1. Theories of Acids and Bases

2. Arrhenius Acid
Substance that contains hydrogen & ionizes to produce H+ as the only positive ion in aqueous solution.
HCl(g)  H+(aq) + Cl-(aq)
HNO3  H+(aq) + NO3-(aq)

3. Arrhenius Base
A substance that contains a hydroxide group & ionizes to produce OH- as the only negative ion in aqueous solution.
NaOH(s)  Na+(aq) + OH-(aq)

4. Arrhenius Salt
Electrolytes where H+ is not the only positive ion and OH- is not the only negative ion in aq. solution.
Ex: NaCl, CaBr2,KNO3, NH4I

5. Salts in Water NaCl(s)  Na+(aq) + Cl-(aq)
CaBr2(s)  Ca+2(aq) + 2Br-(aq)
KNO3(s)  K+(aq) + NO3-(aq)
NH4I(s)  NH4+(aq) + I-(aq)
Memory Jogger

6. Arrhenius Model has limitations
Don’t always use H2O as the solvent.
Arrhenius model only applies when H2O is the solvent.
Doesn’t explain all cases:
NH3 doesn’t contain OH- but it produces OH-.

7. Alternate Theory: Bronsted-Lowry
Acid = a proton donor
All Arrhenius acids are Bronsted-Lowry Acids.
HX(g) + H2O(l)  H3O+ + X-
H+ forms a molecule-ion bond with the water molecule  H3O+, named hydronium ion.

8. Bronsted-Lowry Acids HCl + H2O  H3O+ + Cl- HNO3 + H2O  H3O+ + NO3-
H2SO4 + H2O  H3O+ + HSO4-
HSO4- + H2O  H3O+ + SO4-2

9. Bronsted-Lowry Base Base = proton acceptor.
OH- is a base. H+ + OH-  H2O
Not restricted to aqueous solution.
NH3 + H2O  NH4+ + OH-
NH3 is a base!

10. Amphoteric Substance that can act as both an acid & a base
Water is amphoteric
HX(g) + H2O(l)  H3O+ + X- } H20 = base
NH3 + H2O  NH4+ + OH- } H2O = acid

11. Water is amphoteric!

12. Conjugate Acid / Conjugate Base
HX + H2O  H3O+ + X-
Acid
Base
Conjugate
Acid
Conjugate
Base
Conjugate Acid & Conjugate Base always on product side.
Conjugate Acid = species that got the H+
Conjugate Base = species that lost the H+

13. Bronsted-Lowry Acids & Bases

14. Identify A., B., C.A., & C.B. NH3 + H2O  NH4+ + OH-
HCl + H2O  H3O+ + Cl-
HSO4- + H2O  SO4-2 + H3O+
NH3 + H2S  NH4+ + HS-
Base
Acid
C. Acid
C. Base
C. Base
Acid
Base
C. Acid
Acid
Base
C. Base
C. Acid
Base
Acid
C. Acid
C. Base

15. Lewis Definition NH3 + H2O  NH4+ + OH-
Lewis acid-base theory focuses on the exchange of electron pairs rather than protons to classify as acid or base.
Based on bonding and structure
Includes substances that do NOT contain hydrogen ions.
NH3 + H2O  NH4+ + OH-

16. Lewis Acids & Bases
A Lewis acid is an atom, ion, or molecule that is an electron-pair acceptor.
Associate:
Bronsted-Lowry acid with: proton donor
Bronsted-Lowry base with: proton acceptor
Lewis acid with: electron pair acceptor
Lewis base with: electron pair donor