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Project Day27-3-2009

4B

To determine the percentage of calcium carbonate (CaCO3)

in eggshells

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What is the DDT• DDT is a synthetic chemical compound

once used destroying certain living things that are harmful to plants and animals.

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• DDT effect on wild bird life is the weakening or thinning of the eggshell. The consequence is the breaking of the eggshell before hatching

• Eggshell mainly consists of calcium carbonate.

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Materials and Apparatus Used

0.1015 M NaOH solution

Ethanol

Phenolphthalein

0.1987 M HCl solution

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Mortar and pestle Beakers

Electronic balance Volumetric flasks

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Pipette

Funnel Burette

Filter paper

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procedures1. The egg was boiled and allowed to cool down.

2. The eggshell was taken off and the attached membrane was removed.

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3. The eggshell was dried in an oven a110 for overnight.℃

4. The eggshell was removed from the oven and allowed to cool down.

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5. The eggshell was ground into a fine powder with mortar and pestle.

6. About 0.2 g of powder was weighed accurately and put into a 250-cm3 conical flask.

7. 25.00 cm3 of 0.1987 M HCl solution was pipetted into the flask and 5 cm3 of ethanol was added.

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8. The solution was boiled for 15 minutes and allowed to cool down.

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9. A few drops of indicator solution (phenolphthalein) were added and the solution was then titrated with NaOH solution until a pink colour appeared.

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10. The volume used was recorded.

11. The titration was repeated twice. The volume used was recorded.

12. The above procedure was repeated for brown eggshell, white eggshell and quail eggshell.

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Observations:

1. When the eggshell powder was dissolved in HCl solution, some bubbles came out during stirring and the solution turned into slightly milky.

2. Even after heating, the sample powder was not dissolved completely. Some white precipitate remained in the solution.

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3. The solution turned pink at the end-point.

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Reaction involved

CaCO3(s) + 2 H+(aq) → Ca2+(aq) + H2O(l) + CO2(g)

OH-(aq) + H+(aq) → H2O(l)

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Data, Calculation and Results:

Brown Eggshell ：Volume of 0.1987M HCl solution used: 25.00 cm3

Trial 1 2 3Weight of eggshell powder (g) 0.20 0.19 0.20

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Trial 1 2 3Burette final reading (cm3) 17.82 26.60 30.30Burette initial reading (cm3) 5.80 13.70 18.43Volume of NaOH solution used (cm3) 12.02 12.90 11.87

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10001015.002.121987.000.25 ×−×

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20.0100001874.0 ×

For trial 1：Number of moles of CaCO3 in sample

×

= 0.001874 mol

×100%

Weight percentage of CaCO3 in sample

=

= = 93.69%

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Similarly, for trial 2: weight percentage of CaCO3 in sample = 96.27%

Similarly, for trial 3: weight percentage of CaCO3 in sample = 94.07%

Average % weight of CaCO3 in sample = 94.68%

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White eggshell：

Volume of 0.1987M HCl solution used: 25.00 cm3

Trial 1 2 3Weight of eggshell powder (g) 0.20 0.16 0.20

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Volume of NaOH solution used for titration with sample:

Trial 1 2 3

Burette final reading (cm3) 29.18 41.92 36.70Burette initial reading (cm3) 18.35 24.00 25.12

Volume of NaOH solution used (cm3) 10.83 17.92 11.58

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10001015.083.101987.000.25 ×−×

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20.0100001934.0 ×

For trial 1：Number of moles of CaCO3 in sample

×

= 0.001934 mol

×100%

=

Weight percentage of CaCO3 in sample

=

= 96.70%

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Similarly, for trial 2: weight percentage of CaCO3 in sample = 98.39%

Similarly, for trial 3: weight percentage of CaCO3 in sample = 94.80%

Average % weight of CaCO3 in sample = 96.63%

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Quail eggshell：Volume of 0.1987M HCl solution used: 25.00 cm3

Trial 1 2 3Weight of eggshell powder (g) 0.18 0.20 0.17

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Volume of NaOH solution used for titration with sample:

Trial 1 2 3Burette final reading (cm3) 18.35 14.45 22.90Burette initial reading (cm3) 0.80 1.30 3.90Volume of NaOH solution used (cm3) 17.55 13.15 19.00

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10001015.055.171987.000.25 ×−×

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18.0100001593.0 ×

For trial 1：Number of moles of CaCO3 in sample

×

= 0.001593 mol

×100%

=

Weight percentage of CaCO3 in sample

=

= 88.50%

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Similarly, for trial 2: weight percentage of CaCO3 in sample = 90.82%

Similarly, for trial 3: weight percentage of CaCO3 in sample = 89.38%

Average % weight of CaCO3 in sample = 89.57%

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Conclusion:In the present experiment, simple acid-base titration with the technique of back-titration was employed to determine the amount of calcium carbonate in eggshell.

For brown eggshell, the value was found to be in the range of ~93 - 96% in the three trials and the average value was 94.68%.

For white eggshell, the value was found to be in the range of ~95 - 98% in the three trials and the average value was 96.63%. For quail eggshell, the value was found to be in the range of ~88 - 91% in the three trials and the average value was 89.57%.

The weight percentage of calcium carbonate for the smaller quail egg was smaller than the normal sized brown and white eggs.

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