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SOLUTIONS
Solvation, Solubility, and Colligative Properties
PURE SUBSTANCES VS. MIXTURES

Pure Substances- can’t be broken down
without a chemical reaction


Elements and Compounds
Mixtures- can be separated

Heterogeneous- not the same throughout



Suspensions- particles settle
Colloids- particles make “beam” (Tyndall
effect)
Homogeneous- the same throughout

Solutions
SOLUTIONS

Solutions made up of…
Solute- the thing that is dissolved
 Solvent- the substance that the solute is dissolved in
Ex: When making Kool-Aid, the powder is the SOLUTE
and the water is the SOLVENT

WHAT IS HAPPENING WHEN SOMETHING
DISSOLVES?

Polar Solvent & Polar (Ionic) Solute:



Polar ends attract the ions in the solid and pull them
away from the crystal
They become SOLVATED – surrounded by solvent
molecules
If attractions between the ions in the solute are stronger
than the attractions from the solvent, it is
INSOLUBLE

Nonpolar Solvent &
Nonpolar solute
Covalent compounds do
not break up in solutions
like ionic ones do
 Nonpolar- no attractive OR
repulsive forces
 Don’t really “dissolve”,
they mix because of
entropy

SOLUBILITY CURVES

Show the amount of a
solute (g) that can be
dissolved in a certain
amount of solvent (usually
100 g of H2O) at a certain
temperature
Unsaturated solution- can
dissolve more solute (under
line)
 Saturated solution- cannot
hold any more solute at that
temperature (on line)
 Supersaturated- holds more
solute than normal for that
temperature (above line)


Must be heated and cooled
quickly. One seed crystal can
cause crystallization (rock
candy)
PRACTICE PROBLEM

How many grams
of KNO3 should be
added to 250g of
water at 40°C to
make a saturated
solution?
COLLIGATIVE PROPERTIES

Colligative properties are dependent on the
number of particles in a solution
Vapor Pressure Reduction/ Boiling Point Elevation
 Freezing Point Depression

VAPOR PRESSURE REDUCTION AND
BOILING POINT ELEVATION
Vapor Pressure- pressure exerted by vapor of
the liquid in a closed system
 If a solute is added, the vapor pressure is
LOWERED

Dissolved particles at the liquid surface, so less
surface area for the solvent particles to escape
 Results in less solvent in air


Boiling Point Elevation: Because adding a
solute lowers vapor pressure, it takes more
energy to vaporize the particles.
BOILING POINT ELEVATION
FREEZING POINT DEPRESSION
 Freezing
Point Depression: Adding
solute causes the freezing point to be
LOWER
Freezing requires particles to form a crystal
 Solute molecules “get in the way” and prevent
the molecules from freezing (and melting)

FREEZING POINT DEPRESSION
CHANGING COLLIGATIVE PROPERTIES
Colligative properties are changed by adding
solute
 Change is proportional to the number of particles
the solute makes


NaCl would decrease by twice as much as glucose
(C6H12O6) would
glucose= covalent, NaCl= ionic
 Only ionic compounds break up in solution.


MgCl2 (3 particles) would decrease it more than NaCl
(2 particles)