Solutions
•Are homogeneous mixtures
•A physical combination of two or
more substances, that appear to
be only one
• The parts of a solution are referred to as
the solute and the solvent.
• The solute is the part that disappears into
the solvent. (dissolves into the solvent)
• The solvent is the part that does not
disappear.
Types of Solutions
• If you combine the three states of matter
in every possible way, you get 9 types.
Type of solution
example
solute
solvent
Solid in liquid
Tincture
sea water
betadiene
salt
iodine
water
alcohol
Solid in a solid
alloys ( Brass)
Solid in gas
Gas in liquid
or
Or
smoke
Real fine dust
blood
soda
zinc
copper
fine wood
air
CO2
oxygen
water
blood serum
Gas in gas
air
oxygen
Gas in solid
air freshener
Gas mask
odors
tear gas
baking soda
charcoal
alcohol
water
water
air
mercury
silver
Liquid in liquid
vodka
Liquid in gas
humid air
Liquid in solid
amalgam
( Tooth filling )
nitrogen
• Aqueous solutions are ones in which water
is the solvent.
• Tincture is a solution, in which alcohol is
the solvent
• Miscible – liquids that are mutually soluble
in each other. Alcohol and water
• Immiscible – liquids that do not dissolve in
each other. Oil and water
Solubility
• How much of a solute that can dissolve in
a given amount of solvent.
• Normally expressed as grams of solute per
100 grams of solvent. But can be others
• a Saturated solution, Contains the
maximum amount of solute possible.
• Unsaturated does not
• Supersaturated contains more solute than
a normal saturated solution. They are hard
to make and very unstable. The extra
solute precipitates out very easily
The Dissolving Mechanism
• Three things have to happen in order for stuff to
•
•
•
dissolve.
1 The solvent must separate to allow the solute
to enter. ( water moves aside when you jump in)
that requires work, energy.
2 The solute must break apart. (dissociation)
That also requires energy.
3 The solute and solvent must attract each
other. That releases energy
• The combination of those 3 energies
determines if the dissolving mechanism is
endothermic or exothermic.
• Endothermic heat must be added to get it
to dissolve.
• Exothermic will give off heat as it dissolves
• Heat of Solution
• demos would be good.
Factors affecting Solubility
1 Nature of the solute and solvent
are they polar or nonpolar molecules?
polarity is back , look over your old
notes.
likes dissolve likes
polars dissolve other polars,
nonpolar dissolve nonpolar
Solvation ( Hydration)
2 Temperature – an increase in temp will
increase the solubility of substances that
have endothermic dissolving mechanism.
and decrease the solubility of the
exothermic ones.
increase in temp increases the solubility
of most solids in a liquid
you can dissolve more sugar in hot tea
than cold tea.
• You have to be able to read this type of graph and apply the information.
An increase in temp decrease the solubility
of most gases in a liquid.
That why trout die in warm water, there
is not enough oxygen in it.
( Explain in terms of gases dissolving and leaving solution )
3 Pressure
Pressure only affects solutions in which the
solute is a gas.
gas in liquid is most common, more
pressure forces more gas into the solution
That is what causes scuba divers to get the
bends if they come up to fast.
also big fish deep water?
More pressure on the top surface of the liquid causes more
collisions on the top surface, which means more gas goes in than
comes out.
Factors that affect the Rate of
Solubility
• Temperature
• Surface area
• Stirring
• How and why?
• demos
Expressing solution Concectration
• Molarity
• Molality
• Percent by mass
• Normality
• Parts per million
Molarity
Molarity = moles of solute
liter of solution
( Demo use of volumetric flask and the difference between
the two.)
Molality = moles of solute
liters of solvent
Pages 483-484
Percent by mass
Percent by mass = mass of solute X 100
mass of solution
Or mass of solute / mass of solution
times 100
Parts per million is the same as above
except you multiply by 1,000,000
Normality
Normality = gram equivalents
liter of solution
( Explain what a gram equivalent is )
Colligative Properties of solution
colligative properties are properties of a
solvent that are affected by the presence
of a solute.
The properties are affected by the number
of particles not their identity
We will talk about three colligative
properties.
Boiling point
Freezing point
Vapor pressure
The presence of salt in water, will raise the
boiling point and lower the freezing point.
It extends the liquid range in both directions before
there is a phase change
You may ask, how much ?
For boiling - .51°C per mole of solute per liter of solvent
For freezing – 1.86° C per mole of solute per liter of solvent
This is why we put salt on the roads and
anti-freeze in our cars.
How much do we need?
There is math for that!
∆ Tb = Kbm
∆ (delta ) Tb is the change in boiling temp,
Kb is the molal boiling point constant
.51 °C per mole/liter, and m is the molality of
the solution.
∆ Tf = Kfm
∆ (delta ) Tf is the change in freezing temp,
Kf is the molal freezing point constant
1.86°C per mole/liter, and m is the molality
of the solution.
Every solvent has its own Kb and Kf value.
“That’s all folks”