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Chapter 17: Complexation Reactions & Titrations

Chapter 17: Complexation Reactions & Titrations. CHE 321: Quantitative Chemical Analysis Dr. Jerome Williams, Ph.D. Saint Leo University. Overview. Complexation Reactions Ligands Classification Chelates & Macrocycles Complexation Equilibria Complexometric Titrations EDTA.

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Chapter 17: Complexation Reactions & Titrations

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  1. Chapter 17: Complexation Reactions & Titrations CHE 321: Quantitative Chemical Analysis Dr. Jerome Williams, Ph.D. Saint Leo University

  2. Overview • Complexation Reactions • Ligands • Classification • Chelates & Macrocycles • Complexation Equilibria • Complexometric Titrations • EDTA

  3. Complexation Reactions • Complexation reactions are widely used in analytical chemistry • Applications include • Spectrophotometric determinations • Gravimetric • Precipitation titrations

  4. Ligands • Ligand - ion or molecule that forms a covalent bond with a cation or neutral metal atom by donating a pair of electrons which are then shared by the two. • Ligands function in the same fashion as a Lewis base (electron pair donor). • Coordination Number – number of covalent bonds a cation forms with electron donors.

  5. Ligands: Classification • Unidentate one donor group (electron pair) • Example: Ammonia complexation with Copper (II) • Bidentate two donor groups (electron pair) • Example: Glycine with Copper (II) • Tridentate three donor groups (electron pair) • Tetradentate four donor groups (electron pair) • Example: EDTA • Higher order ligands possible (penta-, hexa-, etc.)

  6. p401

  7. Ligands: Chelates & Macrocycles • Chelate is produced when metal ion coordinates with two or more donor groups of a single ligand to form a five or six membered heterocyclic ring. • Macrocycles are a type of complex formed between metal ions and cyclic organic compounds (e.g., crown ethers).

  8. p401

  9. Complexation Equilibria • Consider reaction sequence Cu (II) and NH3 • Cu2+ + NH3 → Cu(NH3) 2+ • Cu2+ + 2 NH3 → Cu(NH3)22+ • Cu2+ + 3 NH3 → Cu(NH3)32+ • Cu2+ + 4 NH3 → Cu(NH3)42+ • Complexations occur stepwise; equilibrium constants are termed formation constants.

  10. Figure 17-1 p406

  11. Table 17-1 p407

  12. Table 17-2 p408

  13. Figure 17-2 p409

  14. Figure 17-3 p410

  15. Figure 17-4 p411

  16. Table 17-3 p414

  17. EDTA • EDTA Ethylenediaminetetraacetic acid • Most widely used complexometric titrant • Hexadentate ligand; free acid (H4Y) available primary standard • Disodium salt (Na2H2Y) most often used in experimental work. Behaves like an amino acid. • Reagent combines with metals in 1:1 ratio. • Often found in food preservatives & biological samples

  18. p414

  19. Figure 17F-1 p416

  20. Figure 17-1a p416

  21. Figure 17-1b p416

  22. Figure 17-1c p416

  23. Figure 17-1d p416

  24. Figure 17-1e p416

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