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Paper or Plastic? (3 Favorites)

LAB in Observations, Physical Properties, Physical Change, Polymers. Last updated December 20, 2018.


Summary

In this lab students will research and compare the physical properties of various types of plastic bags. The recorded data will be analyzed by students, and they will use the results to design a plastic bag to meet a given set of criteria.

Grade Level

Elementary and Middle School

Objectives

By the end of this lab, students should be able to

  • Identify physical properties of materials, such as plastics.
  • Carryout a set of controlled experiments in order to collect and compare data.
  • Understand that polymers are a component that makes up plastics.

Chemistry Topics

This lab supports students’ understanding of

  • Physical properties
  • Physical Change
  • Observations
  • Polymers

Time

Teacher Preparation: 10-15 minutes

Lesson: 2 hours (1 hour per day)

Materials

Station 1: Testing Strength

  • Meter Stick
  • Ruler
  • Hole Punch
  • String
  • Weights
  • Samples of each type of plastic bag

Station 2: Tearing Test

  • Samples of each type of plastic bag

Station 3: Stretch Test

  • Meter stick and/or ruler
  • Samples of each type of plastic bag precut into 12 inch strips

Station 4: Air Capacity

  • Air pump
  • Samples of each type of plastic bag

Station 5: Water Capacity

  • Water
  • Sink/Dump bucket
  • Samples of each type of plastic bag
  • Measuring cups/graduated cylinders

Station 6: Puncture Test

  • Pencil
  • Samples of each type of plastic bag

Safety

  • Always wear safety goggles when handling chemicals in the lab.
  • Students should wash their hands thoroughly before leaving the lab.
  • When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.

Teacher Notes

  • Background:
    • Molecules are the building blocks of matter.
    • Polymers are a chain of similar units of molecules that can allow materials to be flexible.
    • To become familiar with the production of plastic layers the first 2:22 minutes of this video is insightful.
  • Classroom management:
    • This best works if students are placed into groups of 3-4.
    • The stations should be set-up prior to the start of the class. Instructions for each station can be found as a separate file download. I suggest printing these instructions and placing them at each station with the required materials.
    • Any of the stations can be omitted depending on student ability or availability of materials.
    • Many samples of plastic bags will be needed in order to allow student groups to each complete all of the testing. If materials or time are limited, you can have the groups complete selected stations and share the results with the entire class.
    • The number/types of bags that are tested can be changed, depending on the materials available.
  • Differentiation: As an option you may ask advanced learners to conduct the same properties test as the class, but with an alternate questions (students could design the procedures themselves):
    • Do two bags hold twice as much as 1 bag?
    • Do three bags hold three times as much as 1 bag?
  • Engage students through informal conversation about shopping at the grocery store guiding them to the final question at check-out “Do you want plastic or paper bags?” Ask students which bag they would choose and why.
  • The teacher should demonstrate the test for each station with a paper bag, so that students understand the procedure and steps of each test that they will do with plastic bags. This will also allow students to easily see the difference in properties between paper and plastic.
  • Inform students that these tests reveal characteristics that describe an object, and those characteristics are known as physical properties.
  • Make sure students understand that they will test the properties of various plastic bags, in order to make recommendations for improvements as well as make a design plan for a plastic bag that meets a given set of criteria.

For the Student

Lesson

Background

Properties of matter have been observed in many lessons. This activity will show the importance of identifying and testing physical properties in the real-world. Today’s focus is on plastics. Large companies such as Dow Chemical are responsible for producing many different types of plastics for their customers, and so they are only as successful as the plastic products they produce. Testing the plastic materials that they produce is very important.

Pre-lab Questions

  1. There are many types of plastic bags for sale in the grocery store. How do you select which type to purchase?
  2. What makes one plastic bag better than another in your opinion?
  3. What physical properties, if any, did you identify in questions 1 and 2?

Objective

You will research and investigate the physical properties of a variety of plastic bags in order to design and develop a prototype bag.

Safety

  • Always wear safety goggles when handling chemicals in the lab.
  • Wash your hands thoroughly before leaving the lab.
  • Follow the teacher’s instructions for cleanup of materials and disposal of chemicals.

Procedure

  1. There are 6 Testing Stations. Instructions for completing each test are provided at each station.
  2. Follow the instructions at each station. You will complete the test for each plastic bag sample provided at the station. This means you will complete the same test multiple times while at the station.
  3. When you have completed a station, rotate to another testing station. You must complete the tests at each station.
  4. Record all of your test results in the data table provided below.

Data

Record all test results in the provided data table below.

Analysis

  1. Based on the collected data which plastic bag would you consider to be the best? Explain why.
  2. Plastics are made of molecules called polymers. Based on your testing, are all polymers the same? What similarities and differences did you observe?
  3. Choose the bag that you believe is the worst of the bags you tested. What improvements would you suggest to improve it?
  4. Were the tests that you completed during this lab reliable? Suggest a way that one of the tests you completed could be improved to make the results more reliable?

Conclusion

Pretend you are an employee for Dow Chemical Company. A customer wants you to design a special plastic bag for them that can hold 15lbs of sand, and it must be able to be lifted quickly without breaking as well as not puncture easily.

You have access to all of the materials needed to make any of the plastic bags that you tested today. Explain what materials you would use to design this bag (you can combine the materials from a variety of bags to make a unique bag!), be sure to explain why you are making these choices.