18
Understanding pH Theory
Defining pH
The measurement of pH plays an important
role in identifying and controlling acidity
and alkalinity levels for industry and
research. pH is a measure of the acidity
or alkalinity of a solution and can be
represented by this equation:
pH = -log [H
+
]
with [H
+
] representing the concentration
of hydrogen ions in the solution. pH is
sometimes referred to as the power of the
hydrogen ion in a solution.
By using a pH meter, you can determine
exact pH levels of solutions. For example,
rather than say that lemon juice is quite
acidic, you can say that lemon juice has
a pH of 2.4. An exact pH value can be
used to control or measure acidity levels
for manufacturing processes or for basic
research.
pH values generally range from 0 to14,
with a pH of 7 being the neutral point,
or the value of pure water. pH values
greater than 7 represent increasing
alkalinity, whereas pH values below 7
represent increasing acidity (Figure 1).
pH
0 Strong Acid
1
2 Lemon Juice
3
4 Tomato Juice
5 Coffee
6
Neutral 7 Pure Water
8 Baking Soda
9
(sodium hydrogen carbonate)
10
11
12 Ammonia
13
14 Strong Base
more acidicmore basic
Figure 1.
pH scale showing
the relative acidity
or basicity of some
common substances.
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