Lecture_overheads_-_Ch11

Lecture_overheads_-_Ch11 - CHEM 321 Quantitative Analysis...

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Unformatted text preview: CHEM 321 Quantitative Analysis Ch. 11 EDTA Titrations 11-1 Metal-Chelate Complexes 11-2 EDTA 11-3 EDTA Titration Curves 11-6 Metal Ion Indicators 11-7 EDTA Titration Techniques 11-1 Metal-Chelate Complexes Metal ions are Lewis acids and can accept electron pairs most transition metal ions can bind 6 ligands (octahedral orientation) Ligands are Lewis bases and can donate electron pairs monodentate ligand can bind metal ion through 1 lone pair bidentate ligand can bind to metal ion through 2 lone pairs Together, a metal ion and a ligand form a complex Examples Ag + + CN- AgCN- Cu 2+ + NH 3 CuNH 3 2+ Cu 2+ + H 2 N-CH 2-CH 2-NH 2 5-membered ring Ca 2+ + EDTA complex Expt 6 11-2 EDTA Ethylene-Diamine-Tetraacetic Acid (EDTA or H 4 Y) EDTA is a hexadentate ligand that (ideally, in its fully deprotonated form Y 4- ) forms a strong 1:1 complex with different metal ions [ ] [ ][ ] 10 4 2- 2 10 5 . 4 Y Ca CaY = =- + f K M n+ + Y 4- MY n-4 Ca 2+ + Y 4- CaY 2- Pb 2+ + Y 4- PbY 2-- Mn 2+ + Y 4- MnY 2- Expt 6 K f = ? Note trends as charge , K f (why?) as metal ion size approaches optimal EDTA cage size, K f EDTA is a hexaprotic system Diamine 2 amine groups that can be protonated Tetraacetic acid 4 acid groups that can be deprotonated EDTA can exist in 7 different forms (H 6 Y 2+ to Y 4- ) Which form would be best suited for complexing M n + (i.e., give largest K f )?...
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This note was uploaded on 11/28/2011 for the course CHEM 321 taught by Professor P.palmer during the Spring '11 term at S.F. State.

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Lecture_overheads_-_Ch11 - CHEM 321 Quantitative Analysis...

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