poke but don't soak - missmillersroom.weebly.com · monomers form polymers through the process of...
Transcript of poke but don't soak - missmillersroom.weebly.com · monomers form polymers through the process of...
Activity: Poke, But Don’t Soak! Question that students will be investigating: Can you poke a pencil through a plastic bag without it leaking? Related NGSS Content Standards: MS-‐PS1-‐1: Develop models to describe the atomic composition of simple molecules and extended structures. MS-‐PS1-‐3: Gather and make sense of information to describe that synthetic materials come from natural resources and impact society Related NGSS Science/Engineering Process: Developing and Using Models: Modeling in 6-‐8 builds on K-‐5 and progresses to developing, using and revising models to describe, test, and predict more abstract phenomena and design systems. Develop a model to predict and/or describe phenomena. (MS-‐PS-‐1), (MS-‐PS1-‐4) Materials:
-‐ 2 pencil sharpers to be used periodically -‐ 1 small/snack-‐sized Ziploc bag per student -‐ 10 standard-‐sized wooden pencils (2 per pair) -‐ 1 large pitcher of water -‐ tray to catch dripping water -‐ paper towels
Disposables: -‐ Ziploc baggies (small/snack-‐sized)
Procedure:
1. Show students a Ziploc bag filled about half way with water and ask them the following questions:
a. Do you think you can poke a pencil through this plastic bag without it leaking?
b. Why or Why not? 2. Provide students with their own Ziploc baggies in groups of 2, and have them fill
their bag about ½ to ¾ of the way full with water and zip it up tightly. 3. After ensuring their pencil is sharp, they will poke it through the middle of one
side of the bag. Note that no water spills out! 4. Take a short moment to discuss these results using the following discussion
questions. a. How does the bag fit around the pencil (tightly or loosely)? b. Do you think you can keep pushing the pencil out the other side of the bag
without water spilling? (Have students try this after they answer) c. Do you think you can poke more than one pencil through the bag without
any water spilling? (Have students try this after they answer) 5. Discuss the results. Explain how polymers make this experiment possible.
a. Is this what you expected to happen? Why or why not?
b. What did you expect to happen? c. Why is it helpful to push the pencil through quickly rather than slowly?
i. Potential answers should be about stretching out the bag while pushing the pencil through so the pencil won’t fit as tightly and water will leak out. Help guide students to this conclusion.
d. What do you think will happen when you pull the pencil out of the bag? 6. Follow up: Ask students if they think this same experiment is possible with other materials as well. Suggest that they try it at home with a balloon.
Anticipated Results: Students should be able to poke their pencil through the entire water-filled plastic bag in a quick, stabbing motion without the water leaking or spilling out of the baggie through the hole they formed.
Developmentally Appropriate Explanation of Science Content: A polymer is made up of many smaller molecules, called monomers, which are bonded together. For example, if I have one paper clip, do you think it will represent a monomer or a polymer? (Students should guess ‘monomer’) So then what do you think a chain of paper clips all linked together would represent? (Students should guess ‘polymer’) The two main types are synthetic and natural polymers. Natural polymers include things like wood, wool, and silk. Do you think that Ziploc bags are made up of synthetic or natural polymers? (Students should guess ‘synthetic,’ but if they’re struggling, give them some examples of synthetic polymers; i.e. Tupperware) In order to make Ziploc baggies, monomers must undergo chemical reactions to become polymers. Once the polymers are produced, they create flexible fibers that are all intertwined together through physical interactions (demonstrate this with your fingers), which are the fibers inside of the Ziploc bag. (You may also mention the difference between chemical and physical reactions/interactions here.) By pushing the pencil through the plastic bag, you are not breaking the bonds in the fibers, but rather are just pushing through them, like how you would squeeze your way in between two people that are standing close together. You’re not breaking the
Figure 1: Buggy and Buddy
people or causing them any harm, you’re simply forcing them to stand just far enough apart for you to fit through. In this experiment, you are the pencil, and the two people that you’re trying to get through are the fibers in the Ziploc bag.
College Level Explanation: A polymer consists of many monomers chemically bonded together. There are two main types of polymers: synthetic and natural. Natural polymers can be found everywhere, so that there are many familiar examples readily available to point out to young students. The proteins that we use in our bodies are polymers made up of amino acid monomers, and glucose monomers make up the cellulose polymers in plants. However, based on the huge variety of plants all over the world, we can infer that different types of glucose, such as amylose and cellulose, interact differently to create distinct properties of the polymers. Figure 3 provides an example of glucose monomers composing the polymer, amylose, through a condensation reaction.
Natural polymers make up things like wool and wood that people have been using for hundreds of years and continue to use today. Synthetic polymers on the other hand, were not put into practical use until the 1900’s, but these are what make up our Ziploc bags and all other types of plastics. The molecules most commonly used to form plastics include ethylene, propylene, styrene, phenol, formaldehyde, ethylene glycol, vinyl chloride, and acetonitrile. These
Figure 3: Ohio State University
Figure 2: Chemistry Need
monomers form polymers through the process of either condensation reactions or addition reactions. Condensation reactions occur when two molecules form a covalent bond. They do this by getting rid of smaller molecules attached to them which leave and form either water or alcohol, leaving an open bonding position for the remainder of the two molecules to create a bond with each other. Figure 3 shows the water molecules forming in between each monomer of amylose above. Addition reactions involve rearranging double bonds to form single bonds, lengthening and forming a polymer chain. Ziploc bags are a thermoplastic invented by John Rex Whinfield, made up of polyethylene and terephthalate, created through a condensation reaction between glycol and terephthalic acid. Once the reaction is completed and cooled, the polymers are formed, leaving relatively flexible fibers that can be used to make Mylar, film, Dacron, and of course, Ziploc Bags.
Figure 4: Polymers and Plastics
Additional Resources for this Topic: Chelsey. "Science For Kids: Baggie and Pencil Magic." Weblog post. Buggy and Buddy. Buggy and Buddy, 20 Apr. 2013. Web. 28 Oct. 2013. <http://buggyandbuddy.com/author/cmarashian/>. References: Abedon, Stephen T. "Carbohydrates." Carbohydrates. Ohio State University, n.d. Web. 28 Oct. 2013. <http://www.mansfield.ohio-state.edu/~sabedon/biol1025.htm>. Fruedenrich, Craig, Ph.D. "How Plastics Work." HowStuffWorks. A Discovery Company, n.d. Web. 24 Oct. 2013. <http://science.howstuffworks.com/plastic4.htm>. Lower, Stephen. "Polymers and Plastics: A Chemical Introduction." Polymers and Plastics: A Chemical Introduction. Creative Commons Attribution, 2009. Web. 24 Oct. 2013. <http://www.chem1.com/acad/webtext/states/polymers.html>. "Polymers | Chemistry.need.org." Polymers | Chemistry.need.org. Need, 2013. Web. 24 Oct. 2013. <http://chemistry.need.org/curriculum/polymers>.