6.4
Separating Mixtures
Page 148
PRESCRIBED LEARNING OUTCOMES
Time
• classify substances as elements, compounds, and mixtures
45–60 min
KNOWLEDGE
Key Ideas
• matter is anything that has mass and volume; it is generally classified
as pure substances or mixtures
• mixtures have two or more kinds of particles
• mixtures can be classified as solutions, suspensions, or mechanical
mixtures
• mixtures can be separated physically or chemically by removing one of
the components (evaporation, crystallization, filtration, dissolving,
magnetism, flotation)
• solutions are mixtures that appear as a single substance
Mixtures can be classified as
mechanical mixtures,
suspensions, or solutions.
Mixtures can be separated
by a variety of methods.
SKILLS AND ATTITUDES
• demonstrate curiosity, skepticism, creativity, open-mindedness, accuracy,
precision, honesty, and persistence as important scientific attributes
Vocabulary
• dissolve
Program Resources
BLM 6.4-1 Separating the
Ingredients of Instant
Soup Packets
SM 6.4 Separating Mixtures
Nelson Science Probe 7
Web site
www.science.nelson.com
ICT OUTCOMES
• work cooperatively using information technology tools
• synthesize information from a variety of electronic sources for
presentations
• apply the principles of good design when developing electronic documents
• develop interactive hypertext documents for presentations
• produce multimedia presentations
SCIENCE BACKGROUND
• The particle theory explains why
some substances can be separated
by filtration, while others cannot.
Filter paper has many tiny holes or
pores, so it acts like a sieve. Small
solute (the substance dissolved in a
solution) particles are able to pass
through the holes in a filter, while
larger particles, such as those in a
mechanical mixture, are trapped by
the filter paper.
• More expensive filters may consist
of resins or other substances that
attract certain kinds of particles and
provide many spaces for the
particles to become trapped.
Commercial filters usually report
pore size in microns. Each micron is
equivalent to 0.000001 m.
• Filters of many shapes and sizes are
used in both residential and
commercial applications.
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• Biological filtering systems include
nose hairs and mucous membranes.
• Flotation uses the principle of
relative density as a separation
technique. In a mechanical mixture,
for example, a substance that is less
dense than water will float, while a
substance that is denser than water
will sink. The floating substance can
be skimmed off the surface, and the
substance that sinks can be filtered.
• Evaporation can be used to remove a
liquid from a solution, leaving a solid
behind. For example, evaporation of
a salt solution will remove the water
and leave the salt crystals behind.
Evaporation can also be used to
separate two liquids. For example,
the property of boiling point can be
applied to separate a solution of
alcohol and water. Because alcohol
has a lower boiling point than water,
Chapter 6
Matter can be classified.
261
Related Resources
Wertheim, Jane, Chris
Oxlade, and John
Waterhouse. The
Usborne Illustrated
Dictionary of Chemistry.
London, UK: Usborne
Publishing, 2000.
raising the temperature to the boiling
point of alcohol will evaporate the
alcohol but leave the water behind.
The alcohol can be condensed by
collecting the gas and reducing its
temperature, so that it changes back
to the liquid state again. This process
of evaporation and condensation is
referred to as distillation.
• The process of distillation is used in
the refining of crude oil. Different
types of organic compounds in the
crude oil have different boiling points.
The crude oil goes through a series
of evaporation processes (called
fractional distillation), each of which
evaporates a certain fraction of the
oil at a specific temperature. The
evaporated component is then
condensed to change it back to a
liquid state again.
TEACHING NOTES
1 Getting Started
• Check for Misconceptions
– Identify: Students may think that because solutions appear to be
one substance, they cannot be separated.
– Clarify: Remind students that all substances have properties and
characteristics that make them unique. Review these properties with
students (colour, taste, texture, odour, lustre, clarity, magnetic
attraction, freezing point, boiling point, density). Indicate that some
of these properties, especially freezing point, boiling point, and
density, can be applied to separate mixtures that are solutions. For
example, if a solution contains two liquids that have different boiling
points, they can be separated by bringing the mixture to the lower
boiling point. The substance with this boiling point will evaporate,
leaving behind the substance with the higher boiling point. Likewise,
if a solid is dissolved in a liquid, the liquid can be removed by
evaporation, leaving behind the solid that was dissolved.
– Ask What They Think Now: Ask students to think of a mixture
(solution) that can be separated by evaporation or boiling. Ask
them what would be left behind if a sugar solution were allowed to
evaporate.
• Introduce the section by showing students a common household
filter (e.g., a water filter, a furnace or air conditioner filter) and
asking them to explain its purpose.
• Ask students to think of as many uses as possible that people have
for sieves and filters (e.g., baking/cooking, gardening, in clothes
dryers, vacuum cleaners, water purifiers, coffee machines, furnaces,
air conditioners, aquariums, cigarettes, etc.). Have students identify
the mixture that is being separated in these examples.
• Ask students to use Reading and Thinking Strategies: Preview to
predict how many methods of separating mixtures there are.
• Have students assemble in small groups of three to four members.
Assign a separation method to each small group, and have them
summarize the method, identify the principle that it is based on, and
give one or two common examples of its application. Each small
group should then report to the whole class.
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2 Guide the Learning
• Visit each of the small groups. Ensure they are focused on the task.
Encourage students to identify the property of matter that their
method relies on (e.g., flotation uses the property of density, filtering
uses the size of the particles, picking apart relies on the properties
that can be observed with the senses such as colour, texture, etc.).
• Students should come up with a different example of the application
of the method than the one given in the student book.
• For students who need additional support with the reading in this
section, use SM 6.4 Separating Mixtures.
3 Consolidate and Extend
• To wrap up, quickly review each method of separation with the whole
class (dissolving one of the two substances, filtration, attracting one of
the substances to a magnet, floating and/or sinking the parts in water,
evaporating one component, crystallizing one component, distilling a
solution, manual or physical separating by hand).
• Assign the Check Your Understanding questions.
CHECK YOUR UNDERSTANDING — SUGGESTED ANSWERS
1. a) Marbles and foam balls could be manually picked apart based on their size
and shape.
b) Sand and water could be separated using a filter, with the filter catching the
sand particles, or the water could be evaporated from the mixture.
c) Oil and water could be separated using density. Oil floats on water and
could be skimmed off the surface of the water.
d) Salt and pepper could be separated by adding water to the mixture. The salt
would dissolve, leaving the pepper particles in a liquid. The pepper could
then be filtered out of the solution of saltwater. To recover the salt, the
water could be evaporated.
e) Wood chips and pieces of brick could be picked apart based on their size and
shape, or water could be added to the mixture. The wood chips would float
and could be skimmed off the water surface. The pieces of brick could
then be filtered out of the water.
f) Sand and pebbles could be separated by picking apart (depending on the
size of the pebbles), or they could be separated using filtration. A filter
would be needed with pores large enough to let the sand through but small
enough to stop the pebbles.
g) To recover sugar from a sugar-water solution, the water could be evaporated,
leaving sugar crystals behind.
h) Aluminum nails and iron nails could be separated using magnetism. If a
magnet were held over this mixture, the iron nails would be attracted to the
magnet, while the aluminum nails would not.
At Home
Challenge students to
separate other mixtures at
home into different-sized
particles using various
methods. Have students
record their results.
Ensure students ask their
parents or guardians for
permission before
conducting this activity.
BLM 6.4-1 Separating the
Ingredients of Instant
Soup Packets can be sent
home with students to
help with this activity.
2. Student answers may vary. Some examples include a furnace filter that prevents
large particles from entering the heating ducts, an aquarium tank filter that
cleans the tank of impurities, a car air filter that prevents large particles from
entering the engine block, a kitchen strainer or colander that strains water from
vegetables or pasta, and a kitchen sink drain filter that prevents large particles of
food or garbage from entering and blocking the drain.
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Chapter 6
Matter can be classified.
263
LEARNING TIP
Reading and Thinking Strategies: Preview
Before reading this
section, “walk” through it,
looking at the headings.
What ways of separating
mixtures do you think you
will learn about?
Before reading this section, have students “walk”
through it, looking at the headings. Ask students what
ways of separating mixtures they think they will learn
about. Refer to the Learning Tip on page 148. Ask
students how many ways of separating mixtures they
are familiar with. Ask students to explain each of their
answers.
Meeting Individual Needs
Extra Support
• Ensure that students work in mixed-ability groups so they can support
each other with their individual strengths.
• For students who need additional support with the reading in this
section, use SM 6.4 Separating Mixtures.
ESL
• Encourage students to participate. They may require a scribe to note
their observations.
• Demonstrate the process of separating items if necessary. Allow
students to learn and experience vocabulary in context by making their
own mixtures and solutions under direct teacher supervision. If
available, the ESL resource teacher can do this.
• Focus on the pictures in the text to develop appropriate vocabulary for
separation techniques.
Extra Challenge
• Have students research how their municipality purifies water before it
reaches their taps. (Tap water in most places has been purified in a
water-treatment plant. To remove solid particles mixed with the water,
it is passed through sand filters.)
• Have students, on their own or with a partner, select a method of
separation (dissolving one of the two substances, filtration, attracting
one of the substances to a magnet, floating and/or sinking the parts in
water, evaporating one component, crystallizing one component,
distilling a solution, manual or physical separating by hand) and
develop a presentation that will define, explain, and provide examples
and applications of their selected method to the class. Possible
presentation formats could include oral presentations that include a
demonstration, posters, skits, songs, multimedia and/or hypertext
presentations.
ASSESSMENT FOR LEARNING
What To Look For in Student Work
Suggestions for Teaching Students Who Are Having Difficulty
Evidence that students can
• describe and evaluate methods for
separating a mixture
• use technical language correctly (dissolve)
Have students review the section with a resource person. Review vocabulary and
terms in the previous sections. Use examples that are familiar to the students.
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