2. Solution
Solutions are homogeneous mixtures of two or more pure
substances.
In a solution, the solute is dispersed uniformly throughout the
solvent.
A homogenous mixture of a solute dissolved in a solvent.
The solubility (ability to dissolve) of a solute in a solvent is
dependent on the
a. Temperature
For solid solutes
as temperature increases, solubility increases.
For gas solutes
:as temperature increases, solubility decreases.
3. b. Pressure
For solid solutes
as pressure increases, solubility remains the same.
For gas solutes:
as pressure increases, solubility increases
c. Nature of Solute/Solvent
“Like dissolves in like.”
Solute Type Non Polar Solvent Polar Solvent
Non Polar (Fat Grease) Soluble (Soap) Insoluble (Water)
Polar Insoluble Soluble (Water)
Ionic (Salt) Insoluble Soluble (Water)
High Solubility-Soluble Low Solubility-insoluble
4. Solubility
Maximum grams of solute that will dissolve in 100 g of solvent at
a given temperature.
Solubility=
Varies with temperature
Based on a saturated solution
Gram of solute
100 g of Water
The bond between solubility and
temperature can be expressed by a
solubility curve. The solubility curves
of several compounds are shown on
the right. Such curves disclose the
maximum amount of solute that can
be dissolved in 100 grams of water
over a range of temperatures.
The solubility of most compounds
increases as temperature increases,
although exceptions do exist.
5. Types of Solution1. An unsaturated solution is a solution in which more solute can
be dissolved at a given temperature.
2. A saturated solution is a solution containing the maximum
amount of solute that will dissolve at a given temperature.
3. A supersaturated solution is a solution that contains more solute
than would dissolve in a saturated solution at a given
temperature.
SATURATED SOLUTION
no more solute dissolves
UNSATURATED SOLUTION
more solute dissolves
SUPERSATURATED SOLUTION
becomes unstable, crystals form
increasing concentration
6. Saturated
Solvent holds as much solute as is possible at that
temperature.
Dissolved solute is in dynamic equilibrium with
solid solute particles.
Types of Solution
Unsaturated
Less than the maximum amount of solute for that temperature is
dissolved in the solvent.
Saturated
Supersaturated
Solvent holds more solute than is normally possible at that
temperature.
These solutions are unstable; crystallization can usually be stimulated
by adding a “seed crystal” or scratching the side of the flask.
7. Solubility Rules
1. Not all ionic compounds are water soluble.
2. There are some general rules for compounds that are water
soluble:
Group 1 ionic compounds and ammonium (NH4+) are always
water soluble
Group 17 ionic compounds are water soluble except when paired
with Ag, Pb, and Hg ions
1. A salt is soluble in water if it contains any one of the following
ions:
NH4
+ Li+ Na+ K+ or NO3
-
Examples: Soluble salts
LiCl Na2SO4 KBr Ca(NO3)2
8. Solubility Rules
2. Salts with Cl- are soluble, but not if the positive ion is :
Ag+, Pb2+, or Hg2
2+.
Examples:
Soluble Insoluble
MgCl2 AgCl , PbCl2
3. Salts with SO4
2- are soluble, but not if the positive ion is Ba2+,
Pb2+, Hg2+ or Ca2+.
Examples:
Soluble Not soluble
MgSO4 BaSO4 PbSO4
9. The stronger the attraction between solute and solvent
molecules, the greater the solubility.
Like dissolves like (the substances have similar
intermolecular attractive forces.)
Polar substances tend to dissolve in polar solvents. Non-polar
substances do not dissolve in polar solvents.
Factors Affecting Solubility
10. Chemists use the axiom “like dissolves like”:
Polar substances tend to dissolve in polar solvents.
Nonpolar substances tend to dissolve in nonpolar solvents.
Factors Affecting Solubility
The more
similar the
intermolecular
attractions, the
more likely one
substance is to be
soluble in another.
11. Glucose (which
has hydrogen
bonding) is very
soluble in
water, while
cyclohexane
(which only has
dispersion
forces) is not.
Factors Affecting Solubility
12. Vitamin A is soluble in nonpolar compounds (like fats).
Vitamin C is soluble in water.
Factors Affecting Solubility
13. Concentration
Concentration of a solution can be expressed either quantitatively
or qualitatively (dilute or concentrated).
Methods of Expressing Concentrations of Solutions
Mass Percentage
Mass percentage is expressed using the equation:
Mass % of component = X
Mass of component in solution
Total mass of solution 100
Parts per Million (ppm)
ppm =
mass of A in solution
total mass of solution
106
Parts per Billion (ppb)
ppb =
mass of A in solution
total mass of solution
109
14. Mole Fraction
This is how many moles of substance are in the solution.
Mole fraction of component =
Moles of component
Total moles of all components
Molarity
Relates the volume of solution to the quantity of solute that it
contains.
Molarity =
Moles solute
Liters solution
Molality(m)
mol of solute
kg of solventm =
Because both moles and mass do not change with temperature,
molality (unlike molarity) is not temperature dependent.
15. Changing Molarity to Molality
If we know the density of the
solution, we can calculate the
molality from the molarity,
and vice versa.
16. Raoult’s Law
Psoln = Vapor pressure of the solution
solvent = Mole fraction of the solvent
P solvent = Vapor pressure of the pure solvent
The presence of a nonvolatile solute lowers the vapor pressure
of a solvent.
Psoln = solventP solvent
The presence of a
nonvolatile solute
lowers the
concentration of solvent
molecules in the
solution, thus lowering
the vapor pressure.
Demonstration of Raoult’s Law
17. Water is transported to the
solution due to difference in
vapor pressure.
An Aqueous Solution and Pure
Water in a Closed Environment
Demonstration of Raoult’s Law
18. Psoln = solventP solvent
Vapor Pressure of a Solution
Containing a Nonvolatile Solute
Ideal solutions
• obey Raoult’s law exactly
• solute-solute, solvent-
solvent, and solute-solvent
interactions are identical
• do not exist
Real Solutions
• are nonideal
• may approach ideal behavior
if solute and solvent are
similar
• Example: sucrose in water
19. Vapor Pressure of an Ideal Solution
Two Volatile Solvents
Ptotal = PA + PB = XAPA
0 + XBPB
0
20. Raoult’s Law Vapor Pressure for a Solution
of Two Volatile Liquids
IDEAL
SOLUTION
NONIDEAL SOLUTIONS
Positive
Deviation
Negative
Deviation
21. Colligative Properties
Depend only on the number, not on the identity, of the
solute particles in an ideal solution.
Boiling point elevation
Freezing point depression
Osmotic pressure
Boiling Point Elevation
Kb = Molal boiling point elevation constant
m = Molality of the solute
A nonvolatile solute elevates the boiling point of the solvent.
T = Kbmsolute
22. Freezing Point Depression
Kf = Molal freezing point depression
constant
m = Molality of the solute
A nonvolatile solute depresses the freezing point of the solvent.
T = Kfmsolute
Phase Diagram for an Aqueous Solution
In effect, a dissolved
solute acts to extend
the liquid range of
the solvent
24. Colligative Properties of Electrolyte Solutions
T = imK
= iMRT
i =
moles of particles in solution
moles of solute dissolved
van’t Hoff factor, “i”, relates to the number of ions per formula
unit.
NaCl = 2, K2SO4 = 3
Data for 0.05 m Solutions
Electrolyte i (expected) i (observed)
NaCl 2.0 1.9
MgCl2 3.0 2.7
FeCl3 4.0 3.4
25. Osmosis
Some substances form semipermeable membranes, allowing
some smaller particles to pass through, but blocking other
larger particles.
In biological systems, most semipermeable membranes allow
water to pass through, but solutes are not free to do so.
26. In osmosis, there is net movement of solvent from the area of
higher solvent concentration (lower solute concentration) to
the are of lower solvent concentration (higher solute
concentration).
Osmosis
• The pressure required to stop osmosis, known as
osmotic pressure, , is
where M is the molarity of the solution
If the osmotic pressure is the same on both sides of a membrane
(i.e., the concentrations are the same), the solutions are isotonic
n
V
= ( )RT = MRT
Osmotic Pressure
27. Colloids Colloids are particles that are large on the molecular scale but still
small enough to remain suspended indefinitely in a solvent system.
(aka colloidal dispersions.)
They are intermediate between solutions and heterogeneous
mixtures.
They have the ability to scatter light; known as the Tyndall effect.
Hydrophilic and Hydrophobic Colloids
The most important colloids are those in which water is the
solvent, or dispersing agent.
Hydrophilic colloids are water loving and are found in the
human body and help keep molecules suspended in water.
(enzymes, antibodies)
Hydrophobic colloids are water fearing and must be stabilized
before they can be mixed into water. (droplets of oil.)
28. Colloids in Biological Systems
Some molecules have a
polar, hydrophilic (water-
loving) end and a
nonpolar, hydrophobic
(water-hating) end.
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