1. Acid-Base chemistry Acidity of blood (pH range of
Heartburn (acid-reflux) – Tums, Rolaids, Milk of Magnesia; The Purple Pill, Nexium
Acidity regulation (tropical fish / goldfish tanks)
Pepsi (most sodas); just how acidic?
Loosens rusty bolts; cleans windshields
Battery acid (H2SO4)
Acid Rain (SO2, NO2, CO2)
Drain cleaners (Drano, Liquid Plumber)

2. Nature of acids and bases
Acids – sour, tart taste (vinegar, lemon juice)
Bases – bitter taste, slippery feel between fingers (drano, detergent)
Arrhenius definitions (1884):
Acids: produce H+ ions (protons) in solution
Bases: produce OH- (hydroxide) ions in solution

3. Lowry-Brønsted definitions
Danish & British chemists
More general definitions than Arrhenius definition:
Acids: Proton donors
Bases: proton acceptors
H2O HCl  H3O Cl-

4. Lewis Acids / Lewis Bases
LA: electron pair acceptor
LB: electron pair donor
NH3(aq) + H+(aq)  NH4+(aq)
LB LA
OH-(aq) + H+(aq)  H2O(l)

5. General reaction for HA + H2O
HA(aq) + H2O(l)  H3O+(aq) + A-(aq)
Acid Base Conjugate Conjugate
Acid Base
Position of equilibrium dictated between bases in equation (competition for H+)
H2O stronger base:
A- stronger base:
Keq = [H3O+][A-] Ka = Acid dissociation constant
[HA][H2O] [H3O+] = [H+] in H2O
Ka = [H3O+][A-] Ka = Acid dissociation constant
[HA]

6. Acid dissociation reactions
Dissociation of acid (HA) most important here
HA (aq)  H+(aq) + A-(aq)
H2O still important (required for aqueous conditions)
Ka for this equilibrium process?
Can predict dissociation reaction for any acid (no matter how complex-looking)
HCl (aq)
HC2H3O2 (aq)
NH4+ (aq)
C6H5NH3+ (aq)
[Al(H2O)6]3+ (aq)

7. Acid Strength
Defined by equilibrium position of dissociation reaction:
HA(aq) + H2O(l)  H3O+(aq) + A-(aq)
Strong acid – lies far to right side (a)
Weak acid – lies far to left side (b)

8. Describing acid strength
Insert Figure 14.6
Insert table 14.1
strong acid weak base
Property Strong Acid Weak Acid
Ka value
Equilibrium Posn.
[H+]e vs [HA]o
Strength of conj.
base compared
to water

9. Common strong acids HCl, HClO4, HNO3 (monoprotic acids)
H2SO4 (diprotic acid)
Ka values – very large

10. Relative base strengths
Arrange H2O, F-, Cl-, NO2-, CN- in order of increasing base strength:

11. Water: Amphoteric substance
Can exist as both an acid and a base
Autoionization of water
H2O(l) + H2O(l)  H3O+(aq) + OH-(aq)
Kw = [H3O+][OH-]; Kw = Dissociation constant for H2O
Kw = [H+][OH-]
[H+]=[OH-] = 1.0 x 10-7 M (at 25 °C, in pure water)
Kw = [H+][OH-] = 1.0 x 10-14
In any aqueous solution, the product of [H+] and [OH-] must always equal 1.0 x 10-14

12. Kw Kw = [H+][OH-] = 1.0 x 10-14 3 possible situations:
Neutral solutions; [H+] = [OH-]
Acidic solutions; [H+] > [OH-]
Basic solutions; [H+] < [OH-]
In all cases: Kw = [H+][OH-] = 1.0 x 10-14
Varies with T (as do all K values)

13. Calculating [H+],[OH-]
[H+] with [OH-] = 1.0 x 10-5 M
[OH-] with [H+] = 10.0 M
[OH-] and [H+] in neutral solution at 60 °C (Kw = 1x10-13 at 60 °C)

14. pH scale (acidity measurement)
pH = -log [H+]
[H+] = 1.0 x 10-7 M; pH =
pOH = -log[OH-]; pK = -log Ka
Log scale; pH changes by 1 for every power of 10 change in [H+]
pH decreases as [H+] increases

15. Calculating pH / pOH 1.0 x 10-3 M OH- 1.0 M H+ pH + pOH = 14.00
pH of sample of human blood = 25 °C. Calculate pOH, [H+], [OH-]

16. pH of strong acid solutions
What species are present? 1M HCl
What are the major species that can furnish H+ ions?
pH of 0.10 M HNO3
pH of 1.0 x M HCl

17. pH of weak acid solutions
pH of 1.00 M HF (weak acid); Ka = 7.2 x 10-4
Major species in solution? HF, H2O
Major species which furnish H+?
Which of these two is the stronger acid?
Ka = [H+][F-] / [HF] = 7.2 x 10-4
In order to calculate pH, need equilibrium value of [H+]
[HF]o = 1.00 M
[H+]o = 0 M (approximation, as H+ from H20 not included here)
[F-]o = 0 M
Let x be the change required to reach equilibrium…..

18. pH of weak acid solutions
Equilibrium concentration of [HF] =
Equilibrium concentration of [H+] =
Equilibrium concentration of [F-] =
Substitute these into Ka = [H+][F-] / [HF] = 7.2 x 10-4 eqn, and solve for x….

19. Bases Cleaning solutions (ammonia, bleach)
Antacids (Tums, Rolaids, Milk of Magnesia)
Arrhenius: produces OH- ions
Lowry – Brønsted: H+ acceptor
Strong Bases - NaOH

20. pH of strongly basic solution
5.0 x 10-2 M NaOH solution (same procedure as for acidic pH calculations); Expected pH range?
Major species:

21. Weak bases
Many types of bases don’t contain OH-, but do increase [OH-] when dissolved in water (through reaction with water).
Base Acid
Lone pair of electrons on N picks up H+ from H2O

22. Weak bases General reaction with H2O: Kb =
Kb always refers to reaction of a base with H2O to produce a conjugate acid and OH-

23. pH of weak bases - calculations
Very similar to those of weak acids
pH of 15.0 M solution of NH3 (Kb = 1.8 x 10-5)

24. Polyprotic acids More than 1 acidic H; H2SO4, H3PO4; H2CO3
Consider H3PO4
Only 1st dissociation step usually important for [H+] determination
Ka1 >>> Ka2 >>> Ka3

25. Polyprotic acids
pH of 5.0 M H3PO4 solution; eq. concs. of H3PO4, H2PO42-, HPO43- and PO43-.

26. Sulfuric acid (H2SO4) Unique acid Strong acid in 1st dissociation step
Weak acid in 2nd dissociation step
pH of 1.0 M H2SO4 solution
Does HSO4- make significant contribution to [H+]? No.

27. Acid-base properties of salts
Salts producing neutral solutions
Salts producing basic solutions
Salts producing acidic solutions

28. Acid-base properties of salts

29. Structure effects on acid/base properties
Oxyacids
Hydrogen halides