THE SLIME LAB!
PURPOSE:
- To create a polymer from monomer units
- To observe a non-Newtonian fluid
- To learn about the versatility of carbon
- To learn about polymers and their usefulness
BACKGROUND INFORMATION:
Organic chemistry is the study of compounds that contain the element carbon. It is the most studies and broadest of all the chemistry fields – it encompasses the pharmaceutical industry, the study of biochemistry, the plastics industry, the entire field of DNA research – virtually all aspects of life involve organic chemistry. The carbon atom forms many long-chained molecules because of its unique electron structure. Carbon has four valence electrons, allowing it to bond covalently four times, or any combination it chooses in double or triple bonds. It will even bond with itself, forming long-chained molecules, with each carbon atom needing to bond with three other atoms. Hydrogen will usually complete carbon’s need for bonding, considering that it needs only one valence electron to meet the octet rule. Compounds containing C and H are called hydrocarbons. There are thousands of known hydrocarbons. Certain hydrocarbons will bond with themselves, forming long chains of molecules called polymers. A single unit of a polymer is known as a monomer. Giant molecules of polymers are created by putting together monomer units. Examples of natural polymers are cellulose, starch, proteins, and nucleic acids. Some examples of artificial or synthetic polymers are plastics, insulation, clothing, carbon fibers (materials used to make fighter planes, golf clubs, bicycles, bullet-proof vests) super glue, and slime.
This lab creates slime by taking a polymer compound called polyvinyl alcohol (PVA) and combining it with borax, or borate, creating a cross-linked molecule. PVA is shown below – notice the molecule is an alcohol because of the –OH bonds in it. In addition, notice the slight charge on the hydrogen and oxygen atoms, indicative of an –OH bond.
Here are some examples of common monomers and the polymers they form:
Monomer Name structure Polymer Name Uses
Ethylene, or ethane Polyethylene plastic bags,
milk bottles
Propene, or propylene Polypropylene bottles, fibers,
Toys, carpet
Vinyl Chloride PVC (polyvinyl chloride) pipes, floor
tiles, credit
cards, toys, clothing,
Styrene Styrofoam or polystyrene insulation,
Foam cups, toys
Borax is a cleaning agent that contains the molecule borate. The borate ion is shown below:
When PVA is placed into a solution containing the borate ion, the borate ion acts as a cross link “glue”, or connector for the PVA. The PVA molecules are joined together by the borate ion by hydrogen bonding with the borate ion. The hydrogens are partially positive, and the oxygens are partially negative. These bonds are easily broken, and will easily reassemble themselves. Draw two PVA molecules cross-linked by the borate ion in your conclusion. This is what the slime molecule consists of.
Procedure:
1. Add 40 mL of PVA solution to a small beaker.
2. Add 1 or 2 drops of food coloring to the beaker; stir with a glass rod.
3. Add 10 mL of borax solution to the PVA.
4. Stir until the solution begins to polymerize into slime.
5. Add to a Ziploc bag and gently massage in your hand until the water has been expelled from the slime. You can remove the slime and play with it at this point!
Conclusions:
1. Why are polymers so useful in science and every day society?
2. Slime does not act as a conventional fluid; it can flow like a fluid, yet resist motion like a solid. Why does slime do this?
3. Why can slime be pulled apart like a fluid, yet return to the solid state when reassembled?
4. Draw two PVA molecules cross-linked by the borate ion – the slime molecule!
These questions should also be answered for your conclusion after reading the article on slime from ChemMatters magazine.
5. What is viscosity?
6. Give one example of a Newtonian fluid.
7. What factor can affect the viscosity of a non-Newtonian fluid?
8. What type of non-Newtonian fluids decrease in viscosity when shear stress is applied? Offer an example of this type of non-Newtonian fluid.
9. What type of non-Newtonian fluids increase in viscosity when shear stress is applied? Offer an example of this type of non-Newtonian fluid.
10. Are slimes shear-thickening or shear-thinning fluids?
11. Slime, silly putty, and cornstarch are examples of what type of chemical molecules?
12. What acts as the cross-link to connect PVA or glue molecules?