Content Benchmark P.12.A.3
Students know identifiable properties can be used to separate mixtures. E/S
All of our daily activities involve recognizing, evaluating and using physical properties. From
selecting the clothes we wear to the food we eat, we are using, evaluating and sorting based on
physical properties. If it is warm outside, we select lighter colored, and lighter weight clothing
rather than dark, heavy, wool type materials. We intuitively evaluate the insulating properties of
the clothes as well as the interaction of the clothing fibers with the energy of the sun. Similarly,
we select our foods the same way evaluating color, texture, smell and freshness. We are not apt
to select foods to eat that are beginning to rot. We bring our childhood experiences of knowing
that some materials are repelled by magnets while some are attracted and others do nothing at all.
We also learn early that metal containers become hot when warm liquids are poured into them
while as other materials to a lesser degree. We know that metals tend to be shiny and warm up
in the sun while non-metallic materials do not have the shiny quality. Physical properties are part
of our everyday experience.
Physical properties are characteristics of a material that can be measured. They are properties
that do not change the chemical nature of matter. Some physical properties vary with the amount
of the material such as volume, size, and mass. These physical properties are called extensive
physical properties. Some properties do not change with the amount of the material and allow the
material to be categorized and identified. These properties are called intensive physical
properties and can include such characteristics color, odor, density, boiling point, melting point.
For more information about properties, please see
http://www.iun.edu/~cpanhd/C101webnotes/matter-and-energy/properties.html,
and to learn more about the distinction between extensive and intensive properties, go to
http://antoine.frostburg.edu/chem/senese/101/matter/faq/extensive-intensive.shtml
Physical properties are important to understand when trying to separate mixtures. There are two
types of mixtures that scientists considered: homogeneous and heterogeneous. This content
standard focuses on heterogeneous mixtures and the uses of physical properties to separate them.
Heterogeneous mixtures are composed of different substances (compounds or elements) that
remain separate and distinct. A very common example used in physical science classrooms is a
mixture of sulfur and iron filings. Using the magnetic property of iron, a simple magnet will pull
the iron filings away from the sulfur and the mixture has been separated.
For more information about heterogeneous mixtures please see,
http://antoine.frostburg.edu/chem/senese/101/matter/faq/what-is-heterogeneous.shtml
and
http://www.usoe.k12.ut.us/curr/science/sciber00/8th/matter/sciber/matter.htm
Examples of Separation Techniques
An excellent presentation which covers the most widely used separation techniques and their
practical uses can be found at the following website.
http://www.iupac.org/didac/Didac%20Eng/Didac05/Content/Separation%20Technigues.htm
Figure 1. Examples of separation of solid-solid mixtures. (from
http://www.iupac.org/didac/Didac%20Eng/Didac05/Content/ST02.htm)
For example, these M&M’s can be separated based on their color differences.
Figure 2. Color differences in candy can be used as an
analogy for separating solid-solid mixtures. (from
http://f.hatena.ne.jp/images/fotolife/J/Jehoshaphat/2
0060208/20060208233237.jpg)
Figure 3.This columns contain oil and water and can be
separated based on the density differences between the two
different liquids. (from
http://www.unis.no/research/technology/Environmental/en
v_research.htm)
Figure 4. Filtration is another method to
separate a solid from a liquid (from
http://phys.free.fr/images/filtrani.gif)
One interesting heterogeneous mixture is iron fortified cereal. The iron can be removed by
mixing the cereal with water and then using a magnet to extract the iron.
Figure 5. Lab setup to separate solids from liquids using
magnetism (from
http://www.colorado.edu/chem/genchem/demoman/Photos/To
tal1.jpg)
Liquids can be separated from one another using a method known as distillation which is based
upon the differences in the boiling points of the substances.
Figure 6. A distillation apparatus (from
http://www.chemheritage.org/EducationalService
s/pharm/antibiot/activity/distil.htm)
For more information on distillation please see,
http://www.chemheritage.org/EducationalServices/pharm/antibiot/activity/distil.htm.
Content Benchmark P.12.A.3
Students know identifiable properties can be used to separate mixtures. E/S
Common misconceptions associated with this benchmark.
1. Students incorrectly think that “pure” substances mean without “harmful” components
and many don’t recognize that pure substances mean unmixed substances.
It is important to separate experiential misconceptions from instructional misconceptions.
Misunderstandings about the word “pure” can lead to much confusion. Inquiry activities
designed to examine and provide evidence for conceptual understandings would lead to the
dissolution of many of the above student notions. The students understand “pure” in terms of
clean or without contamination. When defining an element, it is important to emphasize that an
element is composed of one type of atom with its own set of properties. Additionally, some
things look like “pure” substances to students but rather are often mixtures with multiple sets of
properties. Assessing students prior to instruction will help guide the instructional activities.
To learn more about common misconceptions about science, go to
http://www.amasci.com/miscon/opphys.html
2. Students incorrectly believe that particles possess the same properties as the materials
they compose.
Molecules, atoms, and subatomic particles make up all materials. Many students think that these
particles have the same identifiable properties on the microscopic scale that do on larger,
macroscopic scale. For example, students incorrectly think that atoms of copper are "orange and
shiny", gas molecules are transparent, and solid molecules are hard.
To learn more about student misconceptions in chemistry go to
http://educ.queensu.ca/~science/main/concept/chem/c07/C07CDTL1.htm
Content Benchmark P.12.A.3
Students know identifiable properties can be used to separate mixtures. E/S
Sample Test Questions
1. Which of the following is considered to be a pure substance?
a. granite
b. sodium chloride
c. muddy water
d. a medicine that says “shake” before using
2. Physical properties are associated with
a. The atomic structure of the substance.
b. The amount of substance.
c. The volume of the substance.
d. The number of protons present in the nucleus.
3. A student has three unknown metals. Which series of tests would be the most appropriate
to use to distinguish among the metals?
a. Solubility point, density and color
b. Color, density and mass
c. Density, mass and volume
d. Conductivity, density and color
4. Filtration can be used to separate
a. solids from solids
b. liquids from solids
c. liquids from liquids
d. liquids from gases
5. A student has a mixture of sand, water, salt and iron pieces. Which procedure would
separate the mixture?
a. Evaporate the water to separate the sand and salt, use a magnet to remove the
iron, and freeze the remaining sand and salt to isolate the salt crystals.
b. Filter the water to separate the sand, use a magnet to remove the iron, and freeze
the water to isolate the salt crystals.
c. Filter the sand and iron from the water, use a magnet to remove the iron from the
sand, and distill the water to separate the salt.
d. Use a magnet to remove the sand, filter the remaining iron from the water, and
then distill the water to separate the salt.
6. Examples of physical properties that depend on the quantity of a substance include
a. boiling point, color
b. color, density
c. melting point, solubility
d. volume, mass
Content Benchmark P.12.A.3
Students know identifiable properties can be used to separate mixtures. E/S
Answers to Sample Test Questions
1.
2.
3.
4.
5.
6.
(b)
(a)
(d)
(b)
(c)
(d)
Content Benchmark P.12.A.3
Students know identifiable properties can be used to separate mixtures. E/S
Intervention Strategies and Resources
The following list of intervention strategies and resources will facilitate student understanding of
this benchmark.
1. Mixtures and Solutions Information Clearinghouse
The Science, Technology, and Children Web site has a section that covers mixtures and
solutions. This site is a clearinghouse that lists many educational and professional
organizations that discuss mixtures in detail. This site is an excellent resource for student
research into mixtures.
To access the mixtures and solutions site, to
http://www.stcms.si.edu/pom/pom_student_pt2.htm
2. Mixture Basics
Rader’s chem4kids.com site has two sections that discuss mixtures. This site includes
general information with a True-False quiz that students can use to check their
knowledge.
To access the chem4kids.com mixture site, go to
http://www.chem4kids.com/files/matter_intro.html
3. Physical Properties Lesson
The American Chemical Society has developed a lesson that allows students to explore
the physical properties of matter. This lesson can be downloaded at
http://www.chemistry.org/portal/resources/ACS/ACSContent/education/wande/resourcec
hem/matter/Matter_Act_2.pdf
4. Chemistry Activities Listing
Lapeer County, Michigan has an excellent site serving as a Science Resource Center.
Their chemistry activities listing includes demonstrations, labs, and teaching tips. This
site has been acknowledged by the National Science Teachers Association as SciLinks
site.
You can check out the site at http://chem.lapeer.org/Chem1Docs/Index.php
5. Chemistry Activities and PowerPoint Presentations
Mr. Allan, a science teacher at El Diamante High School in Visalia, California, has
created a site that with a large variety of activities, PowerPoint presentation, and other
resources. The site is located at http://www.sciencegeek.net/Chemistry/index.shtml