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 source Acid + Base = Salt + Water; HCl + NaOH  NaCl + H2O Works in aqueous solutions only
Brønsted-Lowry: Acid is proton donor, base is proton acceptor Acid(1) + Base(1)  Acid(2) + Base(2) Can this happen without water?
Conjugate acid-base pairs Reaction favors the weaker acid/base pair Non-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 pKion H2SO4 H3SO4+ HSO4– 3.4 at 10 ºC H2O H3O+ OH– 14 NH3 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, PCl5 2 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 BrF3 Acid Base Solvent
Broader definition - acid/base character is related to the solvent

9. Lewis Acid-Base Theory Frontier 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 Bases Examples: 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 Bases Examples: Complexation

17. Hard and Soft Acids and Bases Examples: 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+

19. Hard and Soft Acids and Bases Definitions
Hard base: small, not polarizable
Soft base: large, highly polarizable

20. Hard and Soft Acids and Bases Definitions
Hard acid: small, not polarizable
Soft acid: large, highly polarizable

27. Relate to oxoanions.