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Kitchen Chemistry Experiment
26
Scooting Glue
This test
indicates the movement of the glue is related to the surface
tension of water. The glue does not move unless it is on the
surface. Detergent and oil, both of which greatly reduce surface
tension, destroy the effect.
| Materials |
Substitutions |
| large
culture dish |
aluminum
pie pan |
| Duco
Cement |
|
| toothpicks |
|
| liquid
detergent |
|
| ground
pepper |
|
| oil |
|
| water |
|
| food
coloring (optional) |
|
Procedure
- Add a
small drop of fresh Duco Cement or a similar clear household
cement to the center of a large shallow pan of water. Observe
what happens for several minutes as the activity slows. Does
the glue move continuously or intermittently? Remove the used
glue with a toothpick and place both in the trashcan.
- Add a
sprinkling of ground pepper to the surface of the water to better
observe what is happening. Repeat Step #1.
- Try immobilizing
a glue drop on the surface of the water with a toothpick. Observe
the pepper. Push the glue under the surface with the toothpick
and observe. Remove the used glue with a toothpick and discard.
- Repeat
Step #2. Sprinkle with ground pepper. Add a drop of liquid detergent
to the water. What do you observe?
- Rinse
the pan and try again with a light drop of oil added to the water.
What other variations can you think of trying?
Teacher's
Notes
- The Duco-Cement
is made up of a polymer in a water-soluble solvent. Before the
drop of glue even hits the water, a skin of polymer forms around
it. As solvent slowly diffuses out of the skin, the skin shrinks
and repeatedly ruptures, momentarily allowing solvent to diffuse
rapidly out of one side or another of the drop. When this happens,
the surface tension of the water in the vicinity of the rupture
suddenly decreases. The effect is like poking a hole in a stretched
rubber membrane: the drop of glue is pulled in one direction,
while the solvent is pulled across the surface tension in the
opposite direction
- This
activity works well as a demonstration using the shallow glass
pie pan on an overhead projector.
- You must
rinse the pie pan well. If the dirt or oil from your skin are
on the pan, it will cause the surface tension to be broken.
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