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Acid-Base and Donor-Acceptor Chemistry

Acid-Base and Donor-Acceptor Chemistry. Chapter 6. Acids and Bases. The Major Acid-Base Definitions:. Acids and Bases. Arrhenius: Acid is proton source in water, base is hydroxide source Acid + Base = Salt + Water; HCl + NaOH  NaCl + H 2 O Works in aqueous solutions only

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Acid-Base and Donor-Acceptor Chemistry

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  1. Acid-Base and Donor-Acceptor Chemistry Chapter 6

  2. Acids and Bases The Major Acid-Base Definitions:

  3. Acids and Bases • Arrhenius:Acid is proton source in water, base is hydroxide sourceAcid + Base = Salt + Water; HCl + NaOH  NaCl + H2OWorks in aqueous solutions only • Brønsted-Lowry:Acid is proton donor, base is proton acceptorAcid(1) + Base(1)  Acid(2) + Base(2) Can this happen without water? • Conjugate acid-base pairsReaction favors the weaker acid/base pairNon-aqueous solvents, gas and solid phase reactions

  4. Acids and Bases • Solvent system definition: If a species can autoionize (autodissociate, form a cation and an anion), the cation is an acid and the anion is a base • In this system, an acid increases [cation] and a base increases [anion] Water: 2 H2O  H3O+ + OH– • HCl is an acid in this solvent system (increases [cation])HCl + H2O  H3O+ + Cl–

  5. Protic Acids and Bases

  6. Protic Acids and Bases • Kion is K for the autoionization of the pure solvent Solvent Acid Base pKionH2SO4 H3SO4+ HSO4– 3.4 at 10 ºCH2O H3O+ OH– 14NH3 NH4+ NH2– 27 • Acetic acid is acid in water, but base in H2SO4 CH3CO2H + H2SO4 HSO4– + CH3CO2H2+ • Urea is a base in water, but an acid in liquid NH3 (NH2)2CO + NH3 NH4+ + (NH2)(NH)CO–

  7. Aprotic Acids and Bases

  8. Aprotic Acids and Bases • Aprotic solvent systems: BrF3, PCl52 NH3 NH4+ + NH2- 2 BrF3 BrF2+ + BrF4–2 PCl5 PCl4+ + PCl6– In BrF3, SbF5 is an acid and KF is a base SbF5 + BrF3 SbF6– + BrF2+KF + BrF3 K+ + BrF4– In this definition, Acid + Base = Solvent • BrF2+ + BrF4– 2 BrF3Acid Base Solvent • Broader definition - acid/base character is related to the solvent

  9. Lewis Acid-Base TheoryFrontier Orbitals: HOMO and LUMO

  10. Lewis Acid vs. Lewis Base vs. Oxidation vs. Reduction

  11. Lewis Acid vs. Lewis Base vs. Oxidation vs. Reduction

  12. Lewis Acid vs. Lewis Base vs. Oxidation vs. Reduction

  13. Lewis Acid vs. Lewis Base vs. Oxidation vs. Reduction

  14. Measuring Lewis Acid-Base Interaction Strength via Electronic Spectra

  15. Hard and Soft Acids and BasesExamples: Ionic Compound Solubility AgF(s) + H2O(l)  Ag+(aq) + F-(aq) Ksp = 205 AgCl(s) + H2O(l)  Ag+(aq) + Cl-(aq) Ksp = 1.8 x 10-10 AgBr(s) + H2O(l)  Ag+(aq) + Br-(aq) Ksp = 5.2 x 10-13 AgI(s) + H2O(l)  Ag+(aq) + I-(aq) Ksp = 8.3 x 10-17 Similarly, solubility: Hg2F2 > Hg2Cl2 > Hg2Br2 > Hg2I2 BUT, LiF < LiI MgF2 is less soluble than MgCl2 AlF3 is less soluble than AgCl3

  16. Hard and Soft Acids and BasesExamples: Complexation

  17. Hard and Soft Acids and BasesExamples: Thiocyanate Bonding to Metals SCN- can bond through S or N S-binding with M = large, polarizable metals like Hg2+, Au+, Pd2+ N-binding with M = smaller, less polarizable metals: Zn2+, Ni2+

  18. Hard and Soft Acids and BasesDefinitions Hard base: small, not polarizable Soft base: large, highly polarizable

  19. Hard and Soft Acids and BasesDefinitions Hard acid: small, not polarizable Soft acid: large, highly polarizable

  20. Relate to oxoanions.

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