The Chemistry of Acids and
Bases
Acids and Bases: Define and
Calculate pH/pOH
At the conclusion of our time
together, you should be able to:
1.
2.
3.
4.
Define pH and pOH
Explain the pH scale and what it means
Change any pH reading to pOH
Convert pH to concentration of hydronium
ion concentrations, hydronium ion
concentrations to pH
Page 1
What is pH???
The pH scale is a way of
expressing the strength of
acids and bases.
This scale is defined by:
pH = - log [H+]
Under
Over
7 = acid
7 = neutral
7 = base
What is pH???
 p = count
 H = Hydronium ion (H3O+)
 Measures the concentration of the hydronium
ion.
 Scale ranges from 0-14
 < 7 is acidic, more H3O+
 7 = neutral, H3O+ = OH > 7 is basic, OH- > H3O+
Page 2
Let’s Try Some Calculations by Not
Using
Calvin’s Approach to Math in Chemistry:
Calculating the pH
pH = - log [H+]
(Remember that the [ ] mean Molarity)
Example: If [H+] = 1 X 10-10
pH = - log 1 X 10-10
pH = 10
Example: If [H+] = 1.80 X 10-5
pH = - log 1.80 X 10-5
pH =
4.7
Page 3
pH Calculations – Solving for H +
If the pH of Coke is 3.12, [H+] = ???
Because pH = - log [H+] then
- pH = log [H+]
Divide both sides by log or
Take antilog (10x) of both
sides and get
10-pH = [H+]
10-3.12 = [H+] = 7.6 x 10-4 M
*** to find antilog on your calculator, press
“Shift” or “2nd function” and then the log button
What is the pOH?
 A measure or count of the hydroxide ion
concentration.
 It is the opposite of the pH scale.
 Scale ranges from 0-14
 < 7 is basic
 7 = neutral
 > 7 is acidic
Page 4
Calculating the pOH
pOH = - log [OH-]
(Remember that the [ ] mean Molarity)
Example : If [OH-] = 5.00 x 10-3
pOH = - log 5.00 x 10-3
pOH = 2.3
pH + pOH = ???
 pH + pOH = 14
 [H+] [OH-] = 1x10-14
Page 5
Calculating [H3O+], pH, [OH-], and pOH
Page 8, Problem 1: What is the [H3O+], [OH-],
and pOH of a solution with pH = 3.78? Is this an
acid, base, or neutral?
[H3O+] =
pOH =
[OH-] =
Acid
1.66 x 10-4 M
10.22
6.03 x 10-11 M
Calculating [H3O+], pH, [OH-], and pOH
Problem 2: A chemist dilutes concentrated
hydrochloric acid to make
:
0.000 389 M.
Calculate the pH, [OH-], and pOH
pH =
pOH =
[OH-] =
Acid
3.41
10.59
2.57 x 10-11 M
Page 6
[OH-]
[H+]
pOH
pH
There are Several Ways to
Test for pH
 There are three basic types:




Paper
pH meter
Liquid indicators
(Some are natural liquid indicators like
red cabbage, radishes)
Page 7
Paper Testing
 Paper tests like litmus paper and pH
paper
 Put a stirring rod into the solution
and stir.
 Take the stirring rod out, and
place a drop of the solution from
the end of the stirring rod onto a
piece of the paper
 Read and record the color
change. Note what the color
indicates.
 Use a small portion of the paper.
You can use one piece of paper
for several tests.
pH Indicators
 Indicators are dyes that can
be added that will change
color in the presence of an
acid or base.
 Some indicators only work
in a specific range of pH
 Once the drops are added,
the sample is ruined
 Some dyes are natural, like
radish skin or red cabbage
Page 8
pH Meter
 Tests the voltage of the
electrolyte
 Converts the voltage to pH
 Expensive, but very
accurate
 Must be calibrated with a
buffer solution
The “p” in pH stands for?
20%
20%
20%
20%
Priority
Count
Number
Molarity
Not listed
Page 9
d
lis
te
No
t
M
ol
a
r it
y
be
r
Nu
m
Co
un
t
y
Table
Pr
io
r it
1.
2.
3.
4.
5.
20%
The “H” in pH stands for?
20%
20%
20%
20%
Hy
dr
d
Table
lis
te
n
tio
No
t
nt
ra
Co
nc
e
og
e
n
io
ns
Ac
id
House
Hydrogen ions
Acid
Concentration
Not listed
Ho
us
e
1.
2.
3.
4.
5.
20%
If a solution has a pH of 6.5, what is the
pOH of that same solution?
17%
No
t
lis
te
d
17%
12
.5
17%
0
17%
6.
5
17%
7.
5
1. 4.5
2. 7.5
3. 6.5
4. 0.0
5. 12.5
6. Not listed
4.
5
17%
Page 10
Table
If a solution has a pH of 6.2, what is the
[H+] of that solution?
7.8
17%
17%
Table
No
t li
ste
d
17%
10
7.8
10
6.2
17%
1.0
x
6.3
x
10
-7
6.2
1. 6.2
2. 6.3 x 10-7
3. 1.0 x 106.2
4. 1.0 x 107.8
5. 7.8
6. Not listed
17%
1.0
x
17%
If a solution has a pOH of 9.44, what is
the [OH-] of that same solution?
Page 11
9.4
4
17%
17%
No
t li
ste
d
17%
4.5
6
17%
10
-10
10
9.4
4
1.0
0x
.98
1. 0.98
2. 1.00 x 109.44
3. 3.63 x 10-10
4. 4.56
5. 9.44
6. Not listed
17%
3.6
3x
17%
Table
Red litmus paper will turn what color in
an acid?
20%
1.
2.
3.
4.
5.
20%
20%
20%
20%
Blue
White
Red
Clear
Not listed
lis
te
d
ar
d
No
t
Cl
e
Bl
W
hi
Re
te
ue
Table
Which of the following would be the most
accurate way to test for pH?
17%
17%
17%
17%
17%
17%
d
lis
te
No
t
or
ce
ca
t
sa
l
ve
r
Un
i
Page 12
in
di
in
le
ej
ui
ba
g
th
a
Ca
b
us
p
ny
l
Ph
e
Lit
m
m
et
ap
er
er
pH meter
Litmus paper
Phenylthalein
Cabbage juice
Universal indicator
Not listed
pH
1.
2.
3.
4.
5.
6.
Table
Several liquids are tested for pH. Which
of these liquids would be the weakest
acid?
17%
17%
f,
p
H
pH
=.
..
=.
..
Table
ui
d
e,
Liq
ui
d
ui
d
Liq
Liq
c,
p
ui
d
Liq
17%
=.
..
=.
..
17%
H
=.
..
=.
b,
pH
H
a,
p
Liq
ui
d
ui
d
Liq
17%
d,
pH
17%
Liquid a, pH = 1.0
Liquid b, pH = 4.5
Liquid c, pH = 6.5
Liquid d, pH = 8.5
Liquid e, pH = 10.5
Liquid f, pH = 13.0
..
1.
2.
3.
4.
5.
6.
If a solution has a [H3O+] of 6.20 x 10-8,
what is the pH of that solution?
17%
No
t
lis
te
d
17%
7.
21
17%
4.
56
17%
5.
21
17%
8.
79
1. 6.79
2. 8.79
3. 5.21
4. 4.56
5. 7.21
6. Not listed
6.
79
17%
Page 13
Table
If a solution has a [OH-] of 1.05 x 10-3,
what is the pH of that solution?
17%
No
t
lis
te
d
17%
10
.9
8
17%
3.
02
17%
1.
17%
2.
98
1. 11.02
2. 2.98
3. 1.00
4. 3.02
5. 10.98
6. Not listed
11
.0
2
17%
Extra Quiz Questions
 Name these:





 Write the formula:





HBr
HNO4
H2CO
Fe(OH)2
H2SO4
Page 14
Hydroselenic acid
Phosphoric acid
magnesium hydroxide
Sulfurous acid
Perbromic acid
Table
The Chemistry of Acids and
Bases
Acids and Bases: Strength and
Indicators
At the conclusion of our time
together, you should be able to:
1. Determine the relative strength of acids and
bases and the reason for the strengths
2. List the 3 basic types of indicators
3. Explain each indicator’s strengths and
weaknesses
4. Use an appropriate indicator to determine
the pH of a substance
Page 15
Remember: the pH scale
is a way of expressing
the strength of acids and
bases.
Under
Over
7 = acid
7 = neutral
7 = base
What makes an acid
strong or weak??
Strong or Weak Acids/Bases
The strength of an acid (or base) is
determined by the amount of IONIZATION.
HNO3, HCl, H2SO4 and HClO4 are among
the only known strong acids.
Page 16
Strong Acids
Generally divide acids and bases into
STRONG or WEAK ones.
STRONG ACID: HNO3 (aq) + H2O (l) --->
H3O+ (aq) + NO3- (aq)
HNO3 is about 100% dissociated in water.
Weak Acids
 Weak acids are much less than 100% ionized in
water.
One of the best known is acetic acid = CH3CO2H
Page 17
Strong ACID
pH H2O H+
0
55
1
1
550
1
2
5500 1
HCl Hydrochloric acid
H2SO4
Sulfuric acid
HNO3
Nitric acid
Weak ACID
CH3COOH
H2CO3
Acetic acid
Carbonic acid
Citric acid
Strong Bases
Strong Base: 100% dissociated in water.
NaOH (aq) ---> Na+ (aq) + OH- (aq)
Other common strong
bases include KOH and
Ca(OH)2.
CaO (lime) + H2O -->
Ca(OH)2 (slaked lime)
CaO
Page 18
Weak Bases
Weak base: less than 100% ionized in water
One of the best known weak bases is
ammonia
NH3 (aq) + H2O (l)  NH4+ (aq) + OH- (aq)
Weak Bases
Page 19
Strong or Weak Acids/Bases
Summary
Strong acids and bases dissolve in water
Hydrochloric, Hydrobromic, Hydroiodic,
(All Binaries)
Nitric, Sulfuric, Perchloric Acids
(Ternary Acids with 2 more O than H)
Group I hydroxides
Page 20