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Discovering the Physical and Chemical Properties of Polymers

Grades: 5-8
Author: Jon Valasek


Abstract

Module Description

In this lesson participating teachers will be led through an exercise using their observation skills to discover the physical and chemical properties of polymers. This is an example of an inquiry based lesson, whose methodology can be adopted in other lessons. No prior knowledge of polymers is necessary. The instructor for this exercise should be familiar with resources that define the physical and chemical properties of polymers, given in the Explanation of Science section.


Objectives

  • Participants will be able to analyze and draw conclusions from the their observations.
  • Participants will be able to discover the physical and chemical properties of polymers.
  • Participants will be able to produce and implement a lesson plan to lead their students through the discovery of the physical and chemical properties of polymers.

Materials

In this activity facilitators will need to gather polymers from various food containers, recycling codes 1 through 6. Cut each type into small pieces and place in separate containers.

Facilitators will need the following reagents: distilled water, ethanol, acetone, 3.0 M sulfuric acid, ethyl acetate, 3.0 M sodium hydroxide, 2.5 M nitric acid, mineral oil, and 3.0 M sodium chloride.

Potassium carbonate, sodium chloride, and distilled water.

Electronic balances or else use large pieces of polymers and manual balances to determine their densities.

Alcohol lamps or candles.

Beakers or small containers to hold reagents.

Bunsen burner


Procedures

The following is a guide that the participants will use to conduct the exercise. However, they should be encouraged to modify the instructions below to conform to the learning cycle model and inquiry practices. This exercise should be changed to make use of the resources available. If a fume hood is not available then delete that portion of the procedures that requires that equipment.

Engagement

Polymers are all around us. Polymers are versatile as you note from the various uses in the materials around and on you and resource efficient as polymers consume only 4 percent of the world's oil supply. Polymers reduce oil consumption and carbon dioxide emissions. This investigation focuses on the physical and chemical properties of polymers. Facilitators will ask participants what physical and chemical characteristics of polymers they would test. Ask each group to brainstorm the question.

Assessment: After the brainstorming have each group report their findings to the group. Make a list of these and arrive at agreement. The list might include: physical appearance, density, strength, solubility, chemical reactions, combustion, melting, and biodegradability. These are the areas you are planning to have them explore. If others are suggested say that you did not bring materials for those investigations.

Exploration

Next have the participants devise test procedures for each investigation. A sample set of procedures follows. You might have to guide them to use solutions of known densities to determine the density of their polymer because polymers are light and their volumes are hard to measure.

Sample procedures. You will be given a sample of a polymer from your teacher. For each polymer perform the following:

  1. Describe the polymer to include color, hardness, flexibility, opaque or transparent, odor, etc. and record your observations on the data sheet. Compare your results.
  2. Determine the density of your sample by placing the sample in the test solutions provided by your teacher. Record whether the sample sinks or floats in each solution and decide the approximate density. To find a more precise density for each sample, mass your sample, find the volume by water displacement, then divide mass by volume to calculate density. Compare your results with the tests you preformed at the beginning of this procedure.
  3. Determine the strength of your sample by attempting to tear, bend, twist, or stretch it. Record your results for each sample. What happens when you hit your sample with a hammer?
  4. Use the fume hood and place a small piece of your sample in the second blue flame of a Bunsen burner. That is the part of the flame further from the barrel. Observe and record results.
  5. Introduce your sample close to a candle flame. Make observations and record results.
  6. Place 10 mL of each of the following in separate test tubes or glass containers: water, ethyl alcohol, acetone, ethyl acetate, 3M sulfuric acid, 3M nitric acid, 3M sodium hydroxide, 3M sodium chloride, and mineral oil and then add a small piece of your sample to each container. Stopper test tubes or place the lid on the glass containers. Make initial observations and then record results after 30 minutes, and 24 hours.
  7. Place a piece of your sample in the "Is it biodegradable" container and observe monthly.

Assessment: Have groups compare their test procedures and arrive at agreement on which procedures they will use and how they will document the test results. This could be in the form of tables or narratives but all participants need to agree on the same format. Discuss why that is important.

Explanation

AHave participants compare results and communicate their findings to the entire group. Have the participants discuss how they would insure that their students should communicate their results. Conduct a discussion about various kinds of polymeric materials and the physical and chemical properties of each.

Assessment: Check the participants' findings and reports for accuracy and completeness.

Elaboration

Have participants develop a plan (see below) to implement this activity into their science courses. Possibly they could have groups of students form companies and test unknown polymers to determine their identity. Also the participants could plan for their students to adopt a polymer and generate a report which would include the test data. Also teachers could help form student advocacy groups for polymer use and education.

Assessment: Have groups correctly identify unknowns. Have participants give oral reports on their advocacy efforts.


Rationale

Teaching with inquiry can be defined as giving: "students ample opportunities to apply the reasoning and procedural skills of scientists while learning the principles and concepts of science along the way." Typically teachers use activities as a way to introduce students to new concepts. This exercise is designed to lead teachers in a series of observations to discover the physical and chemical characteristics of polymers. Once the teacher feels comfortable with this activity, he/she can guide his/her own students through the same process and allow them to become more independent and actively involved in their own learning processes. Also this activity can lead to lessons on recycling and recyclable materials.


Science Standards

Content, Technology, and Professional Development:

Content:

Science as Inquiry: as a result of activities, in grades 5-8, all students should develop:

  • Abilities necessary to do scientific inquiry.

Physical Science: as a result of activities, in grades 5-8, all students should develop an understanding of:

  • Properties and changes of properties in matter.

Professional Development:

Standard A: Professional development for teachers of science requires learning essential science content through the perspectives and methods of inquiry. Science learning experiences for teachers must:

  • Involve teachers in actively investigating phenomena that can be studied scientifically, interpreting results, and making sense of findings consistent with currently accepted scientific understanding.
  • Build on teacher's current science understanding, ability and attitudes.

Standard B: Professional development for teachers of science requires integrating knowledge of science, learning, pedagogy, and students; it also requires applying that knowledge to science teaching. Learning experiences for teachers of science must

  • Use inquiry, reflection, interpretation of research, modeling and guided practice to build understanding and skill in science teaching.

Best Teaching Practices

  • Observation
  • Inquiry
  • Learning Cycle
  • Synthesis

Time Frame

Preparation time: 120 minutes

Lesson time: 60-90 minutes


Preparation

  • Acetone is available in finger nail polish remover.
  • Prepare 3.0 M sulfuric acid by pouring 16.6 mL of concentrated acid into 63.4 mL of water.
  • Prepare 3.0 M sodium hydroxide by dissolving 12.0 grams of NaOH into enough water to make 100 mL of solution.
  • Prepare 2.5 M nitric acid by pouring 12.5 mL of acid into 87.5 mL of water.
  • Prepare 3.0 M sodium chloride by dissolving 17.6 grams of NaCl in enough water to make 100 mL of solution.
  • Prepare a 0.868 g/mL density solution by mixing 80.0 mL of ethanol with enough water to make 100 mL of solution.
  • Prepare a 0.914 g/mL density solution by mixing 60.0 mL of ethanol with enough water to make 100 mL of solution.
  • Prepare a 0.945 g/mL density solution by mixing 43.0 mL of ethanol with enough solution by mixing 43.0 mL of ethanol with enough water to make 100 mL of solution.
  • Distilled water should have a density close to 1.00 g/mL.
  • Prepare a 1.09 g/mL density solution by dissolving 12.0 grams of sodium chloride in 88.0 mL of distilled water.
  • Prepare a 1.25 g/mL density solution by dissolving 54.0 grams of sucrose in 46 mL of distilled water.
  • Prepare a 1.48 g/mL density solution by dissolving 45 grams of potassium carbonate in 55 grams of distilled water.
  • Prepare a biodegradable container by cutting the base of a 2.0 L soda bottle. Invert the top into the base and fill the bottle with moisten soil. The soil can be enriched with lime, worms, or other materials that would simulate what is found at a dump site.

Safety

Specific information on the reagents can be found at www.ilpi.com/msds/index.html Your should use the following precautions with acids and bases: avoid contact with skin, eyes, and mucous membranes. If you come in contact with the acid, base or acetone flush with plenty water and if the eyes are affected see a physician. Do not breathe acetone vapors. Wear goggles, aprons, and gloves when handling these chemicals. Solutions should be neutralized and poured down the drain with plenty of water. Acetone and ethyl acetate can be put under the fume hood and allowed to evaporate.


Assessment

The participants should show through lesson plans and student work the implementation of the activity into their course.


Explanation of Science

The densities of the polymers are as follows:

  • Recycle code 1, PET, polyethyleneterphthalate, 1.39 g/mL
  • Recycle code 2, HDPE, high density polyethylene, 0.95-0.97 g/mL
  • Recycle code, 3, PVC, polyvinylchloride
  • Recycle code 4, LDPE, low density polyethylene, 0.92-0.94 g/mL
  • Recycle code, 5, PP, polypropylene, 0.90-0.91 g/mL
  • Recycle code, 6, PS, polystyrene, 1.05-1.07 g/mL
  • PMP, poly-4methyl-1-pentene, 0.83 g/mL
  • Plexiglas, polymethyl metacrylate 1.24 g/mL
  • PTFE, Teflon, polytetrafluoroethylene, 2.2 g/mL

Handouts

None available for this module.


Extensions

None available for this module.


Lesson Implementation Template

Download Lesson Implementation Template: Word Document or PDF File


Equity

Be sensitive to gender, ethnic, and religious backgrounds.


Resources

None available for this module


References

This exercise was modified from Polymers: A General Experiment in Polymer Chemistry, Robert Liscomb, National Science Teachers Association, 1997, pp 203-205