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Ch. 4. AQUEOUS COMPLEXES

Ch. 4. AQUEOUS COMPLEXES. 4-1. A Few Definitions Aqueous complexes Association of dissolved (c,a)ions or molecules Ligands Ions or molecules binding to a central metal to form a complex (by donating electron pair) Addend Pieces of complexes (either cations or anions)

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Ch. 4. AQUEOUS COMPLEXES

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  1. Ch. 4. AQUEOUS COMPLEXES • 4-1. A Few Definitions • Aqueous complexes • Association of dissolved (c,a)ions or molecules • Ligands • Ions or molecules binding to a central metal to form a complex (by donating electron pair) • Addend • Pieces of complexes (either cations or anions) • Monodendate (Cl-), bidendate (CO32-), polydendate • Chelates • P. 91, Table 3.2

  2. Description: Chemical structure of EDTAchelate (from wikipedia.org)

  3. 4-2. Significance of Complexes • Speciation of metals • Adsorption • Toxicity • Solubility

  4. 4-3. Outer vs. Inner Sphere Complexes • Hydration (shell) • Outer sphere complex (ion pair): ex) CaSO4 • Weak, electrostatic (depending on charges) • Inner sphere coplex: ex) AgS- • Strong, covalency • Most complexes are in between

  5. 4-4. Geometry of Common Inorganic Ligands • All depends on the radius ratio (p.89) • Plan triangular triangle (NO3-, CO3-, BO3-) • Regular trigonal low pyramidal (PO33-, AsO33- ) • Regular tetrahedron (PO43-, SO42-, CrO43- ) • Distorted tetrahedron (MoO42-) • Spherical (halogens) • Dumbel shape (UO22- ) • See page 89 & 90 tables

  6. 4-5. Complexation Mass Balance & Equilibria Extent of complex formation (average ligand number) P. 90, eqn (3.17) Stepwise formation constant P. 92, eqn (3.18) Cumulative formation constant P.92, eqn (3.21)

  7. 4-6. Hydrolysis of Cations in Water and Ionic Potential Hydrolysis? Ionic potential? How these two factors affect the behavior of the dissolved ions in water? See p.98, Fig. 3.4; p.99, Table 3.3.; p.100, Fig. 3.5

  8. 4-7. Electronegativities & the Stability of Inner-Sphere Complexes What is EN? (p.101, Tanle 3.4) How does EN controls bonding character ? Conseq., the stabilities of complexes? (p.102, Fig. 3.6)

  9. 4-8. Schwarzenbach’s & Pearson’s Classification of Acids & Bases (forming Complexes) Schwarzenbach’s classes A, B, & C A: Those of noble gas configuration (p.103, bottom table) B: Those of Nio, Pdo, Pto electron config. C: Transient metals Pearson’s hard & soft Hard: Rigid & nondeformable elctron cloud, tend to form ionic bonding Soft: Deformable & polarizable electron cloud, tend to form (more) covalent bonding See p.104, Table 3.5; p.105, Fig. 3.7; p.106, Fig. 3.8; p.108, Fig. 3.9.

  10. 4-9. Thermodynamics of Complexation DGo = -RT ln Kassoc DGo = DGo - TDSo Mostly due to entropy change DSo = DSonet charge + DSotr + DSorot + DSovibr + DSodehyd DSodehyd is probably contributing most

  11. 4-10. Distribution of Complex Species as a Function of pH Write down the association reactions Express Kassoc in terms of species Convert them into a function of pH See p.113, Fig. 3.12

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