1. Chapter 15 Water and Aqueous Systems 15.3 Heterogeneous Aqueous
15.1 Water and Its Properties
15.2 Homogeneous Aqueous
Systems
15.3 Heterogeneous Aqueous
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2. Why are some sunsets red?
CHEMISTRY & 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.
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3. What is the difference between a suspension and a solution?
Suspensions
Suspensions
What is the difference between a suspension and a solution?
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4. What is the difference between a suspension and a solution?
Suspensions
Suspensions
What is the difference between a suspension and a solution?
A suspension is a mixture from which particles settle out upon standing.
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5. Suspensions
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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6. By contrast, the particle size in a solution is usually about 1 nm.
Suspensions
A suspension differs from a solution because the particles of a suspension are much larger and do not stay suspended indefinitely.
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.
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7. A solution is a homogeneous mixture.
Suspensions
A solution is a homogeneous mixture.
Suspensions are heterogeneous because at least two substances can be clearly identified.
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8. Suspensions
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.
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9. Explain why a mixture of sand and water can be separated by filtration, but a mixture of salt and water cannot.
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10. 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.
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11. What distinguishes a colloid from a suspension and a solution?
Colloids
Colloids
What distinguishes a colloid from a suspension and a solution?
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12. Colloids
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.
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13. Some Colloidal Systems
Colloids
The first substances to be identified as colloids were glues.
Some Colloidal Systems
System
Type
Example
Dispersed phase
Dispersion medium
Gas
Liquid
Foam
Whipped cream
Solid
Marshmallow
Emulsion
Milk, mayonnaise
Aerosol
Fog, aerosol
Smoke
Dust in air
Sols, gels
Egg white, jelly, paint, blood, starch in water, gelatin
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14. Colloids
Colloids have particles smaller than those in suspensions and larger than those in solutions.
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15. Colloids
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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16. Colloids
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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17. Colloids
The Tyndall Effect
The scattering of visible light by colloidal particles is called the Tyndall effect.
Flashlight
Solution Colloid Suspension
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18. Suspensions also exhibit the Tyndall effect.
Colloids
Suspensions also exhibit the Tyndall effect.
The particles in solutions are too small to scatter light.
Flashlight
Solution Colloid Suspension
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19. What would be the ideal conditions to see a red sunset?
CHEMISTRY & YOU
What would be the ideal conditions to see a red sunset?
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20. What would be the ideal conditions to see a red sunset?
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.
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21. Colloids
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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22. Colloids
Brownian Motion
The chaotic movement of colloidal particles, which was first observed by the Scottish botanist Robert Brown (1773–1858), is called Brownian motion.
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23. Colloids
Brownian Motion
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.
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24. Colloids
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.
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25. Colloids
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.
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26. Colloids
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.
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27. An emulsion is a colloidal dispersion of a liquid in a liquid.
Colloids
Emulsions
An emulsion is a colloidal dispersion of a liquid in a liquid.
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28. An emulsion is a colloidal dispersion of a liquid in a liquid.
Colloids
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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29. Oils and greases are not soluble in water.
Colloids
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.
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30. Colloids
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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31. Properties of Solutions, Colloids, and Suspensions
This table summarizes the properties of solutions, colloids, and suspensions.
Properties of Solutions, Colloids, and Suspensions
Property
System
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
Effect of gravity
Stable, does not separate
Unstable, sediment forms
Filtration
Particles not retained on filter
Particles retained on filter
Uniformity
Homogeneous
Heterogeneous
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32. Which of the following is a colloidal system?
A. mud
B. gasoline
C. blood
D. a mixture of sugar and water
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33. Which of the following is a colloidal system?
A. mud
B. gasoline
C. blood
D. a mixture of sugar and water
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34. 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.
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35. Glossary 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
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36. emulsion: the colloidal dispersion of one liquid in another
Glossary 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
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37. END OF 15.3
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