Methods of Separating Mixtures
NCERT Class 9 • Science • Chapter "Is Matter Around Us Pure" | NCERT Class 6 • Science • Chapter on separation of substances
Methods of Separating Mixtures
Every separation method works by using a difference in a physical property between the components: size, weight, solubility, boiling point, magnetic behaviour or adsorption. Choosing the right method is simply a matter of identifying which property differs most sharply.
Simple Physical Methods
- Handpicking removes large visible impurities such as stones from grain.
- Threshing separates grain from stalk, and winnowing separates lighter husk from heavier grain using wind.
- Sieving separates components of different particle size, as in flour and bran.
- Filtration separates an insoluble solid from a liquid, as in tea leaves from tea.
- Sedimentation and decantation let a heavier insoluble solid settle, after which the liquid is poured off.
- Magnetic separation removes iron particles from a mixture using a magnet.
- Evaporation recovers a dissolved solid by driving off the liquid, as in obtaining salt from sea water.
Advanced Methods
- Sublimation separates a sublimable solid such as camphor or ammonium chloride from a non sublimable one.
- Distillation separates a dissolved solid from a liquid, or two miscible liquids with a large boiling point difference.
- Fractional distillation separates liquids whose boiling points are close, as in the refining of petroleum.
- Separating funnel separates two immiscible liquids such as oil and water using the difference in density.
- Centrifugation spins a mixture fast so that denser particles move outward, as in separating cream from milk.
- Chromatography separates dissolved substances that travel at different rates over an absorbing material, as in separating dyes in ink.
- Crystallisation gives purer crystals of a solid from its solution and is better than simple evaporation.
- Many real separations need two or more methods in sequence, as in obtaining pure salt from sea water.
| Method | Property Used | Example |
|---|---|---|
| Filtration | Solubility and particle size | Tea leaves from tea |
| Distillation | Difference in boiling point | Water from salt solution |
| Separating funnel | Difference in density, immiscible | Oil and water |
| Chromatography | Different rate of travel | Dyes in ink |
Crystallisation — the process of obtaining pure crystals of a solid from its hot saturated solution on cooling.
Hindi me samjhein
आसवन में क्वथनांक का अंतर काम आता है, पृथक्कारी कीप में घनत्व का, और क्रोमैटोग्राफी में चलने की गति का। जिस गुण में अंतर सबसे अधिक हो, वही विधि चुनी जाती है।
Exam me kaise aata hai
- Separating dyes in ink uses — chromatography
- Oil and water are separated using a — separating funnel
- Cream is separated from milk by — centrifugation
- Petroleum is refined by — fractional distillation
UPSC/State PSC ke liye
- Crystallisation is preferred over evaporation for purification, because simple evaporation leaves impurities behind with the solid while crystals exclude them.
- Fractional distillation works by repeated vaporisation and condensation along a column, which is why it can separate liquids with close boiling points.
Yahan confuse hote hain
✗ Filtration can separate a dissolved salt from water | Filtration works only on insoluble solids | ✓
✗ Distillation and evaporation are the same | Distillation recovers the liquid; evaporation lets it escape | ✓
✗ A separating funnel works for miscible liquids | It works only for immiscible liquids | ✓
Ek nazar me
- Every method uses a difference in a physical property.
- Filtration for insoluble solids; evaporation and crystallisation for dissolved ones.
- Distillation uses boiling point; separating funnel uses density.
- Chromatography separates dissolved substances by rate of travel.