• homogeneous mixtures
 composition may vary from one sample to another
 appears to be one substance, though really contains multiple materials
• most homogeneous materials we encounter are actually solutions
 e.g., air and sea water
• nature has a tendency toward spontaneous mixing
 generally, uniform mixing is more energetically favorable
2

solute is the dissolved substance
 seems to “disappear”
 “takes on the state” of the solvent
solvent is the substance solute dissolves in
 does not appear to change state
• when both solute and solvent have the same state, the solvent is the component present in the highest percentage
• solutions in which the solvent is water are called aqueous solutions
3

• drinking seawater will dehydrate you and give you diarrhea
• the cell wall acts as a barrier to solute moving
• the only way for the seawater and the cell solution to have uniform mixing is for water to flow out of the cells of your intestine and into your digestive tract
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Solution Phase gaseous solutions liquid solutions
Solute
Phase gas gas liquid solid solid
Solvent
Phase Example gas air (mostly N
2
& O
2
) liquid liquid liquid soda (CO
2 in H
2
O) vodka (C
2
H
5
OH in H
2
O) seawater (NaCl in H
2
O) solid brass (Zn in Cu) solid solutions
• solutions that contain Hg and some other metal are called amalgams
• solutions that contain metal solutes and a metal solvent are called alloys
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Type
Gilding
Commercial bronze
Jewelry
Red redish bronze 87.5
12.5
golden 85 15
Low deep yellow
Cartridge yellow
Common yellow
Muntz metal yellow
95
90
80
70
67
60
5
10
20
30
33
40
Color % Cu % Zn Density g/cm 3
MP
°C
8.86
1066
8.80
1043
8.78
1035
8.75
1027
8.67
8.47
8.42
8.39
999
954
940
904
Tensile
Strength psi
50K
Uses
61K pre-83 pennies, munitions, plaques door knobs, grillwork costume jewelry 66K
70K electrical sockets, fasteners & eyelets
74K musical instruments, clock dials
76K car radiator cores
70K
70K lamp fixtures, bead chain nuts & bolts, brazing rods
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• when one substance (solute) dissolves in another
(solvent) it is said to be soluble
 salt is soluble in water
 bromine is soluble in methylene chloride
• when one substance does not dissolve in another it is said to be insoluble
 oil is insoluble in water
• the solubility of one substance in another depends on two factors – nature’s tendency towards mixing, and the types of intermolecular attractive forces
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8

• there is usually a limit to the solubility of one substance in another
 gases are always soluble in each other
 two liquids that are mutually soluble are said to be miscible
 alcohol and water are miscible
 oil and water are immiscible
• the maximum amount of solute that can be dissolved in a given amount of solvent is called the solubility
• the solubility of one substance in another varies with temperature and pressure
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• formation of a solution does not necessarily lower the potential energy of the system
 the difference in attractive forces between atoms of two separate ideal gases vs. two mixed ideal gases is negligible
 yet the gases mix spontaneously
• the gases mix because the energy of the system is lowered through the release of entropy
• entropy is the measure of energy dispersal throughout the system
• energy has a spontaneous drive to spread out over as large a volume as it is allowed
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• energy changes in the formation of most solutions also involve differences in attractive forces between particles
• must overcome solute-solute attractive forces
 endothermic
• must overcome some of the solvent-solvent attractive forces
 endothermic
• at least some of the energy to do this comes from making new solute-solvent attractions
 exothermic
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Solute-to-Solute +
Solute-to-Solvent > Solution Forms
Solvent-to-Solvent
Solute-to-Solvent =
Solute-to-Solute +
Solvent-to-Solvent
Solution Forms
Solute-to-Solvent <
Solute-to-Solute +
Solvent-to-Solvent
Solution May or
May Not Form
• when the solute-to-solvent attractions are weaker than the sum of the solute-to-solute and solvent-to-solvent attractions, the solution will only form if the energy difference is small enough to be overcome by the entropy
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