Identifying Unknown Polymers Using Density Measurements
Author: Vitaliy Baranovskiy
Source: This material is based upon work supported by the National Science Foundation under Grant No. EEC- 1542358.
Float/sink test on polymers adapted from: https://www.soinc.org/sites/default/files/uploaded_files/crimebusters/PolymersEnclosure.pdf
There are many different polymers with wide applications and uses. Basic polymers can be described by recycling code such as code 1 for PETE, polyethylene terephthalate. In this lesson activity students will become knowledgeable in six types of polymers and their common uses. Students will identify polymers by performing density measurements of each polymer. Results will be confirmed by float/sink test of each polymer.
What should students know as a result of this lesson?
Students will be able to identify:
- I can name and describe common uses of six polymers.
- I can classify polymers based on their density.
- I can classify polymers based on the recycling code.
What should the students be able to do as a result of this lesson?
Students will be able to do the following:
- Students will be able to measure density of unknown polymer via volume discplacement method.
- Students will be able to measure density of unknown polymer via geometrical volume calculation.
- Students will be able to explain how density can be used to identify unknown substances and its limitations.
- Polymer density cubes, cylinders, and pellets
- Electronic balance, graduated cylinder, water, and ruler
- Beakers, 46% isopropanol alcohol solution, 10% NaCl solution, saturated NaCl solution, vegetable oil
Students will be assigned one polymer to research information including chemical name of polymer, chemical/physical properties, recycling code, common uses and applications. (This activity can be individual assignment or pair students in groups of 2). Students will report their results on a small poster that shall include all information about that polymer and at least 2 pictures/examples.
List of polymers includes: PETE, HDPE, PVC, LDPE, PP, PS
Students will perform second analysis on unknown polymer sample by doing float/sink test.
- Teacher must prepare five beakers including:
- 46% isopropyl alcohol
- Vegetable oil
- 10% NaCl solution
- Saturated NaCl solution
Students will follow the chart to confirm their results on unknown polymer sample.
Students will report their results by identifying unknown polymer sample and answering following conclusion questions:
- Is density measurement accurate method for identifying polymers/elements? Why?
- Can density measurements correctly identify PVC and PETE? Why?
- What other tests can be used to identify unknown polymers/elements?
- Are higher density materials stronger or weaker than low density materials? Why?
- Students should be knowledgeable in procedure how to measure density of substances including geometrical projects and volume displacement method.
- Students should be knowledgable how to calculate density of materials. (D=M/V).
Best Teaching Practices
Prior to doing this activity, students will do information research into polymers to elevate their understanding of what polymers are and typical examples where they are used.
Alignment with Standards
- HS-PS1-3. Planning and Carrying Out Investigations
Planning and carrying out investigations in 9-12 builds on K-8 experiences and progresses to include investigations that provide evidence for and test conceptual, mathematical, physical, and empirical models.
Plan and conduct an investigation individually and collaboratively to produce data to serve as the basis for evidence, and in the design: decide on types, how much, and accuracy of data needed to produce reliable measurements and consider limitations on the precision of the data (e.g., number of trials, cost, risk, time), and refine the design accordingly.
- HS-PS1-3. Plan and conduct an investigation to gather evidence to compare the structure of substances at the bulk scale to infer the strength of electrical forces between particles.
- MS-PS1-3. Gather and make sense of information to describe that synthetic materials come from natural resources and impact society.
Identify questions that can be answered through scientific investigations;
- Design and conduct a scientific investigation
- Use appropriate mathematics, tools and techniques to gather data and information
- Analyze and interpret data
- Develop descriptions, models, explanations and predictions
- Think critically and logically to connect evidence and explanations
Density measurements and calculations
Applications (Where is this content applied in the “real world?”) When polymers are recycled, they must be property identified and sorted. In recycling industry, it is a big challenge to property identify and sort polymers. This activity will explore and answer those questions.
This will be assessed on their responses to four conclusion questions.
- When students are working on researching information for polymer poster, they should be working individually or in small group (2).
- When students are working on density measurements and float/sink test, they can work in groups up to 4 students per group.
- This activity can be implemented in two segments - information research on polymer (45 minutes) and density measurements/conclusions (45 minutes).
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