Science · Grade 7

Active learning ideas

Filtration and Decantation

Active learning works because separation techniques like filtration and decantation rely on hands-on observation of physical changes, not just abstract concepts. Students must see particles settle or get trapped to truly grasp why density and size matter in mixtures. These techniques become real when students test them themselves rather than just hearing about them.

• Ontario Curriculum Expectations
• MS-PS1-2

• 20–50 min
• Pairs → Whole Class
• 4 activities

Activity 01

• Stations Rotation
• 45 min · Small Groups

Stations Rotation: Separation Stations

Set up four stations with mixtures like sand-water, gravel-water, soil-water, and chalk-water. Students test filtration using coffee filters and funnels, then decantation after settling. They record clarity, time, and residue in journals before rotating. Discuss comparisons as a class.

Explain how filtration separates insoluble solids from liquids.

Facilitation Tip

During Separation Stations, set up each station with clear labeled equipment and safety reminders so students move efficiently and focus on the separation, not setup.

What to look for

Provide students with two scenarios: 1) Separating fine sand from water. 2) Separating small pebbles from water. Ask them to choose the best separation method (filtration or decantation) for each scenario and write one sentence explaining why.

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

Activity 02

• Experiential Learning
• 50 min · Pairs

Design Challenge: Custom Separators

Provide mixtures of sand, salt, and water. In pairs, students design and test a sequence using filtration and decantation. They sketch procedures, predict outcomes, perform trials, and refine based on results. Share best methods with the class.

Design a method to separate sand from water using decantation.

Facilitation Tip

When students build Custom Separators, circulate with guiding questions like 'How will your design catch the sand but let the water through?' to push their thinking.

What to look for

During a hands-on activity, circulate and ask students: 'What physical property are you using to separate these components?' and 'How do you know when to stop pouring in decantation?'

• Apply
• Analyze
• Evaluate
• Self-Awareness
• Self-Management
• Social Awareness

Activity 03

• Experiential Learning
• 30 min · Individual

Filter Material Testing

Give students cloth, paper towels, sand, and sieves. They filter muddy water samples individually, measure filtrate clarity with a scale, and rank materials. Graph results and explain choices based on pore size.

Compare the effectiveness of filtration and decantation for different mixtures.

Facilitation Tip

During Filter Material Testing, provide a timer and data table for students to record how long each filter takes and how clear the filtrate becomes.

What to look for

Pose the question: 'Imagine you have a mixture of salt and water, and another mixture of sand and water. Which separation technique, filtration or decantation, could you use for each? Explain your reasoning, considering what happens when salt dissolves.'

• Apply
• Analyze
• Evaluate
• Self-Awareness
• Self-Management
• Social Awareness

Activity 04

• Experiential Learning
• 20 min · Whole Class

Mixture Comparison Demo

As a whole class, prepare large containers of settling mixtures. Demonstrate decantation with a turkey baster, then filter samples. Students vote on best method per mixture and justify with observations.

Explain how filtration separates insoluble solids from liquids.

Facilitation Tip

In the Mixture Comparison Demo, pause after each step to ask, 'What do you notice about the liquid now?' so students connect observations to separation progress.

What to look for

Provide students with two scenarios: 1) Separating fine sand from water. 2) Separating small pebbles from water. Ask them to choose the best separation method (filtration or decantation) for each scenario and write one sentence explaining why.

• Apply
• Analyze
• Evaluate
• Self-Awareness
• Self-Management
• Social Awareness

A few notes on teaching this unit

Teach this topic by letting students experience the limits of each method firsthand. Start with simple mixtures where decantation works, then introduce fine particles that challenge it. Avoid telling them which method to use immediately; instead, let them try and fail, then guide them to analyze why. Research shows this trial-and-error approach builds deeper understanding than lectures about density or solubility alone. Always connect the activities back to real-world examples, like cleaning water or separating recyclables, to show relevance.

Successful learning looks like students confidently choosing the right method for a given mixture, explaining their choice based on particle behavior, and demonstrating clean separation without losing materials. You will notice students comparing techniques, adjusting their procedures, and critiquing results with peers. The goal is for them to see filtration and decantation as practical tools, not just classroom tasks.

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Watch Out for These Misconceptions

• During Filter Material Testing, watch for students who assume all filters will produce clear water regardless of material.

  Have students test the filtrate from salt water and food coloring, then taste the filtrate to notice the salt remains, directly addressing the idea that filtration removes dissolved substances.

• During Mixture Comparison Demo, watch for students who believe decantation works well for all solids.

  Ask students to time how long it takes clay, sand, and pebbles to settle, then have them observe which mixtures leave cloudy liquid after pouring, linking settling speed to method choice.

• During Separation Stations, watch for students who think filtration and decantation produce identical results.

  Set up side-by-side trials with the same mixture and ask students to compare speed, clarity, and material loss, then discuss why one method might be better for fine particles.

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Methods used in this brief

• Stations Rotation
• Experiential Learning