Chemistry Reference
In-Depth Information
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A process called
reverse osmosis
is used to remove salts from seawater
to make drinking water for human consumption. If a pressure greater than
the osmotic pressure is applied to the solution side of an apparatus such
as shown in Figure 15.6, water is forced from the solution (the seawater)
to the pure solvent (water) side. This process is used industrially for water
purification.
ITEM OF INTEREST
EXAMPLE 15.23
Calculate the osmotic pressure of a 0.0150 M solution of glucose,
C
6
H
12
O
6
,
in
water at
25°C.
Solution
nRT
V
a
n
V
b
RT
(0.0150 M) (0.0821 L
#
atm/mol
#
K) (298 K)
0.367 atm
Practice Problem 15.23
Calculate the concentration of sucrose in
water at
25°C
that would yield an osmotic pressure of 68.3 torr.
Example 15.23 shows that osmotic pressure is rather high, even for a very
dilute solution.
Osmotic pressure is extremely important in biological systems. For exam-
ple, in trees, it helps in moving liquids from the root systems to the tops. Water
returns from human tissue to blood capillaries because of the greater concen-
tration of solutes in the blood. The use of saline solution when replacing blood
in accident victims must be carefully controlled so that the fluid's osmotic pres-
sure is the same as that of blood.
EXAMPLE 15.24
Calculate the height of a column of water that can be supported by a pressure
of 1.00 torr.
Solution
Since 1.00-torr pressure can support a column of mercury to a height of 1.00 mm,
it can support a column of water 13.6 mm high, since mercury has a density
13.6 times that of water. That is an easily measurable distance.
Snapshot Review
❒
Vapor-pressure
lowering,
freezing-point
depression,
boiling-point
elevation,
and
osmotic pressure
all depend on the number of solute
particles in a given quantity of solution.
ChemSkill Builder 15.4, 15.5
