ACID-BASE TITRATIONS
An acid-base titration is an experimental technique used to acquire information
about a solution containing an acid or base. Specifically, an acid-base titration
can be used to figure out the following:
concentration of an acid or base
- whether an unknown acid or base is strong or weak
- pKa of an unknown acid or pKb of unknown base
All titration experiments are carried out in the same way. The procedure consists
of adding a strong acid or base of known identity and concentration, called the
titrant, to the unknown acid or base solution. The titrant is carefully added step-
wise, and changes in pH are monitored and recorded. With each small sample of
titrant, a fraction of the unknown base or acid molecules is neutralized and
converted into its conjugates.
This procedure continues until either the pH of the solution starts to level off or a
color change is observed using a pH indicator.
Analyzing a titration curve—a curve obtained by plotting pH as a function of
the volume of added titrant—provides information about the unknown solution’s
concentration.
The Equivalence Point
The most important feature of any titration curve is the equivalence point. This
is the point during the titration where just enough titrant (in moles) has been
added to completely neutralize the subject acid or base. At the equivalence point,
no unreacted titrant or unknown base/acid remains in solution. Keep in mind that
conjugate acids and bases need not be neutral (recall the conjugate rules).
Therefore, do not make the mistake of automatically associating the equivalence
point with pH 7.
Different Ways to Say It
The equivalence point is