Re: Procedure for finding the calcium content of an egg shell through titratio

Dear Nicholette:

I found a method for the determination of calcium and magnesium in water samples. This procedure utilizes EDTA (ethylenediaminetetraacetic acid). Of course in order to calculate the amount of calcium in an egg shell you will need dissolve the egg shell in some type of solution.

The procedure can be found in the following reference:

Standard Methods for the Examination of Water and Wastewater 16 th Edition Prepared & published jointly by: American Public Health Association, American Water Works Association and the Water Pollution Control Federation Arnold E. Greenberg Editor Published by the American Public Heatl Association 1985. Page 199 - 200

Admin Note: Use of the chemicals below should be carried out under adult supervision and in appropriate facilities (your school's chemistry lab) that have adequate ventilation and means for storing chemicals. In addition, safety goggles and protective clothing such as a lab coat and latex gloves, should be worn. Solutions of sodium hydroxide are irritating to the skin and can cause damage to the lungs if the fumes are inhaled. Links are provided to relevant Materials Safety Data Sheets for each compound.

Principle: EDTA when added to water specimens containing calcium and magnesium, combines first to Calcium, Magnesium precipitates out and one or two indicators will give a color change when calcium has been complexed by EDTA at a pH of 12 to 13.

Reagents:

• Sodium Hydroxide ( NaOH, 1 N)
• Murexide (ammonium purpurate) 150 mg dissolved in 100 g absolute ethylene glycol
• Eriochrome Blue Black R (sodium-1-(2-hydroxy-1-naphthylazo)-2-naphthol- 4-sulfonic acid. 200 mg + 100 g NaCl
• EDTA titrant 0.01 M

• Add 2 ml NaOH to solution to raise pH to 12 - 13.
• Stir , add 0.1 to 0.2 g (Eriochrome Blue Black R) indicator or 1 - 2 drops (Murexide) indicator
• Add EDTA slowly until endpoint.

a = mL titrant for sample
b = mg CaCO3 equivalent to 1.00 mL EDTA titrant at the calcium indicator end point.

The following references were cited in the above method:

1.)  Diehl, H & Ellingboe, J Indicator for titration of calcium in the 
presence of magnesium using disodium dihydrogen ethylenediamine 
tetraacetate  Anal. Chem. 28: 882 (1956)

2.)  Patton, J & Reeder, W.:  New indicator for titration of calcium with 
(Ethylenedinitrilo) tetraacetate.  Anal Chem. 28:1026 (1956)

3.)   Furman, N Standard Methods of Chemical Analysis, 6th ed.  Van 
Nostrand Co., Inc.  Princeton, N.J.

4.)  Katz, H & Navone, R.:  Method for simultaneous determination of 
calcium and magnesium,  J. Amer. Water Works Ass.  56:121 (1964)