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Topic: Properties of Water
Keyword: HX4149
32 CHAPTER 2Chemistry of Life
When sodium chloride, NaCl, is dissolved in water, sodium ions, Na+, and
chloride ions, Cl–, become surrounded by water molecules, H 2 O.
Figure 6 Water dissolves ionic compounds
Chloride ion, Cl–
Water molecules, H 2 O Sodium ion, Na+
NaCl
Sodium
chloride,
NaCl
Aqueous Solutions
Many substances dissolve in water. For example, when you add salt
to water, the resulting mixture is a saltwater solution. A is
a mixture in which one or more substances are evenly distributed in
another substance. Many important substances in the body have
been dissolved in blood or other aqueous fluids. Because these sub-
stances can dissolve in water, they can more easily move within and
between cells. For example, sugar could not be delivered to your
cells if it were not dissolved in water.
Polarity
The polarity of water enables many substances to dissolve in water.
Ionic compounds and polar molecules dissolve best in water. When
ionic compounds are dissolved in water, the ions become sur-
rounded by polar water molecules. As Figure 6shows, ions are
attracted to the ends of water molecules with the opposite charge.
The resulting solution is a mixture of water molecules and ions. A
similar attraction results when polar molecules are dissolved in
water. In both cases, the ions or molecules become evenly distrib-
uted in the water.
Nonpolar molecules do not dissolve well in water. When nonpolar
substances, such as oil, are placed in water, the water molecules are
more attracted to each other than to the nonpolar molecules. As a
result, the nonpolar molecules are shoved together. This explains
why oil forms clumps or beads in water. The inability of nonpolar
molecules to dissolve in polar molecules is important to organisms.
For example, the shape and function of cell membranes depend on
the interaction of polar water with nonpolar membrane molecules.
solution
