Solutions
COLLEGE CHEMISTRY
Types of Solutions
 Remember, a solution is a homogenous mixture of two or
more substances
 Saturated solution – contains the maximum number
of solute that will dissolve in a solvent at a specific
temperature
 Supersaturate solution – contains more solute than
is present in a saturated solution
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Not stable
Eventually the extra solute will come out through crystallization as
crystals
 Unsaturated solution – contains less solute that is
present in a saturated solution
Types of Solutions
Molecular View of the Solution Process
 the intermolecular attractions that hold molecules
together in liquids in solids is also responsible for the
formation of solutions
 The ease of solution formation depends on these
three types of interactions:
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1. solvent-solvent interaction
2. solute-solute interaction
3. solvent-solute interaction
Molecular View of the Solution Process
 For simplicity, we can think of the solution process
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as happening in three distinct steps
1. separation of solvent molecules
2. separation of solute molecules
3. solvent and solute molecules mix
Process can be endothermic or exothermic
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DHsoln = DH1 + DH2 + DH3
Molecular View of the Solution Process
Molecular View of the Solution Process
 Solute-solvent interaction > solute-solute AND
solvent-solvent
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Reaction is favorable and exothermic
DHsoln < 0
 Solute-solvent interaction < solute-solute AND
solvent-solvent
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Reaction isn’t favorable and is endothermic
DHsoln > 0
Molecular View of the Solution Process
 So if particles are more attractive to each other than
the solute-solvent, why does dissociation take place?
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Two things govern dissociation
1. energy (exothermic is more favorable)
 2. tendency towards disorder (entropy)
 Molecules want to be in a state of disorder (solution), do not enjoy
being in order (just solute or just solvent)

BP Oil Spill
Predicting Solubility
 “like dissolves like” help us determine what is soluble
(or dissolves) in another molecule
 non-polar solute will dissolve in non-polar solvents
and polar solutes will dissolve in polar solvents
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This is why oil (non-polar) and water (polar) will not mix
 Also, compounds with similar intermolecular forces
will be solubility in each other
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Ex: CCl4 (carbon tetrachloride) and C6H6 (benzene) are both
non-polar and have dispersion forces only  fairly soluble
Ex: alcohols (with –OH) dissolve in water
Predicting Solubility
 Miscibility – ability of two liquids to be completely
soluble in each other in all proportions
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Immiscible – not soluble
 Solubility rules allows us to determine what ionic
compounds will dissolve in water
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Generally, ionic compounds will dissolve in polar solvents and
covalent compounds will dissolve only in nonpolar solvents
 Covalent compounds lack a dipole moment and
cannot effectively solvate an ionic compound (such
as NaCl)
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Solvation – process in which an ion or molecule is
surrounded by solvent molecules in a specific manner
Solvation
Example 12.1
 Predict the relative solubilities of the following cases:
 (a) Bromine (Br2) in benzene (C6H6, m = 0 D) and in
water (H2O, m = 1.87 D)
 (b) KCl in carbon tetrachloride (CCl4, m = 0 D) and
in liquid ammonia (NH3, m = 1.46 D)
 (c) formaldehyde (CH2O) in carbon disulfide (CS2, m
= 0 D) and in water
Example 12.1
 Predict the relative solubilities of the following cases:
 (a) Bromine (Br2) in benzene (C6H6, m = 0 D) and in
water (H2O, m = 1.87 D)
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Br2 is nonpolar as in benzene (dispersion forces), water is polar
Br2 should only dissolve in benzene
 (b) KCl in carbon tetrachloride (CCl4, m = 0 D) and in
liquid ammonia (NH3, m = 1.46 D)
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KCl is ionic, more soluble in ammonia since it has a larger dipole
 (c) formaldehyde (CH2O) in carbon disulfide (CS2, m = 0
D) and in water
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Formaldehyde is polar, carbon disulfide is nonpolar, and water is
polar
Formaldehyde can also hydrogen bond with water and it is more
soluble in water