INTRODUCTION TO SOLUTION MATHEMATICS
Section I. GRADES OF LABORATORY CHEMICALS
Chemicals available from various manufacturers are usually assigned one of
several common grades. The particular grade assigned to a chemical depends upon
the purity. However, the differentiation between the various grades is unofficial. There
seems to be no agreement between chemical manufacturing companies concerning the
various degrees of purity.
A standard is a solution that contains a known amount of analytically pure
(weighed or titrated) substance in a specific volume of solvent.
a. Primary Standards. Primary standards are highly purified chemicals which
assay to be at least 99.95 from the National Bureau of Standards (NBS), U.S.
Department of Commerce. A primary standard must fulfill the following criterion: (1) it
can be accurately weighed or measured, (2) it must be stable, (3) it must be extremely
pure, and (4) it must be nonhygroscopic (not absorb water readily).
b. Secondary Standards. If a standard is prepared from a substance whose
concentration cannot be determined accurately either by weighing or measuring, it is
called a secondary standard. The normality (concentration) of the secondary standard
must be determined by titration (or other means) using a primary standard. HCl, H2SO4,
and NaOH are laboratory reagents that fall into the category of secondary standards. If
an exact concentration is desired, these reagents must be standardized prior to use.
REAGENT GRADE OR ANALYTICAL REAGENT GRADE
The chemicals, reagent grade or analytical reagent grade (ACS), that are
assigned this grade are manufactured to meet specifications needed in both quantitative
and qualitative analysis and are generally the purest form of laboratory chemicals
available. This grade of chemical appears in two different forms: (1) lot analyzed, in
which each lot is individually analyzed and the amount of impurities noted on the bottle,
and (2) maximum impurities, which lists the maximum allowed impurities on the bottle.
This grade of chemical also contains certain types of chemicals and solvents which are
designed for specific laboratory determinations. These specialized reagents are:
a. High Performance Liquid Chromatography Solvents. This grade of
solvent is designed to be used in high performance liquid chromatography (HPLC).