Separation
Filtration, evaporation, sieving mixtures.
Separation
Separation Techniques
What you'll learn
- Methods to separate mixtures without chemical change: filtration, evaporation, sieving, hand-picking, magnetic separation.
- Which method fits which mixture — decision table approach.
- NCERT Looking Around 5, Chapter 7 (Experiments with Water) — cleaning muddy water, salt from water.
Key concepts
Level 1 — Choose the method
Verbal: Separation uses differences in size, solubility, magnetism, or boiling point.
Symbolic: Mixture → technique → pure components (physical separation).
| Mixture | Method | Reason |
|---|---|---|
| Muddy water | Filtration | Sand/mud insoluble — trapped in filter |
| Salt water | Evaporation | Water evaporates; salt remains |
| Rice and stones | Hand-picking / sieving | Size difference |
| Iron filings + sand | Magnet | Iron is magnetic |
NCERT link: Ch 7 — filter paper funnel; drying salt from seawater (concept).
Level 2 — Filtration and evaporation details
Verbal: Filtration needs filter paper/cloth; evaporation needs heat and open container.
Real-life: Tea strainer (filtration); making salt from sea water in coastal areas; wheat flour sieved before baking.
| Tool | Separates |
|---|---|
| Sieve (chhalni) | Fine flour from bran |
| Filter funnel | Solid from liquid |
| Sun + shallow pan | Water from salt (evaporation) |
Worked example
How to get clean water from muddy pond water?
Step 1 — Allow heavy mud to settle (decantation intro).
Step 2 — Pour upper layer through filter cloth/paper.
Step 3 — Optional: boil before drinking (kill microbes — biology link).
Answer: Settling + filtration; boil for safety.
Recover salt from salt solution.
Step 1 — Pour solution in wide dish.
Step 2 — Heat or leave in sun — water evaporates.
Step 3 — White salt crystals remain.
Answer: Evaporation.
Common mistakes
| Mistake | Why it happens | Fix |
|---|---|---|
| Filter dissolves salt from water | Filter only removes insoluble solids | Salt passes through — need evaporation |
| Evaporation loses salt | Thinking salt evaporates | Water evaporates; salt stays |
| Any mixture needs one method only | Multi-step needed | Muddy salt water: filter mud, then evaporate salt |
| Sieving separates dissolved sugar | Size vs dissolved | Sugar in water — use evaporation or distillation (intro) |
Quick check
- Method for iron filings in sand?
- How to separate salt from seawater?
- Why doesn't filtration remove dissolved sugar?
- Stretch: Order steps to clean muddy salty water completely.
Revision tip: Build a mini filter with bottle, cloth, sand, gravel (Ch 7 style) — test with muddy water outdoors.
Open the Practice tab for graded questions on Separation Techniques.
Key Takeaways (TL;DR)
- What you'll learn
- Key concepts
- Worked example
- Common mistakes
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