Free sample lesson · Grades 7–10 Science · about 45 minutes
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Goal
I can tell the difference between a pure substance and a mixture, classify mixtures as homogeneous or heterogeneous, and choose a way to separate them.
1. Warm-up
Think of halo-halo and a glass of clear salt water. In which one can you still see the different parts? Why can’t you see the salt in the water?
2. Learn
- Pure substance — has a fixed composition. It can be an element (one kind of atom, like copper or gold) or a compound (elements chemically joined, like water or table sugar).
- Mixture — two or more substances mixed physically. Each keeps its own properties and the amounts can change.
- Homogeneous mixture — looks the same throughout; you cannot see the parts (salt water, air, vinegar).
- Heterogeneous mixture — you can see the different parts (halo-halo, sand and water, oil and water).
3. Separating mixtures
| Method | How it works | Example |
|---|---|---|
| Filtration | A filter lets liquid through and traps solid bits | Sand from water |
| Decantation | Let solids settle, then pour off the liquid | Muddy water |
| Evaporation | Heat the liquid until it becomes gas; the dissolved solid is left | Salt from salt water |
| Magnet | Pulls out magnetic materials | Iron filings from sand |
4. Practice: classify each
Write P (pure substance), HOM (homogeneous mixture) or HET (heterogeneous mixture).
- Halo-halo
- Salt water
- Distilled water
- Copper wire
- Air
- Garden soil
- Table sugar
- Oil and water
Choose a method: 9. Get salt back from salt water. 10. Remove iron filings from sand. 11. Get clear water from sandy water.
Show answers
- HET
- HOM
- P (compound)
- P (element)
- HOM
- HET
- P (compound)
- HET
- Evaporation
- Magnet
- Filtration (or decantation, then filtration)
5. Home investigation (with an adult)
Stir one teaspoon of salt into half a cup of water. Describe what you see. Pour a little into a saucer and leave it in the sun for a day or two. What is left? Explain using the words mixture and evaporation.
6. Reflect
Name one mixture you use every day and say whether it is homogeneous or heterogeneous.
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