Instant Notes: Analytical Chemistry

Section C – Analytical reactions in solution

C5 TITRIMETRY I: ACID–BASE

TITRATIONS

Titrimetry In order to obtain accurate quantitative data for a reaction in solution, it is
necessary that the reaction be fast, complete and occur in fixed, reproducible
amounts. The requirement for fast reaction is achieved readily when ionic
species are involved, although in some other cases, it is necessary to warm the
solutions or add a catalyst. The reaction will be completeprovided the equilib-
rium constant is large (see Topic C1).
The technique of volumetric analysisis the simplest type of titrimetry, and
involves the addition of controlled volumes of a reagent solution, the titrant, to
a known volume of another solution, the titrand in a volumetric titration. This
procedure may be automated, and the changes detected instrumentally (Topics
C2, C3, C9 and C10). In some cases, excess of a reagent is added and the excess
measured by back titration.
The volumes and concentrations can be measured with high accuracy.
Calibration of volumetric glassware by discharge into weighed containers

Key Notes

Titrimetry is an analytical technique for the determination of the

stoichiometry of a reaction by the addition of controlled amounts of a

standard reagent.

Titrations usually involve the addition of controlled volumes of a

standard solution, whose concentration is known accurately, to a solution

of reactant of unknown concentration.

The theoretical amount of solution that must be added until the reaction

is just complete is the equivalence point and the end point in a titration is

the point at which change is detected accurately. In an ideal case, these

points should be the same.

In order to detect the end point, a visual indicator may be added.

Instrumental methods may also be used.

The use of an electrochemical cell with an indicator electrode and a

reference electrode to measure the concentration at each stage in the

titration facilitates the detection of the end point and the automation of

titrations.

The major applications for acid-base reactions are the determination of

the concentrations or amounts of acids or bases.

Related topics Other topics in this Section (C1-C4, C6-C10)

Titrimetry

Standard solutions

Equivalence points

and end points

Indicators

Potentiometric

titrations

Applications