An Introductory Course of Quantitative Chemical Analysis
PART I.
INTRODUCTION
SUBDIVISIONS OF ANALYTICAL CHEMISTRY
A complete chemical analysis of a body of unknown composition involves
the recognition of its component parts by the methods of qualitative
analysis, and the determination of the proportions in which these
components are present by the processes of quantitative analysis.
A preliminary qualitative examination is generally indispensable, if
intelligent and proper provisions are to be made for the separation of
the various constituents under such conditions as will insure accurate
quantitative estimations.
It is assumed that the operations of qualitative analysis are familiar
to the student, who will find that the reactions made use of in
quantitative processes are frequently the same as those employed in
qualitative analyses with respect to both precipitation and systematic
separation from interfering substances; but it should be noted that
the conditions must now be regulated with greater care, and in such
a manner as to insure the most complete separation possible. For
example, in the qualitative detection of sulphates by precipitation
as barium sulphate from acid solution it is not necessary, in most
instances, to take into account the solubility of the sulphate
in hydrochloric acid, while in the quantitative determination of
sulphates by this reaction this solubility becomes an important
consideration. The operations of qualitative analysis are, therefore,
the more accurate the nearer they are made to conform to quantitative
conditions.
The methods of quantitative analysis are subdivided, according
to their nature, into those of gravimetric analysis, volumetric
analysis, and colorimetric analysis. In gravimetric
processes the constituent to be determined is sometimes isolated in
elementary form, but more commonly in the form of some compound possessing
a well-established and definite composition, which can be readily and
completely separated, and weighed either directly or after ignition.
From the weight of this substance and its known composition, the
amount of the constituent in question is determined.
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