ZIPLOC BAG CHEMISTRY

Polymers: Fill a ziploc bag to 1/2 full of water, and seal it. Quickly insert a sharp pencil through both sides of the bag below the water level. (I like to do it over someone's head.) The bag will not leak! Try two pencils?? WHY: Polymers are long chains of molecules which are wrapped around each other. When a hole is punched in the bag the polymers separate. However, the chain of molecules simply re-tighten around the pencil forming a seal.

Slime (GAK): Squirt about 1 tablespoon of Elmer's glue into a sandwich size ziploc bag. Dilute with 1 tablespoon of water. Make a strong Borax solution (20 mule team from grocery store) (1 teaspoon Borax in 1 tablespoon of water) and add to the diluted glue. Close the bag and have students work with their fingers until well mixed. The glue will transform into a glob of slimy, gelatinous mass. Pour off excess liquid into a container for disposal later - not the sink, because there may still be cross linking which can clog up the drain. Play! WHY: Elmer's glue is an adhesive polymer made of polyvinyl acetate, which can be modified by a chemical process called cross linking. The 20 mule team Borax (sodium tetraborate decahydrate) can be used as the cross linking agent. Properties of long chain molecules change when they are cross-linked. Elmer's glue changed into slimy glob. A natural polymer, rubber latex, is cross-linked by sulfur in a process discover by Charles Goodyear. That process is known as vulcanization.

above ideas courtesy of:

Karin M. McElvein, Chemistry Teacher, F.W. Cox High
School, Virginia Beach, VA. Reprinted Missouri Science

Large Recipe of Gak

(Mix together)
2 cups Elmer's Glue
1 ½ cups warm water
Separately (mix together)
1 cup warm water
3 teaspoons Borax
Add Borax mixture to glue mixture.
Mix up with hands in large Ziplock Bag.
Hint: If you desire color. . .
add food coloring to the water before mixing with the glue.
Keep sealed for storage.
Add water if the mixture becomes dry.