In the Classroom

Science Discipline(s)

Chemistry

 

Topics

  • Changes in physical properties
  • Polymerization

 

Activity Title

Slime

 

Materials

  • 4% Polyvinyl Alcohol
  • Saturated Borax solution
  • A variety of food colorings or Atomic Glow dye and black light
  • Small condiment cups
  • Stir sticks
  • Ziploc bags

 

Procedure

  1. Pour about 10 mL of PVA solution into a condiment cup (eyeball estimate).
  2. Add a few drops of coloring to the condiment cup.
  3. In a separate condiment cup, pour about 2.5 mL of borax solution (eyeball estimate).
  4. Pour the borax solution into the PVA containing cup and mix with a stir stick to form slime.
  5. The slime formed after the stirring may now be handled.
  6. Give the kid a plastic Ziploc bag for storage.

 

Questions

  1. Is the slime a liquid or a solid?
  2. What are the physical properties that change?
  3. What would happen if all the water was taken out of the slime?
  4. What effect would adding extra borax have on the slime?
  5. Can we turn the slime back into liquid? If so, how?

 

Explanation

When borax is added to water, it hydrolyzes to form boric acid and a hydroxyl anion and the boric acid further reacts with water to form a borate anion. By mixing polyvinyl alcohol with the borate anion, a chemical process known as polymerization takes place. During this process, a covalent bond forms in which the hydroxyl group on the borate anion are replaced with oxygens from the hydroxyl groups on the polyvinyl alcohol backbone. Boron reacts with 1 -2 oxygens from each of two chains resulting in a cross-link. This cross-linking of the borate anion with the polyvinyl alcohol molecules forms long chains of polyvinyl alcohols which traps in water, causing the liquid solution to become more viscous, creating a gel.

Next Generation Science Standards

This activity could be implemented at the 4th-6th grade level as a simple and fun science experiment. Kids will learn about changes in physical properties as well as how polymerization works. A demonstration of cross linking polymers could be done in which two separate groups of students holding hands could freely move around to represent polymers. Then, a student that represent a borax molecule could come in and join hands, linking the two polymer groups together, creating a representation of cross linking between two separate polymer groups. Then, have the newly formed group move around to demonstrate the difficulty of moving as a longer group. This demonstrates how linking has affected their mobility, making it harder to move. Another demonstration of polymers and cross-linking can be found on the Gak website that involves the use of Marti Gras beads.

Areas of the NGSS that this activity links to are: 5-PS1-2 The amount (weight) of matter is conserved when it changes form, even in transitions in which it seems to vanish, 5-PS1-4 When two or more different substances are mixed, a new substance with different properties may be formed, 5-PS1-2 No matter what reaction or change in properties occurs, the total weight of the substances does not change.

Reference material

http://scibus.50megs.com/slime.html