- Changes in physical properties
- 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
- Pour about 10 mL of PVA solution into a condiment cup (eyeball estimate).
- Add a few drops of coloring to the condiment cup.
- In a separate condiment cup, pour about 2.5 mL of borax solution (eyeball estimate).
- Pour the borax solution into the PVA containing cup and mix with a stir stick to form slime.
- The slime formed after the stirring may now be handled.
- Give the kid a plastic Ziploc bag for storage.
- Is the slime a liquid or a solid?
- What are the physical properties that change?
- What would happen if all the water was taken out of the slime?
- What effect would adding extra borax have on the slime?
- Can we turn the slime back into liquid? If so, how?
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.