Investigating Plastics

Active learning works well for this topic because plastics are tangible materials students interact with daily, making abstract molecular concepts concrete through hands-on testing. Investigating real samples builds durable understanding of polymer properties and their environmental impact, which lectures alone cannot achieve.

• 5th Year
• Foundations of Matter and Chemical Change
• 4 activities
• 25 min–50 min

Learning Objectives

1. Classify common plastics into categories based on their chemical structure and observable properties.
2. Analyze the relationship between a plastic's molecular structure and its physical characteristics, such as elasticity and melting point.
3. Evaluate the environmental impact of different plastic types, considering factors like biodegradability and recyclability.
4. Calculate the molar mass of the repeating unit for common polymers like polyethylene and polystyrene.
5. Design a simple experiment to compare the solubility of different plastics in common solvents.

Stations Rotation

⏱ 45 min·Small Groups

Stations Rotation: Plastic Property Tests

Prepare stations with plastic samples (PET, HDPE, PP). Include float/sink for density, bend tests for flexibility, and hot pin for burn characteristics. Groups rotate every 10 minutes, tabulate results, and identify plastics by code. Conclude with class chart comparing properties.

Prepare & details

What are plastics made of?

Facilitation Tip: For Station Rotation: Plastic Property Tests, pre-label each station with clear safety instructions and sample disposal guidelines to prevent cross-contamination.

Setup: Tables/desks arranged in 4-6 distinct stations around room

Materials: Station instruction cards, Different materials per station, Rotation timer

• Remember
• Understand
• Apply
• Analyze
• Self-Management
• Relationship Skills

⏱ 40 min·Whole Class

Whole Class: School Waste Audit

Collect one week's plastic waste from classrooms. Sort into types, weigh portions, and calculate percentages by category. Discuss sources and recycling feasibility, graphing data to visualize waste patterns.

Prepare & details

Why do we use so much plastic?

Facilitation Tip: During Whole Class: School Waste Audit, assign roles such as data recorder, sorter, and observer to ensure all students contribute meaningfully.

⏱ 25 min·Pairs

Pairs: Polymer Chain Models

Use pipe cleaners or straws as monomers to build linear and branched polymer models. Test model flexibility to link structure to properties. Pairs present how changes in repeat units alter real plastic behaviors.

Prepare & details

What are the problems with plastic waste?

Facilitation Tip: With Pairs: Polymer Chain Models, provide pipe cleaners or paper clips in two colors to clearly distinguish monomers and cross-linkers.

⏱ 50 min·Small Groups

Small Groups: Recycling Challenge Design

Provide mixed plastic scraps. Groups design and prototype a useful item like a planter, considering sorting and joining methods. Share prototypes and evaluate feasibility for waste reduction.

Prepare & details

What are plastics made of?

Facilitation Tip: For Small Groups: Recycling Challenge Design, give each group a different plastic type to research so findings can be shared across the class.

Teaching This Topic

Experienced teachers approach this topic by emphasizing direct observation first, then connecting observations to molecular explanations. Avoid rushing to definitions—instead, let students puzzle through why plastics behave differently before introducing terms like thermoplastic or thermoset. Research shows students retain concepts better when they test predictions and revise their models through evidence.

What to Expect

Successful learning looks like students confidently classifying plastics by properties, connecting molecular structures to material behaviors, and proposing realistic solutions to recycling challenges. They should articulate why plastics vary in use and waste impact using evidence from their investigations.

Watch Out for These Misconceptions

Common Misconception

During Station Rotation: Plastic Property Tests, watch for students assuming all plastics melt when heated.

What to Teach Instead

Have students compare a thermoplastic like polyethylene with a thermoset like Bakelite during burn tests, noting differences in melting and charring. Ask them to sketch observations and explain how cross-linking affects behavior.

Common Misconception

During Whole Class: School Waste Audit, watch for students assuming plastics disappear over time like food waste.

What to Teach Instead

Use the waste audit to collect plastic samples and bury them in soil in small containers for long-term observation. Have students record daily changes and discuss why plastics persist rather than biodegrade.

Common Misconception

During Small Groups: Recycling Challenge Design, watch for students overestimating recycling's effectiveness.

What to Teach Instead

Give groups contaminated plastic samples to sort and explain why these would be rejected in real recycling facilities. Ask them to calculate contamination rates and propose solutions to reduce waste in the sorting process.

Assessment Ideas

Quick Check

After Station Rotation: Plastic Property Tests, provide samples of PET, HDPE, LDPE, and PP. Ask students to record density, flexibility, and texture observations, then assign recycling codes. Collect responses to check accuracy and reasoning.

Discussion Prompt

After Whole Class: School Waste Audit, pose the question: 'How can we reduce plastic waste in our school while maintaining safety and convenience?' Facilitate a discussion where students reference their audit data to propose realistic changes.

Exit Ticket

During Pairs: Polymer Chain Models, ask students to write down the plastic type they modeled, its monomer structure, and one property that makes it suitable for its common use. Collect tickets to assess understanding of structure-property relationships.

Extensions & Scaffolding

• Challenge: Ask early finishers to research biodegradable alternatives for one of the plastics tested and present their findings to the class.
• Scaffolding: For students struggling with density tests, provide a labeled density column setup with known liquids (water, oil, syrup) to help them compare plastic samples.
• Deeper: Invite students to design an experiment testing plastic degradation over time, using ultra-violet light or soil burial as variables.

Key Vocabulary

Polymer	A large molecule made up of many repeating smaller units called monomers. Plastics are synthetic polymers.
Monomer	The small, repeating molecular unit that links together to form a polymer. For example, ethylene is the monomer for polyethylene.
Polymerization	The chemical process where monomers join together to form a long polymer chain.
Biodegradability	The ability of a material to break down naturally through the action of microorganisms over time. Many plastics are not readily biodegradable.
Recycling Codes	Numbers within a chasing arrows symbol used to identify different types of plastic resins, aiding in sorting for recycling.