Plastics and Purposes

Overview

In this lesson, students identify common plastics and relate key properties to real-world uses. This builds toward the unit “Exploring Organic Chemistry Layers” by linking chemistry concepts to everyday materials and product design choices.

Learning intentions

• WALT identify common plastics used in consumer products.
• WALT describe key properties (e.g., strength, flexibility, heat resistance, chemical resistance, recyclability).
• WALT explain why designers select particular plastics for specific products using evidence from properties.
• WALT communicate findings clearly using scientific language and supported reasoning.

Success criteria

• I can correctly match at least 3 plastics to common uses and justify the match.
• I can describe how a plastic’s properties affect its suitability for a product.
• I can record fair test observations or evidence and use them to support a conclusion.
• I can use scientific terms accurately when explaining my choices.

Curriculum links

• NZ Curriculum Science: Developing understanding of materials and substances by linking observable properties to underlying science ideas.
• AS91187 (Carry out a practical Earth and Space Science investigation): Today supports the investigation process skills used across practical work (purpose, method, data, conclusion, reporting), even though the focus is plastics chemistry rather than Earth/space.
• Nature of Science and practical investigation expectations: using a method to collect raw data and then interpreting it to draw conclusions.
• Key competencies: Thinking (making evidence-based links), Managing self (staying safe and on task), Using language/symbols (scientific communication), Participating and contributing (group roles and shared data).

Lesson structure (60 minutes)

1. 0–5 min · Hook and purpose. Teacher displays 6–8 item images/real samples (e.g., water bottle, takeaway lid, shopping bag, food wrap, yoghurt tub, phone case) and asks: “Which plastic do you think it is and why?” Students turn-and-talk, then share one guess with a reason.

2. 5–15 min · Mini-teach: common plastics overview. Teacher introduces the most common plastics students will encounter: PET, HDPE, PVC, LDPE, PP, PS, and (where relevant) PP/PE blends; focus is on properties relevant to uses (mouldability, toughness, stiffness, transparency, flexibility, temperature tolerance, barrier properties, and typical recycling pathways). Students complete a quick “properties-to-uses” table using prompts.

3. 15–30 min · Practical stations: property “clues”. Teacher sets up 3 stations with safe, teacher-guided checks that reveal usable evidence without requiring hazardous heating.

• Station A: Density/float test in water (for relevant samples with different densities) and record which float/sink.
• Station B: Flexibility/rigidity (bend tests on comparable pieces; measure approximate “bend” distance if possible or use a qualitative scale).
• Station C: Solubility/chemical resistance clue (wipe test with common mild liquids used in daily life, or observation of surface changes; teacher controls materials and ensures safe handling). Students rotate in groups, recording raw observations in a shared table (what they saw, measured, or categorised). Teacher circulates to prompt fair method thinking (same sample size/shape, record consistently).

4. 30–38 min · Data processing and pattern finding. Teacher guides students to convert observations into processed information: e.g., create a simple classification (flexible vs rigid; float vs sink; surface change vs none) and then link to likely plastics and uses. Students use their table to draft 2–3 claims: “Because it floats and is flexible, it is likely … and therefore fits a use like …”

5. 38–52 min · Apply: “Design the product” reasoning task. Teacher gives each group a product scenario strip:

• Option examples: “Choose packaging for take-home salad that must resist leaks,” “Choose a sturdy storage container for a garage,” “Choose a transparent bottle for fizzy water,” “Choose a flexible bag for groceries,” “Choose a lid material for microwavable convenience food.” Groups must propose the most suitable plastic(s) using property reasoning, including at least one trade-off (e.g., stiffness vs flexibility; temperature limits; recyclability considerations). Students write a brief explanation that includes evidence from their station observations or provided property summaries.

6. 52–58 min · Whole-class sharing and clarification. Teacher selects 2–3 groups to share their reasoning, then asks the class to question the evidence: “What property in your explanation matches the product requirement?”

7. 58–60 min · Exit ticket. Students answer:

• “Name one plastic and one everyday product it suits, and justify using a property.”
• “List one property trade-off designers must consider.”

Resources

• Assorted plastic samples (or labelled cut pieces) representing PET, HDPE, PVC, LDPE, PP, PS
• Station worksheets with data tables (raw and processed columns)
• Water trays, measuring cups, and labelled waste containers
• PPE: safety glasses for all students, lab coats/aprons where available, disposable gloves as needed
• Timer, rulers/measure tapes, bend-rating sheet (e.g., 1–5 scale)
• Mild household liquids for surface observation (teacher-selected and controlled)
• Cloths/paper towels, tongs or clamps for handling samples
• Scoring rubric card (optional) for “property → product” justification sentence starters

Assessment

• Formative checks during stations: teacher observes recording of raw data (clarity and consistency) and safe, controlled method choices.
• Formative check in the design task: teacher reviews group claims to ensure they link property evidence to product requirements.
• Exit ticket to confirm individual understanding of “plastic type → properties → use.”

Differentiation

• Support: Provide sentence starters for justification (e.g., “The property that makes this suitable is… because…”) and a simplified properties-to-uses reference card.
• Support: Offer a worked example of converting raw observations into a processed classification.
• Extension: Challenge students to include recyclability or end-of-life considerations and justify why certain plastics are preferred or avoided in specific products.
• EAL/SEN: Allow diagrams and icons in data tables; pre-teach key terms (flexible, rigid, transparent, barrier, density, resistance) and permit vocabulary banks during the design task.