Separation Techniques

• Physical methods to separate mixture components without chemical change.
• Filtration — insoluble solid from liquid.
• Evaporation/crystallisation — soluble solid from solution.
• Distillation, fractional distillation, chromatography, centrifugation, separating funnel.

1. Filtration — filter paper retains residue; filtrate passes (sand from water).
2. Evaporation — obtain salt from sea water; solvent vaporises.
3. Centrifugation — denser particles forced to bottom (blood, butter from curd).
4. Separating funnel — immiscible liquids (oil and water).
5. Distillation — separate liquids by boiling point (water from ink).
6. Fractional distillation — crude oil fractions; air separation.
7. Chromatography — separate dyes/pigments on paper (different solubility).
8. NCERT Ch. 2 — activity with ink, salt water, iron filings + sulphur.

Separating iron filings and sulphur powder (before and after heating)

Before heating (mixture):
Step 1 — **Magnetic separation** — magnet attracts iron filings.
Step 2 — Sulphur remains — physical separation.
After heating (compound FeS formed):
Step 3 — Magnetic separation **fails** — chemical change occurred.
Step 4 — Need chemical reaction to reverse.
Conclusion: physical methods work only on mixtures, not compounds.

• Using filtration for salt from salt water (need evaporation/crystallisation).
• Misconception: distillation destroys solute (recovers both if volatile difference).
• Confusing evaporation with distillation (distillation condenses vapour).
• Trying to separate compounds by magnet or filter.
• Forgetting chromatography separates by differential movement.

• Which method separates sand from water?
• How is common salt obtained from sea water?
• When is a separating funnel used?
• Name the method to separate dyes in black ink.

Open the Practice tab for graded questions on Separation Techniques.