General Chemistry Principles and Modern Applications 8ed

1. Philip Dutton
University of Windsor, Canada
N9B 3P4
Prentice-Hall © 2002
General Chemistry
Principles and Modern Applications
Petrucci • Harwood • Herring
8th
Edition
Chapter 17: Acids and Bases

2. Prentice-Hall General Chemistry: Chapter 17Slide 2 of 47
Contents
17-1 The Arrhenius Theory: A Brief Review
17-2 Brønsted-Lowry Theory of Acids and Bases
17-3 The Self-Ionization of Water and the pH Scale
17-4 Strong Acids and Strong Bases
17-5 Weak Acids and Weak Bases
17-6 Polyprotic Acids
17-7 Ions as Acids and Bases
17-8 Molecular Structure and Acid-Base Behavior
17-8 Lewis Acids and Bases
Focus On Acid Rain.

3. Prentice-Hall General Chemistry: Chapter 17Slide 3 of 47
17-1 The Arrhenius Theory:
A Brief Review
HCl(g) → H+
(aq) + Cl-
(aq)
NaOH(s) → Na+
(aq) + OH-
(aq)
H2O
H2O
Na+
(aq) + OH-
(aq)+ H+
(aq) + Cl-
(aq) → H2O(l) + Na+
(aq) + Cl-
(aq)
H+
(aq)+ OH-
(aq) → H2O(l)
Arrhenius theory did not handle non OH-
bases such as ammonia very well.

4. Prentice-Hall General Chemistry: Chapter 17Slide 4 of 47
17-2 Brønsted-Lowry Theory of
Acids and Bases
• An acid is a proton donor.
• A base is a proton acceptor.
NH3 + H2O  NH4
+
+ OH-
NH4
+
+ OH-
 NH3 + H2O
base acid
baseacid
conjugate acid
conjugate base

5. Prentice-Hall General Chemistry: Chapter 17Slide 5 of 47
Base Ionization Constant
NH3 + H2O  NH4
+
+ OH-
Kc=
[NH3][H2O]
[NH4
+
][OH-
]
Kb= Kc[H2O] =
[NH3]
[NH4
+
][OH-
]
= 1.810-5
base acid
conjugate conjugate

6. Prentice-Hall General Chemistry: Chapter 17Slide 6 of 47
Acid Ionization Constant
CH3CO2H+ H2O  CH3CO2
-
+ H3O+
Kc=
[CH3CO2H][H2O]
[CH3CO2
-
][H3O+
]
Ka= Kc[H2O] = = 1.810-5
[CH3CO2H]
[CH3CO2
-
][H3O+
]
baseacid
conjugateconjugate

7. Prentice-Hall General Chemistry: Chapter 17Slide 7 of 47
Table 17.1 Relative Strengths of Some Brønsted-Lowry Acids and Bases
HClO4 + H2O  ClO4
-
+ H3O+
NH4
+
+ CO3
2-
 NH3 + HCO3
-
HCl + OH-
 Cl-
+ H2O
H2O + I-
 OH-
+ HIH2O + I-
 OH-
+ HI

8. Prentice-Hall General Chemistry: Chapter 17Slide 8 of 47
17-3 The Self-Ionization of Water and
the pH Scale

9. Prentice-Hall General Chemistry: Chapter 17Slide 9 of 47
Ion Product of Water
Kc=
[H2O][H2O]
[H3O+
][OH-
]
H2O+ H2O  H3O+
+ OH-
base acid
conjugate conjugate
KW= Kc[H2O][H2O] = = 1.010-14
[H3O+
][OH-
]

10. Prentice-Hall General Chemistry: Chapter 17Slide 10 of 47
pH and pOH
• The potential of the hydrogen ion was defined in
1909 as the negative of the logarithm of [H+
].
pH = -log[H3O+
] pOH = -log[OH-
]
-logKW = -log[H3O+
]-log[OH-
]= -log(1.010-14
)
KW = [H3O+
][OH-
]= 1.010-14
pKW = pH + pOH= -(-14)
pKW = pH + pOH = 14

11. Prentice-Hall General Chemistry: Chapter 17Slide 11 of 47
pH and pOH Scales

12. Prentice-Hall General Chemistry: Chapter 17Slide 12 of 47
17-4 Strong Acids and Bases
HCl CH3CO2H
Thymol Blue Indicator
pH < 1.2 < pH < 2.8 < pH

13. Prentice-Hall General Chemistry: Chapter 17Slide 13 of 47
17-5 Weak Acids and Bases
Acetic Acid HC2H3O2 or CH3CO2H

14. Prentice-Hall General Chemistry: Chapter 17Slide 14 of 47
Weak Acids
Ka= = 1.810-5
[CH3CO2H]
[CH3CO2
-
][H3O+
]
pKa= -log(1.810-5
) = 4.74
glycine H2NCH2CO2H
lactic acid CH3CH(OH) CO2H
C
OH
O
R

15. Prentice-Hall General Chemistry: Chapter 17Slide 15 of 47
Table 17.3 Ionization Constants of Weak Acids and Bases

16. Prentice-Hall General Chemistry: Chapter 17Slide 16 of 47
Example 17-5
Determining a Value of KA from the pH of a Solution of a
Weak Acid.
Butyric acid, HC4H7O2 (or CH3CH2CH2CO2H) is used to make
compounds employed in artificial flavorings and syrups. A
0.250 M aqueous solution of HC4H7O2 is found to have a pH of
2.72. Determine KA for butyric acid.
HC4H7O2 + H2O  C4H77O2 + H3O+
Ka = ?
Solution:
For HC4H7O2 KA is likely to be much larger than KW. Therefore
assume self-ionization of water is unimportant.

17. Prentice-Hall General Chemistry: Chapter 17Slide 17 of 47
Example 17-5
HC4H7O2 + H2O  C4H7O2 + H3O+
Initial conc. 0.250 M 0 0
Changes -x M +x M +x M
Eqlbrm conc. (0.250-x) M x M x M

18. Prentice-Hall General Chemistry: Chapter 17Slide 18 of 47
Example 17-5
Log[H3O+
] = -pH = -2.72
HC4H7O2 + H2O  C4H77O2 + H3O+
[H3O+
] = 10-2.72
= 1.910-3
= x
[H3O+
] [C4H7O2
-
]
[HC4H7O2]
Ka=
1.910-3
· 1.910-3
(0.250 – 1.910-3
)
=
Ka= 1.510-5
Check assumption: Ka >> KW.

19. Prentice-Hall General Chemistry: Chapter 17Slide 19 of 47
Percent Ionization
HA + H2O  H3O+
+ A-
Degree of ionization =
[H3O+
] from HA
[HA] originally
Percent ionization =
[H3O+
] from HA
[HA] originally
 100%

20. Prentice-Hall General Chemistry: Chapter 17Slide 20 of 47
Percent Ionization
Ka =
[H3O+
][A-
]
[HA]
Ka =
nH3O+
A-
n
HA
n
1
V

21. Prentice-Hall General Chemistry: Chapter 17Slide 21 of 47
17-6 Polyprotic Acids
H3PO4 + H2O  H3O+
+ H2PO4
-
H2PO4
-
+ H2O  H3O+
+ HPO4
2-
HPO4
2-
+ H2O  H3O+
+ PO4
3-
Phosphoric acid:
A triprotic acid.
Ka = 7.110-3
Ka = 6.310-8
Ka = 4.210-13

22. Prentice-Hall General Chemistry: Chapter 17Slide 22 of 47
Phosphoric Acid
• Ka1 >> Ka2
• All H3O+
is formed in the first ionization step.
• H2PO4
-
essentially does not ionize further.
• Assume [H2PO4
-
] = [H3O+
].
• [HPO4
2-
] Ka2 regardless of solution molarity.

23. Prentice-Hall General Chemistry: Chapter 17Slide 23 of 47
Table 17.4 Ionization Constants of Some Polyprotic Acids

24. Prentice-Hall General Chemistry: Chapter 17Slide 24 of 47
Example 17-9
Calculating Ion Concentrations in a Polyprotic Acid Solution.
For a 3.0 M H3PO4 solution, calculate:
(a) [H3O+
]; (b) [H2PO4
-
]; (c) [HPO4
2-
] (d) [PO4
3-
]
H3PO4 + H2O  H2PO4
-
+ H3O+
Initial conc. 3.0 M 0 0
Changes -x M +x M +x M
Eqlbrm conc. (3.0-x) M x M x M

25. Prentice-Hall General Chemistry: Chapter 17Slide 25 of 47
Example 17-9
H3PO4 + H2O  H2PO4
-
+ H3O+
[H3O+
] [H2PO4
-
]
[H3PO4]
Ka=
x · x
(3.0 – x)
=
Assume that x << 3.0
= 7.110-3
x2
= (3.0)(7.110-3
) x = 0.14 M
[H2PO4
-
] = [H3O+
] = 0.14 M

26. Prentice-Hall General Chemistry: Chapter 17Slide 26 of 47
Example 17-9
H2PO4
-
+ H2O  HPO4
2-
+ H3O+
[H3O+
] [HPO4
2-
]
[H2PO4
-
]
Ka=
y · (0.14 + y)
(0.14 - y)
= = 6.310-8
Initial conc. 0.14 M 0 0.14 M
Changes -y M +y M +y M
Eqlbrm conc. (0.14 - y) M y M (0.14 +y) M
y << 0.14 M y = [HPO4
2-
] = 6.310-8

27. Prentice-Hall General Chemistry: Chapter 17Slide 27 of 47
Example 17-9
HPO4
-
+ H2O  PO4
3-
+ H3O+
[H3O+
] [HPO4
2-
]
[H2PO4
-
]
Ka=
(0.14)[PO4
3-
]
6.310-8
= = 4.210-13
M
[PO4
3-
] = 1.910-19
M

28. Prentice-Hall General Chemistry: Chapter 17Slide 28 of 47
Sulfuric Acid
Sulfuric acid:
A diprotic acid.
H2SO4 + H2O  H3O+
+ HSO4
-
HSO4
-
+ H2O  H3O+
+ SO4
2-
Ka = very large
Ka = 1.96

29. Prentice-Hall General Chemistry: Chapter 17Slide 29 of 47
General Approach to Solution Equilibrium
Calculations
• Identify species present in any significant amounts
in solution (excluding H2O).
• Write equations that include these species.
– Number of equations = number of unknowns.
• Equilibrium constant expressions.
• Material balance equations.
• Electroneutrality condition.
• Solve the system of equations for the unknowns.

30. Prentice-Hall General Chemistry: Chapter 17Slide 30 of 47
17-7 Ions as Acids and Bases
NH4
+
+ H2O  NH3 + H3O+
baseacid
CH3CO2
-
+ H2O CH3CO2H + OH-
base acid
[NH3] [H3O+
] [OH-
]
Ka=
[NH4
+
] [OH-
]
[NH3] [H3O+
]
Ka=
[NH4
+
]
= ?
=
KW
Kb
=
1.010-14
1.810-5
= 5.610-10
Ka Kb = Kw

31. Prentice-Hall General Chemistry: Chapter 17Slide 31 of 47
Hydrolysis
• Water (hydro) causing cleavage (lysis) of a bond.
Na+
+ H2O → Na+
+ H2O
NH4
+
+ H2O → NH3 + H3O+
Cl-
+ H2O → Cl-
+ H2O
No reaction
No reaction
Hydrolysis

32. Prentice-Hall General Chemistry: Chapter 17Slide 32 of 47
17-8 Molecular Structure and
Acid-Base Behavior
• Why is HCl a strong acid, but HF is a weak one?
• Why is CH3CO2H a stronger acid than CH3CH2OH?
• There is a relationship between molecular structure
and acid strength.
• Bond dissociation energies are measured in the gas
phase and not in solution.

33. Prentice-Hall General Chemistry: Chapter 17Slide 33 of 47
Strengths of Binary Acids
HI HBr HCl HF
160.9 > 141.4 > 127.4 > 91.7 pm
297 < 368 < 431 < 569 kJ/mol
Bond length
Bond energy
109
> 108
> 1.3106
>> 6.610-4
Acid strength
HF + H2O → [F-
·····H3O+
]  F-
+ H3O+
ion pair
H-bonding
free ions

34. Prentice-Hall General Chemistry: Chapter 17Slide 34 of 47
Strengths of Oxoacids
• Factors promoting electron withdrawal from the
OH bond to the oxygen atom:
– High electronegativity (EN) of the central atom.
– A large number of terminal O atoms in the molecule.
H-O-Cl H-O-Br
ENCl = 3.0 ENBr= 2.8
Ka = 2.910-8
Ka = 2.110-9

35. Prentice-Hall General Chemistry: Chapter 17Slide 35 of 47
S OO
O
O
H H
··
··
··
··
-
2+
··
··
··
··
··
··
-
S OO
O
H H
··
··
··
··
-
+
··
··
··
··
S OO
O
O
H H
··
··
··
··
··
··
··
··
S OO
O
H H
··
··
··
·· ··
··
··
Ka 103
Ka =1.310-2

36. Prentice-Hall General Chemistry: Chapter 17Slide 36 of 47
Strengths of Organic Acids
C OC
O
H H
··
··
··
··
H
H
OCH H
··
··
H
H
C
H
H
Ka = 1.810-5
Ka =1.310-16
acetic acid ethanol

37. Prentice-Hall General Chemistry: Chapter 17Slide 37 of 47
Focus on the Anions Formed
OCH
··
··
H
H
C
H
H
C
O
C
O
H
-
··
··
··
H
H
··
··
C
O
C
O
H
-··
··
··
H
H
··
··
··
-

38. Prentice-Hall General Chemistry: Chapter 17Slide 38 of 47
Structural Effects
C
H
H
C
O
C
O
H
-
··
··
··
H
H
··
··
CH
H
H
C
O
O
-
··
··
··
··
··
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
Ka = 1.810-5
Ka = 1.310-5

39. Prentice-Hall General Chemistry: Chapter 17Slide 39 of 47
Structural Effects
C
O
C
O
H
-
··
··
··
H
H
··
··
Ka = 1.810-5
Ka = 1.410-3
C
O
C
O
H
-
··
··
··
H
Cl
··
··

40. Prentice-Hall General Chemistry: Chapter 17Slide 40 of 47
Strengths of Amines as Bases
NH
H
H
··
NBr
H
H
··
pKb = 4.74 pKa = 7.61
ammonia bromamine

41. Prentice-Hall General Chemistry: Chapter 17Slide 41 of 47
Strengths of Amines as Bases
CH
H
H
C
H
H
CH
H
H
C
H
H
CH
H
H
C
H
H
pKb = 4.74 pKa = 3.38 pKb = 3.37
methylamine ethylamine propylamine
NH2
NH2
NH2

42. Prentice-Hall General Chemistry: Chapter 17Slide 42 of 47
Resonance Effects

43. Prentice-Hall General Chemistry: Chapter 17Slide 43 of 47
Inductive Effects

44. Prentice-Hall General Chemistry: Chapter 17Slide 44 of 47
17-9 Lewis Acids and Bases
• Lewis Acid
– A species (atom, ion or molecule) that is an electron
pair acceptor.
• Lewis Base
– A species that is an electron pair donor.
base acid adduct

45. Prentice-Hall General Chemistry: Chapter 17Slide 45 of 47
Showing Electron Movement

46. Prentice-Hall General Chemistry: Chapter 17Slide 46 of 47
Focus On Acid Rain
CO2 + H2O  H2CO3
H2CO3 + H2O  HCO3
-
+ H3O+
3 NO2 + H2O  2 HNO3 + NO

47. Prentice-Hall General Chemistry: Chapter 17Slide 47 of 47
Chapter 17 Questions
Develop problem solving skills and base your strategy not
on solutions to specific problems but on understanding.
Choose a variety of problems from the text as examples.
Practice good techniques and get coaching from people who
have been here before.