Embed Size (px)
Citation preview
Chapter 16 Notes 1
Chapter 16 Aqueous Equilibria: Applications1. 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 2
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 3
Titration Curve: Strong Acid with Strong Base
02468
101214
0 10 20 30 40 50 60
volume added base (ml)
pH
a.
b.c.
a. before adding baseb. halfway to equivalence pointc. 1 ml before equivalence point
d.
e.
f.
d. equivalence pointe. 1 ml after equivalence point(f. beyond equivalence point)
Chapter 16 Notes 4
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 5
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 6
0
2
4
6
8
10
12
14
0 10 20 30 40 50 60
volume added base (ml)
pH
note rapid change in pH near the equivalence point
7
Titration Curve: Weak Acid with Strong Base
02468
101214
0 10 20 30 40 50 60
volume added base (ml)
pH a.c.
b.
buffer
a. before adding baseb. halfway to equivalence pointc. 1 ml before equivalence point
e.
d.
f.
d. equivalence pointe. 1 ml after equivalence point(f. beyond equivalence point)
Chapter 16 Notes 8
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 9
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 10
0
2
4
6
8
10
12
14
0 10 20 30 40 50 60
volume added base (ml)
pH pH, strong acid
pH, weak acid
Note change in pH near equivalence point.
Contrast strong-strong and strong-weak: what are the 2 most important differences?
Chapter 16 Notes 11
Figure 16.7
Chapter 16 Notes 12
Figure 16.8
Chapter 16 Notes 13
Figure 16.9: Titration of weak base with strong acid
buffer: use base form of H-H equation
Chapter 16 Notes 14
Figure 16.9: Titration of polyprotic weak acid with strong base
pH=(pKa1+pKa2)/2
