Science · Year 7

Active learning ideas

Separation Techniques: Filtration and Decantation

Active learning lets students test ideas immediately with real mixtures, turning abstract ideas about particle size and solubility into tangible results. When students handle sand, water, and filter paper themselves, they see why some particles pass through and others get trapped, building lasting understanding.

• ACARA Content Descriptions
• AC9S7U06

• 20–45 min
• Pairs → Whole Class
• 4 activities

Activity 01

• Inquiry Circle
• 25 min · Pairs

Pairs: Sand-Water Filtration Race

Pairs mix sand and water in beakers, then filter using coffee filters over funnels into clean containers. They time the process and rate the filtrate clarity on a scale of 1-5. Compare results with a partner who uses decantation instead.

Differentiate between filtration and decantation as separation techniques.

Facilitation Tip

During Sand-Water Filtration Race, circulate to ensure pairs fold filter paper correctly and pour slowly to avoid spills, preventing lost time and wasted materials.

What to look for

Provide students with two beakers: one containing muddy water and another containing clear water. Ask them to write down which separation technique, filtration or decantation, would be most effective for each sample and why. They should also identify what the residue and filtrate would be in the muddy water sample.

• Analyze
• Evaluate
• Create
• Self-Management
• Self-Awareness

Activity 02

• Inquiry Circle
• 35 min · Small Groups

Small Groups: Decantation Design Challenge

Groups layer different-sized sand in water, let settle for 5 minutes, then decant into test tubes. They predict settling times, pour slowly to avoid disturbance, and measure solid residue left behind. Discuss why larger particles settle faster.

Design an experimental procedure to separate sand from water using appropriate techniques.

Facilitation Tip

In Decantation Design Challenge, remind groups to sketch their plan before testing so they connect theory to measurable outcomes like settling time and clarity.

What to look for

Display images of different scenarios: a tea bag steeping, a sieve separating pasta from water, and a settled mixture of oil and vinegar. Ask students to identify which scenarios demonstrate filtration and which demonstrate decantation, and to briefly explain their reasoning for each.

• Analyze
• Evaluate
• Create
• Self-Management
• Self-Awareness

Activity 03

• Inquiry Circle
• 45 min · Whole Class

Whole Class: Purification Effectiveness Test

Class prepares contaminated water samples with soil and leaves. Each student filters a sample, tests pH and turbidity before/after, and shares data on a class chart. Vote on the best method for clean drinking water.

Evaluate the effectiveness of filtration in purifying contaminated water.

Facilitation Tip

For the Purification Effectiveness Test, prepare two identical muddy water samples so every group compares results directly, reinforcing the idea of controlled variables.

What to look for

Pose the question: 'Imagine you need to separate salt from water. Would filtration or decantation work? Explain why or why not, and what property of salt makes these methods unsuitable.' Guide the discussion towards the concept of solubility.

• Analyze
• Evaluate
• Create
• Self-Management
• Self-Awareness

Activity 04

• Inquiry Circle
• 20 min · Individual

Individual: Procedure Planning Worksheet

Students draw and label steps to separate gravel, sand, and salt water using both techniques. They list materials, safety steps, and success criteria, then test their plan with teacher-provided mixtures.

Differentiate between filtration and decantation as separation techniques.

What to look for

Provide students with two beakers: one containing muddy water and another containing clear water. Ask them to write down which separation technique, filtration or decantation, would be most effective for each sample and why. They should also identify what the residue and filtrate would be in the muddy water sample.

• Analyze
• Evaluate
• Create
• Self-Management
• Self-Awareness

A few notes on teaching this unit

Start with a quick demo of pouring dirty water through a coffee filter to show immediate visual results, then have students predict what will get caught. Avoid long lectures on solubility; instead, let evidence from their own tests drive concept development. Research shows hands-on mixing and observing outperforms diagrams alone for Year 7 learners.

Students will confidently choose the right technique based on solid properties, describe how each method works, and explain their reasoning using precise terms like residue, filtrate, and insoluble. You’ll notice clear links between procedure choices and outcomes during their explanations.

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Watch Out for These Misconceptions

• During Sand-Water Filtration Race, watch for students assuming dyed salt water filters cleanly.

  Have pairs test dyed salt water at their station after filtering sand-water mixtures, then discuss why color remains in the filtrate and what this shows about dissolved substances.

• During Decantation Design Challenge, watch for students believing decantation works instantly regardless of particle size.

  Ask groups to time how long fine sand vs coarse sand takes to settle, then adjust their pouring speed and record observations to connect particle behavior with method effectiveness.

• During Purification Effectiveness Test, watch for students thinking filtration and decantation work the same way for all solids.

  Set up stations with fine clay, coarse sand, and gravel so students compare clogging rates and clarity differences, prompting them to articulate when to choose each method.

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Methods used in this brief

• Inquiry Circle