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Acids and Bases

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Chapter 15 Acids and Bases 4. Cation is conjugate acid of weak base; anion is from weak acid. Qualitative Prediction Ka Kb, Acidic, pH 7 Ka ... – PowerPoint PPT presentation

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Title: Acids and Bases


1
Chapter 15 Acids and Bases
2
What are acids and bases?
Learned in Chem 1211
Acid gives H in aqueous solution
HCl(aq) ? H(aq) Cl-(aq)
Base gives OH- in aqueous solution
NaOH(aq) ? Na(aq) OH-(aq)
Arrhenius acids and bases
3
A more general definition Brønsted-Lowrey acids
and bases
Acid proton (H) donor
Base proton (H) acceptor
4
HCl(aq) H2O(l)
? H3O(aq) Cl-(aq)
Lewis structure?
H3O hydronium ion
actual form of H in aqueous solutions
5
HAc(aq) H2O(l)
? H3O(aq) Ac-(aq)
NH3(aq) H2O(l)
? NH4(aq) OH-(aq)
6
Conjugate acid-base pair
- H
Acid
Base
7
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8
Amphiprotic or Amphoteric
9
Brønsted-Lowrey acids and bases are not limited
to aqueous solutions
10
Structural requirement on Brønsted-Lowrey acids
and bases
HCl, Cl-, NH3, NH4, H2O
11
Strong acids complete dissociation/ionization
Weak acids partial dissociation/ionization
12
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13
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14
7 common strong acids to remember
HCl, HBr, HI, HNO3, HClO3, HClO4, H2SO4
Names Dissociation equations
15
H2SO4(aq) H2O(l) ? H3O(aq)
HSO4-(aq)
HSO4-(aq) H2O(l) ? H3O(aq)
SO42-(aq)
HCl monoprotic acid H2SO4 polyprotic acid
16
Weak monoprotic acid
HA(aq) H2O(l) ? H3O(aq)
A-(aq)
17
HA(aq) H2O(l) ? H3O(aq) A-(aq)
HA(aq) ? H(aq) A-(aq)
Acid dissociation/ionization constant
Strength of an acid how easy it dissociates to
give a H
Relative strength of weak acids larger Ka ?
stronger acid (HA)
18
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19
HA(aq) ? H(aq) A-(aq)
Reverse reaction is base accepting H
Strength of a base its ability to obtain a H
Relative strength larger Ka ? stronger acid (HA)
? weaker base (A-)
20
Use table 15.5, arrange the following
species according to their strength as bases
F-, Cl-, NO2-, and CN-.
21
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22
Quiz for 2 extra points
Write down the chemical formulae for the 7
common strong acids Write down the dissociation
reaction of nitric acid
23
7 common strong acids to remember
HCl, HBr, HI, HNO3, HClO3, HClO4, H2SO4
Names Dissociation equations
24
Amphiprotic or Amphoteric
25
Autoionization of Water
H2O(l) H2O(l)
? H3O(aq) OH-(aq)
Dissociation constant or ion-product constant of
water
26
H2O(l) ? H(aq) OH-(aq)
At 25 C in water, H OH- 1.0 x 10-7 mol/L
Kw 1.0 x 10-14
True for ANY aqueous solution at 25 C.
27
H OH- neutral solution or water
H gt OH- acidic solution
H lt OH- basic solution
Note
H ? 0, OH- ? 0 in any aqueous solution
28
Example 15.2, page 669
  • Calculate OH at 25 ?C for each solution and
    determine whether it is acidic, basic, or
    neutral.
  • H3O 7.5 ? 105 M
  • (b) H3O 1.5 ? 109 M
  • (c) H3O 1.0 ? 107 M

29
At 60 C, the value of Kw is 1.0 x 10-13. a)
Use Le Châteliers principle, predict whether the
reaction 2H2O(l) ? H3O(aq) OH-(aq) is
exothermic or endothermic. b) Calculate H
and OH- in a neutral solution at 60 C.
30
pH - log H
H 1.0 x 10-7 mol/L
pH - log (1.0 x 10-7) 7.00
Number of decimal places of log is equal to the
number of sig figs of the original number.
H 2.35 x 10-7 mol/L
pH - log (2.35 x 10-7) 6.629
31
pH - log H
pOH - log OH-
pKa - log Ka
pKw - log Kw
32
pH - log H
One unit change of pH corresponds to a change
of H by a factor of 10
e.g. H 0.1 mol/L
? pH 1.0
H 0.01 mol/L
? pH 2.0
33
pH - log H
H
pH
34
H
pH
35
Quiz for 2 extra points
Write down the chemical formulae for the 7
common strong acids Write down the dissociation
reaction of nitric acid
36
7 common strong acids to remember
HCl, HBr, HI, HNO3, HClO3, HClO4, H2SO4
Names Dissociation equations
37
Example 15.3, page 671
  • Calculate the pH of each solution at 25 ?C and
    indicate whether it is acidic or basic.
  • H 1.8 ? 104 M
  • (b) OH 1.3 ? 102 M

pOH?
Same questions at 60 C, Kw 1.0 x 10-13.
38
Relationship between pH and pOH
pH pOH pKw
39
The pH of a sample of human blood was measured to
be 7.41 at 25 C. Calculate pOH, H, and OH-
for the sample.
Same questions at 60 C, Kw 1.0 x 10-13.
40
Acidity in terms of pH at 25 C
pH 7, neutral pH lt 7, acidic pH gt 7, basic
41
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42
pH Meters are Used to Measure Acidity
43
pH / pOH Calculations
  • Strong acids
  • Strong bases
  • Weak acids
  • Weak bases
  • Salts

Default aqueous solution, 25 C
44
pH of strong acids
  • Calculate the pH of 0.10 mol/L HNO3.
  • a) Calculate the pH of 0.15 mol/L HCl.
  • b) Calculate the pH of 1.0 x 10-10 mol/L HCl.

45
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46
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47
pH of strong bases
Calculate the pH of a 5.2 x 10-2 mol/L NaOH
solution at 25 C.
pH for strong base OH- ? pOH ? pH
Calculate the pH of a 5.2 x 10-2 mol/L NaOH
solution at 60 C. At 60 C, Kw 1.0 x 10-13.
48
pH of strong bases
Calculate the pH of a 6.2 x 10-4 mol/L Ba(OH)2
solution at 25 C and at 60 C, respectively.
49
Quiz 8 up to this point
50
pH / pOH Calculations
  • Strong acids
  • Strong bases
  • Weak acids
  • Weak bases
  • Salts

51
pH of weak acids
HA(aq) ? H(aq) A-(aq)
Calculate the pH of a 1.00 mol/L HF solution. Ka
7.2 x 10-4.
52
HF(aq) ? H(aq) F-(aq)
Valid ?
lt 5
pH -logH -log(2.7 x 10-2) 1.57
53
pH of weak acids
HA(aq) ? H(aq) A-(aq)
Calculate the pH of a 1.00 mol/L HF solution. Ka
7.2 x 10-4.
Calculate the pH and percent dissociation of a
0.50 mol/L HF solution. Ka 7.2 x 10-4.
54
HF(aq) ? H(aq) F-(aq)
I
0.50
0
0
C
-x
x
x
E
0.50 - x
x
x
Valid ?
pH -logH -log(1.9 x 10-2) 1.72
55
pH of weak acids
HA(aq) ? H(aq) A-(aq)
Calculate the pH of a 1.00 mol/L HF solution. Ka
7.2 x 10-4.
Calculate the pH and percent dissociation of a
0.50 mol/L HF solution. Ka 7.2 x 10-4.
Calculate the pH and percent dissociation of a
0.10 mol/L HF solution. Ka 7.2 x 10-4.
56
HF(aq) ? H(aq) F-(aq)
I
0.10
0
0
C
-x
x
x
E
0.10 - x
x
x
Invalid ?
Literally solve the original quadratic equation
for x
57
HF(aq) ? H(aq) F-(aq)
I
0.10
0
0
C
-x
x
x
E
0.10 - x
x
x
pH -logH -log(8.1 x 10-3) 2.09
58
Percent dissociation
HF
1.00 mol/L
2.7
1)
2)
0.50 mol/L
3.8
0.10 mol/L
8.1
3)
59
Dissociation
60
Try Examples 15.5, 15.6 and 15.7 on page 674
61
value of Kc or Kp
equilibrium concentrations or pressures
62
Example 15.8, page 677
A 0.100 M weak acid (HA) solution has a pH of
4.25. Find Ka for the acid.
63
In a 0.100 mol/L lactic acid (HC3H5O3) aqueous
solution, lactic acid is 3.7 dissociated.
Calculate the value of Ka for this acid.
Ka 1.4 x 10-4
64
Monoprotic acids
Polyprotic acids
H3PO4
65
H3PO4(aq) ? H(aq) H2PO4-(aq) Ka1
H2PO4-(aq) ? H(aq) HPO42-(aq) Ka2
HPO42-(aq) ? H(aq) PO43-(aq) Ka3
Ka1 gtgt Ka2 gtgt Ka3
66
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67
Calculate the pH of a 5.0 mol/L H3PO4 solution
and the equilibrium concentrations of the
species H3PO4, H2PO4-, HPO42-, and PO43-.
68
H3PO4(aq) ? H(aq) H2PO4-(aq) Ka1
H2PO4-(aq) ? H(aq) HPO42-(aq) Ka2
HPO42-(aq) ? H(aq) PO43-(aq) Ka3
Ka1 gtgt Ka2 gtgt Ka3
69
Calculate the pH of a 5.0 mol/L H3PO4 solution
and the equilibrium concentrations of the
species H3PO4, H2PO4-, HPO42-, and PO43-.
H 0.19 M, pH 0.72
70
H3PO4(aq) ? H(aq) H2PO4-(aq) Ka1
H2PO4-(aq) ? H(aq) HPO42-(aq) Ka2
HPO42-(aq) ? H(aq) PO43-(aq) Ka3
Ka1 gtgt Ka2 gtgt Ka3
71
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72
Example 15.18, page 695
Calculate the pH of a 0.0100 M H2SO4 solution.
73
Try Examples 15.17, 15.18 and 15.19 on page 695
74
pH / pOH Calculations
  • Strong acids
  • Strong bases
  • Weak acids
  • Weak bases
  • Salts

75
higher Kb ? stronger base
76
NH3(aq) H2O(l)
? NH4(aq) OH-(aq)
Base must have a pair of nonbonding electrons.
77
NH3
CH3NH2
C5H5N
78
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79
pH for weak base ICE ? OH- ? pOH ? pH
80
Example 15.12, page 684
Calculate the pH of a 0.100 mol/L NH3 solution.
Kb 1.76 x 10-5
81
Calculate the pH of a 1.0 mol/L methylamine
CH3NH2 solution. Kb 4.38 x 10-4
OH- 0.021 M, pH 12.32
82
HA(aq) ? H(aq) A-(aq)
Reverse reaction is base accepting H
Strength of a base its ability to obtain a H
Relative strength larger Ka ? stronger acid (HA)
? weaker base (A-)
83
higher Kb ? stronger base
84
Relation between Ka and Kb for a conjugate
acid-base pair
Kb
BH(aq) H2O(l) ? H3O(aq) B(aq)
Ka
2H2O(l) ? H3O(aq) OH-(aq)
Kw
Sum of reactions ? Product of equilibrium
constants
85
Relation between Ka and Kb for a conjugate
acid-base pair
Kb
BH(aq) H2O(l) ? H3O(aq) B(aq)
Ka
2H2O(l) ? H3O(aq) OH-(aq)
Kw
KaKb Kw
pKa pKb pKw
86
high
low
high
low
87
Find Ka, pKa, pKb from this table, and write down
the acid dissociation reactions.
88
pH / pOH Calculations
  • Strong acids
  • Strong bases
  • Weak acids
  • Weak bases
  • Salts cation anion

89
Quiz 9, this week after lab
Ka ? pH and percent dissociation of a weak
acid pH of polyprotic acid pH of weak base
90
pH / pOH Calculations
  • Strong acids
  • Strong bases
  • Weak acids
  • Weak bases
  • Salts cation anion

91
1. Cation is from strong base anion is from
strong acid.
Cations from strong bases and anions from strong
acids have no effect on pH.
Solution is neutral
Other examples?
92
2. Cation is from strong base anion is from weak
acid.
Cation has no effect on pH, Anion acts as a base.
Solution is basic
Other examples?
93
Calculate the pH of a 0.30 mol/L NaF solution.
Ka for HF is 7.2 x 10-4
pH for weak base ICE ? OH- ? pOH ? pH
KaKb Kw
x OH- 2.0 x10-6, pH 8.31
94
Example 15.14, page 689
Find the pH of a 0.100 M NaCHO2 solution. The
salt completely dissociates into Na(aq) and
CHO2(aq) and the Na ion has no acid or base
properties. Ka for HCHO2 is 1.8 x 10-4.
95
3. Cation is conjugate acid of weak base
anion is from strong acid.
96
3. Cation is conjugate acid of weak base
anion is from strong acid.
NH4Cl, NH4NO3, CH3NH3Br
Cation acts as an acid, Anion has no effect on pH.
Solution is acidic
97
Calculate the pH of a 0.10 mol/L NH4Cl solution.
Kb for NH3 is 1.76 x 10-5
x H 7.5 x 10-6 M, pH 5.13
98
4. Cation is conjugate acid of weak base
anion is from weak acid.
NH4F, NH4Ac, NH4CN, CH3NH3CN
99
NH4F, NH4Ac, NH4CN, CH3NH3CN
NH3 Kb 1.76 x 10-5 CH3NH2 Kb 4.4 x 10-4
HAc Ka 1.76 x 10-5 HF Ka 7.2 x
10-4 HCN Ka 6.2 x 10-10
100
5. Cation is highly charged metal ions
anion is from strong acid.
AlCl3, Fe(NO3)3
Al3(aq) 6H2O(l) ? Al(H2O)63(aq)
101
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102
Calculate the pH of a 0.010 mol/L AlCl3
solution. Ka for Al(H2O)63 is 1.4 x 10-5
Al(H2O)63(aq) ? Al(OH)(H2O)52(aq) H(aq)
Answer pH 3.43
103
Acid-Base Properties of Various Types of Salt Acid-Base Properties of Various Types of Salt Acid-Base Properties of Various Types of Salt Acid-Base Properties of Various Types of Salt
Type of Salt Examples pH of Solution Reason
Cation is from strong base anion is from strong acid KCl, KNO3, NaCl, NaNO3 Neutral Neither acts as an a acid or a base
Cation is from strong base anion is from weak acid NaF, KCN, NaAc, KNO2 Basic Anion acts as a base cation has no effect on pH
Cation is conjugate acid of weak base anion is from strong acid NH4Cl, NH4NO3 Acidic Cation acts as acid anion has no effect on pH
Cation is conjugate acid of weak base anion is conjugate base of weak acid NH4Ac, NH4CN Acidic if Ka gt Kb, Basic if Kb gt Ka, Neutral if Ka Kb Cation acts as an acid anion acts as a base
Cation is highly charged metal ion anion is from strong acid Al(NO3) 3, FeCl3 Acidic Hydrated cation acts as an acid anion has no effect on pH
Try Example 15.16 on page 692
104
Example 15.16 on page 692
  • Determine whether the solution formed by each
    salt is acidic, basic, or neutral
  • SrCl2
  • AlBr3
  • (c) CH3NH3NO3
  • (d) NaCHO2
  • (e) NH4F

105
Arrhenius acids and bases
Brønsted-Lowrey acids and bases
Lewis acids and bases
Acids electron pair acceptor Bases electron
pair donor
106
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107
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108
pH / pOH Calculations
  • Strong acids
  • Strong bases
  • Weak acids
  • Weak bases
  • Salts cation anion

109
Quiz 10, next week
KaKb Kw Acid/base strength comparison Predict
acidity of a salt solution pH calculation for
salt solutions
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