Transcript Chemistry 15.3

Chemistry 15.3
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15.3
Heterogeneous Aqueous Systems
In 1996, American astronaut
Shannon Lucid shared a
gelatin dessert with her
Russian crewmates. Gelatin is
a heterogeneous mixture
called a colloid. You will learn
more about the characteristics
of colloids and a related
mixture called a suspension.
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15.3
Heterogeneous Aqueous > Suspensions
Systems
Suspensions
What is the difference between a
suspension and a solution?
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15.3
Heterogeneous Aqueous > Suspensions
Systems
A suspension is a mixture from which particles
settle out upon standing.
A suspension differs from a solution
because the particles of a suspension
are much larger and do not stay
suspended indefinitely.
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15.3
Heterogeneous Aqueous > Suspensions
Systems
Suspensions are heterogenous because at least
two substances can be clearly identified.
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15.3
Heterogeneous Aqueous > Colloids
Systems
Colloids
What distinguishes a colloid from a
suspension and a solution?
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15.3
Heterogeneous Aqueous > Colloids
Systems
A colloid is a heterogeneous mixture
containing particles that range in size
from 1 nm to 1000 nm. The particles
in a colloid are spread throughout the
dispersion medium.
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15.3
Heterogeneous Aqueous > Colloids
Systems
Colloids have particles smaller than
those in suspensions and larger than
those in solutions.
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15.3
Heterogeneous Aqueous > Colloids
Systems
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15.3
Heterogeneous Aqueous > Colloids
Systems
The Tyndall Effect
The scattering of visible light by colloidal
particles is called the Tyndall effect.
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15.3
Heterogeneous Aqueous > Colloids
Systems
Particles in colloids and suspensions reflect or
scatter light in all directions. Solutions do not
scatter light.
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15.3
Heterogeneous Aqueous > Colloids
Systems
Brownian Motion
• The chaotic movement of colloidal particles,
which was first observed by the Scottish
botanist Robert Brown (1773–1858), is called
Brownian motion.
• Brownian motion is caused by collisions of the
molecules of the dispersion medium with the
small, dispersed colloidal particles.
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15.3
Heterogeneous Aqueous > Colloids
Systems
Coagulation
• A colloidal system can be destroyed, or
coagulated, by the addition of ions having a
charge opposite to that of the colloidal
particles.
• The added ions neutralize the charged
colloidal particles. The particles can clump
together to form heavier aggregates and
precipitate from the dispersion.
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15.3
Heterogeneous Aqueous > Colloids
Systems
Emulsions
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.
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15.3
Heterogeneous Aqueous > Colloids
Systems
Mayonnaise is heterogeneous mixture of oil and
vinegar. Such a mixture would quickly separate
without the presence of egg yolk, which is the
emulsifying agent.
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15.3
Heterogeneous Aqueous > Colloids
Systems
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15.3 Section Quiz.
Assess students’ understanding
of the concepts in Section 15.3.
Continue to:
-or-
Launch:
Section Quiz
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15.3 Section Quiz.
1. One characteristic that is unique to a
suspension is that the particles in it
a. settle due to gravity.
b. are too small to be seen.
c. cannot be filtered.
d. produce the Tyndall effect.
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15.3 Section Quiz.
2. Homogenized milk contains finely divided
particles that do not settle out rapidly and
are not readily filtered. Thus, homogenized
milk is a
a. colloid.
b. substance.
c. suspension.
d. solution.
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15.3 Section Quiz.
3. The scattering of light known as the Tyndall
effect can be seen in
a. emulsions and solutions.
b. colloids and suspensions.
c. solutions and suspensions.
d. colloids and solutions.
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Heterogeneous Aqueous > Concept Map 15
Systems
Concept Map 15 Solve the Concept Map
with the help of an interactive guided tutorial.
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END OF SHOW