1. Chapter 11: Acids and Bases
University Chemistry
Chapter 11: Acids and Bases
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2. Arrhenius Definition of Acids and Bases
Arrhenius acid is a substance that produces H+ in water
Arrhenius base is a substance that produces OH- in water

3. Properties of Acids
Have a sour taste. Vinegar owes its taste to acetic acid. Citrus
fruits contain citric acid.
Acids cause color changes in plant dyes, for example, they change the color of litmus from blue to red.
React with certain metals to produce hydrogen gas.
2HCl (aq) + Mg (s) MgCl2 (aq) + H2 (g)
React with carbonates and bicarbonates
to produce carbon dioxide gas
2HCl (aq) + CaCO3 (s) CaCl2 (aq) + CO2 (g) + H2O (l)
Aqueous acid solutions conduct electricity.

4. Properties of Bases Have a bitter taste.
Feel slippery. Many soaps contain bases.
Bases cause color changes in plant dyes, for example, they change the color of litmus from red to blue.
Aqueous base solutions conduct electricity.

5. Brønsted Definition of Acids and Bases
Acid is a proton* donor
Base is a proton acceptor
* In solution exists as a hydrated proton (H3O+) or hydronium ion.

6. Hydronium ion, hydrated proton, H3O+
4.3

7. Strong acids for all practical purposes are completely ionized in water.
Strong bases for all practical purposes are completely ionized in water.
Weak acids ionize only to a limited extent in water.
Weak bases ionize only to a limited extent in water.

8. Monoprotic acids Diprotic acids Triprotic acids HCl H+ + Cl-
Strong electrolyte, strong acid
HNO H+ + NO3-
Strong electrolyte, strong acid
CH3COOH H+ + CH3COO-
Weak electrolyte, weak acid
Diprotic acids
H2SO H+ + HSO4-
Strong electrolyte, strong acid
HSO H+ + SO42-
Weak electrolyte, weak acid
Triprotic acids
H3PO H+ + H2PO4-
Weak electrolyte, weak acid
H2PO H+ + HPO42-
Weak electrolyte, weak acid
HPO H+ + PO43-
Weak electrolyte, weak acid

9. Amphoteric: refers to a substances that can act as both a Brønsted acid and a Brønsted base

10. Neutralization Reaction
An ionic compound made up of a cation other than H+ and an anion other than OH- or O2-.
acid + base salt + water
molecular equation
HCl (aq) + NaOH (aq) NaCl (aq) + H2O
H+ + Cl- + Na+ + OH Na+ + Cl- + H2O
H+ + OH H2O
net ionic equation
spectator ions

11. Conjugate Acid-Base Pairs
Defined as an acid and its conjugate base or a base and its conjugate acid.
The word conjugate means “joined together”.
base1
acid2
acid1
base2
base
acid
conjugate acid
conjugate base

13. Conjugate acid-base pairs:
The conjugate base of a strong acid has no measurable strength.
H3O+ is the strongest acid that can exist in aqueous solution.
The OH- ion is the strongest base that can exist in aqueous solution.

14. Lewis Definition of Acids and Bases
A Lewis acid is a substance that can accept a pair of electrons
A Lewis base is a substance that can donate a pair of electrons
+ OH- •
H O H • H+
acid
base
N H • H
N H H + H+ +
acid
base

17. Acid-Base Properties of Water hydroxide ion hydronium ion
autoionization of water
hydroxide ion hydronium ion O H + - [ ]
conjugate acid
base
H2O + H2O H3O+ + OH-
acid
conjugate base

18. The Ion Product of Water
The ion-product constant (Kw) is the product of the molar concentrations of H+ and OH- ions at a particular temperature.
Solution is
[H+] = [OH-]
neutral
At 250C
Kw = [H+][OH-] = 1.0 x 10-14
[H+] > [OH-]
acidic
[H+] < [OH-]
basic

20. pH – A Measure of Acidity
Solution Is
At 250C
neutral
[H+] = [OH-]
[H+] = 1 x 10-7
pH = 7
acidic
[H+] > [OH-]
[H+] > 1 x 10-7
pH < 7
basic
[H+] < [OH-]
[H+] < 1 x 10-7
pH > 7 pH
[H+]

21. [H+][OH-] = Kw = 1.0 x 10-14
-log [H+] – log [OH-] = 14.00

25. Temperature Dependence of Kw and pH
Le Châtelier’s principle: the equilibrium of an endothermic process will shift in the direction of products when the temperature is increased, leading to a corresponding increase in the equilibrium constant.

27. Weak Acid: HF
Strong Acid: HCl

28. Weak Acids (HA) and Acid Ionization Constants
HA (aq) + H2O (l) H3O+ (aq) + A- (aq)
HA (aq) H+ (aq) + A- (aq)
Ka is the acid ionization constant
weak acid
strength Ka

30. Solvent leveling: All acids with Ka>1 will yield identical H3O+ concentrations in water, independent of their individual Ka values
Proton exchange reaction:
Ka = 1
The strongest acid that can exist in aqueous solution is the hydronium ion (H3O+).

31. Weak Bases and Base Ionization Constants
Kb is the base ionization constant
weak base
strength Kb

32. Solvent leveling: All bases with Kb>1 will yield identical OH- concentrations in water, independent of their individual Kb values
Proton exchange reaction:
Kb = 1
The strongest base that can exist in aqueous solution is the hydroxide ion (OH-).

34. Ionization Constants of Conjugate Acid-Base Pairs
HA (aq) H+ (aq) + A- (aq) Ka
A- (aq) + H2O (l) OH- (aq) + HA (aq) Kb
H2O (l) H+ (aq) + OH- (aq) Kw
KaKb = Kw
Weak Acid Conjugate Base
Ka = Kw Kb
Kb = Kw Ka

39. Ionization Constants for Diprotic and Triprotic Acids

43. Solving weak acid ionization problems:
Identify the major species that can affect the pH.
In most cases, you can ignore the autoionization of water.
Ignore [OH-] because it is determined by [H+].
Use initial concentration and change to express the equilibrium concentrations in terms of single unknown x.
Write Ka in terms of equilibrium concentrations. Solve for x by the approximation method.
4, If approximation is not valid, solve for x exactly.
5. Calculate concentrations of all species and/or pH of the solution.

47. For a monoprotic acid HA
Percent Ionization
For a monoprotic acid HA
Percent ionization =
[H+]
[HA]0
x 100%
[HA]0 = initial concentration

52. pH of Dilute Acid and Base Solutions
Dilute Solutions of Weak Acids
H2O(l) = H+(aq) + OH-(aq)
Need two more equations:
mass balance
charge balance
Use if H+ ion concentration is expected to be less than 10-6 M.
Very Dilute Solutions of Strong Acids
Only the terms containing Ka are significant.
If neglect Kw

55. pH of Diprotic and Triprotic Acids
H2A + H2O = H3O+(aq) + HA-(aq) Ka1
HA-(aq) + H2O = H3O+(aq) + A-(aq) Ka2
Concentration of H+ ions is the product of only the first stage of ionization.
Concentration of the conjugate base for the second stage of ionization is numerically equal to

59. Molecular Structure and Acid Strength
H X
H+ + X-
Hydrohalic Acids
The stronger the bond
Two competing effects:
The weaker the acid
The polar the bond
The stronger the acid
HF << HCl < HBr < HI

60. Oxoacids Z O H O-
+ H+ d- d+
The O-H bond will be more polar and easier to break if:
Z is very electronegative or
Z is in a high oxidation state

61. Acid strength increases with increasing electronegativity of Z
1. Oxoacids having different central atoms (Z) that are from the same group and that have the same oxidation number.
Acid strength increases with increasing electronegativity of Z
H O Cl O O •
H O Br O O •
Cl is more electronegative than Br
HClO3 > HBrO3

62. Acid strength increases as the oxidation number of Z increases.
2. Oxoacids having the same central atom (Z) but different numbers of attached groups.
Acid strength increases as the oxidation number of Z increases.
HClO4 > HClO3 > HClO2 > HClO

64. Lewis structures can be generalized as:
Carboxylic Acids
Lewis structures can be generalized as:
R is part of the acid molecule
Carboxyl group (-COOH).
Strengths of carboxylic acids depend on the nature of the R group.
Electronegative groups in the R group polarize the –O—H bond thereby increasing acidity

65. Acid-Base Properties of Salts
Salts producing neutral solutions:
Salts containing an alkali metal or alkaline earth metal ion (except Be2+) and the conjugate base of a strong acid (e.g. Cl-, Br-, and NO3-).
NaCl (s) Na+ (aq) + Cl- (aq)
H2O
Salts producing basic solutions:
Salts derived from a strong base and a weak acid.
NaCH3COOH (s) Na+ (aq) + CH3COO- (aq)
H2O
CH3COO- (aq) + H2O (l) CH3COOH (aq) + OH- (aq)

69. Salts producing acidic solutions:
Salts derived from a strong acid and a weak base.
NH4Cl (s) NH4+ (aq) + Cl- (aq)
H2O
NH4+ (aq) NH3 (aq) + H+ (aq)
Salts with small, highly charged metal cations (e.g. Al3+, Cr3+, and Be2+) and the conjugate base of a strong acid.
Al(H2O)6 (aq) Al(OH)(H2O)5 (aq) + H+ (aq) 3+ 2+

70. Acid Hydrolysis of Al3+

71. Salts in which both the cation and the anion hydrolyze:
Kb for the anion > Ka for the cation, solution will be basic
Kb for the anion < Ka for the cation, solution will be acidic
Kb for the anion  Ka for the cation, solution will be neutral

73. Salts of amphoteric ions:

74. Oxides of the Representative Elements
In Their Highest Oxidation States

75. Antacids and the Stomach pH Balance
NaHCO3 (aq) + HCl (aq)
NaCl (aq) + H2O (l) + CO2 (g)
Mg(OH)2 (s) + 2HCl (aq)
MgCl2 (aq) + 2H2O (l)

76. Alkali metal hydroxides Alkaline earth metal hydroxides except Be(OH)2
Basic hydroxides:
Alkali metal hydroxides
Alkaline earth metal hydroxides except Be(OH)2
Amphoteric hydroxides:
Be(OH)2, Al(OH)3, Sn, Pd, Cr, Cu, Zn & Cd hydroxides
Al(OH)3(s) + 3H+  Al3+(aq) + 2H2O(l)
Al(OH)3(s) + OH- = Al(OH)4-(aq)