Solutions: homogeneous mixtures
2 or more solids (metal alloys)
2 or more liquids
2 or more gases
gas in liquid
solid in liquid
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Definitions:
solute: the component in the lesser amount
(what is being dissolved).
solvent: the component in the greater amount.
(dissolving media)
miscible: fluids that mix completely in all proportions.
(water and isopropyl alcohol)
immiscible: (oil and water)
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Definitions (continued):
saturated solution: solution at equilibrium in which
dissolving and crystallizing are occurring at the same
rate. (no more will dissolve).
dissolved solute
crystals:
Dissolving and crystallizing are occurring at the same rate.
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DYNAMIC EQUILIBRIUM
Definitions (continued):
unsaturated solution: more will dissolve.
super saturated solution: “more solute dissolved than
equilibrium will allow” (more than solution should hold,
unstable)
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Concentration:
Molarity: M  mol of solute  mol
L of solution
mOLALITY:
mass %:
L
moles of solute
m
kg of solvent
mass of solute
mass % 
x 100
total mass of solution
ppm = same as above but x’s 1,000,000
ppb = same as above but x’s 1,000,000,000
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mole fraction:
moles A
nA
XA 

total moles n total
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H2O “ionizes” ionic compounds
when they dissolve.
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Crystal Structures:
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In ionic cmpds, the ions are held together by electrical
attractions (ionic bonds: cation--anion).
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The dipoles of H2O are attracted to the charges of the ions.
ion-dipole forces
If the ion-dipole forces exceed the lattice energy the ionic cmpd
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will dissolve.
NaCl is soluble in water: NaCl(s)  Na+(aq) + Cl-(aq)
AgCl is insoluble in water: AgCl(s) + H2O  insoluble
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Which of the following would be most soluble and which
would be least soluble?
a. Mg(OH)2
b. Ca(OH)2
c. Sr(OH)2
d. Ba(OH)2
HINT: look at size/charge ratios.
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2 factors affecting solubility:
1. Natural tendency to mix: (disorder is favored = entropy)
2. Relative forces of attraction between species:
solvent-solvent
solvent-solute
solute-solute
“likes dissolve likes”
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“likes dissolve likes”
polar ---polar: H2O and CH3CH2OH
polar---ionic: H2O and NaCl
nonpolar---nonpolar: C5H12 and C6H6
Why doesn’t water dissolve in gasoline (C8H18)?
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molecular solutions: both solute and solvent are molecules
Which pairs would you expect to form solutions and why?
a. C6H12 + C7H14
“likes dissolve likes”
b. C6H12 + H2O
c. C6H12 + C2H5OH
d. H2O + C2H5OH
e. H2O + KNO3
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Solubility is temperature
dependent.
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Colligative (collective) properties of solutions:
Boiling point is raised: Vapor pressure is lowered.
Tb = Kbm
molality of solution. ”particles”
boiling pt. elevation constant
(solvent dependent)
Kb(H2O) = 0.512 oC kg
mol
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Colligative properties of solutions:
Freezing point is lowered:
Tf = Kfm
molality of solution”particles”
freezing pt. depression constant
(solvent dependent)
Kf(H2O) = 1.86 oC kg
mol
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Which would lower the freezing point of water the most?
CaCl2 forms 3 particles when dissolved
NaCl
sugar
forms 2 particles when dissolved
forms 1 particle when dissolved
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Which solution would have the lowest freezing point?
0.1 m CaCl2
0.2 m NaCl
0. 2 m sugar
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An aqueous solution is 0.035 m in glucose. Determine the
boiling and freezing points of the solution.
Kf for H2O = 1.86oC/m
Kb for H2O = 0.512oC/m
Tb = Kbm
Tf = Kfm
Tb = 0.512oC
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Osmosis: solvent molecules moving through a
semipermeable membrane. The net movement of
solvent molecules is always toward the solution with the
higher concentration.
The solvent tries
to dilute the
concentration.
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BEFORE
AFTER
Osmotic pressure:
n
    RT  MRT
V
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Bacteria in a “pickle barrel”
A blood vessel with too
much salt.
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Soap
Eating Bran and Cholesterol.
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Colloids:
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