Transcript Chapter 16 Aqueous Equilibria: Applications 1. neutralization reactions: K large,

Chapter 16 Aqueous Equilibria: Applications
1. neutralization reactions:
K large,
~100% completion due to formation of water;
salts can be neutral, basic, or acidic
2. common ion effect; buffers:
common ion reduces % ionization of weak acid;
buffers: neutralization plus weak acid/base equilibrium
3. titrations:
acid (base) is systematically and quantitatively
added to base (acid)
in order to determine the concentration of the base (acid)
Chapter 16 Notes
1
strong acid - strong base:
1. examples:
HCl with NaOH; HClO4 with KOH; NaOH with HNO3
2. salts:
all neutral therefore NO acid-base equilibria;
the chemistry is all neutralization
3. the pH titration curve:
plot pH (y-axis) vs. volume added base (x-axis)
Chapter 16 Notes
2
Titration Curve: Strong Acid with Strong Base
e.
pH
14
12
10
8
6
4
2
a. 0
0
10
d.
c.
b.
20
30
f.
40
50
60
volume added base (ml)
a. before adding base
d. equivalence point
b. halfway to equivalence
e. 1 ml after equivalence
point
point
c. 1 ml before equivalence Chapter 16(f.
beyond equivalence
Notes
point
point)
3
example: 40.0 ml of 0.10 M HCl is titrated with 0.10 M
NaOH; calculate pH at points a-f.
Hints:
•Don’t forget dilution!
•Calculate pH as though adding base from the beginning.
•What volume NaOH is required to reach equivalence point?
a. before adding base
pH=-log[H1+]=-log(0.10)=1.00
b. halfway to equivalence point: 20.0 ml added base (total)
chemistry :
H1+ + OH1-  H2O
c. 1 ml before equivalence point: 39.0 ml added base (total)
chemistry :
Chapter 16 Notes
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d. equivalence point: 40.0 ml added base (total)
chemistry :
e. 1 ml after equivalence point (total)
chemistry :
f. beyond equivalence point (total)
chemistry :
Chapter 16 Notes
5
14
12
pH
10
note rapid change in
pH near the
equivalence point
8
6
4
2
0
0
10
20
30
40
50
60
volume added base (ml)
Chapter 16 Notes
6
pH
Titration Curve: Weak Acid with Strong Base
f.
14
12
10
8
6
4
2
0
e.
d.
b.
a.
c.
buffer
0
10
20
30
40
50
60
volume added base (ml)
a. before adding base
b. halfway to equivalence
point
c. 1 ml before equivalence
point
d. equivalence point
e. 1 ml after equivalence
point
(f. beyond equivalence point)
7
a. before adding base: pH of a weak acid (equilibrium)
chemistry:
b. halfway to equivalence point:
chemistry:
c. 1 ml before equivalence point:
chemistry:
Chapter 16 Notes
8
d. equivalence point:
chemistry:
[pH of a conjugate base of a weak acid; look up Kb or
calculate using Kb=Kw/Ka]
e. 1 ml after equivalence point:
chemistry:
[pH of a strong base (OH1- contribution from conjugate base is
insignificant)]
(f. beyond equivalence point: see e.)
Chapter 16 Notes
9
14
12
pH
10
8
pH, strong acid
pH, weak acid
6
4
2
0
0
10
20
30
40
50
60
volume added base (ml)
Note change in pH near equivalence point.
Contrast strong-strong and strong-weak:
what are the 2 most important differences?
Chapter 16 Notes
10
Figure 16.7
Chapter 16 Notes
11
Figure 16.8
Chapter 16 Notes
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Figure 16.9: Titration of weak base with strong acid
buffer: use base form of H-H equation
Chapter 16 Notes
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Figure 16.9: Titration of polyprotic weak acid with strong
base
pH=(pKa1+pKa2)/2
Chapter 16 Notes
14