Acids and Bases
Think back to a time when you have
eaten something very sour…
Think back to a time when you have
eaten something very bitter…
What were your reactions to each?
SOUR!!
SOUR!!
SOUR!!
SOUR!!
Bitter taste…
Bitter taste…
What causes some things to taste
sour, and others to taste bitter?
It’s all about ACIDS and BASES
 Its all about H+ and (OH –) ions
The pH Scale 
Things you need to know
about the pH scale
• The pH scale measures
how acidic or basic a
substance is
• The pH scale ranges
from 0 -14
• 0 - 6.99 = acids
• 7.0 = neutral
• 7.01-14 =bases
• 0 = most acidic
• 14= least acidic / MOST
BASIC
The pH Scale 
Things you need to know
about the pH scale
• The pH scale measures
the concentration of H+
ions in a solution
• A solution with a pH of
0 is very acidic, with a
high H+ concentration
(lots of H+ ions and not
a lot of OH- ions)
• Acid- a compound that
release H+ ions in a
solution
The pH Scale 
Things you need to know
about the pH scale
• A solution with a pH of 14
is very basic, with a low H+
concentration (lots of OHions and not a lot of H+
ions)
• Base- compounds that
remove H+ ions from a
solution
• A solution with a pH of 0 is
neutral - neither acidic nor
basic, with equal number
of H+ and OH- ions
Why do acids have more H+ ions and
bases have less H+ and more OH- ions?
• Acid – donates H+ when added to aqueous
solutions
• Base – breaks up into hydroxide (OH-) ions when
added to a aqueous solution
**An aqueous solution is a solution in which the
solvent (what is doing the dissolving) is water
Where have you heard the word
“buffer” in your everyday life?
• For example, “Family and friends can provide
a buffer against stress.”
Definition
• Buffer - a person or thing that prevents
incompatible or antagonistic people or things
from coming into contact with or harming
each other.
A Buffer in Science works the same
way!
• Buffers- regulate the pH in an organisms
– A compound that can bind to an H+ ion when the
concentration increases, and can release H+ ions
when the concentration decreases
– Buffers “lock up” ions and helps the organism
maintain homeostasis
ACIDIC
Basic
If the pH in a stomach increases from a pH of 4 to
a pH of 6, how does the hydrogen ion
concentration change?
-If the pH in a
stomach increases
from a pH of 4 to a
pH of 6, how does
the hydrogen ion
concentration
change?
-In other words, how
many MORE H+ ions
do you have at a pH
of 4 compared to a at
pH of 6?
pH Value
H+ Concentration
Relative to Pure Water
Example
0 10,000,000
battery acid
1 1,000,000
concentrated sulfuric acid
2 100,000
lemon juice, vinegar
3 10,000
orange juice, soda
4 1,000
tomato juice, acid rain
5 100
black coffee, bananas
6 10
urine, milk
7 1
pure water
8 0.1
sea water, eggs
9 0.01
baking soda
10 0.001
Great Salt Lake, milk of
magnesia
11 0.000 1
ammonia solution
12 0.000 01
soapy water
13 0.000 001
bleach, oven cleaner
14 0.000 000 1
liquid drain cleaner
-If the pH in a substance increases from
a pH of 4 to a pH of 6, how does the
hydrogen ion concentration change?
• pH of 4 = 1,000
• pH of 6 = 10
• How does the hydrogen ion concentration
change?
-If the pH in a substance increases from a pH of 4 to a
pH of 6, how does the hydrogen ion concentration
change?
• pH of 4 = 1,000
• pH of 6 = 10
• How does the hydrogen ion concentration
change?
ANSWER - the hydrogen concentration
decreased by a factor of 100
-If the pH in a substance increases from
a pH of 2 to a pH of 5, how does the
hydrogen ion concentration change?
• pH of 2 = 100,000
• pH of 5 = 100
• How does the hydrogen ion concentration
change?
-If the pH in a substance increases from a pH of 2 to a
pH of 5, how does the hydrogen ion concentration
change?
• pH of 1 = 100,000
• pH of 5 = 100
ANSWER - the
hydrogen
concentration
decreased by a factor
of 1,000
-If the pH in a substance decreases from a pH of 7 to
a pH of 5, how does the hydrogen ion concentration
change?
• pH of 7 = 1
• pH of 5 = 100
• How does the hydrogen ion concentration
change?
-If the pH in a substance decreases from a pH of 7 to
a pH of 5, how does the hydrogen ion concentration
change?
• pH of 7 = 1
• pH of 5 = 100
ANSWER - the hydrogen concentration increases
by a factor of 100
Practice
• pH Lab!!