chapter 17: complexation reactions & titrations
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
Chapter 17: Complexation Reactions & Titrations
CHE 321: Quantitative Chemical AnalysisDr. Jerome Williams, Ph.D.
Saint Leo University
Overview
• Complexation Reactions• Ligands– Classification– Chelates & Macrocycles
• Complexation Equilibria– Complexometric Titrations– EDTA
Complexation Reactions
• Complexation reactions are widely used in analytical chemistry
• Applications include– Spectrophotometric determinations– Gravimetric– Precipitation titrations
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.
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.)
p401
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).
p401
Complexation Equilibria
• Consider reaction sequence Cu (II) and NH3
• Cu2+ + NH3 → Cu(NH3) 2+
• Cu2+ + 2 NH3 → Cu(NH3)2 2+
• Cu2+ + 3 NH3 → Cu(NH3)3 2+
• Cu2+ + 4 NH3 → Cu(NH3)4 2+
• Complexations occur stepwise; equilibrium constants are termed formation constants.
Figure 17-1 p406
Table 17-1 p407
Table 17-2 p408
Figure 17-2 p409
Figure 17-3 p410
Figure 17-4 p411
Table 17-3 p414
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
p414
Figure 17F-1 p416
Figure 17-1a p416
Figure 17-1b p416
Figure 17-1c p416
Figure 17-1d p416
Figure 17-1e p416