Acids
105
come this difficulty and to clarify some subtler points, the International Union
of Pure and Applied Chemistry (IUPAC) has in recent years recommended the
adoption of a system that, when applied to a positive ion, requires that the name
of the element be used and that it be followed immediately by its charge in
Roman numerals within parentheses. For example, Au
+ would be gold(I), and
Au
3+ would be gold(III); they would be read as "gold one" and "gold three,"
respectively. Until there is unanimous adoption of the IUPAC system, chemists
will have to use both systems. In any case, neither system relieves the student
of the responsibility of knowing the usual charge states of the common
elements.
BASES
We define abase as any substance that can accept or react with a hydrogen ion,
H
+ . This definition includes a wide variety of compounds, but for the present it
is convenient to limit our discussion to one special type of base called a hydroxide. A hydroxide is any compound that has one or more replaceable hydroxide ions, OH~. Any of the positive ions cited in the preceding sections might
combine with the hydroxide ion, the principle being that the resulting compound must be electrically neutral. Naturally there must be as many OH~ ions
as there are positive charges on the other ion. In naming, the word "hydroxide" is preceded by the name of the positive ion; for example,
NaOH
sodium hydroxide
Co(OH) 2
cobaltous hydroxide or cobalt(II) hydroxide
Sn(OH) 4
stannic hydroxide or tin(IV) hydroxide
ACIDS
We define an acid as any substance that has one or more replaceable hydrogen
ions (H
+ ); we often say that an acid can donate one or more hydrogen ions to a
base. No matter how many H atoms a molecule might have, if none of them can
be replaced by some positive ion, then the molecule does not qualify as an acid.
On the other hand, if a molecule does have several H atoms, of which only one
is replaceable, that alone is enough to qualify it as an acid. In writing the
formula of an acid, it is traditional to show the replaceable H ions at the
beginning of the formula, separated from those that are not replaceable. For
example, in acetic acid, HC 2 H 3 O 2 , there is one replaceable H
+ and there are
three H atoms that are not replaceable. Besides identifying the number of
replaceable H atoms, this traditional method also provides a simple way of
knowing the charge of the negative ions; for every H
+ that is removed from an
105
come this difficulty and to clarify some subtler points, the International Union
of Pure and Applied Chemistry (IUPAC) has in recent years recommended the
adoption of a system that, when applied to a positive ion, requires that the name
of the element be used and that it be followed immediately by its charge in
Roman numerals within parentheses. For example, Au
+ would be gold(I), and
Au
3+ would be gold(III); they would be read as "gold one" and "gold three,"
respectively. Until there is unanimous adoption of the IUPAC system, chemists
will have to use both systems. In any case, neither system relieves the student
of the responsibility of knowing the usual charge states of the common
elements.
BASES
We define abase as any substance that can accept or react with a hydrogen ion,
H
+ . This definition includes a wide variety of compounds, but for the present it
is convenient to limit our discussion to one special type of base called a hydroxide. A hydroxide is any compound that has one or more replaceable hydroxide ions, OH~. Any of the positive ions cited in the preceding sections might
combine with the hydroxide ion, the principle being that the resulting compound must be electrically neutral. Naturally there must be as many OH~ ions
as there are positive charges on the other ion. In naming, the word "hydroxide" is preceded by the name of the positive ion; for example,
NaOH
sodium hydroxide
Co(OH) 2
cobaltous hydroxide or cobalt(II) hydroxide
Sn(OH) 4
stannic hydroxide or tin(IV) hydroxide
ACIDS
We define an acid as any substance that has one or more replaceable hydrogen
ions (H
+ ); we often say that an acid can donate one or more hydrogen ions to a
base. No matter how many H atoms a molecule might have, if none of them can
be replaced by some positive ion, then the molecule does not qualify as an acid.
On the other hand, if a molecule does have several H atoms, of which only one
is replaceable, that alone is enough to qualify it as an acid. In writing the
formula of an acid, it is traditional to show the replaceable H ions at the
beginning of the formula, separated from those that are not replaceable. For
example, in acetic acid, HC 2 H 3 O 2 , there is one replaceable H
+ and there are
three H atoms that are not replaceable. Besides identifying the number of
replaceable H atoms, this traditional method also provides a simple way of
knowing the charge of the negative ions; for every H
+ that is removed from an