Chemistry Comes Alive
Water is the body’s chief solvent. Most solutions in the body
containing gases, liquids, or solids dissolved in
water. True solutions are usually transparent. Examples are sa-
line solution [table salt (NaCl) and water], a mixture of glucose
and water, and mineral water. ±e solutes of true solutions are
minute, usually in the form of individual atoms and molecules.
Consequently, they are not visible to the naked eye, do not settle
out, and do not scatter light. In other words, if a beam of light is
passed through a true solution, you will not see the path of light.
Concentration of Solutions
We describe true solutions in
terms of their
, which may be indicated in various
ways. Solutions used in a college laboratory or a hospital are
oFen described in terms of the
(parts per 100 parts) of
the solute in the total solution. ±is designation always refers
to the solute percentage, and unless otherwise noted, water is
assumed to be the solvent.
Milligrams per deciliter
) is another common concen-
tration measurement. (A deciliter is 100 milliliters or 0.1 liter.)
Still another way to express the concentration of a solution
is in terms of its
ĭ-te), or moles per liter, indi-
. ±is method is more complicated but much more
useful. To understand molarity, you must understand what a
mole is. A
of any element or compound is equal to its
atomic weight or
(sum of the atomic weights)
weighed out in grams. ±is concept is easier than it seems, as
illustrated by the following example.
characteristics of the compound. ±is concept is important be-
cause the properties of compounds are usually very diﬀerent
from those of the atoms they contain. Water, for example, is very
diﬀerent from the elements hydrogen and oxygen. Indeed, it is
next to impossible to tell what atoms are in a compound without
analyzing it chemically.
are substances composed of two or more components
. Most matter in nature exists in the form of
mixtures, but there are only three basic types:
are homogeneous mixtures of components that may
be gases, liquids, or solids.
means that the mixture
has exactly the same composition or makeup throughout—a
sample taken from any part of the mixture has the same com-
position (in terms of the atoms or molecules it contains) as a
sample taken from any other part of the mixture. Examples in-
clude the air we breathe (a mixture of gases) and seawater (a mix-
ture of salts, which are solids, and water). ±e substance present
in the greatest amount is called the
(or dissolving me-
dium). Solvents are usually liquids. Substances present in smaller
amounts are called
Solute particles are very tiny,
do not settle out or scatter light.
Solute particles are larger than
in a solution and scatter light;
do not settle out.
Solute particles are very large,
settle out, and may scatter light.
The three basic types of mixtures.