Aqueous Solutions and
the Concept of pH
Chapter 16
provided by acids and bases in
aqueous solutions
 also provided by the solvent, water
 water is considered the “ripper” that
causes both acids and bases to
dissociate in water solution
 water actually causes molecules to
separate into their ions

Hydronium and Hydroxide Ions
Kw = [H3O+][OH-] = 1.0 x 10-14
Memorize this!!
Square brackets indicate the concentration of the
ion in moles per liter. (Molarity)
Kw is the equilibrium constant for water. Its very
small value indicates that few ions form before the
equation reverses itself.
Equilibrium
Expression
Also known as the ionization
constant of water, Kw, increases
as temperature increases.
-because [H3O+] and [OH-] are the same in
pure water, it is neutral
[H3O+] = [OH-] = 1 x 10-7
-any solution where they are equal is also
neutral
-if [H3O+] is greater it is acidic; in basic
solutions the [OH-] is greater
Neutral, Acidic, and Basic
Solutions
-compounds whose colors are sensitive to
pH
-change colors because they are either
weak acids or weak bases
-come in many colors
HIn + H2O  H3O+ + In- (weak acid)
HIn and In- are different colors
-range over which an indicator changes
colors also varies
Transition interval – the pH range over
which an indicator changes color
Acid-Base Indicators
Color Ranges
of Indicators
Table page 495
pH Meter
-determines the pH of a solution by
measuring the voltage between the 2
electrodes that are placed in the solution
-used to find exact pH
-voltage changes as [H3O+] changes
Titration
-the controlled addition
and measurement of
the amount of a
solution of known
concentration
required to react
completely with a
measured amount of a
solution of unknown
concentration
-sensitive means for
determining
chemically equivalent
volumes of acid and
base
Equivalence Point –
-the point at which the 2
solutions used in a
titration are present in
chemically equivalent
amount
-indicators and pH
meters can be used to
determine equivalence
point
-pH meter will show
large voltage change
End Point –
-the point in a titration
at which an indicator
changes color
Litmus: broad range pH
5.5 – 8.0
Bromthymol blue:
limited transition pH
6.0 – 7.6
-indicators that undergo
transition at about pH
7 are used to
determine equivalence
point of strongacid/strong-base
titrations
Titration Terminology
Titration Curve for Strong
Acid/Strong Base
Titration Curve for Strong Base
and Weak Acid
Standard solution
–
-the solution that
contains the
precisely known
concentration of a
solute
-often called the
“known” solution
Titration
Primary standard
–
-a highly purified
solid compound
used to check the
concentration of
the known solution
in a titration
-to be certain of
concentration of
known solution,
titration is done
with the primary
Completed