Mixtures
E. Haniff
Objectives
• Define mixture
• Distinguish between homogeneous and
heterogeneous mixtures
• Distinguish among different types of
mixtures: Solutions, suspensions and
colloids
• List the properties of mixtures and
solutions
• Prepare various mixtures
Introduction
Sodium chloride…(table salt)
Mixture or compound?
Mixtures vs Compounds
Activity
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Sand
Marbles
Container
Spoon
Instruction: Place marbles in container of
sand and gently stir…what have you
created?
Activity
• You have prepared a mixture…
• Mixtures contain two or more materials
physically combined
• Question:
• How does a mixture differ from a
compound?
Answer
• Mixtures are physically combined and can
be separated using physical means
• Compounds are chemically combined and
cannot be physically separated. The
compound does not resemble the
“parents” and melts and boils at a specific
temperature while mixtures do not.
Properties of mixtures
• Mixtures are two or more substances
physically combined
• Mixtures melt and boil over a range of
temperatures
• Properties of mixtures are a combination
of the properties of its components
• Mixtures can be separated using physical
means
Types of mixtures
Mixture
Alloys
Homogeneous
Heterogeneous
Evenly mixed
Unevenly mixed
Solutions
Suspensions,
colloids
Types of mixtures
A Solution is a mixture
Solutions
• A homogeneous mixture containing one or
more solutes dissolved in a solvent
• The solvent is present in the greater
quantity
• Solutions where water is the solvent are
called aqueous solutions
• An alloy is a solution of a metal and
another solid (usually another metal)
Types of solutions
Solute
Gas
Solvent
liquid
Liquid
Liquid
Solid
Liquid
Solid
Solid
Examples
Oxygen in water
Carbon dioxide in fizzy drinks
Alcoholic drinks (alcohol in water)
Gasoline
Sugar in water
Iodine in Ethanol
Alloys eg. Brass, bronze, coinage
metals
Comparing mixtures
Heterogeneous
Homogeneous
Properties of solutions
• Solute and solvent are evenly mixed: all parts of
the solution have the same chemical
composition, chemical properties and physical
properties
• Solute and solvent do not separate when
allowed to stand
• The particles of the solute are not visible, even
under an optical microscope
• The solution may be coloured but is usually
transparent if the solvent is a liquid
• The solute may be separated by purely physical
means
Heterogeneous Mixtures
• Suspensions
• Colloids
Suspensions
Suspensions
• A heterogeneous mixture in which the
solid components do not dissolve, but are
dispersed in the other component
• Eg. Mud water, chalk and water
• Particles settle out when left to stand
• Particles are the largest in size and visible
to the naked eye
• Scatters a beam of light
Colloids
• A heterogeneous mixture in which the
particles do not settle out but are not
dissolved in the solvent.
• Eg. Milk, smoke, clouds
• Particles do not settle out when left standing
• Particles cannot be separated by simple
filtration
• Particles are intermediate in size between
true solutions and suspension.
Comparing Solutions, suspensions and
colloids
• Refer to table 5.4 on page 68 of text
Light scattering
Question…
• Is blood a solution or suspension?
• Justify your answer…
Answer
• Blood is a heterogeneous mixture…but a
microscope is needed to observe the
components
• If blood is spun in a centrifuge chamber,
the solids settle out.
Assessment Activity
• Crossword (for homework)
Solubility
E. Haniff
Objectives
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Distinguish between solute and solvent
Define solubility
Describe the factors that affect solubility
Explain concentration with respect to
solutions
Introduction
• What would happen if we were to place a
small amount of sodium chloride in a glass
of water and stir it?
• Why do the salt crystals seem to
disappear?
• The crystals dissolve and become evenly
distributed throughout the water
Activity
• Mixing of Kool aid
Concentration
• Each glass contains a different amount of
solute in the same quantity of solvent
• Some appear lighter and others darker in
colour
• Concentration is a measure of the amount
of solute that is dissolved in a fixed volume
of solvent
Concentrated solutions
• A saturated solution contains the
maximum amount of solute a solvent can
hold at a particular temperature and
pressure
• A supersaturated solution contains more
solute than the solution can normally hold
at a particular temperature and pressure.
• Seeding of a supersaturated solution can
cause it to throw out excess solute
Concentration
Solubility
• Recall that a solution contains solutes
dissolved in a solvent
Solubility
• The solubility of a solute is the mass in
grams that dissolves in 100 grams of
solvent at a given temperature and
pressure.
• The extent to which a solute dissolves in a
given solvent depends on the nature of the
solute and solvent, the temperature and
the pressure
Factors affecting solubility
• Surface area (crushing increases surface
in contact with solvent)
• Stirring (mechanically brings solvent and
solute into closer contact)
• Heating (increases the movement of
solute particles causing more mixing)
• Nature of solvent and solute
The nature….
• What do we mean by the nature of the
solvent and solute?
• Consider this…
• Salt and water
• Water is polar (has charged ends)
• Salt is a compound containing charged
particles
• The charges are pulled apart by the water
molecules
• We say that “Like dissolves like”
Maybe this will help…
Like dissolves like
• Substances that are charged are
described as polar (eg Water)
• Substances that are not charged are nonpolar (eg. Hexane)
• Charged solutes usually dissolve in polar
solvents (eg salt and water)
• Uncharged solutes usually dissolve in nonpolar solvents (eg Iodine in Bromine liquid)
Water…the universal solvent
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Water is an important solvent because:
It dissolves most substances
It dissolves both acids and alkalis
The chemical reactions needed for life
require water
• Many nutrients required by plants and
animals are taken up by water
Effect of solute on cooling curve
Activity
• Define solubility
• In a solution of salt and water, distinguish
between the solute and solvent
• What are the factors that affect solubility?
• Chalk is made from Calcium carbonate which
is a naturally occurring rock. The rock also
contains sodium chloride as an impurity.
Suggest a method for the purification of chalk
and justify your answer.
Activity 2…
• In an experiment to compare how many
teaspoons of sugar dissolved in samples
of water at different temperatures, the
following results were obtained:
Sample (50 ml)
Temperature of
water
Spoons of sugar
used
A
10 ° C
3
B
60 ° C
6
C
90 ° C
8
Activity 2…
• Predict the number of teaspoons of sugar
that will dissolve in another sample D,
which is at 30 ° C.
Solubility Curves
E. Haniff
Solubility Curves
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Objectives:
Interpret solubility curves
Construct solubility curves from given data
Perform solubility calculations
Solubility
• Remember the definition of solubility?
• Solubility is defined as the amount of solute
that can be dissolved in 100 grams of a
solvent at a given temperature and pressure
• Solubility is usually represented using a
graph called a solubility curve.
• Solubility curves display the change in
solubility of a substance with increasing
temperature.
Solubility curve of some solutes
Interpreting the graph
• The vertical scale (y axis) describes the
solubility in grams per 100 grams of water
• The horizontal scale (x axis) measures the
solubility at different temperatures
What do you notice?
Did you notice a
general trend that as
the temperature
increases the solubility
of the salts increases
as well?
Linking our knowledge
• Remember…
• One of the factors that affects solubility is
the temperature.
• So we expect to see greater solubility as
the temperature increases.
Let’s try this…
Activity
Which salt is the most soluble
at 100 °C?
At approximately what
temperature does Potassium
Nitrate and Sodium Chloride
have the same solubility?
Estimate the solubility of KNO3
at 50 ° C.
If KNO3 was cooled from 100 to
60 ° C approximately how much
solute (in grams) would settle
out?
Which substance is the least
affected by an increase in
temperature?
Activity 2
• Construct a solubility curve given the data
for Copper sulphate
Temperature of water(°C)
Mass of CuSO4 in 100g of H2O
0
15
10
16
20
19
30
24
40
28
50
34
60
40
70
48
80
56
90
66
100
78
Activity 2
• If the solution was cooled from 80 to 30
°C, what mass of copper sulphate would
precipitate out of solution?
Separating
Mixtures
Why is it important?
• Materials contain impurities, may need to
be purified by separation techniques
before being used in manufacture etc.
• Substances are not usually found in a pure
state
Before we decide on a method..
• We need to know what is present
• What phases are the substances in?
• We need to know the nature of the
components of the mixture
• Can one be dissolved?
• Do we need a polar or non-polar solvent?
• Are the particles large enough to filter?
Experiment
• To separate one solid from another and
retrieve the sample as a solid
• We have a mixture of copper sulphate and
sand
Template for report
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Lab report:
Group Members: _____________________________________________________________________
Title: Separation Techniques
Aim: To separate the components of a mixture of copper sulphate and sand (solid from solid)
Theory:________________________________________________________________________________________
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Materials and apparatus
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Method:
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Diagrams/Observations
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Sources of Error
Conclusion and Discussion
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Ideas
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Is sand soluble?
Is coppers sulphate soluble?
What is a good solvent?
Suggest a method to separate the two
Instructions…
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Work in groups
Dissolve the mixture
Filter the mixture
What is your residue?
Where is the copper sulphate?
Suggest a method to retrieve the solid
copper sulphate
Filtration
Filtration…
What’s next?
• The copper sulphate is dissolved in the
water.
• How do we get back the solid copper
sulphate?
Evaporation
• Heat a small quantity of the solution in a
crucible until the water is driven off….
Template for report
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Lab report:
Group Members: _____________________________________________________________________
Title: Separation Techniques
Aim: To separate the components of a mixture of copper sulphate and sand (solid from solid)
Theory:________________________________________________________________________________________
_______________________________________________________________________________________________
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Materials and apparatus
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Method:
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Diagrams/Observations
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Sources of Error
Conclusion and Discussion
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