ACID AND BASE
Mr. Luis A. Velázquez
Research Biology
What is pH ?
pH stands for the potential of Hydrogen
 Is the concentration of hydrogen in a
given substance.
 [ ] is the symbol for concentration.
 In other words pH is [H+] in a substance.

What is the pH scale ?
Is a scale that goes from 0 to 14
 Any substance above the pH of 7 is consider a
base.
 Any substance below the pH of 7 is consider a
acid.
 Any substance at a pH of 7 is not consider an
acid or a base.
 pH of 7.00 is consider a neutral pH.

What is hydrogen ion?
Hydrogen is an positive ion.
 Hydrogen is H+
 In terms of pH we use [H+]
+
 Acids have high [H ]
 Bases have very low [ H+ ]

What is hydroxide ?
Hydroxide is an negative ion.
 Hydroxide is OH
 In terms of pH we use [OH ]
 Acids have low [OH ]
 Bases have very high [OH ]

pH Scale in terms of
[ H+]
+
[H ]
[ H+]
7
14
0
Acids
Base
pH Scale in terms of
[
[OH ]
[ OH-]
OH-]
7
14
0
Acids
Base
pH Scale
Neutral
[ OH-]
[ H+] [ OH-]
[ H+]
7
0
14
Acids
[ H+]= [ OH-]
H2O
Equilibrium
Base
Some important pH
A
C
I
D
S
B
A
S
E
Problem
Sea water has a pH of 8.50
 If a substance x has more [H+] than sea
water.
Sea water
pH more than
pH less than
8.5

UpDown
[H+] [H+]
Important information
pH for any living thing is between 6.50
and 7.50
 Blood has a constant pH of 7.4
 If the pH goes up to 7.5 your blood will
become more alkaline or basic. (basidosis)
 If your bloods pH goes down you blood
will become more acids. ( Acidosis)

What is an acid ?
An acid pH is to have a number below
7.00.
 The smaller the number the more acidic
is the substance.
+
 Acids have very high [H ]
 Acids have very low [OH ]

What is base ?
A basic or alkaline pH is to have a
number above 7.00.
 The greater the number the more
alkaline is the substance.
 Bases have very low [H+]
 Bases have very high [OH-]

Stronger and weaker acid
Strong
Strong
Weak
Weak
Understanding Cabbage
The purple color in red cabbage comes from a
class of pigment molecules called
anthocyanins.
 It turns out that anthocyanins are found in
flower petals, leaves (it makes them turn red in
the fall!) and some fruits such as blueberries.
 Anthocyanins are plant pigments known as
flavenoids and produce red, pink, violet and
magenta colors in the various plant parts.

Cabbage Lab

The anthocyanin turns into:
 bright pink in acids
reddish-purple in neutral solutions
 green in alkaline or basic solutions.

Cabbage Lab
This water-soluble pigment is also found in
apple skin, plums, poppies, cornflowers,
and grapes.
 Therefore, it is possible to determine the
pH of a solution based on the color it
turns the anthocyanin pigments in red
cabbage juice.

Cabbage Lab Analysis
pH
2
Color Red
4
6
8
10
12
Pink
Violet
Blue
BlueGreen
Greenish
Yellow
What are buffers?


A substance that eliminates large sudden
changes in pH.
Buffers help organisms maintain the pH of body
fluids within the narrow range necessary for life.
combinations of H+ acceptors and
donors forms in a solution of weak acids
or bases
 Work by accepting H+ from solutions
when they are in excess and by donating
H+ when they have been depleted.
 Are
Acids and Bases


An acid is a substance that
increases the hydrogen ion
concentration in a solution.
Any substance that reduces the
hydrogen ion concentration in a
solution is a base.



Some bases reduce H+ directly by
accepting hydrogen ions.
Strong acids and bases complete
dissociate in water.
Weak acids and bases dissociate
only partially and reversibly.
Classify the following pH













A. 3.90
B. 9.99
C.1.40
D. 2.02
E. 5.78
F. 0.34
G. 8.45
H. 6.30
I. 7.00
J. 13.8
K. 4.08
L. 7.40
M. 1.63
____
____
____
____
____
____
____
____
____
____
____
____
____
A = Acid
B = Base
N = Neutral
1. How many acids?_______
2. How many bases?_______
3. Who is the weakest base? ___
4. Who is the strongest acid? ___
5. Who is the weakest acid? ___
6. Who is the strongest base? ___