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EDTA Titration as an Analytical Method for Environmental Concerns Introduction: A growing concern among environmentalists and biologist is the demise of the bird population caused by pesticides such as DDT. Such pesticides are thought to metabolically cause a reduction in the calcium content of the hen s eggshell. Since calcium is an important component in keeping these shells thick and strong, a lack of this essential element can result in brittle fragile eggs. In this experiment, the analyst will calculate the calcium content of either a white or brown egg shell sample by first standardizing an EDTA solution with CaCO 3. The now standardized solution is titrated with an aliquot of the dissolved eggshell solution. Since the weight of the eggshell is known, the concentration can be calculated by using: MEDTA VEDTA = MCa VCa.
The overall reaction is the 1: 1 metal complex: Ca 2 + + EDTA = Ca (EDTA) 2 + Procedure: Mabrouk, Patricia, Ann. Analytical Chemistry Lab Manual. Patricia Ann Mabrouk and Ron Jon Publishing, Tx: 1993. Pg 75 - 9. The eggshell was white in color.
At the instructor s request, the results were not compared with other analyst s conducting the same experiment. Conclusions are based solely on individual calculations. The thickness of the eggshell sample was not determined. The solution used to standardize EDTA was Calcium Carbonate. The analysts were put into groups were duties for experimental procedures were shared. The indicator used was Eriochrome Black T.
A buffer of NH 4 Cl was prepared to compensate for any pH change. The molecular weight of Ca is 40. 08 g / mol . The eggshell was dissolved by 1: 1 HCL. Experimental Data: Wt. Of Na 2 EDTA 9. 333 g Wt of CaCO 3 4. 009 g Wt of NH 4 Cl 71. 09 g Calculations: For the standardization of EDTA MEDTA VEDTA = M CaCo 3 V CaCo 3 i. e. , (X) (9. 00 mL) = (. 00801 mmol / m L) (50 mL) X = . 0445 mol/L for Trial I For the rest of the trials: Table I Trial# Color Change occurred (mL) Molarity of EDTA (mol/L) II 10. 00 mL. 0400 III 9. 3 mL. 0430 Ave Molarity: . 0400 +. 0430 +. 0445 / 3 = . 0425 mol/L For the Concentration of Calcium in the eggshell sample Table II Trial# Color Change Occurred mL I 2. 9 II 2 III 2 To calculate the concentration of calcium in the eggshell sample, do the following: MEDTA VEDTA = MCa VCa For Trial I (. 0425 mmol / m L) (2. 9 mL) = (X) (10 mL) The 10 mL represents an aliquot of a 250 mL dissolved eggshell solution For Trial I: X = . 0123 mmol / m L To find the mg of Ca in the eggshell sol n: For Trial I: . 0123 mmol / m L (10 mL) = 3. 075 mmol 3. 075 mmol (. 4008 mg) = 1. 232 mg Table III Trial# Molarity of Ca (mmol / m L) #mmol in 250 mL eggshell sol n mg Ca in 250 mL sol / n I. 0123 3. 075 1. 232 II. 0085 2. 125 0. 852 III. 0085 2. 125 0. 852 To find the percent Ca in the eggshell: %Ca = grams of Ca determined experimentally / # grams the initial eggshell sample weighted (g) 100 For Trial I: %Ca = . 001232 g/. 1562 g 100 = 0. 804 % Table IIII Trial # %Ca in sample I 0. 787 % II 0. 545 % III 0. 545 % Mean %Ca = 0. 626 % S.
D. = . 140 % Confidence Limits (90 %) = . 626 plus or minus. 236 Discussion: Just by the way the experiment was conducted, it can be confidently assumed that the results are off. When the eggshell solution was supposed to be brought to 250 mL using a volumetric flask, an erlenmeyer was used instead. So the final volume could be somewhere between 240 - 260 or so. Another point in the experiment where determinant errors played a part was when the analyst was supposed to pipet 10 mL of the eggshell sol n to titrate with the standardized EDTA. A graduated cylinder was used instead.
This not only increases the uncertainly of the volume delivered, but throws off calculations. Conclusion: Since a lack of experience on the analyst s part played a major role in the determination of calcium, the results are inconclusive. Next time the analyst should make sure to use the right glassware in order to get accurate and precise results.
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