Science · Grade 7

Active learning ideas

Suspensions and Colloids

Active learning works for suspensions and colloids because students need hands-on experience to see how particle size affects mixture behavior. Direct observations at lab stations and timed tests let students connect theory to what they can feel, see, and measure.

• Ontario Curriculum Expectations
• MS-PS1-1

• 30–45 min
• Pairs → Whole Class
• 4 activities

Activity 01

• Stations Rotation
• 45 min · Small Groups

Lab Stations: Mixture Preparation

Set up stations for solution (dissolve salt in water), suspension (mix sand in water), and colloid (dilute milk). Students shake mixtures, observe initial appearance, then let stand to check settling. Test Tyndall effect with a laser pointer through each.

Differentiate between a solution, a suspension, and a colloid.

Facilitation Tip

During Lab Stations: Mixture Preparation, set out clear labels and safety reminders so students focus on mixing and observing rather than setup.

What to look for

Present students with three unlabeled beakers, each containing a different mixture (e.g., salt water, sand in water, milk). Ask them to observe each mixture, perform a flashlight test for the Tyndall effect, and then classify each mixture as a solution, suspension, or colloid, providing one reason for each classification.

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

Activity 02

• Stations Rotation
• 30 min · Pairs

Tyndall Effect Challenge: Light Scatter Test

Prepare samples of solution, suspension, and colloid in clear containers. Pairs shine flashlights through samples in a darkened room, sketch light paths, and classify based on beam visibility. Discuss results as a class.

Explain why particles in a suspension eventually settle out.

Facilitation Tip

For the Tyndall Effect Challenge: Light Scatter Test, use a single flashlight beam in a darkened corner to maximize the scatter effect for all groups.

What to look for

Pose the question: 'Imagine you are a scientist trying to determine if a new liquid is a solution, suspension, or colloid. What two tests would you perform, and what would you look for in the results of each test to make your determination?' Facilitate a class discussion where students share their proposed tests and expected observations.

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

Activity 03

• Stations Rotation
• 35 min · Small Groups

Settling Race: Prediction and Timing

Students mix suspensions with varying particle sizes like flour, chalk dust, and soil in water. Predict and time settling rates in graduated cylinders. Graph results to identify patterns in particle behavior.

Analyze how the Tyndall effect helps distinguish colloids from solutions.

Facilitation Tip

During Settling Race: Prediction and Timing, have students record predictions first to make the timing data meaningful and debatable.

What to look for

Provide students with a scenario: 'A student mixes flour and water. After stirring, the mixture looks cloudy, and some bits of flour are visible. What type of mixture is this most likely, and what will happen if it sits for an hour?' Students write their answers, justifying their choice based on particle size and settling.

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

Activity 04

• Stations Rotation
• 40 min · Individual

Colloid Maker: Everyday Examples

Individuals create colloids like gelatin or starch suspension, then test stability and Tyndall. Compare to homemade suspension and solution. Journal differences in appearance and behavior over 24 hours.

Differentiate between a solution, a suspension, and a colloid.

Facilitation Tip

For Colloid Maker: Everyday Examples, provide labeled containers of common colloids so students can connect lab work to familiar items.

What to look for

Present students with three unlabeled beakers, each containing a different mixture (e.g., salt water, sand in water, milk). Ask them to observe each mixture, perform a flashlight test for the Tyndall effect, and then classify each mixture as a solution, suspension, or colloid, providing one reason for each classification.

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

A few notes on teaching this unit

Teach this topic by letting students experience the differences firsthand rather than explaining them upfront. Use guided inquiry so students notice patterns, then name the concepts. Avoid lecturing about particle sizes; instead, let observations drive the discussion. Research shows students retain concepts better when they test predictions and explain discrepancies.

Students will confidently classify mixtures by particle size, predict settling behavior, and explain observations using evidence from their experiments. They will use terms like Tyndall effect, Brownian motion, and particle size to justify their answers.

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Watch Out for These Misconceptions

• During Lab Stations: Mixture Preparation, watch for students labeling all cloudy mixtures as solutions.

  Have students test each mixture with a flashlight in the Tyndall Effect Challenge afterward. Ask them to note which mixtures scatter light and which remain clear, using the scatter as evidence for particle size.

• During Settling Race: Prediction and Timing, watch for students assuming colloids settle like suspensions.

  After the Settling Race, review the data as a class. Ask students to explain why some mixtures settled quickly while others did not, pointing to particle size and Brownian motion in the colloid samples they made.

• During Tyndall Effect Challenge: Light Scatter Test, watch for students thinking particle size does not affect scatter.

  During the Tyndall test, have students compare the brightness and spread of the light beam across different mixtures. Ask them to link the intensity of scatter to particle size, using their observations to refine their understanding of stability.

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Methods used in this brief

• Stations Rotation