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Chemistry Lab: Eggshell Calcium Analysis

This experiment determines the percentage of calcium carbonate in egg shells through acid-base titration. Egg shell is crushed and reacted with excess hydrochloric acid to ensure all calcium carbonate reacts. The leftover acid is diluted and titrated with sodium hydroxide solution. The volume of sodium hydroxide used indicates the original amount of calcium carbonate. Calculations determine the percentage of calcium carbonate from the titration data. Uncertainty in the result is also calculated.

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Ankit Reddy
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483 views3 pages

Chemistry Lab: Eggshell Calcium Analysis

This experiment determines the percentage of calcium carbonate in egg shells through acid-base titration. Egg shell is crushed and reacted with excess hydrochloric acid to ensure all calcium carbonate reacts. The leftover acid is diluted and titrated with sodium hydroxide solution. The volume of sodium hydroxide used indicates the original amount of calcium carbonate. Calculations determine the percentage of calcium carbonate from the titration data. Uncertainty in the result is also calculated.

Uploaded by

Ankit Reddy
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Title: Determine the percentage of calcium carbonate in egg shells

Background: In this experiment, you will determine the percentage of calcium carbonate in an
egg shell. Calcium carbonate reacts with hydrochloric acid according to the following equation:
CaCO3(s) + 2HCl(aq) → CaCl2(aq) + CO2(g) + H2O(l)
It is difficult to determine exactly when all the solid calcium carbonate has reacted to one drop
of standard hydrochloric acid solution if it is titrated directly. In this experiment a known
amount of excess acid is added to the sample to ensure that all the calcium carbonate has
reacted. The excess acid is then diluted and made upto a known volume. Aliquots of this
diluted excess acid solution are then titrated with a standard solution of sodium hydroxide.
Procedure:

1. Clean and dry an eggshell, removing as much of the egg membrane as possible.
2. Weigh 0.60 g of crushed eggshell and place in a conical flask.
3. Slowly add 20.00 cm3 of 1.00 mol dm-3 HCl to the egg shell in the conical flask.
4. When the reaction has finished, add about 20 cm3 of distilled water to the solution.
5. Transfer the solution to a 100.00 cm3 volumetric flask and make up to 100.00 cm3 with
distilled water.
6. Measure 10.00 cm3 of this solution and place in a clean conical flask.
7. Add a few drops of phenolphthalein indicator and titrate with 0.100 mol dm-3 NaOH.

Results:

Trial 1 (rough) 2 3 4 5
Initial volume
of NaOH
(±0.05 cm3)
Final volume
NaOH
(±0.05 cm3)
Total volume
NaOH used
(±0.10 cm3)
Colour change

Choose results that are within 0.10 cm3 of each other and calculate the average volume of
NaOH used.
Average volume of NaOH =
Calculations:
1. Calculate the amount (in mol) of hydrochloric acid present initially in 20.00 cm 3 of 1.00
mol dm-3 HCl(aq)

2. Calculate the amount of sodium hydroxide (in mol) present in the volume of 0.100 mol
dm-3 NaOH(aq) used for the titration.

3. Determine the amount (in mol) of unreacted HCl(aq) present in the 10.00 cm3 sample.

4. Determine the amount (in mol) of unreacted HCl(aq) present in the 100 cm3 solution.

5. Determine the amount (in mol) of HCl(aq) that reacted with the egg shell.

6. Calculate the amount (in mol) of calcium carbonate present in the egg shell.

7. Calculate the mass of calcium carbonate present in the egg shell.

8. Determine the percentage by mass of calcium carbonate in the egg shell.


9. Determine the total percentage uncertainty associated with your result.

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