Chemistry Reference
In-Depth Information
in Chapter 19. Salts and strong bases are ionic even when they are pure, and
their interaction with water is more a physical process than a chemical reaction.
The solution process for them is called
dissociation
because the ions dissociate
from each other; that is, they get out of each other's sphere of influence and are
able to move relatively independently of ions of the opposite charge.
Weak acids and bases ionize only slightly in aqueous solution. Because
their solutions conduct electricity poorly, they are called
weak electrolytes.
Compounds whose solutions do not conduct electricity at all are called
non-
electrolytes.
An outline of the electrolytic properties of compounds is presented
in Table 9.2.
A strong electrolyte
in aqueous solution
may be represented as separate ions
because the ions of each type are free to move about independently of the ions
of the other type. However, an ionic solid that is not dissolved in water is not
written as separate ions; the oppositely charged ions in the solid lattice of an
ionic compound are not independent of each other (Figure 9.2).
Thus, compounds must be both soluble and ionic to be written in the
form of their separate ions. A listing of water-soluble compounds was given in
Table 8.3. In addition to the compounds listed there, all strong acids are water
soluble. In summary strong electrolytes—compounds that dissociate or ionize
extensively in aqueous solution—include the following:
Table 9.1
Strong Acids
and Bases
Strong Acids
Strong Bases
HCl
All soluble metal
HBr
hydroxides,
HI
such as NaOH,
KOH, and
*
HClO
3
HClO
4
Ba(OH)
2
HNO
3
H
2
SO
4
*Note that
Ba(OH)
2
has limited solubility.
Table 9.2
Electrolytic
Properties of Various Types
of Compounds
Electrolytes
Strong electrolytes
Salts
Strong acids
Strong bases
Weak electrolytes
Weak acids
Weak bases
Nonelectrolytes
Covalent compounds other than
acids or bases
1. All soluble metal hydroxides
2. All salts (other compounds containing metal or ammonium ions) that are
soluble
3. Strong acids (HCl,
HClO
3
,
HClO
4
,
HBr, HI,
HNO
3
,
H
2
SO
4
)
All other compounds (for example, gases, other covalent compounds, and all
solids) either contain no ions or have ions that are affected by the presence of
the other ions. These weak electrolytes, nonelectrolytes, or solids (ionic or not)
are written using their regular formulas.
Compounds must be both solu-
ble and ionic to be written in
the form of their separate ions.
Positive
electrode
Negative
electrode
Positive
electrode
Negative
electrode
+
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+
(a) Solution of ions
(b) Effect of charged electrodes
(c) Ionic solid
Figure 9.2
Mobility of Ions
(a) Ions in dilute solutions are free to move independently of other ions. In the absence of electrodes, they move in random
directions. (b) Under the influence of the charges on electrodes, the ions move toward the electrode of opposite charge. (c) In
contrast, even if charged electrodes are present, ions in solids cannot move because of the surrounding ions of opposite charge.
