1. % Calcium in Egg Shells By EDTA Complexometric Titration
Experiment 8
% Calcium in Egg Shells
By EDTA Complexometric Titration

2. Announcements Extra Credit Presentations
Final Project Plans Due Next Week
1 per group

3. What are Egg Shells Made Of?
Protein
CaCO3, the material that makes the egg shells hard
We want to determine the amount of calcium.
The calcium in egg shells is in the form of CaCO3. Therefore, we can also determine how much CaCO3 is in them.
CaCO3 is a carbonate.
Are carbonates water soluble? Do egg shells dissolve easily in water?

4. Goals To dissolve a sample of egg shells in water
To quantitatively transfer the dissolved sample
To titrate aliquots of the sample to determine the amount of Ca2+ present

5. Hazards
EDTA
Egg Shells
HCl
Buffer
EBT

6. Refresher What is a titration?
What must you know in order to perform a titration?
When do you stop titrating?
How do you determine the endpoint?

7. EthyleneDiamineTetraacetic Acid
HOOC-CH CH2-COOH
N-CH2-CH2-N
HOOC-CH CH2-COOH
Chelating Agent = “loves” to bind metals
Tetradentate= has 4 binding sites

8. The Ionic form -OOC-CH2 CH2-COO- N-CH2-CH2-N -OOC-CH2 CH2-COO-
Forms a very strong complex with Ca2+
Ca2+ + EDTA4- => [Ca-EDTA]2-

9. The Experiment Weigh out egg shells Add HCl to make soluble Why?
Quantitatively transfer
How?
Vacuum Filter
Set up just like demo in lab
Removes protein. Why do this?
Dilute to volume in volumetric flask (100mL)
Use pipet to transfer aliquot (10mL)
Titrate aliquot with EDTA

10. The Indicator Eriochrome Black T (EBT)
Also forms complex with metal ions
EBT prefers metals to H+ (actually a little more complex than this, but for this course…..)
EBT<EDTA as a complexing agent
At pH 10 (use buffer)
EBT w/ Ca2+ is _____
EBT w/ H+ is _________
As pH decreases, _____________________, this is why we add buffer at last minute

11. How it Works
So, EBT competes with EDTA for Ca ions in solution (use as little EBT as possible)
In the beginning, you have just Ca ions, no EDTA
When the EDTA has bound some Ca from the EBT
When the EDTA has “grabbed” up all of the Ca ions, EBT can no longer be bound to the Ca

12. Data and Results Known MEDTA (mol/L)
Volume EDTA delivered (mL => L)
Mass of sample (g)
Only used 1/10 of sample for each titration
1mol EDTA: 1mol Ca2+
Atomic mass Ca (40.078g/mol)

13. Critical Measurements

14. Experimental Design Variables

15. Introduction (if you had to write one)

16. Applications of This Method
Used to determine concentration of metal ions in solution
Can be used to determine how much calcium (or magnesium or other minerals) is in a food product (milk, orange juice, etc.)
Can be used to determine concentration of good/bad metals in the environment (ie water source)