Teacher
Notes
Author: Mary Harris: Missouri Polymer Ambassador
Video Editing: James Brownlow: George County High School
Recommended for Middle Level or Upper
Elementary.
· This is a three day
laboratory.
· All the polymers for this lab will
grow to several times their original size when placed in distilled water
for twenty-four hours. The bears will also shrink back to their
original
size if they are placed in saturated salt solution.
· Gummy bears work the best since
they are small and compact. Worms tend to break when they are
enlarged
with distilled water.
· If your students observe and
record
mass changes, the handling of the bears must be gentle since the Gummy
animals get quite flexible and fragile after twenty-four hours in
distilled
water.
· I tried Walgreen brand and Black
Forest brand gummy bears and worms. Both bear brands work
well.
The Walgreen brand is larger. Other brands just disintegrate.
· Saturated salt water is made from
Kosher coarse salt so that it will be clear. Make about one liter
of solution for a class. Start with one liter of distilled water
and add Kosher coarse salt. Shake until it dissolves. Add more
salt and shake. It will take about 360 g or 1 3/4 cup of salt to
make the solution saturated. Allow plenty of time for the salt to
dissolve. This usually takes overnight! When some salt remains
undissolved this indicates saturation.
· Saturated sugar water will also
work. This is a bit sticky!
· Have extra gummi animals available
for eating at a different time! Do not allow eating during the
laboratory$
· It is also possible to see a
decrease
in
size from the original bear placed in saturated salt water. I found
a decrease in mass of 41% in 24 hours.
· To introduce the activity and the
concept of diffusion, demonstrate the diffusion of a drop of colored dye
in water or open a perfume bottle in the room. The molecules move
from an area of high concentration to one of lower concentration.
· Typical Data:
|
Original mass (g) |
Day Two mass (g) after DW |
% Change |
Day Three Mass (g)
after Salt |
% Change |
| Bear |
1.7 |
8.1 |
376 |
1.4 |
-18 |
|
Original volume cm3 |
Day Two volume cm3 |
% Change |
Day Three volume cm3 |
% Change |
| Bear |
2.31 |
16.92 |
632 |
1.76 |
-24 |
Written by Mary Harris, Missouri Polymer
Ambassador, email: mharris@jburroughs.org
Movie editing by James Brownlow from George
County High School, Lucedale, MS
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