1. Chapter 15 Water and Aqueous Systems 15.1 Water and Its Properties
15.2 Homogeneous Aqueous
Systems
15.3 Heterogeneous Aqueous
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2. What properties of water make it essential to life on Earth?
CHEMISTRY & YOU
What properties of water make it essential to life on Earth?
Water covers about three quarters of Earth’s surface. All known life forms are made mostly of water.
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3. Water in the Liquid State
What factor causes the high surface tension, low vapor pressure, and high boiling point of water?
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4. Water in the Liquid State
Water, H2O, is a simple molecule consisting of three atoms.
The oxygen atom forms a covalent bond with each of the hydrogen atoms.
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5. Water in the Liquid State
Water, H2O, is a simple molecule consisting of three atoms.
The oxygen atom forms a covalent bond with each of the hydrogen atoms.
Oxygen has a greater electronegativity than hydrogen, so the oxygen atom attracts the electron pair of the covalent O—H bond to a greater extent than the hydrogen atom.
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6. Water in the Liquid State
Water, H2O, is a simple molecule consisting of three atoms.
The oxygen atom forms a covalent bond with each of the hydrogen atoms.
Oxygen has a greater electronegativity than hydrogen, so the oxygen atom attracts the electron pair of the covalent O—H bond to a greater extent than the hydrogen atom.
Thus, the O—H bond is highly polar.
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7. Water in the Liquid State
Molecule has net polarity
Polar bonds δ– δ+
The oxygen atom acquires a partial negative charge (δ–).
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8. Water in the Liquid State
Molecule has net polarity
Polar bonds δ– δ+
The oxygen atom acquires a partial negative charge (δ–).
The less electronegative hydrogen atoms acquire partial positive charges (δ+).
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9. Water in the Liquid State
How do the polarities of the two O—H bonds affect the polarity of the molecule?
Molecule has net polarity
Polar bonds δ– δ+
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10. Water in the Liquid State
How do the polarities of the two O—H bonds affect the polarity of the molecule?
Molecule has net polarity
Polar bonds δ– δ+
The molecule has a bent shape.
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11. Water in the Liquid State
How do the polarities of the two O—H bonds affect the polarity of the molecule?
Molecule has net polarity
Polar bonds δ– δ+
The molecule has a bent shape.
The two O—H bond polarities do not cancel.
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12. Water in the Liquid State
How do the polarities of the two O—H bonds affect the polarity of the molecule?
Molecule has net polarity
Polar bonds δ– δ+
The molecule has a bent shape.
The two O—H bond polarities do not cancel.
The water molecule as a whole is polar.
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13. Water in the Liquid State
In general, polar molecules are attracted to one another by dipole interactions.
The negative end of one molecule attracts the positive end of another molecule. δ+ δ–
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14. Water in the Liquid State
However, in water, this attraction results in hydrogen bonding.
Hydrogen bonds are attractive forces that arise when a hydrogen atom is covalently
bonded to a very electronegative atom and also weakly bonded to an unshared electron pair of another electronegative atom.
Liquid water
Hydrogen bond
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15. Water in the Liquid State
Many unique and important properties of water—including its high surface tension, low vapor pressure, and high boiling point—result from hydrogen bonding.
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16. Water in the Liquid State
Surface Tension
Have you ever noticed that water forms nearly spherical droplets on a leaf?
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17. Water in the Liquid State
Surface Tension
The water molecules within the body of the liquid form hydrogen bonds with the other molecules that surround them on all sides.
The attractive forces on each of these molecules are balanced.
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18. Water in the Liquid State
Surface Tension
The water molecules within the body of the liquid form hydrogen bonds with the other molecules that surround them on all sides.
The attractive forces on each of these molecules are balanced.
Water molecules at the surface of the liquid experience an unbalanced attraction.
As a result, water molecules at the surface tend to be drawn inward.
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19. Water in the Liquid State
Surface Tension
The inward force, or pull, that tends to minimize the surface area of a liquid is called surface tension.
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20. Water in the Liquid State
Surface Tension
The inward force, or pull, that tends to minimize the surface area of a liquid is called surface tension.
All liquids have a surface tension, but water’s surface tension is higher than most.
The surface tension of water tends to hold a drop of liquid in a spherical shape.
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21. Water in the Liquid State
Surface Tension
It is possible to decrease the surface tension of water by adding a surfactant.
A surfactant is any substance that interferes with the hydrogen bonding between water molecules and thereby reduces surface tension.
Soaps and detergents are surfactants.
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22. Water in the Liquid State
Vapor Pressure
Hydrogen bonding between water molecules also explains water’s unusually low vapor pressure.
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23. Water in the Liquid State
Vapor Pressure
Hydrogen bonding between water molecules also explains water’s unusually low vapor pressure.
An extensive network of hydrogen bonds holds the molecules in liquid water to one another.
These hydrogen bonds must be broken before water changes from the liquid to the vapor state, so the tendency of these molecules to escape is low and evaporation is slow.
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24. Water in the Liquid State
Boiling Point
Molecular compounds of low molecular mass are usually gases or liquids with low boiling points at normal atmospheric pressure.
Ammonia (NH3) has a molar mass of 17.0 g/mol and boils at about –33˚C.
Water has a molar mass of 18.0 g/mol, but it has a boiling point of 100˚C.
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25. Water in the Liquid State
Boiling Point
The difference between the boiling points of ammonia and water is due to hydrogen bonding, which is more extensive in water than in ammonia.
It takes much more heat to disrupt the attractions between water molecules than those between ammonia molecules.
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26. Some insects are able to walk across water
Some insects are able to walk across water. How do the properties of water explain their ability?
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27. Some insects are able to walk across water
Some insects are able to walk across water. How do the properties of water explain their ability?
The surface tension of water is relatively high. As long as the forces holding the surface water molecules together are stronger than the forces exerted down on the water by the insect, the insect will not sink.
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28. Water in the Solid State
How can you describe the structure of ice?
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29. Water in the Solid State
Ice cubes float in your glass of iced tea because solid water has a lower density than liquid water.
This situation is not usual for liquids.
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30. Water in the Solid State
As water begins to cool, it behaves initially like a typical liquid.
It contracts slightly, and its density gradually increases.
When the temperature of the water falls below 4˚C, the density of water actually starts to decrease.
Density of Liquid Water and Ice
Temperature (˚C)
Density (g/cm3)
100 (liquid water)
0.9584 50
0.9881 25
0.9971 10
0.9997 4
1.0000
0 (liquid water)
0.9998
0 (ice)
0.9168
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31. Water in the Solid State
Below 4˚C, water no longer behaves like a typical liquid.
Ice, which forms at 0˚C, has about a 10% lower density than water at 0˚C.
Ice is one of only a few solids that floats in its own liquid.
Density of Liquid Water and Ice
Temperature (˚C)
Density (g/cm3)
100 (liquid water)
0.9584 50
0.9881 25
0.9971 10
0.9997 4
1.0000
0 (liquid water)
0.9998
0 (ice)
0.9168
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32. Water in the Solid State
Why is ice less dense than liquid water?
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33. Water in the Solid State
Why is ice less dense than liquid water?
The structure of ice is a regular open framework of water molecules in a hexagonal arrangement.
The hexagonal symmetry of a snowflake reflects the structure of the ice crystal.
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34. Water in the Solid State
The unique properties of ice are a result of hydrogen bonding.
Extensive hydrogen bonding in ice holds the water molecules farther apart in a more ordered arrangement than in liquid water.
Hydrogen bond
Ice
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35. Water in the Solid State
The fact that ice floats has important consequences for all organisms.
The liquid water at the bottom of an otherwise frozen body of water is warmer than 0˚C, so fish and other aquatic life are better able to survive.
If ice were denser than liquid water, bodies of water would tend to freeze solid during the winter months, destroying many types of organisms.
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36. CHEMISTRY & YOU
What properties of water that result from hydrogen bonding make it essential to life on Earth?
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37. CHEMISTRY & YOU
What properties of water that result from hydrogen bonding make it essential to life on Earth?
The low vapor pressure of water keeps the liquid water in all of Earth’s lakes and oceans from evaporating rapidly.
If water did not have such a high boiling point, it would be a vapor at the usual temperatures found on Earth.
The fact that ice floats allows fish and other aquatic life to survive the winter months.
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38. In ice, how many hydrogen bonds can be formed between one hydrogen atom of a water molecule and the oxygen in surrounding water molecules?
A. 0
B. 1
C. 2
D. 3
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39. In ice, how many hydrogen bonds can be formed between one hydrogen atom of a water molecule and the oxygen in surrounding water molecules?
A. 0
B. 1
C. 2
D. 3
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40. Key Concepts
Many unique and important properties of water—including its high surface tension, low vapor pressure, and high boiling point—result from hydrogen bonding.
The structure of ice is a regular open framework of water molecules in a hexagonal arrangement.
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41. Glossary Terms
surface tension: an inward force that tends to minimize the surface area of a liquid; it causes the surface to behave as if it were a thin skin
surfactant: any substance that interferes with the hydrogen bonding between water molecules and thereby reduces surface tension; soaps and detergents are surfactants
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42. Bonding and Interactions
BIG IDEA
Bonding and Interactions
Water molecules are held together through hydrogen bonds.
The hydrogen bonding interactions between water molecules account for the unique properties of water, including its high surface tension, low vapor pressure, and high boiling point.
Hydrogen bonding also accounts for the fact that ice is less dense than liquid water.
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43. Water and Aqueous Systems
Chapter 15
Water and Aqueous Systems
15.1 Water and Its Properties
15.2 Homogeneous Aqueous
Systems
15.3 Heterogeneous Aqueous
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44. How can you make a pickle glow?
CHEMISTRY & YOU
How can you make a pickle glow?
Although it sounds absurd, an ordinary dill pickle from the deli can be a source of light when connected to an electric current!
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45. What types of substances dissolve most readily in water?
Solutions
Solutions
What types of substances dissolve most readily in water?
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46. What types of substances dissolve most readily in water?
Solutions
Solutions
What types of substances dissolve most readily in water?
An aqueous solution is water that contains dissolved substances.
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47. In a solution, the dissolving medium is the solvent.
Solutions
Solvents and Solutes
In a solution, the dissolving medium is the solvent.
The dissolved particles in a solution are the solute.
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48. A solvent dissolves the solute.
Solutions
Solvents and Solutes
A solvent dissolves the solute.
The solute becomes dispersed in the solvent.
Solvents and solutes may be gases, liquids, or solids.
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49. Solutions are homogeneous mixtures.
Solvents and Solutes
Solutions are homogeneous mixtures.
Solute particles can be atoms, ions, or molecules.
If you filter a solution through filter paper, both the solute and solvent pass through the filter.
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50. Solutions
Solvents and Solutes
Substances that dissolve most readily in water include ionic compounds and polar covalent compounds.
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51. Solutions
Solvents and Solutes
Substances that dissolve most readily in water include ionic compounds and polar covalent compounds.
Nonpolar covalent compounds, such as methane, and compounds found in oil, grease, and gasoline, do not dissolve in water.
However, oil and grease will dissolve in gasoline.
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52. Solutions
The Solution Process
A water molecule is polar, with a partial negative charge on the oxygen atom and partial positive charges on the hydrogen atoms.
As individual solute ions break away from the crystal, the negatively and positively charged ions become surrounded by solvent molecules and the ionic crystal dissolves.
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53. Solutions
The Solution Process
Solvated ions
Surface of ionic solid
The process by which the positive and negative ions of an ionic solid become surrounded by solvent molecules is called solvation.
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54. Solutions
The Solution Process
Polar solvents such as water dissolve ionic compounds and polar compounds.
Nonpolar solvents such as gasoline dissolve nonpolar compounds.
This relationship can be summed up in the expression “like dissolves like.”
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55. Which of these compounds should not dissolve in water?
A. HCl
B. C4H10
C. KI
D. NH3
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56. Which of these compounds should not dissolve in water?
A. HCl
B. C4H10
C. KI
D. NH3
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57. Electrolytes and Nonelectrolytes
Why are all ionic compounds electrolytes?
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58. Electrolytes and Nonelectrolytes
Why are all ionic compounds electrolytes?
An electrolyte is a compound that conducts an electric current when it is in an aqueous solution or in the molten state.
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59. Electrolytes and Nonelectrolytes
All ionic compounds are electrolytes because they dissociate into ions.
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60. Electrolytes and Nonelectrolytes
In order for the bulb to light, an electric current must flow between the two electrodes that are immersed in the solution.
To (+) electrode
To (–) electrode
Sodium chloride, a strong electrolyte, is nearly 100% dissociated into ions in water.
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61. Electrolytes and Nonelectrolytes
In order for the bulb to light, an electric current must flow between the two electrodes that are immersed in the solution.
To (+) electrode
To (–) electrode
Mercury(II) chloride, a weak electrolyte, is only partially dissociated in water.
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62. Electrolytes and Nonelectrolytes
In order for the bulb to light, an electric current must flow between the two electrodes that are immersed in the solution.
To (+) electrode
To (–) electrode
Glucose, a nonelectrolyte, does not dissociate in water.
A nonelectrolyte is a compound that does not conduct an electric current in either an aqueous solution or the molten state.
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63. Electrolytes and Nonelectrolytes
Some polar molecular compounds are nonelectrolytes in the pure state but become electrolytes when they dissolve in water.
This change occurs because such compounds ionize in solution.
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64. Electrolytes and Nonelectrolytes
Some polar molecular compounds are nonelectrolytes in the pure state but become electrolytes when they dissolve in water.
For example, ammonia (NH3(g)) is not an electrolyte in the pure state.
Yet an aqueous solution of ammonia conducts an electric current because ammonium ions (NH4+) and hydroxide ions (OH–) form when ammonia dissolves in water.
NH3(g) + H2O(l)  NH4+(aq) + OH–(aq)
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65. Electrolytes and Nonelectrolytes
Not all electrolytes conduct electric current to the same degree.
In a solution that contains a strong electrolyte, all or nearly all of the solute exists as ions.
A weak electrolyte conducts an electric current poorly because only a fraction of the solute in the solution exists as ions.
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66. Electrolytes and Nonelectrolytes
Your cells use electrolytes, such as sodium and potassium ions, to carry electrical impulses across themselves and to other cells.
An electrolyte imbalance can occur if you become dehydrated.
When you exercise, you can lose water and electrolytes from your body through perspiration.
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67. CHEMISTRY & YOU
Pickles contain table salt. Why can electric current flow through a pickle, causing it to glow?
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68. CHEMISTRY & YOU
Pickles contain table salt. Why can electric current flow through a pickle, causing it to glow?
Electrolytes conduct an electric current when they are in an aqueous solution. Table salt, or NaCl, is a strong electrolyte. The water and salt in the pickle form a solution that conducts an electric current. The electric current causes the pickle to glow.
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69. Explain why you must be extremely careful when using electricity near a swimming pool.
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70. Explain why you must be extremely careful when using electricity near a swimming pool.
The chlorinated water in a swimming pool is a solution that can conduct an electric current. If a current is introduced into the water, any swimmers could be shocked.
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71. Why do hydrates easily lose and regain water?
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72. Hydrates
The water contained in a crystal is called the water of hydration or water of crystallization.
A compound that contains water of hydration is called a hydrate.
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73. Hydrates
The forces holding the water molecules in hydrates are not very strong, so the water is easily lost and regained.
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74. Hydrates
The forces holding the water molecules in hydrates are not very strong, so the water is easily lost and regained.
A substance that is anhydrous does not contain water.
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75. CuSO45H2O(s) CuSO4(s) + 5H2O(g)
Hydrates
CuSO45H2O(s) CuSO4(s) + 5H2O(g)
– heat
+ heat
After a time, much of the blue hydrate has been converted to white anhydrous CuSO4.
Heating of a sample of blue CuSO45H2O begins.
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76. Hydrates
A piece of filter paper that has been dipped in an aqueous solution of cobalt(II) chloride and then dried is blue in color (anhydrous CoCl2).
When the paper is exposed to moist air, it turns pink because of the formation of the hydrate cobalt(II) chloride hexahydrate (CoCl26H2O).
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77. Hydrates
Each hydrate contains a fixed quantity of water and has a definite composition.
Some Common Hydrates
Formula
Chemical name
Common name
MgSO47H2O
Magnesium sulfate heptahydrate
Epsom salt
Ba(OH)28H2O
Barium hydroxide octahydrate
CaCl22H2O
Calcium chloride dihydrate
CuSO45H2O
Copper(II) sulfate pentahydrate
Blue vitriol
Na2SO410H2O
Sodium sulfate decahydrate
Glauber’s salt
KAl(SO4)212H2O
Potassium aluminum sulfate dodecahydrate
Alum
Na2B4O710H2O
Sodium tetraborate decahydrate
Borax
FeSO47H2O
Iron(II) sulfate heptahydrate
Green vitriol
H2SO4H2O
Sulfuric acid hydrate (mp 8.6oC)
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78. To determine what percent by mass of a hydrate is water:
Hydrates
To determine what percent by mass of a hydrate is water:
First determine the mass of water in one mole of hydrate.
Then determine the molar mass of the hydrate.
The percent by mass of water can be calculated using the following equation:
Percent by mass H2O =  100%
mass of water
mass of hydrate
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79. Efflorescent Hydrates
The water molecules in hydrates are held by weak forces, so hydrates often have an appreciable vapor pressure.
If a hydrate has a vapor pressure higher than the pressure of water vapor in the air, the hydrate will lose its water of hydration, or effloresce.
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80. Hydrates
Hygroscopic Hydrates
Hydrated ionic compounds that have low vapor pressure remove water from moist air to form higher hydrates.
These hydrates and other compounds that remove moisture from air are called hygroscopic.
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81. Hydrates
Hygroscopic Hydrates
Calcium chloride monohydrate spontaneously absorbs a second molecule of water when exposed to moist air.
Calcium chloride is used as a desiccant in the laboratory.
A desiccant is a substance used to absorb moisture from the air and create a dry atmosphere.
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82. Finding the Percent by Mass of Water in a Hydrate
Sample Problem 15.1
Finding the Percent by Mass of Water in a Hydrate
Calculate the percent by mass of water in washing soda, sodium carbonate decahydrate (Na2CO310H2O).
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83. Analyze List the known and the unknown.
Sample Problem 15.1
Analyze List the known and the unknown. 1
To determine the percent by mass, divide the mass of water in one mole of the hydrate by the molar mass of the hydrate and multiply by 100%.
KNOWN
formula of hydrate = Na2CO310H2O
UNKNOWN
percent H2O = ? %
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84. mass of 10 mol H2O = 10[(2  1.0 g) + 16.0 g] = 180.0 g
Sample Problem 15.1
Calculate Solve for the unknown. 2
Determine the mass of 10 mol of water.
mass of 10 mol H2O = 10[(2  1.0 g) g] = g
For every 1 mol of Na2CO310H2O, there are 10 mol of H2O.
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85. Calculate Solve for the unknown.
Sample Problem 15.1
Calculate Solve for the unknown. 2
Determine the mass of 1 mol of the hydrated compound.
= (2  23.0 g) g + (3  16.0 g) g
= g
molar mass of Na2CO310H2O
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86. Calculate Solve for the unknown.
Sample Problem 15.1
Calculate Solve for the unknown. 2
Calculate the percent by mass of water in the hydrate.
mass of water
mass of hydrate
percent by mass H2O =  100%
180.0 g
286.0 g
=  100%
= 62.94%
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87. Evaluate Does the result make sense?
Sample Problem 15.1 3
Evaluate Does the result make sense?
The mass of the water accounts for more than half the molar mass of the compound.
So, a percentage greater than 50% is expected.
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88. Deliquescent Compounds
Hydrates
Deliquescent Compounds
Some compounds are so hygroscopic that they become wet when exposed to normally moist air.
These compounds are deliquescent, which means that they remove sufficient water from the air to dissolve completely and form solutions.
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89. Pellets of sodium hydroxide are deliquescent.
Hydrates
Pellets of sodium hydroxide are deliquescent.
For this reason, containers of NaOH should always be tightly stoppered.
The solution formed by a deliquescent substance has a lower vapor pressure than that of the water in the air.
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90. Calculate the percent by mass of water in epsom salt, magnesium sulfate heptahydrate (MgSO47H2O).
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91. Calculate the percent by mass of water in epsom salt, magnesium sulfate heptahydrate (MgSO47H2O).
mass of H2O = 7  ( 2  1.0 g g) = g
= 24.3 g g + (4  16.0 g) g
= g
molar mass of
MgSO47H2O
126.0 g
246.4 g
percent by mass H2O =  100% = 51.14%
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92. Key Concepts and Key Equation
Substances that dissolve most readily in water include ionic compounds and polar covalent compounds.
All ionic compounds are electrolytes because they dissociate into ions.
The forces holding the water molecules in hydrates are not very strong, so the water is easily lost and regained.
mass of water
mass of hydrate
percent by mass H2O =  100%
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93. aqueous solution: water that contains dissolved substances
Glossary Terms
aqueous solution: water that contains dissolved substances
solvent: the dissolving medium in a solution
solute: dissolved particles in a solution
solvation: a process that occurs when an ionic solute dissolves; in solution, solvent molecules surround the positive and negative ions
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94. Glossary Terms
electrolyte: a compound that conducts an electric current when it is in an aqueous solution or in the molten state; all ionic compounds are electrolytes, but most covalent compounds are not
nonelectrolyte: a compound that does not conduct an electric current in aqueous solution or in the molten state
strong electrolyte: a solution in which a large portion of the solute exists as ions
weak electrolyte: a solution that conducts electricity poorly because only a fraction of the solute exists as ions
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95. anhydrous: a substance that does not contain water
Glossary Terms
water of hydration: water molecules that are an integral part of a crystal structure
hydrate: a compound that has a specific number of water molecules bound to each formula unit
anhydrous: a substance that does not contain water
effloresce: to lose water of hydration; the process occurs when the hydrate has a vapor pressure higher than that of water vapor in the air
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96. desiccant: a hygroscopic substance used as a drying agent
Glossary Terms
hygroscopic: a term describing salts and other compounds that remove moisture from the air
desiccant: a hygroscopic substance used as a drying agent
deliquescent: describes a substance that removes sufficient water from the air to form a solution; the solution formed has a lower vapor pressure than that of the water in the air
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97. Bonding and Interactions
BIG IDEA
Bonding and Interactions
Ionic compounds and polar covalent compounds dissolve most readily in water to form aqueous solutions.
Ionic compounds dissolve in water when the polar water molecules attract the ions of the solute, causing the individual solute ions to break away from the ionic crystal.
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98. Water and Aqueous Systems
Chapter 15
Water and Aqueous Systems
15.1 Water and Its Properties
15.2 Homogeneous Aqueous
Systems
15.3 Heterogeneous Aqueous
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99. 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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100. 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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101. 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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102. 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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103. 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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104. 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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105. 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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106. 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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107. 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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108. 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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109. 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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110. 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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111. Colloids
Colloids have particles smaller than those in suspensions and larger than those in solutions.
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112. 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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113. 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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114. 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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115. 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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116. 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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117. 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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118. 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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119. 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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120. 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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121. 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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122. 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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123. 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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124. 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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125. 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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126. 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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127. 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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128. 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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129. 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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130. 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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131. 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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132. 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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133. 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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