Titration and Buffers

Neutralization is an important concept in the performance of titrations. Titration (or more
specifically acid-base titration) is a procedure used to determine the molarity of an acid or base.
This is accomplished by reacting a known volume of a solution of unknown concentration with a
known volume of a solution of known concentration. When the number of acid equivalents equals
the number of base equivalents added, or vice versa, the equivalence point is reached. It is
important to emphasize that, while a strong acid/strong base titration will have an equivalence
point at pH 7, the equivalence point need not always occur at pH 7.

STRONG ACID AND STRONG BASE

Consider the titration of 10 mL of a 0.1 N solution of HCl with a 0.1 N solution of NaOH. Plotting the
pH of the reaction solution versus the quantity of NaOH added gives the following curve:

Because HCl is a strong acid and NaOH is a strong base, the equivalence point of the titration will be
at pH 7 and the solution will be neutral. Note that the endpoint shown is close to, but not exactly
equal to, the equivalence point; selection of a better indicator, such as one that changes colors at
pH 8, would have given a better approximation.

In the early part of the curve (when little base has been added), the acidic species predominates,
and so the addition of small amounts of base will not appreciably change either the [OH−] or the pH.