1 / 16

Experiment 8

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 CaCO 3 , the material that makes the egg shells hard

temira
Download Presentation

Experiment 8

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. 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-CH2 CH2-COOH N-CH2-CH2-N HOOC-CH2 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 • Why? • 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)

More Related