Class 6 Science Chapter 9 Notes Methods of Separation in Everyday Life
→ Mixture: Mixing of two or more than two different substances together in any proportion.
→ Methods of separating solid from other solids: It involves the following processes:
→ Handpicking: Removal of unwanted substances such as stone, husk, seeds, etc. by hand from wheat and rice. The basic principle of handpicking is the difference in size, colour, and shape of the particles. The method is conveniently used if the particles to be removed are present in small quantities and can easily be picked up by hand.
→ Threshing: Separating food grains or paddy conveniently from the chaff (dry stalk). Machines are generally used to thresh large quantities of grains. It can be done with the help of bullocks also. Bullocks are made to walk over the chaff. The hoofs of bullocks separate the chaff into husk and grains.
→ Winnowing: Separation of lighter husk particles from heavier food grains using an external agency like wind or blowing air. The heavier food grains fall downward and the lighter husk particles are carried away by the wind to form another heap.
→ Technology advancement has led to the creation of threshing machines, known as threshers. These machines separate grains from stalks and husks. They do two jobs at once: threshing and winnowing.
→ Sieving: Separating the components of a mixture having different sizes from one another with the help of an appropriate sieve.
→ Example: sieving wheat flour (atta) at home separates the small unwanted fine particles of flour from the bigger particles (wheat bran). Similarly, tea leaves are separated from the tea liquid with the help of a tea strainer.
→ Magnetic separation: Separating the components of a mixture based on the difference in the magnetic behavior of two different components.
→ Example: a mixture of sulfur powder or sand particles can be separated from iron filings by using a bar magnet.
→ Similarly, in junkyards and factories, iron objects are separated from the heap of waste materials.
→ Separation of a soluble solid from a liquid: It involves the following process:
→ Evaporation: This method is used to separate solid substances that dissolve in liquids. It is based on the principle that liquids are converted into its vapors on heating leaving behind the solids.
→ Example: salt from seawater is obtained by this method.
→ Separation of insoluble solids from liquids: It involves the following processes:
→ Sedimentation and decantation: The process of settling heavier insoluble solid particles under their gravity is called sedimentation and the process of getting clear liquid (supernatant) without disturbing the heavier insoluble particles in another beaker with the help of a glass rod is decantation.
→ Sedimentation method is used while washing pulses and rice by our mothers.
→ The decantation method is also used to separate two liquids that do not mix.
→ Example: a mixture of oil and water is separated by this method.
→ Filtration: The method used for the separation of insoluble components from a liquid using an appropriate filtration unit.
→ Example: water filters remove impurities and contaminants from drinking water, kidneys filter waste from your body, and activated carbon filters are used to purify air.
→ Chumipg (or centrifugation): This method is used to separate lighter particles of suspended solid from a liquid using hands, grinder, etc., or by the electric handle. Churning can also be done on a smaller scale by centrifugation process.
→ Example: formation of solid butter by churning and formation of cream by agitating milk.
→ Handpicking is used for separating solid materials based on differences in size, colour, and shape from a mixture.
→ The process in which the stalks are beaten to separate grains from them is called threshing.
→ The method of separating lighter husk from heavier grains by wind or blowing air is called winnowing.
→ The process of separating solids from a mixture based on variations in particle size using a sieve is called sieving.
→ Evaporation is the process in which a liquid gets converted into its vapor. It can be used to separate a solid dissolved in a liquid.
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→ The process of settling down heavier insoluble components at the bottom of a liquid is called sedimentation. When the liquid is removed by tilting the vessel, the process is called decantation.
→ Filtration can be used to separate insoluble solid components from a liquid.
→ Churning is used to extract butter from curd.
→ Separation of magnetic and non-magnetic substances by using a magnet is called magnetic separation.
Malli and his sister Valli are excited about their summer vacations. Their parents have planned a trip to visit their relatives and friends living across India. They always stay in touch with their relatives and friends. Do you also keep in touch with your loved ones? Their first halt is at their Nani’s (maternal grandmother’s) house in Haryana. It is surrounded by large fields. Malli and Valli are fascinated by the variety of grains piled up in the courtyard. Their Mami (maternal aunt) and Mama (maternal uncle), along with other community members, are busy separating small stones and husks from the grains with their hands.
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Malli and Valli are curious to know why this is being done. Their Nani notices their curiosity and explains, “We are removing these stones so that the grains are fi for cooking.” They go around the house to see the fields and the cattle. To keep them busy, Nani gives them the challenge of handpicking small stones from grains while keeping their eyes closed.
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The method of picking by hand from a mixture (when two or more substances are mixed) such as small stones and husk from wheat and rice is called handpicking. It is done based on differences in size, colour, and shape of the particles. If the particles to be removed are present in small quantities and can easily be picked by hand, handpicking proves to be a convenient method.
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At lunch, Malli and Valli are served steaming hot vegetable pulao. While eating the pulao, Nani observes that Malli is separating whole black peppers from the pulao and is placing them aside on his plate (Figure). Valli playfully teases, “Wow! This is a handpicking method, nice one!” Nani tells them about the benefits of black pepper and encourages Malli to eat it.
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Later in the day, their Mama takes them to the fields where they observe bundles of harvested wheat stalks lying in the fields. Some stalks are spread in the sun for drying. Both of them pick up a stalk each and notice numerous grains attached to it. A group of farmers are beating the stalks on a large wooden log. Curiously, Valli asks Mama, “Why are they doing this?”
Mama explains, “They are beating the stalks to separate the grains” (Figure). This process of separating grains from the stalks is known as threshing. Farmers work hard, yet they enjoy their work. From time to time, they sing folk songs while working. The separated grains get mixed with piles of husk. Valli whispers to Malli, “Will the farmers handpick the grains to remove them from so much husk?” She wonders, “How much time will the farmers take to separate these?” Let us perform an activity to find out the answers to the questions raised by Valli.
Activity 9.1 Let Us Explore
Take a handful of roasted peanuts and rub them between your palms. What happens? Is it possible to separate the removed skin and the peanuts? Now, try blowing it. What do you observe? Which of these components-removed peanut skins or peanuts are blown away? You observe that blowing air separates the heavier and the lighter components. How do you think farmers separate so many grains from husk? Traditionally, a soop (bamboo tray) is used for separating heavier and lighter components of a mixture (Figure).
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The next day, their Nana takes them to the fields to show this process at work. Malli and Valli observe a farmer standing on a raised platform. The farmer is moving the bamboo tray which contains threshed wheat grains in the direction of air or wind (Figure). What do you infer from the Figure?
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Do both the components, wheat grains, and husk, fall at the same place? Which of the two components gets blown away? Can the wind separate the two components? This method of separating heavier and lighter components of a mixture by wind or by blowing air is called winnowing. Have you seen any similar kind of activity being done at your home?
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Technological developments have resulted in the development of threshing machines called threshers. These machines are used for separating grains from the stalks and husks. They perform both the tasks of threshing and winnowing simultaneously.
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The next day, Malli and Valli board a train to Ahmedabad to visit their father’s friend Ghanshyam Bhai. Before leaving, Valli requests her Mami to prepare methi puri (sweet Indian bread made from wheat flour) for their journey.
Valli: Shall I help you knead the wheat flour?
Mami: To prepare a dish with flour, first we need to remove bran that may be present in the flour.
Valli: How do we do it?
Mami: We use a sieve for this purpose. Sieving allows the fine flour particles to pass through the holes of the sieve as shown in Figure. The bigger particles such as bran and small stones remain on the sieve.
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Carefully observe a sieve. Are all the holes of the sieve the same size? Will sieving work if the holes of the sieve are larger than the substances? Is there any difference in the size between the particles that pass through the sieve and the particles that remain on the sieve? Sieving is used when components of a solid-solid mixture have different sizes. Upon reaching Ahmedabad, they visit Sabarmati Ashram along with Ghanshyam bhai where they learn about the Namak Satyagrah (Dandi March).
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Malli asks, “Where is namak (common salt) obtained from?”
“From seawater”, replies Ghanshyam Bhai.
Seawater is a mixture of salts and some other substances dissolved in water. To obtain salt, the seawater is kept in shallow pits and exposed to sunlight and air. In a few days, the water evaporates completely, leaving behind a solid mixture (Figure). Common salt is then obtained from this mixture by further purification.
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Let us explore how salt can be separated from a salt solution.
Activity 9.2 Let Us Observe and Create
Take a bowl or any container and fill it half with water. Add 2-3 teaspoons of salt into it and stir till the salt dissolves to form a solution. Take a small piece of black or dark-colored thick paper and spread a few drops of the salt solution on it (Figure a). You can also create any art of your choice with this salt solution. Allow it to dry and then observe it (Figure b and Figure c).
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Do you observe some patches on the paper? What do you think is left on the paper? You can feel the presence of salt by touching the paper. Where has the water disappeared? Recall the chapter on ‘A Journey through the States of Water’. Let us probe further to get the answer.
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In the traditional Indian system of holistic health and medicine called Ayurveda, the herbs or parts of plants are prescribed as remedies. These ingredients like roots, leaves, flowers, or seeds of various medicinal plants are often dried in the shade. This practice facilitates the evaporation of excess water, leaving behind an important part of the medicine.
Activity 9.3 Let us Investigate
This activity may be demonstrated by the teacher. Take some salt solution (prepared in Activity 9.2) in a china dish. If a china dish is not available, another suitable vessel may be used. Heat and let the water boil away as shown in Figure.
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Allow the china dish to cool. What do you observe? What is left in the china dish? Did you get the salt back? You can feel the presence of salt in the china dish by touching the salt with your fingers.
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It is now time for them to visit Dada and Dadi (paternal grandparents) residing in Puducherry, located in southern India. Malli and Valli are excited to meet their old neighborhood friend, Balan. After reaching Puducherry, they start talking about the old times and do not realize that it is already evening, Dadi’s tea time.
Dada: I shall prepare tea for you.
Children: We will also help you. As Dada makes the tea, he shares tips on how to make a cup of tea.
Balan: After preparing tea, how do you remove the tea leaves?
Dada: Obviously, with a strainer. You know if we do not have a strainer, we can still remove most of the tea leaves.
Valli: How?
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Dada: Leave the saucepan (vessel) containing tea undisturbed for some time and gently pour the tea into a cup (Figure).
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Valli: Oh Yes! And then the tea leaves will be settled at the bottom. The process of settling down heavier insoluble components at the bottom of a liquid is called sedimentation. When the water (liquid) is removed by tilting the vessel, the process is called decantation.
Dada: But I can still get a few tea leaves in my mouth because decantation does not completely separate all the tea leaves from the tea.
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Balan: Oh! It means it is not a proper method of separation.
Dada: Yes, you are right. The tea is ready now. Malli picks up the tea strainer from the shelf and gives it to his Dada.
Dada: Let me pour the tea through this strainer. You can see all the tea leaves collected in the strainer. This process of separating tea leaves from tea is called filtration.
Balan asks Malli if he could use a tea strainer to filter muddy water. Let us try and find out.
Dada: Also, try to filter the muddy water through a piece of cloth and observe the difference.
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Malli: Why should we use a piece of cloth?
Dada: In a piece of cloth, there are very small holes or pores between the woven threads. These pores in the cloth can be used as a filter. People of ancient times also followed this practice. But if the water is still muddy, impurities can be separated using a filter with even smaller holes or pores. A filter paper is one such filter that has very few pores in it.
Activity 9.4: Let Us Experiment
Try to fold the fiter paper yourself and make a cone as shown in Figure.
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Place it inside a funnel kept on a conical flask and pour muddy water into it (Figure).
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What do you observe? Do the mud particles pass through the filter paper? The water coming from the funnel will be collected in the conical flask. You will get mud as a residue on the fitter paper and clear water as a filtrate in the conical flask.
Activity 9.5 Let Us Design and Create
Valli goes for a nature walk with her Dadi and collects some water from a pond in a container. She observes some unwanted substances in it. Design and create a working model of a water filter using low-cost materials.
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Tea bags were initially made of soft cloth, like silk, because it could hold the tea leaves and let water pass through. Silk was strong and did not fall apart when it touched hot water. Later, people started using gauze or muslin. Eventually, they began using filter paper, which is what most tea bags are made of today.
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Malli and Valli go on a boat ride in a nearby river with their Dada and his friend, Otukkam. Otukkam is a fiherman. As they cast the fishing net, water drains out through the mesh. Valli recalls the filtration method she had learned and realizes that this method of catching the fish is somewhat similar. Malli is taken aback when he sees plastic bags, broken bottles, a large fish with a straw stuck in its mouth, and food wrappers along with the other fish trapped in the net.
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Malli and Valli take blessings from their Dada and Dadi, bid goodbye to Balan, and travel to Madhya Pradesh. The train reaches Bhopal in Madhya Pradesh. The sun is rising and it is getting hot. On their way to Maasi’s (maternal aunt’s) home, they drink chhach (buttermilk) in the dhaba (roadside eatery). Malli asks the shopkeeper about the big painting, hanging on the wall of the dhaba. The shopkeeper explains that the picture shows a lady performing the process of churning curd using a big machine (churner) to separate butter.
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In this process, the butter is lighter and flats at the top, while the buttermilk is left behind. Their stay at Maasi’s place has become enjoyable and they are looking forward to sharing all their memories with their friends upon returning home. Now, it is time for them to reach their final destination of the trip, Shillong, the capital of Meghalaya. On their arrival at their Bua’s (paternal aunt’s) house in Shillong, they notice a carpenter making a wooden door. While working, he accidentally drops a few iron nails in the sawdust.
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The carpenter starts handpicking the iron nails. The children tell the carpenter to wait. They get a magnet from their Bua. They ask the carpenter to move the magnet through the sawdust. All the nails get attracted to it (Figure). Which method of separation did the carpenter use? Recall the chapter on ‘Exploring Magnets’. The substances which are attracted to a magnet are called magnetic substances. Iron is a common example of a magnetic substance. The separation of magnetic and nonmagnetic substances by using a magnet is called magnetic separation.
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Nowadays, recyclers use magnets to separate iron articles from a heap of waste. In many industries, the waste material often contains scrap iron. This is separated from the heap of waste materials using magnets fitted to a crane. The scrap iron can be recycled and reused.
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Malli and Valli had delightful holidays and the ‘Bharat ki Yatra’ (tour of India) filled with fun will be an ever-lasting memory for them. They not only enjoyed exploring different regions of India but also gained a lot of knowledge about various methods of separation of substances.
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Activity 9.6: Let Us Play
Write the following phrases on small slips of paper:
- Separating small stones from pulses.
- Churning curd to obtain butter.
- Take out green chilies from cooked dalia (a dish made of cracked wheat) or poha (a dish made of flattened rice).
- Taking out seeds from watermelon.
- Sorting piles of sawdust and iron nails from a mixed heap of building material.
- Picking marigold flowers from a heap of other flowers to make a garland.
- Separating pebbles from sand.
- Separating coconut pieces from rice flour.
- Separating oil from water.
- Separating salt from salt solution.
Now, take two baskets, each representing one of the two purposes for which we separate substances. Form two teams and see who will get the maximum correct entries.
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This activity helps in assessing your understanding as to why we separate substances.
Class 6 Science Notes
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