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

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

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?

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

Hazards EDTA Egg Shells HCl Buffer EBT

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?

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

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-

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

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

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

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)

Critical Measurements

Experimental Design Variables

Introduction (if you had to write one)

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)