NCERT Curiosity Class 6

Chapter 9: Methods of Separation

Learn how to separate mixtures using physical techniques such as handpicking, winnowing, sieving, sedimentation, decantation, filtration, and evaporation.

1. Introduction

In our daily life, we frequently separate harmful, non-useful, or desirable substances from a mixture. Whether filtering tea leaves from tea, separating stone pieces from rice, or extracting butter from milk, various techniques are applied based on the physical properties of the components.

Key Concept: The choice of separation method depends on physical attributes such as particle size, weight, magnetic properties, and solubility in liquids.

2. Methods of Separating Solid Mixtures

Click on any technique card below to inspect its mechanism and applications.

Handpicking

Used to remove slightly larger impurities by hand.

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Winnowing

Separates heavier grain from lighter husk using wind.

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Sieving

Separates particles of different sizes through a mesh.

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3. Separating Insoluble Solids from Liquids

When solids do not dissolve in a liquid, we use physical settling and filtering techniques:

Method	Working Principle	Example Application
Sedimentation	Heavier insoluble particles settle at the bottom of a liquid under gravity.	Mud settling down in muddy water.
Decantation	Carefully pouring off the clear liquid without disturbing the settled sediment.	Pouring off clear water after rice washing.
Filtration	Passing a mixture through a porous filter to trap solid particles.	Separating tea leaves using a strainer.

4. Separating Soluble Solids

To recover a solid dissolved in a liquid, thermal techniques are used:

Evaporation: The process of converting a liquid into its vapor phase by heating. For example, common salt is produced commercially from seawater via natural evaporation in shallow pits.

Mathematical representation of concentration ratio in solutions:

$$\text{Concentration (\%)} = \left( \frac{\text{Mass of Solute}}{\text{Total Mass of Solution}} \right) \times 100$$

5. Solved Examples

Example 1: Wheat and Husk Separation

Question: Which method is best suited to separate wheat grains from light husk, and why?

Solution: Winnowing is used because the lighter husk particles are blown away by air currents, while the heavier wheat grains fall straight down.

6. Textbook Exercises

Q1. What is decantation?

Ans: Decantation is the process of gently pouring off the upper clear liquid after the heavier solid impurities have settled at the bottom through sedimentation.

7. Practice MCQs

Q1. Salt is separated from seawater using which of the following processes?