Class 4/Week 4: Polymers
B/N: I missed a week in-between posting Chemistry lesson plans I thought I had posted it already (oops!). Enjoy!
Remember we talked about solids, liquids and gases and how they are all made up of tiny things called atoms. Remember also that elements are the type of atoms we can have and that when atoms join together, they make molecules.
Today we are going to talk about Solids and Liquids that behave in a funny way when we do certain things to them. Specifically, we are going to talk about something called a Polymer.
What is a Polymer?
- A Polymer is a long chain of made of up many molecules. How a polymer will act when you do things to it depends on how its atoms are connected, as well as which atoms or elements it's made up of in the first place.
- Polymers can bend and twist and get tangled up. The longer a polymer chain is the more likely it is that it will get tangled up, just like a jumprope or some string. Since the chains are hard to pull apart once they get all tangled up, a polymer ends up being very strong. So, things made out of polymers are hard to break.
- Polymers can stick together. Some polymers don't get tangled up, though, but they are made up of very neat, straight chains. They are still very strong, though. For example: cellulose is a natural polymer found in wood, which makes trees and wood very very strong and tough to break apart.
- Polymers are lightweight, strong, durable, recyclable- some are easier than others to recycle. However, they last a very long time and this can be bad for the environment when they are thrown away. We should try to recycle the polymers that we can.
- The longer it takes a fluid to flow, the more viscous it is.
- Polymers are very viscous- they move slower because they're so big. The longer the chains, the slower the flow.
Activity: Explain & Observe Viscosity Using Honey (Teacher-Demonstrated)
- Explain viscosity and demonstrate using honey. Show how honey moves more slowly and becomes more viscous when it's cold and less when it's hot/warm (put some honey in a container on ice and then have some at room temp so they can observe the difference in how it flows or behaves.
- Press on each to show that pressure has no effect on it. It is a Newtonian fluid.
Activity: Show kids this video of people running across a pool of Oobleck: http://www.youtube.com/watch?v=yHlAcASsf6U&feature=player_embedded
- Ask them to watch what happens when they run vs. when they stand still.
- Explain that Oobleck is a Polymer. It changes viscosity because of pressure, not because of temperature.
Activity: Observe Oobleck, a Non-Newtonian Fluid (Teacher-Demonstrated)
- Make Oobleck ahead of time, using 2 parts Cornstarch: 1 part water. Place it in a plastic dish that is large enough for your entire hand to fit in if pushed flat into the dish. Cover with a lid until ready to use. A plastic baggie is also great for observing how this fluid behaves- it's very neat and contained but the kids can still press on it then allow it flow inside the bag.
- Allow the kids to observe how it behaves: gently swirl or shake it, press on the liquid firmly to see what happens, pour it to see what happens. Allow kids to take turns pressing on it to feel how it responds to pressure.
- Contrast it with honey in terms of flow, and water (in another dish) in terms of how it behaves when pushed. Water does not clump together and separate from the dish cleanly when stirred with a fork.
Activity: Observe and Play with something like Silly Putty (Silly Putty is a brand name but that's not what we're calling it here)
Make putty Ahead of time using the recipe below and place in individual snack-sized ziploc bags until ready to use. Or, if you have a smaller class, you can allow the kids to make it in class. Be sure to provide plastic snack baggies for them to take their creation home.
This will bounce and pick up pictures from the paper just like the name-brand stuff.
- Add: 1/2 cup water to 1/2 cup Elmer's glue (Not School Glue!)
- Mix and add 3 drops of food coloring (optional)
- Make Borax solution: Take 2 tablespoons borax (You can buy this at a grocery store or online) and add to 1 cup of water and stir.
- Add 1/2 cup of Borax solution to water and glue mixture
- Stir and store in a plastic bag
Mix well. Add food coloring if you wish. Let it dry about an hour. When ready, it will be smooth and rubber-like. Store in an airtight container.
Activity: Make Fake Snow
- Give each child sodium polyacrylate beads in a small, snack-sized ziploc bag and allow them to add a small amount of water to it. Encourage them to observe how super-absorbent it is by watching it expand and change appearance with the addition of water.
- Explain that it's used for many things, but the most common we'd recognize is for fake snow in the movies or in baby diapers to keep them from leaking.
- Emphasize that they can play with it but that they must wash their hands and never, never put it in their mouths or swallow it. It's safe on your hands but not in your mouth!!!!
All Images taken from http://www.publicdomainpictures.net/