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.