Ch 8 - Applications of Equilibrium
 8.1






Solutions of Acids or Bases
Containing a Common Ion
8.2
Buffered Solutions
8.4
Buffer Capacity
8.5
Titrations and pH Curves
8.6
Acid-Base Indicators
8.8
Solubility Product
Sections to Skip: 8.3, 8.7, 8.9, and 8.10
Week 10
CHEM 1310 - Sections L and M
1
Review of an Example
 What is the [H+] and the % dissociation of a
solution containing 1.0 M HF?
HF (aq) ↔ H+ (aq) + F- (aq)
Ka = 7.2 x 10-4
Weak acid
Ka =
[H+] x [F-]
7.2 x
[HA]
10-4
=
X2
1.0
Thus, X = [H+] = √ (7.2 x 10-4) = 0.027 M
% Dissociation =
Week 10
0.027
1.0
CHEM 1310 - Sections L and M
x 100 = 2.7%
2
1
Common Ion Effect
 What happens when more F- is added from
a different source?
NaF (s) → Na+ (aq) + F– (aq)
More F- added
Common Ion
HF (aq) ↔ H+ (aq) + F- (aq)
What impact does
the additional Fhave on [H+]?
Le Châtelier’s Principle:
Equilibrium shifts to left
Week 10
CHEM 1310 - Sections L and M
3
Common Ion Effect
NaF (s) → Na+ (aq) + F– (aq)
[HF] = 1.0 M
[NaF] = 1.0 M
More F- added
HF (aq) ↔ H+ (aq) + F- (aq)
Ka =
[H+] x [F-]
[HA]
Equilibrium Concentrations
[HF] = 1.0 - x, where x is negligible
[H+] = X
[F-] = [F-]from NaF + [F-]from HF = 1.0 + X
Week 10
CHEM 1310 - Sections L and M
4
2
Common Ion Effect
Equilibrium Concentrations
[HF] = 1.0 - X, where X is negligible
Ka =
[H+] x [F-]
[H+] = X
[HA]
[F-] = [F-]from NaF + [F-]from HF = 1.0 + X,
where X is negligible
7.4 x 10-4 =
X x (1.0)
[H+] = 0.00074 M
when a common ion at
1.0 M is added
1.0
Week 10
CHEM 1310 - Sections L and M
5
Common Ion Effect: Impact
Without
Common Ion
0.027M
decrease
pH
1.57
increase
% Dissociation
2.7%
decrease
[H+]
With
Common Ion
0.00074M
3.13
0.074%
HF (aq) ↔ H+ (aq) + F- (aq)
Le Châtelier’s Principle:
Equilibrium shifts to left in this example
Week 10
CHEM 1310 - Sections L and M
6
3
What are Buffered Solutions?
 Most important application of acid-base
solutions is buffering
 Buffer is a solution that resists changes in
pH
 Weak acid + Conjugate Base (Acidic buffer)
 Weak base + Conjugate Acid (Alkaline buffer)
Week 10
CHEM 1310 - Sections L and M
7
Buffers Are Found in Many Places
Foods
Georgia
Aquarium
Human Blood
Shampoos
Week 10
CHEM 1310 - Sections L and M
8
4
How Do Buffers Work?
Week 10
CHEM 1310 - Sections L and M
9
Henderson-Hasselbalch Eqn
[H 3O + ] = K a
[HA]
[A - ]
Ê [HA] ˆ
- log[H 3O ] = - log[K a ] - logÁÁ - ˜˜
Ë [A ] ¯
Ê [HA] ˆ
pH = pK a - logÁÁ - ˜˜
Ë [A ] ¯
+
Ê [A - ] ˆ
˜˜
pH = pK a + logÁÁ
[HA]
Ë
¯
Two useful forms of the Henderson-Hasselbalch equation
Week 10
CHEM 1310 - Sections L and M
10
5
Making Buffer Solutions
From
Wikipedia
Week 10
CHEM 1310 - Sections L and M
11
6