Classification of the reactions in titrimetric analysis:

The reactions employed in titrimetric analysis fall into two main classes…

a. Those in which no change in oxidation state occurs; these are dependent upon the combination of ions.

b. Oxidation-reduction reaction; these involve a change of oxidation state or a transfer of electrons.

For purpose of convenience, these two types of reaction are divided to four main classes. These are ..

ü Neutralization (acid-base) reactions,

ü Complex-forming reactions

ü Precipitation reactions

ü Oxidation-reduction reactions.

1.Neutralization reaction( or Acidimetry and alkalimetry):

These reactions involve the combination of hydrogen and hydroxide ions to form water. These reactions are two types ….

v Acidimetry

v Alkalimetry

Acidimetry:

These include the titration of free bases or those formed from salts of weak acids by hydrolysis, with a standard acid.

Alkalimetry:

The titration of free acids or those formed from by hydrolysis of salts of weak bases, with a standard base.

2.Complex formation reactions:

These depend upon the combination of

ü Ions,

ü Other than hydrogen or hydroxide ions, to form a

o Soluble,

o Slightly dissociated ion or compound.

For example:

In the titration of a solution of a cyanide with silver nitrate

2CN^- + Ag⁺ [Ag (CN) ₂] ^-

or, in the titration of chloride ion with mercury(ІІ) nitrate solution.

2Cl¯ + Hg²⁺ HgCl₂

3.Precipitation reactions:

These depend upon the combination of ions to form a simple precipitate.

For example:

Ag⁺ + Cl¯ AgCl

4.Oxidation-Reduction reactions:

These include all the reactions involving change of oxidation number or transfer of electrons among the reacting substances.

The standard solutions are either oxidizing or reducing agent.

The principle oxidizing agents are…

ü KMnO₄,

ü K₂Cr₂O₇,

ü I₂,

ü KI,

ü KBr.

The principle reducing agents are…

ü Fe(ΙΙ),

ü Sn(ΙΙ),

ü As(ΙΙΙ) oxide,

ü Sodium thiosulphate,

ü Mercury(Ι) nitrate,

ü Chromium(ΙΙ) chloride or Sulphate,