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15.3 Heterogeneous Aqueous Systems >15.3 Heterogeneous Aqueous Systems >
1 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
Chapter 15Water and Aqueous Systems
15.1 Water and Its Properties15.2 Homogeneous Aqueous Systems
15.3 Heterogeneous Aqueous Systems
15.3 Heterogeneous Aqueous Systems >15.3 Heterogeneous Aqueous Systems >
2 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
CHEMISTRY & YOUCHEMISTRY & YOU
Why are some sunsets red?
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.
15.3 Heterogeneous Aqueous Systems >15.3 Heterogeneous Aqueous Systems >
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SuspensionsSuspensions
Suspensions
What is the difference between a suspension and a solution?
15.3 Heterogeneous Aqueous Systems >15.3 Heterogeneous Aqueous Systems >
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SuspensionsSuspensions
Suspensions
What is the difference between a suspension and a solution?
• A suspension is a mixture from which particles settle out upon standing.
15.3 Heterogeneous Aqueous Systems >15.3 Heterogeneous Aqueous Systems >
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A suspension differs from a solution because the particles of a suspension are much larger and do not stay suspended indefinitely.
SuspensionsSuspensions
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A suspension differs from a solution because the particles of a suspension are much larger and do not stay suspended indefinitely.
SuspensionsSuspensions
• The particles in a typical suspension have an average diameter greater than 1000 nm.
• By contrast, the particle size in a solution is usually about 1 nm.
15.3 Heterogeneous Aqueous Systems >15.3 Heterogeneous Aqueous Systems >
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SuspensionsSuspensions
• A solution is a homogeneous mixture.
• Suspensions are heterogeneous because at least two substances can be clearly identified.
15.3 Heterogeneous Aqueous Systems >15.3 Heterogeneous Aqueous Systems >
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SuspensionsSuspensions
The difference between a solution and suspension is easily seen when the type of mixture is filtered.
The small size of the solute particles in a solution allows them to pass through filter paper.
The particles of a suspension can be removed by filtration.
15.3 Heterogeneous Aqueous Systems >15.3 Heterogeneous Aqueous Systems >
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Explain why a mixture of sand and water can be separated by filtration, but a mixture of salt and water cannot.
15.3 Heterogeneous Aqueous Systems >15.3 Heterogeneous Aqueous Systems >
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Explain why a mixture of sand and water can be separated by filtration, but a mixture of salt and water cannot.
A mixture of sand and water is a suspension, and a mixture of salt and water is a solution. The particles in the sand mixture are much larger than the ions in the salt mixture. The sand particles are too large to pass through filter paper; the ions are not.
15.3 Heterogeneous Aqueous Systems >15.3 Heterogeneous Aqueous Systems >
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ColloidsColloids
Colloids
What distinguishes a colloid from a suspension and a solution?
15.3 Heterogeneous Aqueous Systems >15.3 Heterogeneous Aqueous Systems >
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ColloidsColloids
A colloid is a heterogeneous mixture containing particles that range in size from 1 nm to 1000 nm.
• The particles are spread, or dispersed, throughout the dispersion medium, which can be a solid, liquid, or gas.
15.3 Heterogeneous Aqueous Systems >15.3 Heterogeneous Aqueous Systems >
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ColloidsColloids
The first substances to be identified as colloids were glues.
Some Colloidal SystemsSystem
Type ExampleDispersed phase
Dispersion medium
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, gelsEgg white, jelly, paint, blood, starch in water, gelatin
15.3 Heterogeneous Aqueous Systems >15.3 Heterogeneous Aqueous Systems >
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ColloidsColloids
Colloids have particles smaller than those in suspensions and larger than those in solutions.
15.3 Heterogeneous Aqueous Systems >15.3 Heterogeneous Aqueous Systems >
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ColloidsColloids
Colloids have particles smaller than those in suspensions and larger than those in solutions.
• These intermediate-sized particles cannot be retained by filter paper as are the larger particles of a suspension.
• They do not settle out with time.
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ColloidsColloids
The Tyndall Effect
You cannot see a beam of sunlight unless the light passes through particles of water (mist) or dust in the air.
• These particles scatter the sunlight.
• Similarly, a beam of light is visible as it passes through a colloid.
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ColloidsColloids
The Tyndall Effect
The scattering of visible light by colloidal particles is called the Tyndall effect.
Flashlight
Solution Colloid Suspension
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ColloidsColloids
• Suspensions also exhibit the Tyndall effect.
• The particles in solutions are too small to scatter light.
Flashlight
Solution Colloid Suspension
15.3 Heterogeneous Aqueous Systems >15.3 Heterogeneous Aqueous Systems >
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CHEMISTRY & YOUCHEMISTRY & YOU
What would be the ideal conditions to see a red sunset?
15.3 Heterogeneous Aqueous Systems >15.3 Heterogeneous Aqueous Systems >
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CHEMISTRY & YOUCHEMISTRY & 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.
15.3 Heterogeneous Aqueous Systems >15.3 Heterogeneous Aqueous Systems >
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ColloidsColloids
Brownian Motion
Flashes of light, or scintillations, are seen when colloids are studied under a microscope.• Colloids scintillate because the particles
reflecting and scattering the light move erratically.
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ColloidsColloids
Brownian Motion
The chaotic movement of colloidal particles, which was first observed by the Scottish botanist Robert Brown (1773–1858), is called Brownian motion.
15.3 Heterogeneous Aqueous Systems >15.3 Heterogeneous Aqueous Systems >
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ColloidsColloids
Brownian motion is caused by collisions of the molecules of the dispersion medium with the small, dispersed colloidal particles.
• These collisions help prevent the colloidal particles from setting.
Brownian Motion
15.3 Heterogeneous Aqueous Systems >15.3 Heterogeneous Aqueous Systems >
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ColloidsColloids
Coagulation
Colloidal particles also tend to stay suspended because they become charged by adsorbing ions from the dispersing medium onto their surface.
• Adsorption means to adhere to a surface.
15.3 Heterogeneous Aqueous Systems >15.3 Heterogeneous Aqueous Systems >
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ColloidsColloids
Coagulation
All the colloidal particles in a particular colloidal system will have the same charge, although the colloidal system is neutral.
• The repulsion between the like-charged particles prevents the particles from forming heavier aggregates that would have a greater tendency to settle out.
15.3 Heterogeneous Aqueous Systems >15.3 Heterogeneous Aqueous Systems >
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ColloidsColloids
Coagulation
A colloidal system can be destroyed or coagulated by the addition of electrolytes.
• The added ions neutralize the charged colloidal particles.
• The particles can clump together to form heavier aggregates and settle out from the dispersion.
15.3 Heterogeneous Aqueous Systems >15.3 Heterogeneous Aqueous Systems >
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ColloidsColloids
Emulsions
An emulsion is a colloidal dispersion of a liquid in a liquid.
15.3 Heterogeneous Aqueous Systems >15.3 Heterogeneous Aqueous Systems >
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ColloidsColloids
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.
15.3 Heterogeneous Aqueous Systems >15.3 Heterogeneous Aqueous Systems >
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ColloidsColloids
• 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.
Emulsions
15.3 Heterogeneous Aqueous Systems >15.3 Heterogeneous Aqueous Systems >
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ColloidsColloids
• 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.
Emulsions
15.3 Heterogeneous Aqueous Systems >15.3 Heterogeneous Aqueous Systems >
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ColloidsColloids
This table summarizes the properties of solutions, colloids, and suspensions.
Properties of Solutions, Colloids, and Suspensions
Property
System
Solution Colloid Suspension
Particle typeIons, 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
FiltrationParticles not retained on filter
Particles not retained on filter
Particles retained on filter
Uniformity Homogeneous Heterogeneous Heterogeneous
15.3 Heterogeneous Aqueous Systems >15.3 Heterogeneous Aqueous Systems >
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Which of the following is a colloidal system?
A.mud
B.gasoline
C.blood
D.a mixture of sugar and water
15.3 Heterogeneous Aqueous Systems >15.3 Heterogeneous Aqueous Systems >
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Which of the following is a colloidal system?
A.mud
B.gasoline
C.blood
D.a mixture of sugar and water
15.3 Heterogeneous Aqueous Systems >15.3 Heterogeneous Aqueous Systems >
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Key Concepts Key Concepts
A suspension differs from a solution because the particles of a suspension are much larger and do not stay suspended indefinitely.
Colloids have particles smaller than those in suspensions and larger than those in solutions.
15.3 Heterogeneous Aqueous Systems >15.3 Heterogeneous Aqueous Systems >
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Glossary TermsGlossary Terms
• suspension: a mixture from which some of the particles settle out slowly upon standing
• colloid: a mixture whose particles are intermediate in size between those of a suspension and a solute solution
• Tyndall effect: scattering of light by particles in a colloid or suspension, which causes a beam of light to become visible
15.3 Heterogeneous Aqueous Systems >15.3 Heterogeneous Aqueous Systems >
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Glossary TermsGlossary Terms
• Brownian motion: the chaotic movement of colloidal particles, caused by collision with particles of the solvent in which they are dispersed
• emulsion: the colloidal dispersion of one liquid in another
15.3 Heterogeneous Aqueous Systems >15.3 Heterogeneous Aqueous Systems >
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END OF 15.3END OF 15.3
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