Environmental Engineering Reference
In-Depth Information
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Student Exercises
Classroom Exercises
Classroom Exercise 1: Understanding pH
The term pH is derived from the French term for hydrogen power,
pouvoir
hydrog'ne
. In chemistry, pH is a measure of the acidity or basicity of an aqueous
solution. Pure water is considered to be neutral, with a pH close to 7.0 at 25
C.
Solutions with a pH less than 7 are considered to be acidic; solutions with a pH
greater than 7 are considered to be basic or alkaline. From a computational
standpoint, pH is the negative logarithm (base 10) of the
active
hydrogen ion (H
+
)
concentration (in moles/L), or
log [H
+
]. pH does not precisely reflect H
+
concen-
tration, but incorporates an activity factor to represent the tendency of hydrogen ions
to interact with other components of the solution. For purposes of this exercise,
consider the active hydrogen ion concentration to be equal to the hydrogen ion
concentration. Because a pH value represents the negative log of a concentration, a
pH of 4 corresponds to 10
4
mol/L, which corresponds to 0.0001 mol/L. What is the
