Page 31 - Pharmaceutical analytical chemistry |

Neutralization titration curves

By constructing a titration curve, we can easily explain how the end point
of these titrations can be determined as it signals the completion of the
reaction. A titration curve is constructed by plotting the pH of the
solution as a function of the volume of titrant added. The character of the
titration curves depends upon the concentration of the reactants and the
completeness of the reaction.
In discussing the calculation of a titration curve, it is convenient to
consider it as being made up of four distinct parts:

1. The point on the curve before the titration.
2. The interval after adding the titrant but before reaching the

equivalence point.
3. The equivalence point.
4. The interval beyond the equivalence point.
(1) Titration curves of strong acids versus strong bases
These titrations are the simplest and most accurate of acid-base titrations.
The only equilibrium to be considered in the derivation of the titration
curve is:

H+ + OH- ↔ H2O
Derive the titration curve of 50 mL of 0.1 M solution of HCl with
standard 0.1 M NaOH.

1. pH before adding titrant: a strong acid is essentially completely
ionized and so the [H+] is the same as the initial concentration of
the acid, so [H+] = 0.1 M and pH = 1.0.

2. pH during titration: on adding 10 mL of base, an equivalent
amount of the acid is neutralized leaving the equivalent of 40 mL
of acid not neutralized in a volume of 60 mL of solution.

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