Outline:
2/26/07
CAPA 10 & 11 – due today
 Pick up CAPA 12 & 13 – outside
 Turn in seminar reports – to me

Today:
Start Chapter 17
 Acid-base Equilibria:
Acid & Bases: definitions
Defining/Calculating pH
Simple pH Calculations from Ka
Any questions on equilibria?
Lots of suggested problems to do….
16.1, 16.9, 16.11, 16.17, 16.19, 16.21,
16.23, 16.25, 16.27, 16.29, 16.31, 16.33,
16.35, 16.37, 16.43, 16.45, 16.47, 16.49,
16.51, 16.57, 16.59, 16.63. 16.65, 16.67,
16.69, 16.71, 16.73, 16.75, 16.79, 16.81
Quiz #5
Please put books/papers away…
Remember: lots of partial credit for
setting up the problem correctly…
Solving it just gets you the last points
Quiz #5
Please turn your quizzes over and
pass them to your right…
Acids & Bases:
These are all examples of equilibria
big Keq = strong acid (dissociation)
little Keq = weak acid
HCl + H2O  H3O+ + ClKeq = 1000+
HSO3- + H2O  H3O+ + SO32Keq = 6.4  10-8
p. 140
Chapter 17: More Equilibrium!
What exactly is in an aqueous solution?
H2O
HNO3
H3O+
NO3-
p. 141
Does this differ from a weak acid?
H2O
HOAc
A combination of previous chapters:
 Solubility
rules:
= Strong Acids
Highly soluble:
ionic salts of Cl-, Br-, I-,
ionic salts of NO3-, SO4-,
ionic salts of ClO4-, etc.
 Equilibrium rules:
Keq = [products]/[reactants]
Big Keq  large extent of reaction
= Strong Acids
Just a few
strong acids
& bases, the
rest are
weak:
The extent of dissociation:Ka and Kb
 Define
acid dissociation constant:
Ka = [H+][A-]/[ HA]
 Define base dissociation constant:
Kb = [B+][OH-]/[BOH]
 OK,
what exactly is water anyway?
H2O + H2O  H3O+ + OHKeq = [H3O+][OH-] = Kw
= 1  10-14 (by definition)
 Called water dissociation constant
or “autoionization”
Define water as neutral….

Kw = 10-14 (arbitrary scale definition)
then: [H3O+] = [OH-] = x
or: x2 = 10-14 or x = 10-7 M
Define pH = - log [H+]

What’s the pH of neutral water?
= - log(10-7) = 7.0
Same thing for bases….
 Define

pOH = -log(OH-)
Since Kw = [H3O+][OH-] = 10-14
log[H3O+] + log[OH-] = log (10-14)
or
pH + pOH = 14
None of this is really new….using acids
and bases in lab all year!
e.g. pHydron paper, pH electrodes,
Concentration vs. strength!
Calculation Examples:
 Calculate
the pH of a solution of
2.510-2 M HClO4? (perchloric acid)
 Step
#1: identify the acid
If strong acid  complete dissociation
HClO4

H+ + ClO42.510-2 M
0
0
init
0 equil  2.510-2 M 2.510-2 M
 Step #2: pH = - log [H+]
- log (2.510-2) = 1.60
Examples:

Calculate the pH of a solution of
2.510-2 M HClO? (hypochlorous acid)
 Step
#1: identify the acid
if weak acid  look up Ka = 3.5  10-8
HClO
 H+ + ClO2.510-2 M
0
0
init
(2.510-2-x)M x M
x M equil
 Step #2: pH = - log [H+]
- log (2.710-5) = 4.56
Weak Base Example:
Calculate the pH of a solution of
2.510-2 M trimethylamine (CH3)3N ?
 Step #1: identify it as a weak base
look up Kb = 6.5  10-5

(CH3)3N + H2O  OH- + (CH3)3N H+
2.510-2 M
0
0
init
(2.510-2-x)M
xM
x M equil
 Step #2: pOH = - log [OH-]
- log (1.310-3) = 2.89
 Step #3: 14 - pOH = pH = 11.11
Problem solving overview:
Skills needed to solve these problems:
1) Identify strong/weak acid/bases
Know the 6 strong acids / 4 strong bases…
2) Identify conjugate acid/bases & salts
Know solubility rules & acid/base definitions
3) Solving equilibrium problems
Solve for x…forward or backwards...
4) Identifying & making the correct Keq
Add equations to make new one & K’s multiply
And Practice, Practice, Practice…