Author: Jon Valasek
This activity involves the students in an inquiry based examination of the physical and chemical properties of polymers.
What should students know as a result of this lesson?
What should the students be able to do as a result of this lesson?
Note: 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.
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.
State, "You have collected plastic containers that are made up of different kinds of plastics called polymers. If you look on the bottom of your container you will see a triangle with a number in it. This is called a recycling code and refers to the type of polymer in the container. Each type of polymer is different from another in some ways and the same in other ways.
Ask, "In what ways are they different?" Accept answers.
Ask, "In what ways are they the same?" Accept answers.
State, "Scientists categorize these differences into physical and chemical properties."
Ask, "What do you think a physical property is?" A physical property is when a substance can change without it becoming a difference substance. An example would be when you heat a metal and it melts.
Ask, "What do you think a chemical property is?" A chemical property is when a substance when changed becomes a different substance. An example would be adding acid to the same metal would cause the metal to react and become a salt with hydrogen gas given off.
Assessment: Ask students to give you examples of physical and chemical properties and qualify them by putting them on the board. Melting point, boiling point, strength, hardness, density, color, opaqueness, transparency, and electrical conductivity are among the physical properties they might mention. Chemical reactivity such as combustion and biodegradability are common chemical properties.
State, "Let's test these polymers and see how they are the same and how they are different."
Before beginning any handling of materials, remind students to work safely and to use materials/equipment for the intended purposes. Ask, "Which of the physical properties should we test?" Accept input. Lead them to identify the following in the procedures below: Also conduct a discussion how they will record their observations and tests. (Each student can test his/her own or groups can test several polymers.) For each polymer perform the following:
Ask, "Which chemical properties should we test?" Accept input. Again lead students to perform the following:
State, "To test biodegradability let's do the following:"
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 students need to agree on the same format. Discuss why that is important.
Have students report orally and in writing their results with comparisons between the different polymers.
Assessment: Have students compare results and communicate their findings to the entire group.
Possibly students could form companies and test unknown polymers to determine their identity. Also students could 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 students give oral reports on their advocacy efforts.
Common Core Standards:
Observation skills to discern physical changes chemical reactions.
To minimize safety concerns, the teacher should place the chemicals in a baby food jar or similar container that has a lid. The lid is only removed by the student to put the plastic in then quickly closed to prevent any vapors from escaping. The physical test should be supervised by the teacher. Material Safety Data Sheets should be consulted for all chemicals used in this activity.
Prepare reagent as follows
Students should be able to define and give examples of physical and chemical properties of substances in general and polymers specifically.
Grouping Suggestions: Students should be placed in groups of two or three. However a novel idea on grouping is found in, "Cooperative Learning in the Science Classroom," by Emily Lin, the Science Teacher Vol 73 No 5 Summer 2006, pp34-39
Pacing/Suggested Time: Two 45 minutes periods
N/A - Students should devise their own data sheets based on the discussion in class.