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					                        GK12 Module Teacher’s Guide




                  Mixtures, Solutions, Compounds and Separations
                              by: William J. Leggett

Abstract:

This module introduces the students to the unique properties of mixtures and
introduces them to four distinct methods for physically separating mixtures into
their individual components. This process should refine students’ concept of
mixtures, compounds, solutions, filtration, and evaporation. Additionally, it allows
them to practice direct and indirect methods of measuring mass.

Grade Level(s):           8th

Objectives:

1. Refine students’ understanding of the difference between a mixture, a solution
and a compound.

2. Introduce students to a variety of physical separation methods (screening,
filtration, magnetic and evaporation).

3. Give students an opportunity to measure mass both through direct (measuring
with a scale) and indirect (measuring through mathematical deduction) methods.

National Standards:
Standard A: Science as Inquiry; Abilities necessary to do scientific inquiry
Standard A: Science as Inquiry; Understandings about scientific inquiry
Standard B: Physical Science; Properties and changes of properties in matter



New Mexico Standards:
Strand 1, Standard 1: Scientific Thinking and Practice; Understand process of
scientific investigation




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                        GK12 Module Teacher’s Guide




Strand 1, Standard 1: Scientific Thinking and Practice; Use mathematical ideas,
tools, techniques
Strand 2, Standard 1: Physical Science; Forms and properties of matter



Materials:
Gravel                    *Sand
Salt                      Iron Filings
Water                     Screens
Coffee Filters            Plastic cups (16 oz)
Triple beam scales        Plastic spoons
Plastic Tub or Bucket     Plastic wrap
Rubber bands

*Make sure you get sand that is fine enough to pass through the screen but not
the filters!
**One set of cups will be needed for each group. In each set, you should have a cup
for the original compound and each separate (i.e. gravel, sand, iron filings and
salt/evaporites).

Background:

Every type of matter we come in contact with (including ourselves) can be
classified as a certain type of combination of elements: compounds, mixtures or
solutions. Each of these has its own particular set of properties or qualifications
that makes it unique. A commonality between the three is that they are
characterized by the combination of more than one element. Another common
aspect is that each of these can be subjected to processes which reduce them to
their basic components (or elements). Knowing the differences between
compounds, solutions and mixtures is a key concept in understanding the basic
principles of chemistry. It is equally important to know how to characterize the
properties of each, based on the elements of which they are composed, and to
know how easily they can be separated into their basic components.




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                        GK12 Module Teacher’s Guide




      This module will give students a chance to work with compounds, solutions
and mixtures and fortify their understanding of their properties by dissolving and
mixing various compounds and separating them back out again.

Procedures:

Part I:

Pre-Lab:

The students will work in groups of three or four during the activity. If possible,
distribute a set of materials to each of the work areas in advance.

Each work area should have:

6 Plastic Cups                          Mixed Sand & Iron Filings (~2:1)
Gravel                                  1 Plastic Spoon
Salt                                    Triple Beam Balance
1 Magnet

1. Divide the students up into groups of 3 or 4. Distribute worksheets to each
student.

2. The first thing they will need to do is read the instructions. The worksheets are
designed to guide them through the procedures as a group. It may be best to go
through each step as a class. This guarantees that each group finishes each part
together.

3. Their first task will be to create their mixture. Make sure they understand that
the cup holding the mixture should not be included in the mixture’s mass. This
means that they will need to measure and note the mass of the empty cup before
combining the mixture.

4. Each student will first fill their cups approximately 1/3 full with water.


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                         GK12 Module Teacher’s Guide




5. The first thing they will mix with the water is two spoonfuls of salt. However,
before they mix it they need to measure and record the mass of the salt. Once
they have done this, have them mix the salt into the water and stir until all of the
salt is dissolved.

6. The students will then need to measure out two spoonfuls of the sand & iron
filing mixture. They will need to weigh individually the sand and the filings. This will
require them to separate out the iron from the sand with the magnets. The
worksheet hints at how they can do this easily. However, they should be able to
figure out that the magnet will be the best tool for this. Help them out with ideas
toward this end, but try not to give away the answer. They should arrive at their
method through inquiry and discussion.

Once they have extracted the filings from the sand, make sure they measure the
mass of each. Once they have done this, they will dump each into their salt water
solution.

7. The final addition to their mixture will be the gravel. Have them measure out
and weigh two spoonfuls of gravel. Once this is done, have them add the gravel to
the salt water & sand mixture.

8. This is generally a good stopping point. If you decide to do so, have the students
label the cup containing their mixture and set it aside in a safe place. It is
important that, at this stage, none of the water is allowed to evaporate. So, have
them cover their mixture cup with a sheet of plastic and secure it with a rubber
band.




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                        GK12 Module Teacher’s Guide




Part II:

Each work area should have:

6 Plastic Cups                         *4 Coffee Filters
1 Screen (coarse)                      Triple Beam Balance
1 Plastic Spoon                         Rubber bands (~5 to 10)

*You may want to try out various filters. Sometimes coffee filters are so fine as to
make filtration a painfully slow process (especially for 8th graders!!). If time is a
factor, you may want to substitute a fine-mesh screen or other type of filter for
separating the sand & iron filings from the salt water solution.

9. The students will now have to devise a method for separating out each of the
components they added to form their mixtures. Ideally, they should try and
separate out the gravel first and the sand/iron granules second.

They will need to reweigh each of the components after they separate them from
the mixture. This will allow them to test the effectiveness of their separation
methods.

If they have trouble figuring out how to physically separate the gravel and
sand/iron out of the mixture, direct them toward the screen (gravel) and coffee
filters (sand) as possible tools. The worksheets will provide spaces for them to
record changes in the mass of the sand/iron and gravel they separate out, if there
are changes from their pre-mixing mass values.

10. They should be able to easily separate out the gravel. The only problem they
may have is keeping the sand/iron from sticking to the pieces of gravel. They need
to understand that no water can be lost!! As such, if they re-rinse the gravel over
the screen, make sure they do not mix any fresh water into the salt water solution.

There are a number of ways to avoid this problem. Either have them rinse only with
the salt water, or make sure they set the salt water aside and keep the fresh rinse


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                         GK12 Module Teacher’s Guide




separate. Keep in mind that the latter will necessitate additional separation of the
sand/iron from both the salt water and the newly introduced fresh rinse. The
important thing is that they retain and reserve as much of the original salt water
and sand/iron as possible.

Once they have the gravel effectively separated, have them measure its mass.

11. The next step is for them to devise a method to separate the iron and sand
from each other, as well as separating the salt from the water. This is where
evaporation (and some down time) comes in!

In order for the students to separate the iron from the sand, they will need for
the iron/sand mixture to be dry. After the students have used the coffee filters
to separate the iron/sand, have them label and set the filters (with the sand/iron
goop) aside in a safe place. Once the filter/sand/iron are dry, the students should
be able to easily separate out any iron that has not oxidized.

Separating the salt from the water will require a similar process of setting aside
the salt water solution they have left over from the gravel and sand/iron
separations. This will require them to set the cups containing the salt water
solution aside (uncovered!) long enough for all of the water to evaporate. This may
be problematic as far as time is concerned. You will either need to provide enough
time to pass before continuing, or devise a way to accelerate the evaporation
process (eg. beaker and Bunsen burner). The most important thing to keep in mind
is that the students have a way to effectively measure the mass of the salt once
the water is evaporated off.



This, naturally, is a good place to stop.




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                        GK12 Module Teacher’s Guide




Part III:

Each work area should have:

6 Plastic Cups                   1 Magnet
1 Plastic Spoon                  Triple Beam Balance

12. At the beginning of this part, the students should have a cup containing salt
residue and a filter with a sand/iron/rust crust attached to it.

13. Have them measure the mass of the salt first. This should be easily done by
subtracting the mass of the cup from the total mass of the cup and salt residue.
They will have a place to record their measurements on the worksheet.

14. If everything has gone right, the students should have a filter with an orange,
gritty clump stuck to it. What the students have to do now is get that
sand/iron/rust clump separated from the filter.

In order to separate the sand from the iron, the students will need to crush the
clump back into a coarse, sandy consistency. Once this is done, they should be able
to separate out whatever iron is left with a magnet and weigh each separate.

By now, the students will have noticed that much of the iron has been oxidized to
rust. Due to the fact that rust is not magnetic, it will end up primarily in the sand
separate. This will result in the final mass of the sand being slightly greater than
its initial mass and vice-versa for whatever iron they are able to separate out with
the magnet. This is one factor of the activity that the students will have to
consider and explain in their worksheets.

It is also possible that some of the salt from the final salt water solution separate
will have stayed with the water that was stuck to the gravel or sand/iron mixture,
resulting in a decrease in their final salt versus initial salt mass.




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                        GK12 Module Teacher’s Guide




15. This concludes the hands-on analytical part of the module. Once the students
have recorded all their data, have them clean up their work areas. Their worksheet
will guide them through analysis of their data and give them a few questions to
think about regarding their results.




Conclusions:

At the conclusion of this module, students will have worked with compounds,
solutions and mixtures. By taking compounds such as salt and water and mixing
them, they form a solution. Adding sand, iron filings and gravel then creates a
mixture.

The final task of separating out each component of the mixture, as well as
separating the salt from the salt water solution, gives the students a chance to
utilize various separation techniques including screening, filtration and magnetic
separation. This encourages the students to consider general properties of each.
Overall, this module gives the students an opportunity to perform methods of basic
analytical chemistry: measuring the mass of solids and liquids, predicting certain
results from an analytical process (scientific method) and practicing inquiry in
method, execution and analysis of their final data.




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                        GK12 Module Student’s Guide


                                  Name: __________________________



          Mixtures, Solutions, Compounds, and Separations (Part I)

Introduction:

The purpose of this activity is to introduce you to the differences between
compounds, solutions and mixtures. It also will give you a chance to create a
mixture and solution, using different compounds, and to take apart that
mixture using a variety of different separation methods.

There are three different types of combinations of elements that are
common in our everyday lives. They are:

compounds: matter (material) that is composed of two or more kinds of
atoms chemically combined in definite proportions (for example: water H2O,
carbon dioxide CO2, minerals).

solutions: mixture in which one substance is dissolved, or broken down, in
another substance (for example: salt water or coffee).

mixtures: a combination of two or more substances in which each substance
retains its identity (for example: concrete, chocolate chip cookies, rocks!).

This activity will deal with all three of these. What we are going to do is
take a few different compounds and mixtures, combine them to make one big
mixture and then see if we can’t use some different types of separation
methods to get back to our original ingredients.

There are three different kinds of separation methods we are going to use:

1. Filtration: removal of impurities by passing a substance through porous
material.

2. Evaporation: separation of a solute (dissolved substance) and a solvent
(substance that does the dissolving) by evaporating off the solvent and
leaving the solute behind as a solid.



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                        GK12 Module Student’s Guide




3. Magnetic Separation: using a magnet to separate magnetic materials
(such as iron) out of a mixture.

Let’s get started…..

Part I:

Procedure:

1. You should have the following tools and materials in front of you:

sand               spoon                     magnet
gravel             cups
salt               triple beam balance

You will be making a mixture of water, salt, sand and gravel. Don’t mix
anything yet!! We’ve got to make this scientific! You will be measuring the
mass (weighing) each of the materials you put in your mixture. So, follow
these instructions carefully, record your data in the appropriate places and
answer any questions listed in these procedures.

First of all, we need to get some things clear. How would you classify the
materials in front of you: compound, solution or mixture? Why?

sand:

gravel:

water:

salt:




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                         GK12 Module Student’s Guide




2. You will be taking detailed measurements of the mass of each of your
materials before you combine them into one mixture. Keep in mind that the
cup containing your mixture should not be part of that measurement!

So, weigh an empty cup. You will need to record this so that you can subtract
it from the total mass of each of the components you add to your mixture.

Mass of Plastic Cup:



3. Now, take your empty cup and fill it about 1/3 to ¼ full of water (fill it up
to the lowest ridge or line on the plastic cup). Now weigh the water.

Mass of Water+Cup:

Mass of Water:



4. Measure out two spoonfuls of salt into an empty and dry plastic cup.
Weigh the salt.

Mass of Salt+Cup:

Mass of Salt:

Once you have done this, add the salt to the water and stir until all of the
salt is dissolved.

Before you go on, note here what kind of materials (compound, solution or
mixture) are the following:

water:

salt:




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                        GK12 Module Student’s Guide




salt water:

5. Once you have thoroughly stirred the salt into the water, look into the
cup.

Are there salt grains visible after thoroughly stirring the water?



What happened to the salt when you mixed it in with the water?



If you measured the mass of the salt water which of the combined masses
should it equal?

a) the mass of the water from #3

or

b) the sum of the water and salt together

Measure it out and see what you get.

mass of salt water:



6. Now we are going to add a new ingredient: sand. However, the sand on
your table is impure! It is a mixture of both sand and iron filings. You need
to find out the mass of each!

So, what you have to do is figure out some way to separate the iron filings
from the sand. Remember, iron is magnetic. You should be able to use one of
the tools provided to you to separate the two materials!! Once you have done
this, record the mass of each. If you are having trouble, get some help from
the teacher. Remember to subtract the mass of the cup from your
measurements!!!



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                        GK12 Module Student’s Guide




Mass of Sand:

Mass of Iron Filings:



Once you have measured the mass of these two materials, add them to the
salt water.

7. Now for the final ingredient: gravel. Measure out two spoonfuls of gravel
and carefully record its mass.

Mass of the Gravel:




8. This concludes the first part of the experiment. What you need to do now
is cover the cup containing your mixture with plastic and secure it with a
rubber band. You don’t want any water to evaporate (yet!). Once you have
done this, put your name on the cup (very important!!) and store it in a place
designated by your teacher.

9. Once you have secured and stored your mixture
       - clean up any sand, salt, gravel or water you might have spilled on your
table or desk.
       - rinse and dry any cup you used which has salt or sand residue in it.
       - return all materials back to the center of your work area, making it
       as clean an organized as it was when you began!!

10. Turn in this worksheet to your teacher.




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                        GK12 Module Student’s Guide




                      Name:   ___________________________________



         Mixtures, Solutions, Compounds, and Separations (Part II)

Introduction:

In the first part of this activity, you created a mixture of salt water, sand,
iron filings and gravel. Now, your task will be to separate each component of
the mixture (and salt water solution) back out. Hopefully, you will be 100%
successful and will be able to extract all of the sand, iron, gravel and salt
you put in. Each ingredient should weigh just as much as it did when you put
it in….right? Well…let’s see!

You should have the following materials:

spoon                     your mixture from part I rubber bands
cups                      screen
triple beam balance       coffee filters

Now, science can be a messy business. You don’t always get the results you
expected. That’s okay! This is how the scientific method works. As long as
you can reasonably explain why you didn’t get your anticipated results, then
you are covered!

Procedure:

1. The goal of this part of the activity is to separate your mixture into three
components:

      i. Gravel
      ii. Salt water
      iii. Iron+sand sludge/goop/you get the idea!

2. The easiest thing to separate out of the mixture should be the salt water.
Use filtration and/or screening to separate the salt water from your



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                        GK12 Module Student’s Guide




mixture. Try not to lose any of the components of your mixture. You
need to try and get as close as possible to the original masses that you
put in the mixture to begin with….right?

3. Once you have the salt water separated from the sand+gravel+iron, put it
aside where it won’t get spilled.

4. You now need to separate the sand+iron from the gravel. Use the tools
provided (screen, filter, etc.)

5. Once you have separated the sand+iron mixture from the gravel, measure
the mass of the gravel. Does your measurement match the mass of the
gravel that you originally put in the mixture? If not, why do you think it is
different?




6. The next step will be to separate the sand from the iron and the salt
from the water. What do you think needs to be done before you can measure
the mass of the salt? How can the iron be most easily separated from the
sand? (Hint: would it be easier if the sand+iron mixture was dry??)




7. Find out from your teacher how each of your separates will be stored
during the evaporation process.




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                        GK12 Module Student’s Guide




                      Name: _________________________________



         Mixtures, Solutions, Compounds, and Separations (Part III)

Introduction:

In the first part of this activity, you created a mixture of salt water, sand,
iron filings and gravel. In the second part of the exercise, you should have
separated the gravel completely out of the mixture and measured it. You
should also now have a dried up, crusty wad of sand and iron, and a cup with
dried salt residue in it.

You should have the following materials:

Spoon                     your mixtures from part II
triple beam balance       Plastic cups
magnet

Now, science can be a messy business. You don’t always get the results you
expected. That’s okay! This is how the scientific method works. As long as
you can reasonably explain why you didn’t get your anticipated results, you
are covered!

Procedure:

1. How much salt do you have left? Devise a way to measure the mass of the
salt without also measuring the mass of the cup it is dried to. Record the
mass below:




2. Explain how you will separate the iron from the sand. Once you have got it
figured out, describe your method below and do it!



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                       GK12 Module Student’s Guide




3. What is the mass of the sand and the iron separates?




4. Were the masses of each separate the same as the amount you put in? If
not, why?




5. Did any chemical changes occur with any of the materials during the
experiment? What effect did this have on your results?




6. Once you are finished with the questions above, find out how your teacher
would like you to dispose of the leftover materials.



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