Gas Properties Demo

Overview

In this lesson (3 of 8), students investigate gases as matter by observing that gases take up space and have mass. They plan and run a repeatable, fair investigation using hands-on demonstrations and record evidence to explain their observations using particle ideas.

Learning intentions

• WALT investigate observable properties of gases using particle modelling ideas about motion and spacing.
• WALT conduct a repeatable investigation to test whether gases have mass and take up space.
• WALT use equipment to measure, record data, and communicate findings clearly.
• WALT compare results with those of others and consider possible sources of error.

Success criteria

• I can describe that gases take up space using evidence from my investigation.
• I can demonstrate and explain that gases have mass using a comparison (e.g. empty vs filled balloon).
• I can plan a fair test by deciding what to change, measure and control.
• I can record measurements in a table and use them as evidence to support a reasoned conclusion.

Curriculum links

• Science — AC9S5U04: explain observable properties of solids, liquids and gases by modelling the motion and arrangement of particles.
• Science — AC9S5I02: plan and conduct repeatable investigations; decide variables for fair tests; plan safe use of equipment.
• Science — AC9S5I03: use equipment to observe, measure and record data with reasonable precision.
• Science — AC9S5I05: compare methods and findings; recognise possible sources of error; draw reasoned conclusions.

Lesson structure (80 minutes)

1. 0–5 min · Starter prompt. Teacher displays two items: an empty balloon and a balloon filled with air; students quickly predict which one weighs more and why, with a short think-write.
2. 5–15 min · Direct teach: gases and particles. Teacher leads a brief discussion linking observations to particle modelling (gas particles are far apart and move freely; gases can spread out to fill space). Students complete a 3-sentence class scaffold: “Gas particles… / When gas fills a container… / This helps explain why…”.
3. 15–25 min · Safety + investigation planning. Teacher explains the investigation task and fairness: students must compare empty vs filled (or “less air” vs “more air”) under controlled conditions. In groups, students record:

• variable to change (amount of air/gas)
• variable to measure (mass/reading on balance)
• variables to control (balloon type, size, sealing method/time, scale position, distance from drafts). Teacher checks plans and revises misconceptions.

4. 25–50 min · Investigation 1: gases have mass. Students run a repeatable test using a digital balance:

• Place balloon (empty or lightly deflated) on the balance; record mass.
• Inflate to a consistent method (same number of breaths or using a hand pump with a set number of squeezes); tie off; record mass.
• Repeat at least 2 times to build reliability. Teacher circulates for precision (unit use, consistent measurement technique, quiet workspace).

5. 50–63 min · Investigation 2: gases take up space. Students test with a syringe or sealed container (e.g. press plunger and observe resistance, or use a simple container with a balloon/air bag). They record observable evidence (movement/resistance/volume change) and connect it to particle spacing filling the space. Teacher prompts: “What tells you the gas is occupying space?”
6. 63–72 min · Compare + error check. Groups share their two sets of findings. Teacher leads a short compare-and-clarify: possible sources of error (drafts, balloon not fully tied, inconsistent inflation amount, different balloon sizes, balance settling time). Students update their conclusion statement using evidence language (“Our evidence shows…”).
7. 72–80 min · Exit ticket. Individual exit ticket (3 items):

• one sentence explaining gases have mass (with reference to their measurement)
• one sentence explaining gases take up space (with reference to observation)
• one question they could investigate next (e.g. effect of more air or different container size).

Resources

• Digital scales/balances (with appropriate batteries/level surface)
• Balloons (same size/material), hand pump or consistent inflation method (as available)
• Measuring records sheet/table for mass and repeats
• Syringes without needles, or sealed container setup to show gas occupying space
• Sticky notes or whiteboards for quick predictions
• Data recording tools (clipboards, pencils, printed tables)
• Timer for consistent measurement intervals
• Safety goggles (optional but recommended) and a clear area away from drafts

Assessment

• Formative: teacher checks investigation plans for fair-test variables and controlled conditions during the planning step.
• Formative: teacher observes measurement technique and accuracy of recorded units during both investigations.
• Formative/summative in lesson: group discussion identifies sources of error; exit ticket checks evidence-based explanations of mass and space.

Differentiation

• Support: provide a partially completed fair-test planning template (sentence starters for “We will change… We will keep… We will measure…”). Offer guided roles in groups (timekeeper, recorder, equipment manager).
• Support: model one measurement step with students watching closely (where to place the balloon, when to read the balance after settling).
• Extension: challenge students to refine consistency (e.g. create a standard inflation routine and compare results if inflation method differs slightly).
• EAL/SEN: allow oral rehearsal of conclusion sentences before writing; provide word bank for particle explanation (particles, spaced apart, moving freely, spread out, occupies space, has mass, evidence).

Extension (optional)

• Students investigate how changing pressure affects gases using different containers (e.g. compare syringe readings when the plunger is pushed to different depths or compare gas under different container volumes). They record observations and link changes to particle movement and spacing.