Activity 01
Pairs: Marker Chromatography
Pairs draw marker lines on filter paper strips, suspend in shallow water, and observe pigment separation over 10 minutes. They measure travel distances and discuss why colors separate differently. Record results in notebooks for class comparison.
Explain the process of evaporation to recover salt from saltwater.
Facilitation TipDuring Marker Chromatography, remind pairs to handle papers by the edges to avoid smudging and to make a straight baseline above the solvent to ensure clean separation.
What to look forPresent students with three beakers: one with saltwater, one with ink, and one with milk. Ask them to write down which separation technique (evaporation, distillation, or chromatography) would be most appropriate for each mixture and why.
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Activity 02
Small Groups: Salt Evaporation Race
Groups place equal saltwater volumes in shallow dishes under lamps or sunlight, weigh daily, and note when salt crystals form. Compare evaporation rates and purity of recovered salt. Discuss variables like surface area.
Compare the principles behind distillation and chromatography.
Facilitation TipIn the Salt Evaporation Race, circulate with a timer so groups see how heat speed affects crystal appearance and connect time to energy input.
What to look forGive students a card asking them to draw a simple diagram showing how evaporation can be used to separate salt from water. Include labels for the salt, water, heat source, and the recovered salt.
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Activity 03
Whole Class: Tea Bag Distillation
Teacher demonstrates heating tea-stained water through a straw condenser into a cold cup; students predict outcomes and draw particle models before and after. Class discusses boiling point differences in water and solutes.
Assess the most appropriate separation technique for different types of solutions.
Facilitation TipFor Tea Bag Distillation, place the cold surface close enough to the rising steam so condensation happens quickly and students observe the purified water collect.
What to look forFacilitate a class discussion using the prompt: 'Imagine you have a mixture of two different colored marker inks. Which separation technique would you choose to separate the colors and why? What do you expect to happen?'
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Activity 04
Individual: Colloid Filter Test
Students filter milk, muddy water, and saltwater through coffee filters, observe residues, and classify mixtures. Note which pass through completely and explain using size of particles.
Explain the process of evaporation to recover salt from saltwater.
Facilitation TipWhen running the Colloid Filter Test, give each student a dropper to control the flow through filter paper and watch for the moment when clear filtrate appears.
What to look forPresent students with three beakers: one with saltwater, one with ink, and one with milk. Ask them to write down which separation technique (evaporation, distillation, or chromatography) would be most appropriate for each mixture and why.
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Generate Complete Lesson→A few notes on teaching this unit
Teachers should start with quick demos that show surprising results, like ink splitting into colors or salt reappearing after heating. Avoid long explanations before hands-on work; let students notice patterns and ask questions first. Research shows guided inquiry with real materials builds stronger conceptual change than lectures alone.
Students will correctly match separation techniques to mixtures, explain why filters fail on solutions, and describe how heat or solvent flow moves particles. They will use new vocabulary in discussions and diagrams to show understanding of reversible changes.
Watch Out for These Misconceptions
During Marker Chromatography, watch for students who think all colors separate by size alone.
Pause the activity after the first run and ask groups to compare ink colors that traveled far with those that stayed near the baseline, prompting them to notice solubility differences and adhesion to paper.
During Salt Evaporation Race, watch for students who believe the salt disappears when the water boils away.
Have students touch the dry dish with a clean spoon after cooling and taste a pinch to confirm the salt remains, then revisit the idea of solvent removal versus solute loss.
During Colloid Filter Test, watch for students who think filters can remove dissolved particles like salt.
Ask students to compare the clear filtrate from muddy water with the cloudy filtrate from milk, then discuss why filters catch large colloid particles but let dissolved salts pass through.
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