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
Law of Probability
 -The probability of being watched is
directly proportional to the stupidity of
your act
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+)
 In 1 Liter of water, (55+ moles of water),
how many moles of hydronium ions are
there???
 Understanding pH gives me this
number!!!
 If there was 1 mole of H3O+ in 1 Liter of
water, (55+ moles of water), this count
would be 1 mole.
What is pH???
 Remember: pH = - log [H+]
 pH = -log[1]
 Therefore, by definition, the pH of this
solution is

=0
What is the pH of water???
 H2O + H2O
--->
H3O+ + OH
<===
 This equation indicates that most water





molecules stay as molecules, very few
will form hydronium ions
If we count the number of hydrogen ions
in one liter of water (pH) we would get:
.0000001 moles of H3O+/liter of water
or 10-7 moles of H3O+/liter of water
What is the pH of water??
pH = 7
What is the pOH of water???
 H2O + H2O
--->
H3O+ + OH
<===
 This equation indicates that most water





molecules stay as molecules, very few
will form hydroxide ions
If we count the number of hydroxide ions
in one liter of water (pOH) we would get:
.0000001 moles of OH-/liter of water
or 10-7 moles of OH-/liter of water
What is the pOH of water??
pOH = 7
How High is the pH Scale??
 Since 1 mole of OH- in one Liter of water






would be a pOH = 0
And the pH and pOH of water is 7 or
neutral,
Therefore, the pH of a strong base with a
pOH of 0 would be?
pH = 14
Therefore, the pH scale goes from 0-14
Also, any pH can be converted to pOH
by?
Subtracting from 14.
pH- The Amount Of H+ Ions In A Solution.
1
2
3
4
5
ACID
extra H+1 ions
(protons)
6
7
8
9
10
11
12
BASE
fewer H+1 ions.
extra OH-1 ions.
13
14
Where Do You Find a Dog With No Legs?
 Right Where You Left Him.
Let’s Try Some Calculations by Not Using
Calvin’s Approach to Math in Chemistry:
Examples of Converting pH
 If an acid has a pH of 3, what would be





the pOH?
14 – 3 =
11
If an base has a pOH of 2, what would be
the pH?
14 – 2 =
12
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
Try These!
Find the pH of these:
1) A 0.15 M solution of
Hydrochloric acid
pH = 0.82
2) A 3.00 X 10-7 M solution
of Nitric acid
pH = 6.5
But Why Only 2 Significant Figures??
2) A 3.00 X 10-7 M solution
of Nitric acid
pH = 6.5
Remember, we are working with logarithms.
Therefore, we will use the pHAD principle. Add
significant figures after the Decimal Point for pH.
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
pH Calculations – Solving for H+
 A solution has a pH of 3.78. What is the
concentration of hydrogen ions in the
solution? (#1 on handout)
pH
=
3.78
=
-3.78
=
Inverse log -3.78 =
10-3.78
=
1.66 x 10-4
=
-log [H+]
-log [H+]
log [H+]
inverse log (log [H+])
[H+]
[H+]
What is the pOH?
 If an acid has a pH of 3.78, what would be
the pOH? (#1 on handout)
 14 – 3.78 =

10.22
pH Calculations – Solving for H+
 A solution has a pH of 3.78. What is the
concentration of hydroxide ions in the
solution? (#1 on handout)
pOH
= - log [OH-]
10.22
= - log [OH- ]
- 10.22
= log [OH- ]
Inverse log -10.22 = inverse log (log [OH- ])
10-10.22
= [OH-]
6.03 x 10-11
= [OH-]
Calculating [H3O+], pH, [OH-], and pOH
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 the pOH
pOH = - log [OH-]
(Remember that the [ ] mean Molarity)
Example #4 on handout:
If [OH-] = 4.88 x 10-6
pOH = - log (4.88 x 10-6)
pOH = 5.31
Calculating [H3O+], pH, [OH-], and pOH
Problem 2: A chemist dilutes concentrated
hydrochloric acid to make:
0.000 389 M HCl.
Calculate the pH, [OH-], and pOH
pH =
pOH =
[OH-] =
Acid
3.41
10.59
2.57 x 10-11 M
[OH-]
[H+]
pOH
pH
pH
[H+]
[OH-]
pOH
Acids and Bases: Define and
Calculate pH/pOH
Let’s see if you can:
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
The American Medical Association
announced today that the Universal
Choking Sign has been revised:
Old Sign:
New Sign:
Get Your
Clicker!!!
The “p” in pH stands for?
1.
2.
3.
4.
5.
Priority
Count
Number
Molarity
Not listed
The “H” in pH stands for?
1.
2.
3.
4.
5.
House
Hydrogen ions
Acid
Concentration
Not listed
If a solution has a pH of 6.5, what is the
pOH of that same solution?
1. 4.5
2. 7.5
3. 6.5
4. 0.0
5. 12.5
6. Not listed
If a solution has a pH of 6.2, what is the
[H+] of that solution?
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
If a solution has a pOH of 9.44, what is
the [OH-] of that same solution?
1. 0.98
2. 1.00 x 109.44
3. 3.63 x 10-10
4. 4.56
5. 9.44
6. Not listed
Let’s kick back and relax!!
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
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.
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
pH H2O H+
0
55
1
1
550
1
2
5500 1
Strong ACID
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
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
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
Maybe Our Goals Aren’t the Exact Same,
But They’re Similar!!
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)
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 Paper
Red Litmus paper
Blue Litmus paper
pH Meter
 Tests the voltage of the
electrolyte
 Converts the voltage to pH
 Expensive, but very
accurate
 Must be calibrated with a
buffer solution
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
We’ll Chip Away at this a Little at a Time!!
pH of Common Substances
A Former Student Trying to Apply His
Knowledge of Chemistry!!
Acids and Bases: Strength and
Indicators
Let’s see if you can:
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
Get Your
Clicker!!!
Red litmus paper will turn what color in
an acid?
1.
2.
3.
4.
5.
Blue
White
Red
Clear
Not listed
Which of the following would be the most
accurate way to test for pH?
1.
2.
3.
4.
5.
6.
pH meter
Litmus paper
Phenylthalein
Cabbage juice
Universal indicator
Not listed
Several liquids are tested for pH. Which
of these liquids would be the weakest
acid?
1.
2.
3.
4.
5.
6.
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
So – What did you think of today’s
class??
If a solution has a [H3O+] of 6.20 x 10-8,
what is the pH of that solution?
1. 6.79
2. 8.79
3. 5.21
4. 4.56
5. 7.21
6. Not listed
If a solution has a [OH-] of 1.05 x 10-3,
what is the pH of that solution?
1. 11.02
2. 2.98
3. 1.00
4. 3.02
5. 10.98
6. Not listed
Converting pH to pOH
 If an acid has a pH of 6, what would be
the pOH?
 14 – 6 =

8
[H 3 O + ], [OH - ] and pH
Page 14:5
What is the pH of the
0.0001 M NaOH solution?
[OH-] = 0.0001 (or 1.0 X 10-4 M)
pOH = - log 0.0001
pOH = 4
pH = 14 – 4 = 10
Try These! Page 15:9
The pOH of rainwater collected in a certain
region of the northeastern United States on a
particular day was 9.94. What is the H+ ion
concentration of the rainwater?
pH = 4.06
8.91 x 10-5
The OH- ion concentration of a blood sample
is 2.88 x 10-6 M. What is the pH of the blood?
pOH = 5.54
14.0 – 5.54 = 8.46 pH
I wouldn’t do
that if I were
you!!!