Methods Of Separation In Everyday Life
Class 6 Science — Quick Revision Study Guide & Chapter Notes
1. Separation of Substances
In our daily lives, we often need to separate substances from mixtures. Separation is carried out either to obtain two or more useful components separately or to remove an unwanted component. Different mixtures require different methods of separation, depending on the properties of the substances present in them.
Mixture: A mixture is a combination of two or more substances in which each substance retains its own properties. For example, air is a mixture of different gases. Tap water is usually a mixture because it contains dissolved salts and other substances.
Pure substance: A pure substance is a material in which all the particles are identical and have the same properties. For example, distilled water is a pure substance because it contains only water molecules.
We separate substances for two main purposes:
to separate two different but useful components; or
to remove a component that is not useful.
For example: Ria and her brother Aryan visit their grandparents' farm. They notice their grandparents sorting vegetables. Curious, they ask why. Their Dadi explains, "We clean and sort them to make sure they're fresh for cooking." Ria and Aryan help wash and sort the vegetables. They learn how to remove dirt and damaged pieces before cooking. This shows how separation is useful in everyday life.
2. Different Methods of Separation
1. Handpicking
Handpicking is the simplest method of separation. It is used when the unwanted material is present in a small amount and is clearly different in size, shape or colour from the useful material. The unwanted part is removed by hand.
Examples: Removing stones, pebbles, husk or damaged grains from wheat, rice or pulses; and taking whole black peppercorns out of a mixed dish by hand.
A good example of handpicking is when Malli separates whole black peppers from vegetable pulao using his hands. This shows how handpicking is used to remove unwanted substances from a mixture.
2. Threshing
Threshing is the process of separating grains from stalks by beating them.
Threshing machines: How they work
Threshing machines separate grains from stalks and remove some of the husk.
Some machines perform both threshing and winnowing together, making the process faster.
By using threshers, the process of separating grains becomes faster and more efficient.
Winnowing separates lighter particles from heavier particles with the help of wind or moving air.
This process separates lighter components from heavier ones using wind or blowing air. It is used to separate lighter husk from heavier grains. Traditionally, a soop, or bamboo tray, is used to separate the heavier grains from the lighter husk.
In winnowing, the lighter component is blown away by the wind, while the heavier component falls down.
4. Sieving
Sieving is used when the particles are too small to be picked by hand or when there are too many of them. A sieve with appropriately sized holes is used. Larger particles remain on the sieve, while smaller particles pass through the holes.
Smaller particles pass through the holes, while larger particles remain on the sieve.
Examples: Separating bran from wheat flour or separating larger stones from sand.
If the holes in a sieve are larger than the particles being sieved, both fine and larger particles will pass through. Choosing the correct hole size is important for obtaining the desired separation.
5. Evaporation
Evaporation is the process in which a liquid changes into vapour. It can be used to separate a dissolved solid from a liquid, leaving the solid behind as the liquid evaporates.
Example: Salt can be separated from a salt solution by heating it so that the water evaporates, leaving the salt behind.
How is salt obtained from seawater?
Seawater is collected in shallow pits and exposed to sunlight and air. When the water evaporates, a solid mixture is left behind. Common salt is then obtained from this mixture by further purification.
Can we recover both salt and water from a salt solution?
Yes. When a salt solution is heated, water changes into vapour and salt remains in the container. If the water vapour is cooled, it changes back into liquid water. This change of vapour into liquid is called condensation. By collecting the condensed water in another container, both salt and water can be recovered.
Ayurveda: The Ancient Indian Healing System
Ayurveda is a traditional Indian system of health and medicine that focuses on overall well-being.
In Ayurveda, herbs and plant parts such as roots, leaves, flowers and seeds are used to treat various health issues.
The plant materials are often dried in the shade. This process helps remove excess moisture while preserving the medicinal properties of the plants.
Sedimentation: Sedimentation occurs when insoluble particles settle at the bottom of a liquid. For example, in muddy water, soil and sand settle down when the water is left undisturbed.
Decantation: After sedimentation, the clear liquid is carefully poured off by tilting the vessel, leaving the settled solid behind. For example, clear water can be poured off after heavier sand particles have settled at the bottom.
Decantation can also be used to separate liquids that do not mix with each other. When a mixture of oil and water is left undisturbed, oil forms a separate layer above the water. The upper oil layer can be carefully poured into another container, leaving the water behind.
Limitation of decantation
Decantation may not completely separate all insoluble particles from a liquid. For example, when tea is gently poured off after the tea leaves settle, a few leaves may still enter the cup. Passing the tea through a suitable strainer separates the leaves more effectively.
7. Filtration
Filtration is a technique used to separate fine, insoluble solid particles from a liquid. The mixture is passed through a filter. The liquid flows through the filter, while the solid particles are trapped by it.
Example: A strainer can be used to remove tea leaves from brewed tea.
What do you observe when filtering muddy water using filter paper?
When muddy water is poured through filter paper, the mud particles are trapped by the paper, while clear water passes through and is collected.
Residue: The insoluble solid left on the filter. In this example, mud is the residue.
Filtrate: The liquid that passes through the filter and is collected. In this example, the collected clear water is the filtrate.
Filter paper, cotton, muslin or gauze
Charcoal and sand can also be used as filter materials.
A filter has small openings called pores. The choice of filter depends on the size of the particles to be removed. A tea strainer can retain tea leaves, but fine mud particles may pass through its larger holes. Cloth has small pores between its woven threads. If water remains muddy after passing through cloth, filter paper with finer pores can be used to remove smaller suspended particles.
The evolution of tea bags
Tea bags were first made from soft materials such as silk, which could hold the tea leaves while allowing hot water to pass through.
Silk was chosen because it was strong and did not break apart when it came into contact with hot water.
Later, people began using gauze or muslin to make tea bags.
Eventually, filter paper became common, and today most tea bags are made from this material.
Churning is used to extract butter from curd. During churning, the lighter butter collects and floats at the top, while the buttermilk is left behind.
Example: Churning curd separates butter from buttermilk.
Magnetic separation uses a magnet to remove magnetic materials from non-magnetic materials.
Example: A magnet can be used to take out iron nails from a mixture of sawdust and nails.
Recyclers use magnets to remove iron items from piles of waste. In various industries, waste materials often include scrap iron, which can be extracted using magnets attached to cranes. This scrap iron can be recycled and reused.
Many wastes include scrap iron, which is attracted by magnets.
Magnetic substances, such as iron, are separated from non-magnetic substances using magnets.
The extracted scrap iron can be processed for reuse.
A mixture containing more than two components may require a combination of several separation methods. The methods and their sequence are chosen according to the properties of the components, such as size, solubility in water and attraction towards a magnet.
Example: Separating potatoes, salt and sawdust
1. Handpicking: Pick out the potatoes from the mixture.
2. Dissolving: Add enough water to the remaining salt and sawdust mixture and stir. Salt dissolves in water, while sawdust does not.
3. Filtration: Pass the mixture through a suitable filter. Sawdust remains on the filter as the residue, while the salt solution is collected as the filtrate.
4. Evaporation: Evaporate the water from the salt solution to obtain salt. If heating is used, it should be carried out under adult supervision.
Handpicking: Unwanted items are removed manually using differences in size, colour or shape.
Threshing: Grains are separated from stalks by beating.
Winnowing: Wind or air is used to separate lighter husk from heavier grains.
Sieving: A sieve is used to separate particles according to their size.
Evaporation: A liquid is evaporated to obtain a dissolved solid.
Condensation: Vapour changes into liquid on cooling. It can be used to recover water vapour produced while separating salt from a salt solution.
Sedimentation and decantation: Heavy particles are allowed to settle, and the clear liquid is carefully poured off.
Oil and water: These liquids form separate layers and can be separated by careful decantation.
Filtration: A filter medium is used to separate fine, insoluble solids from liquids.
Residue and filtrate: The solid retained on the filter is the residue; the liquid passing through it is the filtrate.
Filter selection: The pore size of the filter must be suitable for the particles to be removed.
Churning: Churning is used to extract butter from curd.
Magnetic separation: Magnets are used to separate magnetic materials from non-magnetic materials.
Combination of methods: Several methods may be needed to separate all the components of a mixture.
Removing small stones from pulses before cooking
Churning curd to make butter
Picking out green chillies from cooked dalia or poha
Removing seeds from watermelon
Separating pebbles from sand
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