Types of Bonding in Crystalline Solids
Physical Properties
of Solutions
Chapter 13
Solution - a homogenous mixture of 2 or more substances
Solute - the substance(s) present in the smaller amount(s)
Solvent - the substance present in the larger amount
Table 13.1
Solutions
The intermolecular forces
between solute and solvent
particles must be strong
enough to compete with
those between solute
particles and those between
solvent particles.
“Like dissolves like”
Solutions
The Effect of Intermolecular forces
How Does a Solution Form?
 As a solution forms, the solvent pulls solute particles
apart and surrounds, or solvates, them.
Fig 13.1 Dissolution of an ionic solid inwater
Solutions
Fig 13.2 Hydrated Na+ and Cl− ions
• The negative end of the water
dipoles point toward the positive ion
• Positive ends point toward the
negative ion
• Result is hydrated ions
Solutions
Three types of interactions in the solution process:
Fig 13.2
•
•
•
solute-solute interaction
solvent-solvent interaction
solvent-solute interaction
DHsoln = DH1 + DH2 + DH3
ΔH1
ΔH2
ΔH3
Energy Changes in Solution Formation
 The enthalpy change of the overall process depends on
DH for each of these steps.
Fig 13.4 Enthalpy changes accompanying solution processes
Solutions
Solution Formation, Spontaneity, and Entropy
Fig 13.6
 Enthalpy is only part of the picture
 Increasing the disorder or
randomness of a system tends to
lower the energy of the system
 Entropy ≡ degree of randomness or
disorder in a system
 Solutions favored by increase in
entropy that accompanies mixing
Solutions
Caveat Emptor!
 Just because a substance disappears when it comes in contact
with a solvent, it doesn’t mean the substance dissolved.
• Dissolution is a physical change — you can get back the
original solute by evaporating the solvent
• If you can’t, the substance didn’t dissolve, it reacted:
Fig 13.7
Solutions
Unsaturated solution - contains less solute than the solvent
has the capacity to dissolve at a specific temperature
Saturated solution - contains the maximum amount of a
solute that will dissolve in a given solvent at a specific
temperature
Supersaturated solution - contains more solute than is
present in a saturated solution at a specific temperature
Sodium acetate crystals rapidly form when a seed crystal is
added to a supersaturated solution of sodium acetate.
Fig 13.10
Solutions
Factors Affecting Solubility
“like dissolves like”
Two substances with similar intermolecular forces are likely
to be soluble in each other:
•
non-polar molecules are soluble in non-polar solvents
CCl4 in C6H6
•
polar molecules are soluble in polar solvents
C2H5OH in H2O
•
ionic compounds are more soluble in polar solvents
NaCl in H2O or NH3 (l)
Factors Affecting Solubility
can hydrogen bond with water
Acetone is miscible in water
Hexane is immiscible in water
C6H14
H2O
Solutions
Factors Affecting Solubility
Fig 13.12 Structure and solubility
 Cyclohexane has no
polar OH groups and is
insoluble in water
 Glucose (which has
hydrogen bonding) is
Solutions
very soluble in water
FACTORS AFFECTING SOLUBILITY
The more similar the intermolecular attractions, the
more likely one substance is to be soluble in
another:
Fig 13.13
Fat-soluble
Water-soluble
Solutions

Solubility of liquids and solids does not change
appreciably with pressure

Solubility of a gas in a liquid is directly proportional
to its pressure
Fig 13.14 Effect of pressure on gas solubility
Solutions
Pressure Effect on Gases in Solution
Henry’s Law:
Sg = kPg
where
• Sg ≡ solubility of the gas
• k ≡ the Henry’s Law
constant for that gas in that
solvent
• Pg ≡ partial pressure of the
gas above the liquid
Fig 13.15 Solubility decreases
as pressure decreases
Temperature Effect on Solids and Liquids
Fig 13.17 Solubilities of several ion compounds
as a function of temperature
• Generally, the solubility
of solid solutes in liquid
solvents increases with
increasing temperature
Temperature Effect on Gases
Fig 13.18 Variation of gas solubility with temperature
• The opposite is true of gases:
•
Carbonated soft drinks are more
“bubbly” if stored in the
refrigerator
• Warm lakes have less O2
dissolved in them than cool lakes
Lake Nyos, West Africa
8/21/86
CO2 Cloud Released
1700 Casualties
•
Earthquake?
•
Landslide?
•
Wind/Rain?
Chemistry In Action: The Killer Lake
Lake Nyos, West Africa