Day Three:
EXPLORE #3:Can You Find the
Floaters and Sinkers?
Teacher Notes
Student Activity Sheet
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Teacher Notes
Purpose: Students experiment with the six types of resin
pellets found in the Hands on Plastics™ Kit Edition Two - HOP 2. Students
working individually, in pairs or in small groups can perform this lab.
Students should be familiar with the concept of density. Look at the picture
(on the next page) of the cups of solutions with the resins pellets to
see how the set-up will appear when the students are doing the experiment.
Materials: (for a class of 30 students working in pairs)
45 salsa cups or small cups that have 60 mL capacity
45 craft sticks (one for water, one for alcohol solutions, and one for
calcium chloride)
These are available at craft stores such as Hobby Lobby or Michael’s.
450 mL 70% isopropyl alcohol (drugstore or grocery store) Color blue
with food
coloring. Make sure it is not 90% alcohol.
450 mL calcium chloride solution Color yellow with food coloring.
If students make their own, they will need to add two level tablespoons
of calcium chloride (30 grams) to 30 mL of distilled water.
This is an exothermic process as the solid dissolves. The cup will get
hot! (It could reach 80° C.) The chemical can be obtained from a
chemical supply company - it is a product
for melting ice on driveways and sidewalks. It can be purchased at stores
such as Wal-Mart Automotive. A 9.5 lb container costs $5.60. Purchase
it in the winter since stores do not carry it in the summer. Be careful
that the product you purchase isn’t a mixture of several salts.
Sodium chloride does not work for this application because its saturated
solutions are not more dense than the densest of the resins.
If you prepare the solution for the class, mix 450 mL of distilled
water with 2 cups of calcium chloride. This solution making process
is exothermic! The 450 ml solution may get as hot as 100° C. Prepare
the solution in a 1 liter beaker or a large glass canning
jar. Place the beaker or jar in a bucket of cold water to help cool
the solution as you mix it. Wear your goggles! Calcium chloride may
irritate your skin. Wash with water if your skin comes in contact with
the solution. Make the solution in a well-ventilated room since the
water vapor from the hot solution may be irritating to breathe.
Be sure to check the calcium chloride solution to make sure that all
3 pellets (Pete, PS and PVC float). Depending on the brand of CaCL2
used you may need to add more of the solute to make the solution dense
enough for these pellets to float.
30 pairs of chemical splash goggles
60 plastic pipets or droppers or teaspoons
6 kinds of plastic resin pellets – 2 of each of the 6 kinds (Each
group will have a total of 12 pellets)
NOTE: This activity is repeated with plastic container pieces
in the Elaborate Phase of the Learning Cycle on Day Seven. So you will
need to have solutions prepared two times for this Learning Cycle. However,
the Elaborate part needs twice as much solution so prepare 3 x 450 mL
of the calcium chloride solution. Do this in three batches not as one
large solution since the reaction is so exothermic.
Time: one class period
Advanced preparation:
1. Students may need help in reading a flow chart. Make an overhead transparency
of the flow chart. Ask students to tell what a person should do next when
two pellets of the same color are observed sinking in water? The answer
should be that the pellets will be removed from the water and placed in
the calcium chloride solution for further testing. Another question to
ask, while reading the flow chart, is how would a student describe the
behavior of pellet “M”? The answer is that “M”
is a floater in water and a floater in 70 % isopropyl alcohol.
2. You need to provide waste containers for the used pellets and colored
solutions at the end of the laboratory period. The pellets may be washed
(by the teacher) and reused many times. The solutions may be disposed
of by washing down the drain.
Key to the Flow Chart:
Notes on Resins:
M. Resin is less dense than 70% isopropyl
alcohol, and is less dense than water. (PP)
Z. Resin is less dense than HDPE but more dense than
PP. (LDPE)
X. Resin is less dense than water, more dense than
70% alcohol and more dense than
LDPE. (HDPE)
Y. Resin is more dense than water and is the most dense
of the three than sink in water.
(PETE)
W. Resin is more dense than water, floats in calcium
chloride solution, floats in the first
test solution, and still floats in the second test solution of calcium
chloride. (PS)
P. Resin is more dense than water, floats in calcium
chloride solution, floats in the first
test solution, and is more dense than PS. (PVC)
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Student Activity Sheet
EXPLORE #3:Can You Find the Floaters and Sinkers?
Student Activity Sheet Name:_________________________
Your Mission: You are working in a plastic recycling
factory. The factory takes used plastic containers and chops them up into
small pieces called “flake”. The flake is melted and made
into pellets. These pellets or resins are used to make more plastic items
like garbage cans, carpeting, and plastic lumber. Someone lost their data
sheet on the identification of the pellets. You have volunteered to help
identify the pellets.
Purpose: To identify the six kinds of recycled plastic
resins by observing them floating and/or sinking in different liquids.
Materials: (for each group of students)
- 6 kinds of resins or pellets (2 pellets of each kind)
- 30 mL 70% isopropyl alcohol (blue)
- 3 small cups (salsa cup size)
- chemical splash goggles
- 3 craft sticks
- plastic pipets or spoons or droppers
- 30 mL of concentrated CaCL2 solution (yellow)
- 30 mL of distilled water
Procedure: Use the flow chart to help you work with
the plastic pellets.
- Put on your goggles. Take the 12 pellets (two of each kind of plastic
resin) and place them in a small cup of water. Stir them with a craft
stick to make sure no bubbles are adhering to the pellets. Observe the
floaters and sinkers.
- Scoop out the floaters and place them in 30 mL of blue alcohol solution
in a small cup. Stir with a craft stick. Record your observations of
the floaters in the notes box on the bottom of the flow chart. Notice
their color and their behavior
in water and alcohol.
- Scoop out the floaters from the blue solution. Add squirts of water
from a plastic pipet or add one half teaspoon of water into the blue
solution containing sinkers. Stir with a craft stick, dropper, or pipet.
Observe. Keep adding small amounts of water until you see some pellets
float. Record your observations in the notes
box at the bottom of the flow chart. You should now have notes on three
kinds of pellets.
- Go back to the water cup and take out the sinkers. Place all of them
into the yellow calcium chloride solution. Observe. Record any notes
about the pellets.
- Using a pipet, add a squirt of water or add one-half teaspoon of
water to the yellow solution. Stir with a craft stick. Observe the pellets.
Add more water and stir. Continue adding water until pellets sink. Stop
and record your observations.
- Continue to add small amounts of water until more pellets sink. Stop
and record your observations. At this time you should have notes on
all six kinds of pellets.
- Take out all pellets from the cups with a craft stick or spoon. Place
the pellets in the containers provided by your teacher.
- Pour the solutions into the color-coordinated containers as directed
by your teacher
- Clean up your work area.
Evaluation:
Complete your notes on the flow chart of your observations for the six
pellets.
Notes on Resins: (Use the back of this page if you need more room.)
M. ____________________________________________________________________
Z. ____________________________________________________________________
X _____________________________________________________________________
Y. ____________________________________________________________________
W ____________________________________________________________________
P. ____________________________________________________________________
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