Some more on solutions
Concept map
please use the following words to create a concept
map relating to solutions...
words:
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Solvent
Solute
Solutions
Dissolving
Dynamic equilibrium
Crystalizing
Temperature
Pressure
volume
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Be creative, you have 8
circles and a square to
work with!
Aqueous Solutions
since water dissolves many substances
easily, pure water never exists in nature
 water can dissolve other polar molecules and
ions
 water containing dissolved substances are
called aqueous solutions
 the dissolving medium is the solvent (what
does the dissolving) *usually H20
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Cont'd
the dissolved particles are solute (what
dissolves)
 examples:
 sodium chloride (salt)  NaCl
(s)
 sodium chloride dissolved in water  NaCl
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(aq)
solutions are homogeneous mixtures and are
stable
Cont'd
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solute particles may be ionic or molecular.
They are usually polar, because non-polar
molecules will not dissolve in water.
However, solute particles will dissolve in
other solvents. Ex. Grease in gasoline
Solvation
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Water molecules, in continuous motion,
collide with the solute particles placed in it.
As a result, solvent molecules attract the
solute particles causing the individual
particles to break away from each other. This
causes the crystal structure to break down
and dissolving occurs.
more
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particles become solvated ie. Surrounded by
solvent molecules, due to attractions
between the solute and solvent particles
if the attractive forces between the particles
in the crystal are greater than those with
water the particles cannot be solvated –
these compounds are insoluble in water eg.
Barium sulphate or calcium carbonate
continued
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nonpolar solvents such as gasoline will
dissolve in non-polar compounds not
because of attractive forces, but rather due to
the lack of repulsion between the solvent and
solute molecules
General rule – Like Dissolves Like!
Solution Formation
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Four factors affect the rate at which a solute
dissolves:
1. Temperature (heat)
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2. Agitation (stirring)
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3. Particle Size
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4. Nature of the particle (solubility)
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Temperature affects the amount of solute that
can dissolve
Stirring, particle size, and temp affect the rate
at which the solute will dissolve
example
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When 36 g of sodium chloride are added to
100g of water at 25º C, all the sodium
chloride will dissolve. However, if one more
gram of salt is added it will not dissolve no
matter how vigorously it is stirred. Since
water particles are in continuous motion they
must collide with, and solvate, the solute
particles
explained..
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The explanation:
Particles are bombarded by water molecules.
The water will release one particle as it
collides with another. In turn, the water
molecules pick up the new particle.
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There is no net change in the overall system
as particles move from solution to solid and
back again.
A state of dynamic equilibrium exists
between the solution and the undissolved
solute.
 It's like stuffing people in the gymnasium,
people out = people in... this is dynamic
equilibrium
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The sodium chloride solution is said to be
saturated
A saturated solution contains:
The maximum amount of solute that
dissolves in a given quantity of a solvent at a
given temp
An unsaturated solution contains:
Less solute than a saturated solution
Solubility
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This is the maximum amount of solute that
can dissolve in a particular volume of solvent
at a particular pressure and temperature
solute is expressed in grams of solute/100
mL of solvent
every pure substance has its unique
solubility
Solubility ranking
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Solubility Table: a reference for how ionic
compounds will behave when added to water
- based on the cut off points between very
soluble (0.1>mol/L ) to slightly soluble (< 0.1
mol/L)
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Comparing the Solubility of Different
Phases of Matter (in an aqueous
environment)
Solids as a rule..
Solubility of Solids
 Have higher solubility in water at higher
temperatures
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Gases as a rule...
Solubility of Gases
 Have higher solubility in water at lower
temperatures (opposite that of solids)
 Have higher solubility in water at higher
pressures
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Liquids as a rule...
Solubility of Liquids
 For polar liquids, the solubility usually
increases with temperature
 Mostly non-polar liquids, do not dissolve in
water to any appreciable extent but form a
separate layer. Liquids that behave in this
way are said to be immiscible
 Examples:
 Olive oil and water
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sometimes...
Some liquids (such as those containing
small polar molecules with hydrogen bonding
(methanol for example), dissolve completely
in water (never become saturated) and are
said to be miscible
Examples:
Ethanol and soda pop
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Elements as a rule...
Elements
 Generally have low solubility in water
 Halogens and oxygen dissolve in water to
only a very tiny extent but they are so
reactive that even in tiny concentrations, they
are often very important in solution reactions
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check
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Based on our knowledge of solution
formation and solubility,
What happens when the temperature of a
saturated solution is raised? Can we add
more solute or will excess solute become
undissolved?
answer
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We can add excess solute to the solution and
it will dissolve
From last week...
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What is a supersaturated solution?
answer...
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A solution which contains more solute than it
can theoretically hold
Ex: Perrier or beer (CO2 in water)
crystallization..
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Crystallization can be initiated in a
supersaturated solution:
A supersaturated solution has more solute
than a saturated solution, and yet the solute
is able to remain in solution. It is UNSTABLE.
If a few crystals of solute are added to serve
as particles on which crystallization can
occur, the excess solute crystallizes quickly.
Practice Questions
Give examples of two liquids that are
immiscible and two that are miscible with
water.
 Can more oxygen dissolve in a litre of water in
a cold stream or a litre of water in a warm
lake? Include your reasoning.
 State why you think clothes might be easier to
clean in hot water.
 Why do carbonated beverages go “flat” when
opened and left at room temperature and
pressure?
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a) The solubility of oxygen in blood is much
greater than its solubility in pure water.
Suggest a reason for this observation.
b) If the solubility of oxygen in blood were the
same as in pure water, how would your life
be different?
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c) Is there an advantage for animals that are
cold blooded? Explain briefly.
For any solute, what important condition
must be stated in order to report the solubility
problem...
1. In a chemical analysis experiment, a
student notices that a precipitate has formed,
and separates this precipitate by filtration. The
collected liquid filtrate, which contains aqueous
sodium bromide, is set aside in an open beaker.
Several days later, some white solid is visible
along the top edges of the liquid and at the
bottom of the beaker.
What does the presence of the solid indicate
about the nature of the solution?
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equlibrium
Write a brief theoretical explanation for
this equilibrium mixture.
State two different ways to convert the
mixture of the solid and solution into a
homogeneous mixture.
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Fishy thinking...
Different species of fish are adapted to live in
different habitats. Some, such as carp, can
survive perfectly well in relatively warm, still
water. Others, such as brook trout, need cold,
fast-flowing streams, and will die if moved to he
carp’s habitat.
Describe and explain the oxygen conditions in
the two habitats.
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More fish
Hypothesize about the oxygen requirements of
the two species of fish.
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