Question

Background: The principle component of eggshells is calcium carbonate. In this experiment the amount of calcium will be determined in both brown and white eggshells.

Questions: Consider why some eggshells are while and some are colored. What causes the color different in an eggshell? Is there a relationship between the color of the egg and the calcium content in the shell?

Purpose: There are two purposes of this experiment. One is to determine whether or not the color of the shell has any correlation with the calcium content. The other is to determine if a gravimetric and titrimetric procedure provide equally reliable results.

*NOTE: During both weeks of this lab a variety of acids will be used and heated. Therefore, for this lab there are the following clothing requirements: long pants, long shirt, closed toed shoes. There will only be a few lab coats provided so it is highly recommended that you wear “old” clothes in case of spills. Anyone not wearing proper clothing will be sent home to change! As always, goggles are provided in the lab or you can bring your own.

*NOTE 2: All measuring of and heating of acids should be completed under the fume hood. Samples can be taken out of the fume hood only after they have been diluted.

Procedure Week 1:

• Sample Preparation
A total of six samples will be analyzed, three white eggshell samples and three brown eggshell samples. Obtain 1 white eggshell and 1 brown eggshell. Clean each egg sample by cracking the egg, discarding the contents into the waste beaker provided by the instructor, and washing the shell. Be sure to remove all organic material from the inside of the egg as this will not dissolve with acid. Dry each shell with a paper towel and place them in a beaker. Place the beakers contain your shells in the oven and allow the shell to dry for 15 minutes. After 15 minutes, take the beakers out of the oven and allow the shells to cool. While cooling, continue on to with gravimetric analysis procedure.

• Gravimetric Analysis of Calcium
Prepare an ammonium oxalate solution by dissolving about 25 g (record exact mass in notebook) of ammonium oxalate {(NH4)2C2O4 H2O} in about 500 mL of high purity water. Heat the solution gently if necessary.

Weight out 0.2XXX g of an eggshell sample and place into a 400 mL beaker. Using samples from two other groups, weigh out two additional samples. Be sure to record the name of the students that you obtained egg samples from. Repeat for the other eggshell. Add 10 mL of high purity water to each beaker (6 total). Under the fume hood, carefully add 10 mL of 6 M HCl to each beaker and cover with a watch glass to avoid losses by splattering. Heat the solutions to boiling on a hot plate (in the fume hood), being careful not to let the solution go dry. After the solid eggshell dissolves wash the watch glass and the sides of the beaker with high purity water and dilute to about 150 mL. Bring the beakers back to your station.
Heat the ammonium oxalate solution in the fume hood to between 60 and 80 °C. Once the appropriate temperature has been achieved the solution can be brought back to your station. To each sample, transfer 50 mL of the warm oxalate solution, and add 3 – 4 drops of methyl red indicator. In the hood, add 6 M NH4OH until the color changes from red to yellow/white.
Note: if you have a significant amount of precipitate the yellow color may not be visible. However, there will be a definite loss of the red/pink, which is the indication that you can stop. Allow the solution to cool for 30 minutes.

While the solution is cooling, wash six Gooch crucibles and dry them with a paper towel. Place the crucibles in the oven to dry further. When dry, place 1 glass micro-filter into each crucible and weigh them. Be sure to record any identifying marks on the crucible so that the mass of each crucible is not confused.
Filter each of the samples, making sure to quantitatively transfer the sample to the crucible. Wash with several portions of high purity water and place the crucibles in the oven to dry. Once dried remove from oven and allow to cool. Reweigh each crucible and determine the mass of calcium oxalate monohydrate. Store the crucibles for use during the next lab period.


Procedure Week 2:

• Standardization of KMnO4
Weigh out 0.25XX g of sodium oxalate into a clean 250 mL Erlenmeyer flask. Dissolve the sample in 75 mL of 1 M H2SO4. Heat the solutions in the fume hood to just below boiling (approximately 80 – 90 °C). While the solutions are being heated, fill a clean 250 mL beaker with 200 mL of 0.2XXX M potassium permanganate (KMnO4) provided by the instructor. Fill your buret with the titrant. Titrate the sodium oxalate sample to the appearance of the first pink color (the lighter the better!). The temperature of the sodium oxalate solution should not be allowed to drop below 60 °C during the titration. Prepare and titrate 3 more samples so that you have performed a total of 4 titrations.

• Indirect Titrimetric Analysis of Calcium
Place each Gooch crucible, with filter paper, into a separate 400 mL beaker. Add 150 mL high purity water and in the fume hood, add 50 mL of 6 M H2SO4. Heat to just below boiling (approximately 80 – 90 °C). Using a stirring rod, pry the filter paper lose from the crucible and stir. While the

Sample is still warm, titrate the contents of the beaker (still containing the Gooch crucible and the filter paper) with your standardized KMnO4 solution.

Calculations:
1. Calculate the mean molarity of the permanganate solution and report the 90% confidence interval.
2. Write the redox reaction for the standardization of the permanganate with the sodium oxalate.
3. Explain why is it not necessary to use an indicator when titrating with permanganate ion.
4. Write the balanced chemical reaction for each step of the gravimetric procedure. Assume that the calcium in the eggshell is calcium carbonate.
5. From the gravimetric results of the analysis of the eggshells, calculate the weight percent of calcium in the white and brown eggshells. Report each to the 90% confidence interval.
6. Based on the calculation in question #5, are the results of the gravimetric analysis consistent with the eggshell being pure calcium carbonate? Use calculations to support your answer. Explain.
7. From the titrimetric results of the analysis of the eggshells, calculate the weight percent of calcium in the white and brown eggshells. Report each to the 90% confidence interval.
8. Based on the calculation in question #7, are the results of the titrimetric analysis consistent with the eggshell being pure calcium carbonate? Use calculations to support your answer. Explain.
9. Using statistical analysis, do the titrimetric and gravimetric results from the each eggshell color agree? Report to the 90% confidence interval.
10. Compare the titrimetric results of the white eggshells with the titrimetric results of the brown eggshells. Is the calcium composition of white eggshells the same as that of brown eggshells? Report to the 90% confidence interval.

Questions:
1. Write the redox reaction for the standardization of the permanganate with the sodium oxalate.
2. Explain why is it not necessary to use an indicator when titrating with permanganate ion.
3. Write the balanced chemical reaction for each step of the gravimetric procedure. Assume that the calcium in the eggshell is calcium carbonate.

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Analysis of Calcium in Egg Shells

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