Separation of Substances - Science and Tech NCERT Notes For UPSC

Methods of Separation:

1. Handpicking
   • Means direct removal by Hand.
   • Used for separating slightly larger sized impurities like the pieces of dirt, stone, and husk from wheat, rice, or pulses.
   • The quantity of such impurities is usually not large.
2. Threshing
   • Plants stalks are beaten to free the grain seeds.
   • Used to separate the grain from the plant stalk.
   • Also done with the help of bullocks and Machines (Thresher).

3. Winnowing
   • It is the separation of heavier and lighter components of a mixture by wind or by blowing air.
   • Used by farmers to separate lighter husk particles from heavier seeds of grain.
   • Husk particles are carried away by the wind. Seed Grains get separated and form a heap near the platform for winnowing.

4. Sieving
   • It involves separation of components of a mixture having different sizes.
   • Fine particles pass through the Sieve holes while the bigger impurities remain on the sieve.
   • Generally used in removing pieces of stones, stalk and husk that may remain with wheat after threshing and winnowing.

5. Sedimentation, Decantation and Filtration
   • Useful for separating lighter impurities which may not be possible by winnowing and handpicking.
   • When the heavier component in a mixture settles after water is added to it, the process is called Sedimentation.
   • When the water (along with the dust) is removed, the process is called Decantation. The same principle is used for separating a mixture of two liquids that do not mix. E.g., oil and water from their mixture.
   • Filtration is a process used to separate solids from liquids or gases using a fine-pored filter medium that allows only the fluid to pass through but not the solid.

6. Evaporation
   • The process of conversion of water into its vapour is called Evaporation. Seawater contains many salts mixed in it like common salt. When seawater stands in shallow pits, water gets heated by sunlight and slowly turns into water vapour, through evaporation. In a few days, the water evaporates completely leaving behind the solid salts.
     Often, we need to use more than one of these methods to separate the different substances present in a mixture. For example, Salt, and Water mixture is separated using processes of decantation, filtration, evaporation, and condensation (the process of conversion of water vapour into its liquid form).

Also Read : What are lab grown diamonds?

Solubility of substances in Water

The dissolution of any substance in water depends on the amount of substance and the volume of water along with their properties.

• A solution is said to be saturated if it cannot dissolve more of the substance in it.
• Larger quantities of salt can be dissolved in water on heating or increasing water volume.
• Water dissolves different amounts of soluble substances in it.

Interesting Fact: 

Water is called the "universal solvent" because it can dissolve more substances than any other liquid.

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