Chemistry Reference
In-Depth Information
Such a substance is called an
acid salt.
The name of the compound includes
the word
hydrogen
to denote the fact that one or more ionizable hydrogen atoms
remain. The prefix
mono-
or
di-
may be used when it is necessary to indicate
how many hydrogen atoms are present:
NaH
2
PO
4
Sodium dihydrogen phosphate
Na
2
HPO
4
Sodium monohydrogen phosphate (or disodium hydrogen phosphate)
NaHCO
3
Sodium hydrogen carbonate
In an older nomenclature system, the word “acid” was used to denote an acid
salt. In another old system, the prefix
bi-
was used for a half-neutralized acid
that originally contained two ionizable hydrogen atoms. Thus, sodium bicarbon-
ate and sodium acid carbonate are other names that have been used for
In the anion of an acid salt, the number of hydrogen atoms plus the mag-
nitude of the charge on the ion equals the magnitude of the charge on the oxoan-
ion and also equals the number of hydrogen atoms in the acid:
NaHCO
3
.
3
PO
The zero hydrogen atoms plus 3 negative charges
on the phosphate ion equals 3.
4
2
HPO
1 hydrogen atom plus 2 negative charges equals 3.
4
H
2
PO
4
2 hydrogen atoms plus 1 negative charge equals 3.
H
3
PO
4
3 hydrogen atoms plus 0 negative charges equals 3.
EXAMPLE 8.22
What is the charge on the hydrogen sulfite ion?
Solution
HSO
3
.
The charge is
1
in
Practice Problem 8.22
What is the charge on the monohydrogen
phosphate ion?
Carbonates and Acid Carbonates
Carbonates
are compounds containing the carbonate ion.
Acid carbonates
are
compounds containing the hydrogen carbonate ion. Just as acid-base reactions
are an important type of double substitution reaction, the reactions of carbonates
and acid carbonates with acids are an important subtype of acid-base reaction.
Carbonates undergo double substitution reactions with acids to form carbon
dioxide and water or acid carbonates, depending on the relative quantity of acid
added:
Na
2
CO
3
(aq)
2 HCl(aq) £ 2 NaCl(aq)
CO
2
(g)
H
2
O(
/
)
Na
2
CO
3
(aq)
HCl(aq) £ NaCl(aq)
NaHCO
3
(aq)
The acid either totally or partially neutralizes the carbonate.
