||All ages with adult supervision
||Mixing two reactive materials
||10 - 20 minutes
colored liquid with rubber-like odor. Mildly toxic by
ingestion and inhalation. Irritating to body tissues and
respiratory tracts. Avoid all body tissue contact. Do
not breathe vapor. |
Identification: Dark brown
liquid; odorless. Irritating to body tissues and
respiratory tract. Avoid all body tissue contact. Do
not breathe vapor. Combustible liquid.
||Understanding of changes caused by chemical
||Golly! WOW! Gee whiz! rating - 8. This
is a great Gee-Whiz demo for all grades and audiences.
Super Foam Demonstration
Good question and answer
help set the stage (see the video), and showmanship is important. Best
done with a member of the audience so that as foaming takes place, they
can respond to questions, give comments and hopefully express surprise
as the foam tries to leave the container.
We've been able to find the
two components at the hobby shop. You can also order it from:
Flinn Scientific, Inc.
P.O. Box 219
Batavia, IL 60510
Catalog No. C0335 - Polyurethane Foam System
The process is very simple: mix approximately equal volumes of the two
components together in a paper or plastic cup, stir and watch the foam
form. Very effective if done in a clear plastic cup so the audience can
see the process. Be sure to use enough so that the foam comes all
the way out of the cup: this is the most effective and interesting part
of the entire demonstration. To be safe, wait 24 hours before touching the foam
Keys to the overall effectiveness include:
Other discussions before and after the demonstration
might focus on changes in properties caused by reactions (color changes,
gaseous by-products, solidification) compared to changes in phase (liquids
going to solids, but with no chemical reaction; this is very different
from what happens here). Questions and observations about the properties
of the material that's generated could include:
Asking questions and getting comments from the students regarding
what might happen when two reactive materials are mixed, and of what is
happening; for example:
Reactions between liquids often generate other materials such as
gases and solids.
During the mixing process, ask for comments on color changes, heat liberated
(are you feeling anything through the cup?), changes in viscosity or thickness
As the foam begins to form, have the student leave the mixing tool (a wooden
spatula or wooden dowel) in the foam as it rises. When he lets go (at your
suggestion), it stays in place and the foam continues to move up and out
of the container
Discussion of applications of science to new technology
(real world use of the results of science) could focus on how chemistry
generates useful products such as polyurethane foam. Applications
of this foam include:
Is this material flexible, light (low density)?
Does it smell? If you touch it, how does it feel?
Does it have good toughness, flexibility, impact resistance? (have the
student pull on it, push on it and hit it with something)
Finally, ask the audience if they know of any other
applications of foam materials. They should come up with lots of
others, most of which will not be of the same kind of foam (polyurethane)
but of other kinds. The answers to this question should lead to discussion
of polystyrene foam and "peanut" foam made out of starch. These are very
different in both chemistry and how the foams are made.
Model airplane wings and model train "mountains"
Insulation for homes, airplanes, refrigerated tankers, refrigerators, ice
chests and coolers, trucks, and inside the walls of most buildings
In-place foamed packaging for protecting electronic devices and computers
Cushions for chairs, sofas and seats in cars, trucks, airplanes and the
Run-flat tires in which the polyurethane foam on the inside of the tire
provides support after the air has leaked out
The polystyrene foam involves thermal release of
a low boiling hydrocarbon (usually pentane) which is trapped in the solid
polystyrene particles. This kind of heat-generated foaming also involves
a phase change for the pentane liquid going to a gaseous state. Unlike
the polyurethane foam, polystyrene foam easily dissolves in organic solvents
such as acetone or toulene (nail polish remover); this makes an effective
demonstration in conjunction with the polyurethane foam (see Shrinking
Peanuts). Polyethylene foam is now being used in insulation as well,
but is even more insoluble than the polyurethane foam: it doesn't dissolve
or absorb much of anything, which makes it great for applications where
water and solvents might be present.
Further discussion of technology and applications
of polyurethane foam may involve:
An activity for the student in which urethane foam is
used to encase an egg (this must be done with supervision and perhaps with
rubber gloves to ensure protection). Follow-on would be dropping the encased
egg from the top of a building to see if it survives.
Use of the foam as an adhesive and support between two rigid materials;
plywood with foam in the middle used in pre-fab wall sections for building
Use of spray-can polyurethane foam for insulating cracks and small holes
in houses and for filling walls after construction is complete (this is
dangerous because pressure can build up that blows the walls out)
Doing the foaming process in a sealed container: this must be done carefully.
A Tupperware container works great because it is clear and the lid will
pop off before dangerous pressure builds up.
PSLC OFFERS THIS SITE AS AN EDUCATIONAL TOOL. PSLC IS NOT
RESPONSIBLE FOR ANY INJURY OR DAMAGE CAUSED TO ANY PERSON,
DIRECTLY OR INDIRECTLY, RELATING TO ANY OF THE DEMOS OR
EXPERIMENTS LISTED AT THIS SITE. YOU ARE WHOLLY RESPONSIBLE
FOR YOUR SAFETY.