CHAPTER 14
Solutions
14.1 WHAT ARE
SOLUTIONS?
Complete the graphic organizer: matter, substance, element,
compound, mixture, homogeneous(solution), heterogeneous.
Characteristics of Solutions




Solutions are homogenous mixtures containing two
or more substances called the solute and the solvent.
The solute is the substance that dissolves.
The solvent is the dissolving medium.
Aqueous solutions are water samples containing
dissolved substances.
 Ex)
salt water
Characteristics of Solutions Cont.

Soluble describes a substance that can be dissolved
in a given solvent.
 Opposite:

insoluble
Miscible describes two liquids that are soluble in
each other.
 Opposite:
immiscible
Solutions Exist in ALL States of Matter
Type of Solution
Example
Solvent
Solute
Gas in gas
Air
Nitrogen
Oxygen
Gas in liquid
Soda
Water
Carbon Dioxide
Liquid in liquid
Vinegar
Water
Ethylene glycol
Solid in liquid
Ocean water
Water
Sodium chloride
Solid in solid
Steel
Iron
Carbon
Solvation: “Like Dissolves Like”

Consider what happens when oil is poured into
water.
 one
is polar, one is nonpolar; they separate and don’t
mix (immiscible liquids)


Polar solutes are soluble in polar solvents.
Nonpolar solvents dissolve nonpolar solutes.
Properties of Solutions

Solubility is the amount of solute that will dissolve in
a given amount of solvent
A
saturated solution contains the maximum amount of
solute for a given amount of solvent at a constant
temperature.
 An unsaturated solution contains less solute than a
saturated solution.
 A supersaturated solution contains more than the
maximum amount of solute in a saturated solution (holds
more than it theoretically should)
Musical Chair Saturation Analogy
When it the music stops, 6 kids try to sit in 5 chairs
(supersaturated). The kids are uncomfortable, just as a
supersaturated solution is comparatively unstable.
When the uncomfortable extra kid gets tired of being
squeezed, she stands up and vacates the chairs. This is
analogous to excess solute crystallizing out of a
saturated solution.
Now the solution is saturated, with five kids and five
chairs.
What would an unsaturated situation look like?
Factors affecting solubility



Solids (temperature)
Gases (temperature and pressure)
As a general rule, dissolved solid solutions increase
in solubility as temperature increases, but gases
decrease as temperature increases.
Factors affecting solution process





Stirring
Agitating
Temperature
Particle size
THESE AFFECT RATE NOT AMOUNT
Henry’s Law


Henrys law: S1P2=S2P1
The ratio of solubility of a gas to the pressure is a
constant.
 As
pressure increases, solubility increases.
Practice Problem

If a gas has a solubility of 0.64 g/L at a pressure
of 94.7 kPa, what will its solubility be at 103.5
kPa?
Homework

Solubility Curves Worksheet
14.2 SOLUTION
CONCENTRATION
Molarity

A measure of concentration
 Concentration
is the amount of solute that is dissolved in
a given quantity of solvent while saturation compares
how much is dissolved to what can be dissolved.

Dilute concentration vs Concentrated
Molarity


Molarity is the number of moles of solute dissolved
per liter of solution.
Dilutions with Molarity
Practice Problems


What is the molarity of a solution if 0.400 g
CuSO4 are dissolved in enough water to make
4.00L of solution?
A student needs 250.0 mL of 3.00M HCl. The stock
bottle says 12.0M. How much does she add?
Molality and Mole Fraction


Molality is another unit of concentration and divides
the moles of solute by the kilograms of solvent.
Mole Fraction can be used to figure out how many
moles of a substance are present in a solution.
Practice Problems


If 9.00 g oxalic acid (H2C2O4) are dissolved in
250.0 g of H2O, what is the molality of the solution?
What is the mole fraction of sucrose (C12H22O11) if
125.0g of sucrose are dissolved in 125g of H2O?
Percent Solutions

Percent by volume
 when
both components are liquids, the one with the
largest volume is the solvent

Percent by mass
Practice Problems


What is the percent by volume of ethanol in the
final solution when 85 mL of ethanol is diluted to a
volume of 250 mL with H2O?
How many grams of glucose would you need to
prepare 2.0 L of 2.8% glucose solution?
Homework

Molarity, Molarity by Dilution, and Molality
worksheets
14.3 COLLIGATIVE
PROPERTIES OF SOLUTIONS
Colligative Properties

Colligative properties of a substance change due to
having dissolved materials in it. (dissolved particles
change the properties by “getting in the way”)
 Vapor
pressure lowering
 Boiling point elevation
 Freezing point depression
 Osmotic pressure
Vapor Pressure

Solvent molecules form a shell around the solute,
leaving fewer molecules to vaporize (lowers the
vapor pressure)
Boiling Point Elevation

Additional kinetic energy must be added in order to
raise the lowered vapor pressure of a solution to
atmospheric pressure
Freezing Point Depression


Solute disrupts the formation of a solid (more kinetic
energy must be withdrawn)
Adding salt to sidewalks (ice melts and forms a
solution with a lower freezing point)
Colligative Properties



ΔTb = Kbmi
ΔTf = Kfmi
where i is equal to the number of ions in the
formula for an ionic compound
 K2SO4


i=3 (2 K+ and 1 SO42-)
m is molality
K is a constant for boiling or freezing.
Practice Problems

What are the boiling and freezing points of a
solution made by dissolving 75.0g NaCl in 500.0g
of H2O?
Osmotic Pressure

Osmosis is the diffusion of solvent particles across a
semipermeable membrane from an area of higher solvent
concentration to an area of lower solvent concentration.



Semipermeable membranes are barriers with tiny pores that allow some
but not all kinds of particles to cross.
Example: kidney dialysis, uptake of nutrients by plants.
Osmotic Pressure is the amount of additional pressure caused
by the water molecules that moved into the solution.

Dependent upon the number of solute particles in a given volume of
solution.
Homework

Effect of a Solute on Freezing and Boiling Points
Worksheet
14.4 HETEROGENEOUS
MIXTURES
14.4 Heterogeneous Aqueous Mixtures


Solutions are homogenous mixtures (the same
throughout, extremely small particles).
Colloids have intermediate sized particles that do
not settle out but are too big to be a solution (can
be seen under a microscope).
 Ex.
Paint, gelatin, milk (emulsions are liquid-liquid
colloids)

Suspensions are mixtures from which particles settle
out upon standing (large particles).
 Can
clearly identify two or more substances (muddy
water)
Properties of Colloids


The random movement of colloidal sized particles
which keeps them from settling is called Brownian
Motion.
The scattering of light by colloid or suspension sized
particles is called the Tyndall effect.
 You
can see a beam of light passed through a colloid,
like a sunbeam in a dusty room or headlights through a
fog.