The pH Scale
Is a substance an
acid or a base?
ACIDS
 An
acid is a compound that increases
the number of hydrogen ions when
dissolved in water (H+)
 An acid solution tastes sour
 An acid can change the color of certain
compounds
What is an ion?
**An ion is an atom that has
lost or gained an electron
giving it a positive (+) or
negative (-) charge.
** Charged Atom
USES OF ACIDS
 Citric
acid and ascorbic acid (Vitamin C)
are found in orange juice
 Carbonic acid and phosphoric acid give a
“bite” to soft drinks
 Acids in your stomach aid in digestion
 Sulfuric acid is the most widely used
industrial acid in the world. It is used in
making metals, paper, paints, and
fertilizers.
BASES
A
base is any compound that increases
the number of hydroxide ions (OH-) when
mixed with water
 A base solution tastes bitter
 A base solution feels slippery
 A base can change the color of certain
compounds
Uses of Bases
 Bases
are used in soaps (remember,
bases are slippery)
 Bases are used to make paper, in
oven cleaners, and to unclog drains
 Ammonia is a base and is used in
many household cleaners
Detecting Acids and
Bases
 You
can detect an acid using an
indicator.
 INDICATOR
- A substance that
changes color in the presence of an
acid or a base.
INDICATORS
 Litmus
paper is an indicator
 An acid turns blue litmus paper red
 A base turns red litmus paper blue
Basic
7
Acid
14
Neutral
pH Scale
Acidic
0
Base
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 515
[H+]
pH
10-14
14
10-13
13
10-12
12
10-11
11
10-10
10
10-9
9
10-8
8
10-7
7
10-6
6
10-5
5
10-4
4
10-3
3
10-2
2
10-1
1
100
0
1 M NaOH
Ammonia
(household
cleaner)
Blood
Pure wate
Milk
Vinegar
Lemon juice
Stomach acid
1 M HCl
pH of Common Substances
Timberlake, Chemistry 7th Edition, page 335
Did we Miss something??
 What
happens when the pH of a
substance is 7?
 Ans:
A pH level of 7 indicates a Neutral
Substance i.e: Water!
Why Learn about pH?
 What
do you think is the pH level of NYC
tap water?
 The
pH of a swimming pool must be
checked periodically. Why?
 Is
it important for Lakes & Rivers to
maintain a certain pH?
How do Antacids Work?
 Normal
pH in your stomach is 3
 If your stomach pH drops below 3 you
don’t feel so well
 An antacid neutralizes the acid in your
stomach and brings the pH up to a 3 or 4
Antacids







A base can't neutralize your acid all by itself.
A base needs some chemical "helpers”
All antacids contain at least one of these four
primary ingredients:
* Sodium
* Calcium
* Magnesium
* Aluminum.
HOW DO WE
MEASURE pH?
N
E
U
T
R
A
L
ACID
0
1
2
3
4
5
6
7
BASE
8
9 10 11 12 13 14
The pH Scale
N
E
U
T
R
A
L
ACID
0
1
2
3
4
5
6
7
BASE
8
9 10 11 12 13 14
The pH Scale
Let’s see what you’ve learned!
 Professor
Know-ItAll wants to know
what you’ve
learned. Answer
the following
questions
carefully.
Question #1
 Lemon
juice
has a pH of
2.2. Is it an
acid or a base?
Question #2
 Detergents
such as Tide
have a pH of
about 10. Is
Tide an acid
or a base?
Question #3
 Seawater
has
a pH of 8.2. Is
seawater an
acid or a base?
Question #4
 The
inside of
your mouth has
a pH of 7. Is it
an acid or a
base?
Question #5
 How
do you
think we came
up with the
term “acid
rain”?
Question #6
 409
cleaner
contains
ammonia that
has a pH of 12.
What will 409
do to red litmus
paper?
Question #7
A
soft drink has
a pH of 3.2.
What will it do
to a piece of
red litmus
paper?