AP Notes Chapter17

1
ACIDS BASES
2
Arrhenius Theory

• 1. in aqueous solution
• 2. Acid produces H
• 3. Base produces OH-

3
Acid
HA H3O A-

O
O
-
HA
A
H
H
H
H
H
4
HCl(g) H2O ?H3O(aq) Cl-(aq)

• CH3COOH(l) H2O H3O(aq) CH3COO-(aq)

5
careless, but often seen

• HCl ? H Cl-
• CH3COOH ??H CH3COO-

6
Base

• NaOH(s) Na(aq) OH-(aq)

7
Arrhenius acid/base reaction

• acid base ? H2O a salt
• HA MOH ? HOH MA

8
Monoprotic acid HCl

• HCl(aq) NaOH(aq) ? H2O(l) NaCl(aq)
• H Cl- Na OH- ? H2O Na Cl-
• H OH- ? H2O
• HCl ?

9
Diprotic acid H2SO4

• H2SO4 (aq) 2NaOH (aq) ? 2H2O(l) Na2SO4 (aq)
• H OH- ? H2O
• H2SO4 ?

10
Triprotic acid H3PO4 Polyprotic

• H3PO4(aq) 3NaOH(aq) ? 3H2O(l) Na3PO4(aq)
• H3PO4 3 OH- ? 3 H2O PO43-
• H3PO4 ?

11
Bronsted-Lowry Theory

• 1. aqueous nonaqueous solutions
• 2. Acid species donating a proton
• HCl ? H Cl-
• H2SO4 ? H HSO4-
• CH3COOH ? H CH3COO-

12
Bronsted-Lowry Theory

• 3. Base species accepting a proton
• OH- H ? HOH
• H2O H ? H3O
• NH3 H ? NH4

13
Conjugate acid-base pairs
acid1 base1 acid2 base2
conjugate pairs
HF HOH
14
Conjugate acid-base pairs
acid1 base1 acid2 base2
conjugate pairs
HF HOH H3O F-
15
ALL Arrhenius reactions are Bronsted-Lowry
reactions HCl NaOH ? H2O NaCl
16
NOT all Bronsted reactions are Arrhenius
reactions CH3COOH NH3 ? NH4 CH3COO-
17
Amphiprotic AmphotericCan act as either an
acid or a base

• HCl HOH ? H3O Cl-
• NH3 HOH ?? NH4 OH-
• NH3 OH- ?? NH2- HOH
• HOH HOH ?? H3O OH-

18
ACID STRENGTH

• Relative ability of a compound to donate a proton
• Base strength is considered a result, not a cause

19
REVIEW

• Strong acid
• 100 dissociation
• Weak acid
• lt100 dissociation
• Notice this is NOT related to concentration

20
Electronegativity is the most significant factor
influencing the strength of acids bases
21
HF gt HCl gt HBr gt HI as acids in non-aqueous
solvents, or as pure gases
22
Look at difference in electronegativities 2.1 H
- F 4.0 2.1 H - Cl 3.0 2.1 H - Br 2.8 2.1
H - I 2.5
23
Most ionic is the most acidic Nonpolar
Polar Ionic ED 0 ED 1.7 ED 4.0
24
However, as acids in aqueous solution HF lt HCl
HBr HI
25
2.1 H - O 3.5 competition! 2.1 H - F 4.0 2.1
H - Cl 3.0 2.1 H - Br 2.8 2.1 H - I 2.5
26
Is methane acidic as a gas or in aqueous
solution? 2.1 H - C 2.5
27
The strength of oxy-acids are also dependent on
electronegativity.
28
Oxy-acids and bases have the same fundamental
structure
29
NaOH Na - O - H 0.9 3.5
2.1 HClO Cl - O - H 3.0
3.5 2.1
30
In water, the more ionic bond dissociates,
forming the acid or base
31
NaOH Na - O - H 0.9 3.5
2.1 HClO Cl - O - H 3.0
3.5 2.1
32
Are alcohols acids or bases? C - O - H 2.5 3.5
2.1
33
Acids in homologous series are of different
strength
34
Acid Strength H2SO4 gt H2SO3 HNO3 gt HNO2 HClO4
gt HClO3 gt HClO2 gt HClO
35
Structurally H2SO4 O2S(OH)2 H2SO3 OS(OH)2
36
Need to examine formal charge of central atom.
37
Acid Strength CH3COOHgt CH3CH2OH CF3COOH gt
CH3COOH
38
Need to examine inductive effect of neighboring
atoms.
39
pH pK Ka , Kb , Kw
40
2H2O H3O OH-
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Keq H2O2 H3O OH- Kw H3O
OH- where Kw (25oC ) 1 x 10-14
42
in a neutral solution H3O OH- 1 x 10-14
H3O 2 OH-2 H3O OH- 1 x 10-7
43
pX -log X pK -log K pH -log
H3O pOH -log OH-
44
leveling effect of H2O limits H3O
OH- to that controlled by H2O
45
upper limit H3O 1 lower limit H3O
1 x 10-14
46
pH scale
acid neutral base
7
14
0
highest H3O on left lowest H3O on
right
47
H3O and OH- must be considered together
48
Kw H3O OH- -log Kw -log H3O
OH- -log Kw -log H3O
-logOH-
49
pKw pH pOH but Kw 1 x 10-14 14 pH
pOH
50
Relationship between conjugate acids
bases HA H2O H3O A- A- H2O
HA OH-
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53
Ka x Kb H3O OH- Kw
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Ka. Kb H3O OH- Kw Ka. Kb Kw
55
SUMMARY pH -log H3O pOH -log OH- H3O
OH- 1 x 10-14 pH pOH 14 Ka. Kb Kw
56
Applications of Acid-Base Concepts
57
for weak acids bases, refer to Appendix H for
Ka Appendix I for Kb values in Kotz Treichel
58
1. What is the pH of a solution that is 0.025 M
KOH?
59
2. What is the pH of a 0.20 M acetic acid
solution?
60
3. 100 mL of 0.10 M CH3COOH are mixed with 20.0
mL of 0.10 M NaOH. What is the pH of the
solution?
61
4. Calculate the percent ionization of 0.10 M
methylamine (CH3NH2).
62
pH of Salts Oxides
63
What effect does the addition of a salt
to water have upon the pH of the water?
64
H2O equilibrium is the prime factor in the
behavior of solutions.
65
pH of a salt solution is dependent upon
the strength of the salt as an electrolyte.
66
Example 1 NaCl(s) HOH NaOH(aq)
HCl(aq)
67
Example 1 NaCl(s) HOH ? NaOH (aq)
HCl(aq) strong
base strong acid Na OH- H Cl- ? Na
HOH Cl-
68
thus, NaCl in water has NO effect on pH
69
Example 2 NaCN(s) HOH NaOH(aq)
HCN(aq)
70
Example 2 NaCN(s) HOH ? NaOH (aq)
HCN(aq)
strong base weak acid ? Na
OH- HCN
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CN- is the anion of the weak acid
HCN CN- HOH HCN OH-
72
NaCN(s) HOH ?Na OH- HCN
strong base weak acid
73
thus, NaCN in water produces a/n ?? solution
74
thus, NaCN in water produces a BASIC solution
75
5. What is the pH of a 0.010 M sodium cyanide
solution?
76
Example 3 NH4Cl(s) HOH ?NH4OH (aq)
HCl(aq)
77
Example 3 NH4Cl(s) HOH ?NH4OH (aq)
HCl(aq) weak base
strong acid ?NH4OH
H Cl-
78
NH4 is the cation of the weak base
NH4OH NH4 HOH NH3 H3O
79
NH4Cl(s) HOH -gt NH4OH H Cl-
weak base strong acid
80
thus, NH4Cl in water produces a/n ??
solution
81
thus, NH4Cl in water produces an ACID
solution
82
6. What is pH of a 0.10 M ammonium chloride
solution?
83
Example 4 NH4CN(s) HOH NH4OH (aq)
HCN(aq) weak
base weak acid
84
NH4 is the cation of the weak base
NH4OH NH4 HOH NH3 H3O
85
CN- is the anion of the weak acid
HCN CN- HOH HCN OH-
86
thus, NH4CN in water produces a/n ??
solution
87
The pH of a solution formed from the cation of
a weak base and the anion of a weak acid is
dependent on the relative strength of the weak
acid and weak base.
88
Ka(HCN) 6.2 x 10-10 Text Table
5.1 Appendix H A-23 Kb(NH4OH) 1.8 x
10-5 Text Table 5.3
Appendix I A-25
89
thus, NH4CN in water produces a/n ??
solution
90
thus, NH4CN in water produces a BASIC
solution, because the weak base is stronger
(ionizes more) than the weak acid
91
Acidity of Oxides
92
SO2 HOH ??
93
SO2 HOH H2SO3
O2
H2SO4
94
SO2 HOH H2SO3
O2
H2SO4 Covalent oxides are acidic are referred
to as acid anhydrides
95
Na2O HOH ??
96
Na2O HOH 2NaOH(aq)
97
Na2O HOH 2NaOH(aq) Ionic oxides are
basic are referred to as basic anhydrides
98
Lewis Acid-Base Theory
99

• Acid
• substance capable of accepting an e- pair

100
Lewis acid

• must have an empty valence level orbital
• i.e. H has an empty 1s orbital which can accept
  an e- pair

101
Thus, H is an acid under all three theories

• Arrhenius
• Bronsted-Lowry
• Lewis

102
Lewis Acid-Base TheoryAcid substance capable of
accepting an e- pair

• Base
• substance capable of donating an e- pair

103
Examples of Lewis bases

• OH- , NH3 , F-
• all have unbonded pairs of e- available for
  donation

104
Elements of Group 13 (3A) form compounds that
make excellent Lewis acids
105
another typical Lewis acid-base reaction
106
Reaction of a Lewis Acid and Lewis Base

• New bond formed using electron pair from the
  Lewis base.
• Coordinate covalent bond
• Notice geometry change on reaction.

107
Lewis Acids Bases

• Formation of hydronium ion is also an excellent
  example.

• Electron pair of the new O-H bond originates on
  the Lewis base.

108
Lewis Acid/Base Reaction
109
?
H3BO3 H2O H2BO3- H3O
NO!
110
H3BO3 2H2O B(OH)4- H3O
111
is Al(OH)3 an acid or base?
112
Amphoterism of Al(OH)3
113

• This explains AMPHOTERIC nature of some metal
  hydroxides.
• Al(OH)3(s) 3 H ? Al3 3 H2O
• Here Al(OH)3 is a Brønsted base.
• Al(OH)3(s) OH- ? Al(OH)4-
• Here Al(OH)3 is a Lewis acid.

114
Transition metal ions also very good Lewis
Acids
115

• Other good examples involve metal ions.

116
..
Zn2 HOH ?
..
Zn2 gt Ar 4s0 3d10 4p0
Zn(H2O)42
117
Reaction of NH3 with Cu2(aq)
118
Formation of complex ions is a
Lewis acid-base reaction
119
Lewis Acid-Base Interactions in Biology

• The heme group in hemoglobin can interact with O2
  and CO.
• The Fe ion in hemoglobin is a Lewis acid
• O2 and CO can act as Lewis bases

Heme group
120
Inclusiveness of the Acid/Base Definitions
Lewis Bronstead Arrhenius