Chapter 3:
Mixtures and
Their Uses
Science 14
Introduction
 Recall:


We have learned that most substances are
mixtures rather than pure substances.
Examples: Salad Dressing, Windex (pg. 43)
Introduction
 What


happens to water in a flood?
It becomes contaminated
Can cause people to become sick from
drinking it
Introduction
 We
can classify water into several
different categories:



Safe water (water you can drink without
getting sick)
Clear water (looks safe but may contain
contaminants that make you sick)
Dirty water (contains silt, sewage and other
debris)
Introduction
 How
can dirty water be
turned into clear water?



Letting solid particles settle to
the bottom
Filtering
Once the dirty water is turned
into clear water, it can then be
treated to make it drinkable.
Introduction
 Dirty
water is a mechanical mixture.
 Clear
water is a solution of water and
other substances.
 Safe
water is also a solution of water and
other minerals.
3.1 Two Kinds of Mixtures
matter
Pure
substance
element
element
compound
mixture
Mechanical
mixture
solution
3.1 Two Kinds of Mixtures
 Mechanical
Mixtures

a mixture in which more than one type of
particle is visible
AKA: Heterogeneous Mixture

Examples:

 Wet
concrete
 Orange juice with pulp
 Sand/gravel
3.1 Two Kinds of Mixtures
 Solutions

A uniform mixture made of
two or more substances
(looks like a pure substance)
AKA: homogeneous mixture

Examples:

 Shampoo
 Pop
 Syrup
3.1 Two Kinds of Mixtures
 Parts



of Solutions
Solute – the substance that dissolves (most
solutions have less solute than solvent)
Solvent - the substance in which the solute
dissolves
Example: salt water
 Solute
– salt
 Solvent - water
 Practice!
 In
each of the following solutions, identify
the solute and solvent(s)



Baking soda and water
air( (78% nitrogen, 22% oxygen and other
gases)
Gold jewelry (90% gold, 10% silver)
Answers

Baking soda (solute) and water (solvent)

air( (78% nitrogen [solvent], 22% oxygen
and other gases [solutes])
Gold jewelry (90% gold [solvent], 10% silver
[solute])

3.1 Two Kinds of Mixtures
 So
what’s the difference between
mechanical mixtures and solutions?
Solutions
Mechanical Mixtures
• appear to contain only one • appear to contain more
substance
than one substance
• may be transparent
• have parts that are easily
• have parts that are not
separated
easily separated
• can be mixed in any
proportion
• have limited solubility
(proportions)
3.1 Two Kind of Mixtures
 How
can we tell the
difference between
mechanical mixtures
and solutions?


Observation – if we can
see more than one
substance then it is
mechanical
Using a filter – if anything
gets caught in the filter
then it is mechanical
Practice Questions
 Hand-in/Email:


Solutions Practice Worksheet
“Check Your Understanding” Questions from
Pg. 44 #1-3
3.2 What Are Solubility and
Concentration?
 Concentration
– describes the amount of
solute in a solution


Manufacturers include the concentration of
the solution on the label of many products
Can be shown in many ways:
 Mass
per unit volume (g/L)
 Percent by mass (% w/w)
 Percent by volume (% v/v)
 Molarity (mol/L)
3.2 What Are Solubility and
Concentration?
1. Mass per unit volume (g/L)
-most common way
-Mass per unit volume is handy when
discussing how soluble a material is in
water or a particular solvent
 Example:


see Figure 3.5 on p. 45
Roundup – solution of glyphosphate and water
Label says the product contains 7.0 g/L
glyphoshpate in 1 L of product
3.2 What are Solubility and
Concentration?

2. Percent by Mass. Also called weight
percent or percent by weight, this is simply
the mass of the solute divided by the total
mass of the solution and multiplied by 100%:

Example: For example, a solution consisting of
30 grams of sodium chloride and 70 grams of
water would be 30% sodium chloride by mass:

(30)/(30+70)*100 = 30%
3.2 What are Solubility and
Concentration?
3. Volume to volume percentage:
 most useful when a liquid - liquid solution is
being prepared (although it is used for
mixtures of gases as well)
 Example: a 40% v/v ethanol solution
contains 40 mL ethanol per 100 mL total
volume
3.2 What are Solubility and
Concentration?
 Also
called volume percent or percent by
volume, this is typically only used for
mixtures of liquids. Percent by volume is
simply the volume of the solute divided by
the sum of the volumes of the other
components multiplied by 100%:
3.2 What are Solubility and
Concentration?
 4.
Molarity: (mol/kg, mol, or m) denotes
the number of moles of solute per
kilogram of solvent (not solution).
3.2 What are Solubility and
Concentration?
 Question:

Explain the meaning of 12g/L.
3.2 What are Solubility and
Concentration?
 Solubility
– how easily a solute will dissolve
in a solvent to make a solution
 When a substance will dissolve in a
solvent, we say that it is soluble.
 If a substance will not dissolve, it is said to
be insoluble.
3.2 What are Solubility and
Concentration?
 Examples:

Rocks have very low solubility in
water
 What
are some other substances that
are insoluble in water?

Sugar is very soluble in water
 What
are some other substances that
are soluble in water?
Investigation:

How Does Temperature Affect Solubility?
 Complete
the investigation on pg. 47
including the analyze and conclude sections
and hand-in/email in your work.
3.2 What are Solubility and
Concentration?
 How


can we increase solubility?
By increasing the temperature
Stirring
3.2 What are Solubility and
Concentration?

How does soap work?



Note that if particles of a solute are attracted to
the particles of a solvent, they will diffuse
throughout the solvent (the solute will dissolve)
Example: oil does not dissolve in water because
the particles of the two substances are not
attracted to each other.
On the other hand, particles of sugar are highly
attracted to particles of water, so the solubility
of sugar is high.
3.2 What are Solubility and
Concentration?
 Soap
will dissolve in both water and oils
because the sodium end of the soap
molecule dissolves in water and the
carbon end dissolves in oils. Cleaning with
soap takes advantage of several
separation techniques.
Practice Questions:
 Hand-in/email
“Check your
understanding” questions from page 50
#3-5.
3.3 Separating Mixtures
 Why
might it be important
to know how to separate
mixtures?


To help prevent illness from
contaminated water
In Canada, drinking water
is generally safe because
several precautions are
taken to make it drinkable
3.3 Separating Mixtures
 There
are several methods to separate
mixtures. These methods range from
simple to complex.
3.3 Separating Mixtures
 Mechanical
separation — One or more
components are picked out of a mixture.
For example, workers in a recycling plant
make piles of different items; magnets
remove metal in a scrap yard. Gold
panning is also a form of mechanical
separation.
 (See “Did You Know” on p. 50)
3.3 Separating Mixtures
 In
the late 1800s, Canadian farmers used
a process called winnowing to separate
wheat kernels from chaff (the wheat
husk). Winnowing involved throwing the
kernels and chaff into the wind. The lighter
chaff was blown away, while the heavier
kernels fell back into the container. This
simple and effective method is still used in
many parts of the world.
3.3 Separating Mixtures
 Settling
— Density causes parts of the
mixture to settle to the bottom. This may
occur naturally as sedimentation, or be
sped up using a centrifuge. During water
filtration, contaminants sink and clear
water is skimmed off.
3.3 Separating Mixtures
 Flotation/coagulation
— Oil, detergents,
or other chemicals are added to a
mixture that is then aerated. This makes
the desired component float (due to
differences in densities) so it can be
skimmed off the surface. The technique is
often used in metal refining and in
separating bitumen (tar) from sand.
Coagulation is also used during water
treatment.
3.3 Separating Mixtures
 Filtration
— A mixture is
passed through material
with many holes.
Anything larger than the
hole is trapped while the
rest of the mixture passes
through.
3.3 Separating Mixtures
 Solvent
extraction — A solvent is used to
dissolve the desired component of the
mixture. For example, soapy water
dissolves the dirt on clothes so the dirt can
be extracted; alcohol dissolves vanilla
from vanilla seedpods, resulting in vanilla
extract.
3.3 Separating Mixtures
 Distillation
— A substance is heated to a
specific temperature to vaporize a
desired component which is then
collected. This method can be used to
desalinate water, extract pure oxygen
from air, and separate the components of
crude oil.
 http://www.footprintsscience.co.uk/index.php?module=2&typ
e=Fractional+distillation&section=Section1
&info=6
3.3 Separating Mixtures


Because different substances evaporate at
different temperatures, the components of a
complex mixture (such as petroleum) can be
evaporated and collected as they condense.
This process of fractional distillation is used to
refine petroleum into fuel for your car, wax for
candles, and asphalt for paving.
In industry, alcohol (such as in liquor and
disinfectants) is distilled in much the same
way. Because ethyl alcohol boils at 78.5ºC, it
can be evaporated and collected, leaving
any water behind.
3.3 Separating Mixtures
 Crystallization
— A dissolved
solid is separated from a
solution by cooling or
concentrating the solution so
the substance forms into
crystals within the solution
(e.g., growing crystals in
sugar water).
 This method is used to
remove salt from salt water.
3.3 Separating Mixtures


Chromatography — This method is
typically used to identify substances
(e.g., in blood, drugs, and petroleum
products) rather than to collect the
substances for other uses.
As the substance is drawn up the
material (usually filter paper), it
carries the solutes with it. The least
dense solutes are drawn farthest up
the filter paper; the most dense are
deposited at lower levels of the
paper.
Compounds and Mixtures
 http://www.bbc.co.uk/bitesize/ks3/scienc
e/chemical_material_behaviour/compou
nds_mixtures/activity/
3.3 Separating Mixtures

Purifying Water
 There
is more than one method to purifying
water.
 Example:
 One method involves adding alum to impure
water.
 Bacteria, viruses, and tiny dirt particles stick to
the alum particles making them very heavy.
 These heavy particles sink to the bottom,
where they can then be separated from the
water.
3.3 Separating Mixtures

Charcoal filters are used to remove
dissolved impurities.

However, the water that leaves the filters is
still not clean and safe to drink.

Water treatment plants add chlorine to
drinking water. The chlorine kills bacteria.

https://www.youtube.com/watch?v=9z14l5
1ISwg
Separating Mixtures
Animations
 http://www.s-
cool.co.uk/gcse/chemistry/atomicstructure/revise-it/separating-mixtures
3.3 Separating Mixtures
 Practice

Questions
Hand-in/Email “Check Your Understanding”
questions on p. 55 #1-4
The End
 Complete
Chapter 2 Assignment
 Review!
 Complete
p. 56 #1-12
Chapter 3 Review on