Vanishing Peanuts

Chemistry, Biology:	Polymers, Solubility, Recycling
Grade Range:	Elementary School, Middle School, High School
Format:	Hands-on, Stage

Students will enjoy watching or performing this demonstration, and will be excited to know that they can do this at home! Be sure to let the polystyrene blob dry before you throw it into a recycling container, otherwise the acetone in it might dissolve the other plastics or the container itself!

Materials

• Acetone
• Large Bowl
• Styrofoam_© or Polystyrene Packing Material (Peanuts, Foam Boards, etc.)
• Rubber Gloves
• Cornstarch Peanuts
• 2nd Large Bowl with Water

Safety Precautions

Please read the Liquid Chemical section of the Demonstration Safety page before performing this demonstration.

This demonstration requires: Safety Glasses

Demonstration

Presentation (Stage)

1. Set the bowl on the table, and set a large amount of polystyrene next to it. Ask the audience to guess how much of it you can fit in the bowl. Try (and fail) to fit it all in the bowl. Let the audience know that you have a trick to make it all fit!
2. Take the polystyrene out of the bowl. Pour enough acetone into the bowl to make a thin layer on the bottom (around 2-3 cups, or 500-700mL)
3. Now start putting the Styrofoam into the bowl one piece at a time, and have the audience watch the pieces as they shrink into the bowl! Don't show them the inside of the bowl yet, but point out the fizzing they hear, and ask for ideas on what is happening.
4. After sticking a few pieces into the bowl, scoop some of the polystyrene goo from the bottom and show it to the audience. Stick a small piece of polystyrene into the goo to show that it is "melting" into it. Be sure to finish by sticking all of the polystyrene into the bowl to prove that you can fit all of it in!

Presentation (Hands-on)

1. Set out the two bowls, one with water and the other with Acetone. You may want to bring something to cover the acetone bowl to keep the fumes at a minimum. Have a pile of polystyrene next to the acetone bowl, and a pile of cornstarch peanuts next to the water bowl.
2. As students come up, have them put a peanut in each bowl and watch what happens. The cornstarch peanut will melt and dissolve in the bowl of water, and the polystyrene peanut will dissolve into the acetone!
   1. Have students wear a rubber glove when they are putting the polystyrene into the acetone. Acetone can dry out the skin, and it will take off any nail polish they might have on.
3. After several pieces of polystyrene have been dissolved in the acetone, you will be able to pick up the blob and let students play with it. When you first take it out, set it aside on a paper towel for a few minutes to let some of the acetone evaporate. Afterwards, kids will be able to mold it, stretch it and see the difference between the solid polystyrene and the packing foam!

Why This Works

Styrofoam_©, or polystyrene, is a type of plastic that we often use in packing materials. It is filled with tiny bubbles so that it can better absorb pressure, and protect the items it is packed around. Polystyrene is between 90% and 95% air, so it can be hard to recycle it if the container holding it is, essentially, only 5-10% filled. Like all plastics, polystyrene is a Polymer, which means that the molecules in it are all connected to each other like a long string or a really big net. However, polystyrene is soluble in acetone. Soluble means that a molecule or compound will dissolve into a liquid, like salt or sugar dissolving in water. Since polystyrene is a polymer, however, the long strings don't want to separate fully into the acetone. Instead, they loosen up and let the air escape, which we hear as the fizzing sound, and will try to stick together without fully dissolving, which is why we get the blob. As the blob dries out, our polystyrene will harden again, only this time it won't have any air pockets and becomes a hard, stiff plastic. If we had a figurine mold or a serving utensil mold, it could be made into one of those! This is one of the ways we can recycle polystyrene, and help prevent it from filling up landfills.

The cornstarch peanuts are another way to look at reducing our use of plastic. Cornstarch peanuts are water soluble, so they will dissolve into water when they get wet. This means they will break down quickly if they end up in a landfill, and be much better for the environment! Cornstarch can behave like a polymer, but if it is dissolved it separates fully, since the bonds between the molecules aren't very strong.

Additional Information

• This is an experiment that students can do at home! Acetone is the primary ingredient in nail polish remover, and Styrofoam_© is a common packing material. Young students should only do this demonstration with a parent. Be aware that acetone can dissolve several types of plastic. Phone cases, clear plastic bottles, some types of carpet, and some plastic food bowls or utensils are soluble, so be careful with acetone!
• This demonstration pairs well with the Polymer Milk Jug.
• This demonstration is a part of the Environmental Show.