46 DIY Science: Illustrated Guide to Home Chemistry Experiments
For example, the following names and numbers all refer to the
same inorganic compound, CuSO 4 · 5H 2 O:
Systematic (IUpAC) name: copper(II) sulfate pentahydrate
Common name: cupric sulfate, copper(II) sulphate,
cupric sulphate
vernacular name: copper sulfate, copper sulphate
Archaic name: sulphate of copper, blue vitriol, vitriol of copper,
copper vitriol, bluestone
CAS number: 7758-99-8Systematic name
The systematic name, also called the IUPAC name, is the
“official” name of a chemical, as determined by the detailed
naming rules published by IUPAC (International Union of Pure
and Applied Chemistry). Every systematic name identifies
exactly one chemical.
Common name
IUPAC uses the term common name differently than you might
expect. To IUPAC, a common name is not merely one that is
used casually or in nontechnical conversation. IUPAC defines
a common name for a substance as one that identifies that
substance unambiguously but does not comply with IUPAC
naming conventions.
For example, the common name cupric sulfate is
unambiguous because it uses the older (and deprecated)
form “cupric” to identify the bivalent copper (Cu2+) cation,
which in the current IUPAC nomenclature is designed
copper(II). Copper(II) sulphate is a common name rather than
a systematic name because it uses the nonstandard “sulphate”
spelling. Cupric sulphate is a common name rather than a
systematic name for both reasons. Chemists, particularly
those whose training predates the common use of IUPAC
systematic names, frequently use common names for well-
known compounds. The latest IUPAC standard approves the
use of common names in addition to or instead of systematic
names where the use of those common names would not lead
to confusion.vernacular name
A vernacular name is one that is commonly used in trade or
industry, but does not identify a substance unambiguously.
For example, the vernacular name copper sulfate may refer
either to copper(II) sulfate (CuSO 4 ) or to copper(I) sulfate
(Cu 2 SO 4 ), which is also known under the common name of
cuprous sulfate.Archaic name
An archaic name predates organized naming schemes.
Chemists no longer use archaic names, although many are still
in common use among nonchemists. For example, artists and
potters may use “blue vitriol” or “bluestone” to mean copper(II)
sulfate, and might have no idea that copper(II) sulfate, cupric
sulfate, and copper sulfate refer to the same compound.
Knowledge of archaic names can be useful to a home chemist,
because many useful chemicals are sold under archaic names.
For example, if you need hydrochloric acid it’s useful to know
that it’s sold in hardware stores under the archaic name
muriatic acid.CAS number
A CAS number unambiguously identifies a particular chemical.
CAS numbers are assigned to any chemical that has been
described in the literature by the Chemical Abstracts Service, a
part of the American Chemical Society, but are used worldwide.
As of late 2007, more than 30 million chemicals had beenCHEmICAL NAmES
It’s important for chemists to be able to identify a specific chemical unambiguously by its
name or other designation. In the past, chemical naming was chaotic. Many chemicals had
multiple names, and one name could refer to more than one chemical. Early names for specific
chemicals, some of which originated with alchemists, have in recent years been largely
superseded by modern, systematic names. Still, many of those older names are so ingrained
that many chemists continue to use them.
ATUoLm S NIqUE
Actually, the name “cupric sulfate” is ambiguous, because
that chemical exists in two distinct forms. The hydrated
blue crystalline form contains five water molecules
tightly bound to each cupric sulfate molecule as water of
crystallization. The anhydrous white powder form contains
no water of crystallization. In practice, “cupric sulfate” is
unambiguous, because chemists who use this older style
of nomenclature always mean the hydrated form unless
they specify “anhydrous cupric sulfate.”