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15.3 Heterogeneous Aqueous Systems >
15.3 Heterogeneous Aqueous Systems >
CHEMISTRY
& YOU
Why are some sunsets red?
Chapter 15
The atmosphere
contains particles of
water and dust. As
sunlight passes
through the
particles, it is
scattered. However,
not all wavelengths
are scattered to the
same extent.
Water and Aqueous Systems
15.1 Water and Its Properties
15.2 Homogeneous Aqueous
Systems
15.3 Heterogeneous Aqueous
Systems
1
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15.3 Heterogeneous Aqueous Systems > Suspensions
2
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15.3 Heterogeneous Aqueous Systems > Suspensions
Suspensions
What is the difference between a
suspension and a solution?
Suspensions
What is the difference between a
suspension and a solution?
3
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•  In a suspension, particles settle out upon
standing.
•  The particles of a suspension are much larger
and do not stay suspended indefinitely.
•  Solution: 1 nm
•  Suspension: greater than 1000 nm
•  Suspensions are heterogeneous mixtures
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15.3 Heterogeneous Aqueous Systems > Suspensions
Solution
15.3 Heterogeneous Aqueous Systems > Colloids
Colloids
Suspension
•  heterogeneous mixture containing
particles that range in size from 1 nm
to 1000 nm.
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15.3 Heterogeneous Aqueous Systems > Colloids
6
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15.3 Heterogeneous Aqueous Systems > Colloids
The first substances to be identified as colloids
were glues.
Some Colloidal Systems
Colloids have particles smaller
than those in suspensions and
larger than those in solutions.
System
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Dispersed
phase
Dispersion
medium
Type
Example
Gas
Liquid
Foam
Whipped cream
Gas
Solid
Foam
Marshmallow
Liquid
Liquid
Emulsion
Milk, mayonnaise
Liquid
Gas
Aerosol
Fog, aerosol
Solid
Gas
Smoke
Dust in air
Solid
Liquid
Sols, gels
Egg white, jelly, paint, blood,
starch in water, gelatin
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•  These intermediate-sized particles cannot
be retained by filter paper; but,
•  they do not settle out with time.
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15.3 Heterogeneous Aqueous Systems > Colloids
15.3 Heterogeneous Aqueous Systems > Colloids
The Tyndall Effect
The Tyndall Effect
You cannot see a beam of sunlight
unless the light passes through particles
of water (mist) or dust in the air.
The scattering of visible light by colloidal
particles is called the Tyndall effect.
•  These particles scatter the sunlight.
Flashlight
Solution
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15.3 Heterogeneous Aqueous Systems > Colloids
10
Colloid
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15.3 Heterogeneous Aqueous Systems >
•  Suspensions also exhibit the Tyndall
effect.
•  The particles in solutions are too small
to scatter light.
Suspension
CHEMISTRY
& YOU
What would be the ideal conditions to
see a red sunset?
A misty or foggy evening would be ideal
for seeing a red sunset. There would be
a large number of particles to scatter the
sunlight.
Flashlight
Solution
11
Colloid
Suspension
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15.3 Heterogeneous Aqueous Systems > Colloids
15.3 Heterogeneous Aqueous Systems > Colloids
Brownian Motion
Brownian Motion
•  Scottish botanist Robert Brown
(1773–1858), is called Brownian
motion.
•  Flashes of light, or scintillations, are
seen when colloids are studied under
a microscope.
The chaotic movement of colloidal
particles, which was first observed by
the
•  Colloids scintillate because the particles
reflecting and scattering the light move
erratically.
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15.3 Heterogeneous Aqueous Systems > Colloids
14
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15.3 Heterogeneous Aqueous Systems > Colloids
Brownian Motion
Brownian motion is caused by collisions
of the molecules of the dispersion
medium with the small, dispersed
colloidal particles.
Emulsions
An emulsion is a colloidal dispersion of
a liquid in a liquid.
•  These collisions help prevent the colloidal
particles from setting.
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15.3 Heterogeneous Aqueous Systems > Colloids
15.3 Heterogeneous Aqueous Systems > Colloids
Emulsions
Emulsions
•  Oils and greases are not soluble in
water.
•  However, oils and greases readily form
a colloidal dispersion if soap or
detergent is added to the water.
An emulsion is a colloidal dispersion of
a liquid in a liquid.
•  An emulsifying agent is essential for the
formation of an emulsion and for
maintaining the emulsion’s stability.
17
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15.3 Heterogeneous Aqueous Systems > Colloids
18
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15.3 Heterogeneous Aqueous Systems > Colloids
Properties of Solutions, Colloids, and Suspensions
System
Emulsions
•  One end of a large soap or detergent
molecule is polar and is attracted to water
molecules.
•  The other end of the soap or detergent
molecule is nonpolar and is soluble in oil or
grease.
•  Soaps and other emulsifying agents thus
allow the formation of colloidal dispersions
between liquids that do not ordinarily mix.
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Property
Solution
Colloid
Suspension
Particle type
Ions, atoms,
small molecules
Large molecules or
particles
Large particles or
aggregates
Particle size
0.1–1 nm
1–1000 nm
1000 nm and larger
Effect of light
No scattering
Exhibits Tyndall effect
Exhibits Tyndall effect
Effect of gravity
Stable, does not
separate
Stable, does not
separate
Unstable, sediment
forms
Filtration
Particles not
retained on filter
Particles not retained on Particles retained on
filter
filter
Uniformity
Homogeneous
Heterogeneous
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Heterogeneous
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15.3 Heterogeneous Aqueous Systems >
15.3 Heterogeneous Aqueous Systems >
Which of the following is a colloidal
system?
21
Which of the following is a colloidal
system?
A. mud
A. mud
B. gasoline
B. gasoline
C. blood
C. blood
D. a mixture of sugar and water
D. a mixture of sugar and water
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