pH
Learning Target: What is pH and pOH?
What does “pH” mean?
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pH stands for “power of hydronium ion”
pH is the negative logarithm of the hydrogen ion
concentration of a solution.
Mathematically: pH = -log [H3O+] or –log [H+]
Acid and Base strength is measured on a scale
that ranges from 0 to 14.
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Neutral solutions have a pH = 7, [H3O+] = [OH-]
Acidic solutions have a pH < 7, [H3O+] > [OH-]
Basic solutions have a pH > 7, [H3O+] < [OH-]
Concentrations of H+ ions are often small
numbers expressed in exponential notation.
pH of Common Substance
More acidic
More basic
pH
NaOH, 0.1 M
Household bleach
Household ammonia
Lime water
Milk of magnesia
Borax
Baking soda
Egg white, seawater
Human blood, tears
Milk
Saliva
Rain
Black coffee
Banana
Tomatoes
Wine
Cola, vinegar
Lemon juice
Gastric juice
14
13
12
11
10
9
8
7
76
5
4
3
2
1
0
[H1+]
[OH1-]
pOH
1 x 10-14
1 x 10-13
1 x 10-12
1 x 10-11
1 x 10-10
1 x 10-9
1 x 10-8
1 x 10-7
1 x 10-6
1 x 10-5
1 x 10-4
1 x 10-3
1 x 10-2
1 x 10-1
1 x 100
1 x 10-0
1 x 10-1
1 x 10-2
1 x 10-3
1 x 10-4
1 x 10-5
1 x 10-6
1 x 10-7
1 x 10-8
1 x 10-9
1 x 10-10
1 x 10-11
1 x 10-12
1 x 10-13
1 x 10-14
0
1
2
3
4
5
6
8
9
10
11
12
13
14
What is pOH?
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pOH = - log [OH-]
pOH of a solution is the negative logarithm of
the hydroxide ion concentration.
pH + pOH = 14
The logarithmic nature of the pH scale means
that a change of one pH unit represents tenfold
change in ion concentration.
A solution having a pH of 3.0 has ten times the
hydrogen ion concentration of a solution with a
pH of 4.0.
pH Calculations
pH
pH = -log[H3O+]
[H3O+]
[H3O+] = 10-pH
[H3O+] [OH-] = 1 x10-14
pH + pOH = 14
pOH
pOH = -log[OH-]
[OH-] = 10-pOH
[OH-]
Example…
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Calculate the pH…
1. If [H3O+] = 0.050 M
2. If [OH-] = 5.20 x 10-12 M
Challenge….
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Calculate [H+] and [OH-] if pH of blood is
7.40.
Challenge…
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The pH of 0.100 M solution of formic acid
HCOOH is 2.38. Calculate it’s Ka.