Chemistry Reference
In-Depth Information
Figure 15.1
Dissolving Action
of Water on an Ionic Solid
All of the ions at the surface of the
solid are affected by water molecules.
However, the ones at the edges and
corners are affected more because
there are more water molecules in the
vicinity and fewer ions of opposite
charge. The ions in solution have the
most water molecules around them.
Negative end of water
dipole attracting
positive ion
Positive ends of water
attracting
negative ion
Positive ion in
solution surrounded
by water molecules
Negative ion in
solution surrounded
by water molecules
Ionic lattice
polar solvents to do the job.) Thus, a general rule emerges: “Like dissolves like.”
That is, polar solvents are more likely to dissolve ionic and polar solutes, and
nonpolar solvents are more likely to dissolve nonpolar solutes.
When sodium chloride dissolves in water, the molecules orient their
dipoles around the and ions so that their oppositely charged ends are
adjacent to each ion (Figure 15.1). Each sodium or chloride ion in solution is sur-
rounded by many water molecules, lessening the attractions between the ions.
Silver chloride, AgCl, does not dissolve in water. Evidently, the ion-dipole attrac-
tions are not sufficient to overcome the ion-ion attractions of this solid lattice. The
nonpolar solvent benzene,
Like dissolves like.
H
2
O
Na
Cl
C
6
H
6
,
cannot dissolve either of these ionic compounds.
EXAMPLE 15.1
Which solvent—liquid ammonia
(NH
3
)
or benzene
(C
6
H
6
)
—is more likely to
dissolve each of the following solutes? (a)
H
2
O
(b)
C
6
H
12
(c) AgCl
Solution
(a)
H
2
O
is more likely to dissolve in
NH
3
because both substances are polar
and capable of hydrogen bonding.
(b) is more likely to dissolve in the nonpolar solvent,
(c) AgCl is more likely to dissolve in the polar solvent,
C
6
H
12
C
6
H
6
.
NH
3
.
Practice Problem 15.1
Which type of solvent—polar, nonpolar, or
hydrogen bonding—is most likely to dissolve methyl alcohol, CH
3
OH?
Snapshot Review
❒
The attractions between solvent molecules and particles of solute must
be sufficient to overcome the attractions of the solvent molecules for
ChemSkill Builder 15.1
