CBSE Class 6- Science Chapter 9: Methods of Separation in Everyday Life – Study Notes (PDF)

Study Notes: Methods of Separation in Everyday Life (Class 6-NCERT(Curiosity) Science

1. Separation of Solid Components from Solids

a. Handpicking

• Description: The method of manually picking out components from a mixture by hand.
• Principle: This method is effective when components differ in size, color, or shape, making them easily identifiable. It is a convenient method when the unwanted particles are present in small quantities.
• Examples from the NCERT Text-Book:
  • Separating small stones and husk from wheat and rice grains in the courtyard of Nani’s house in Haryana.
  • Malli separating whole black peppers from his vegetable pulao during lunch.
  • Picking out seeds from a watermelon.
  • Sorting marigold flowers from a heap of other flowers.

b. Threshing

• Description: The process of separating grains from their harvested stalks.
• Method: Traditionally, farmers beat bundles of stalks on a hard surface, like a large wooden log, to dislodge the grains.
• Technological Advancement: Modern agriculture uses machines called threshers, which can perform both threshing and winnowing simultaneously.
• Example from the Textbook: Farmers in the fields near Nani’s house beating wheat stalks to separate the grains.

c. Winnowing

• Description: A method used to separate heavier and lighter components of a mixture.
• Principle: This process utilizes wind or blowing air. The lighter components, such as husk, are blown away by the air, while the heavier components, like grains, fall down in a heap.
• Method: A person, often standing on a raised platform, holds a mixture (e.g., threshed grains mixed with husk) in a bamboo tray, known as a soop, and allows it to fall. The wind carries the lighter husk away, and the heavier grains fall vertically to form a pile below.
• Example from the Textbook: A farmer separating wheat grains from husk by standing on a platform and letting the mixture fall in the direction of the wind.

d. Sieving

• Description: The process of separating solid components from a solid-solid mixture based on differences in particle size.
• Principle: A sieve, which has holes of a specific size, is used. Fine particles that are smaller than the holes pass through, while larger particles are retained on the sieve.
• Conditions for Use: Sieving is only effective when the components of a mixture have different sizes.
• Examples from the Textbook:
  • Valli’s Mami using a sieve to remove bran and small stones (bigger particles) from wheat flour (fine particles).
  • At construction sites, sieves are used to separate pebbles and stones from sand.

e. Magnetic Separation

• Description: A method used to separate magnetic substances from non-magnetic substances.
• Principle: This method relies on the property of magnetism. A magnet is used to attract the magnetic components, separating them from the rest of the mixture. Substances attracted to a magnet are called magnetic substances (e.g., iron).
• Examples from the Textbook:
  • Malli and Valli helping a carpenter separate accidentally dropped iron nails from sawdust using a magnet.
  • In industries and recycling centers, large magnets fitted to cranes are used to separate scrap iron from heaps of waste material.

2. Separation of Solid Components from Liquids

a. Evaporation

• Description: The process in which a liquid gets converted into its vapor form.
• Application: This method is used to separate a solid that has been dissolved in a liquid. As the liquid evaporates, the solid is left behind.
• Examples from the Textbook:
  • Obtaining common salt from seawater. Seawater is collected in shallow pits, and the water evaporates due to sunlight and air, leaving behind a mixture of salts.
  • Heating a salt solution in a china dish until all the water boils away, leaving the salt behind.
  • The formation of white patches on dark clothes in summer, which are salt deposits left after sweat (salty water) evaporates.

b. Sedimentation and Decantation

• Sedimentation: The process where heavier, insoluble components in a liquid mixture settle down at the bottom of the container.
• Decantation: After sedimentation, the process of gently pouring out the upper layer of liquid without disturbing the settled solid particles (sediment).
• Examples from the Textbook:
  • Making Tea: If tea is left undisturbed, the heavier tea leaves settle at the bottom (sedimentation). The tea can then be gently poured into a cup, leaving most of the leaves behind (decantation).
  • Washing Rice/Pulses: Water is added, and impurities settle. The water is then decanted.
  • Separating Oil and Water: Since oil is immiscible with water and forms a separate layer, this mixture can be separated by decantation.

c. Filtration

• Description: A method used to separate insoluble solid components from a liquid.
• Principle: The mixture is passed through a filter, which is a material with very fine pores or holes. The liquid passes through the pores, while the solid particles, being larger than the pores, are retained by the filter.
• Types of Filters:
  • Strainer: Used for separating tea leaves from tea.
  • Piece of Cloth (e.g., muslin): Pores between the woven threads act as a filter.
  • Filter Paper: Has very fine pores, making it suitable for separating finer impurities like mud from water.
• Key Terms:
  • Residue: The solid particles that remain on the filter.
  • Filtrate: The clear liquid that passes through the filter.
• Examples from the Textbook:
  • Using a tea-strainer to separate all tea leaves from prepared tea.
  • Filtering muddy water through a piece of cloth or, for better results, through a filter paper cone placed in a funnel.
  • A fisherman’s net acts like a filter, allowing water to pass through while trapping fish.

3. Separation in Liquid-Liquid Mixtures

a. Churning

• Description: A process of vigorously agitating a liquid mixture, such as curd or milk, to separate its components.
• Principle: During churning, lighter components separate and float to the top.
• Example from the Text:
  • Separating butter from curd or milk. The mixture is churned using a mathni (churner), causing the lighter butter to collect and float on the surface, leaving the buttermilk behind.

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Quiz

Short-Answer Questions (Answer in 2-3 sentences)

1. What is the principle behind the handpicking method of separation?
2. Provide two distinct examples of handpicking mentioned in the text.
3. Explain the process of threshing as performed by farmers.
4. What modern machine has replaced traditional threshing and what is its advantage?
5. Describe the process of winnowing and explain why it works.
6. What is a soop and how is it used in winnowing?
7. Under what conditions is sieving an effective method of separation?
8. Give an example of sieving used in a kitchen and another from a construction site.
9. How is common salt obtained from seawater on a large scale?
10. What is the name of the process where a liquid turns into its vapor?
11. Define sedimentation and provide an example.
12. Explain decantation and how it follows sedimentation.
13. Why is decantation not always a perfect method for separating tea leaves?
14. What is filtration, and what is the key difference between the liquid and solid components it separates?
15. What is the solid material left on a filter paper called?
16. What is the clear liquid that passes through a filter called?
17. Compare the effectiveness of a piece of cloth versus a filter paper for filtering muddy water.
18. Describe the process of churning to separate butter from curd.
19. Why does butter float to the top during churning?
20. What are magnetic substances? Provide an example from the text.
21. Explain how magnetic separation was used to separate iron nails from sawdust.
22. How is magnetic separation used in recycling industries?
23. Why can’t winnowing be performed effectively in a closed room?
24. What two properties of oil and water allow them to be separated by decantation?
25. How is the use of a fishing net similar to the process of filtration?

Multiple-Choice Questions (MCQs)

1. What purpose does handpicking serve in the process of separation? (a) Filtration (b) Sorting (c) Evaporation (d) Decantation
2. Which of the following substances are commonly separated using the churning method? (a) Oil from water (b) Sand from water (c) Cream from milk (d) Oxygen from air
3. Which factor is usually essential for filtration? (a) Apparatus size (b) Presence of air (c) Pore size (d) Temperature of the mixture
4. Beating stalks to separate grains is known as: (a) Winnowing (b) Sieving (c) Threshing (d) Handpicking
5. Which method uses wind or blowing air to separate components? (a) Sieving (b) Winnowing (c) Decantation (d) Filtration
6. Separating bran from flour is an example of: (a) Threshing (b) Handpicking (c) Sieving (d) Churning
7. To separate a dissolved solid from a liquid, one should use: (a) Filtration (b) Evaporation (c) Sieving (d) Decantation
8. The process of a heavier, insoluble solid settling at the bottom of a liquid is: (a) Decantation (b) Filtration (c) Sedimentation (d) Evaporation
9. Which of the following would be the best method to separate iron filings from sawdust? (a) Handpicking (b) Magnetic separation (c) Winnowing (d) Sieving
10. In the process of filtration, the clear liquid collected is called the: (a) Residue (b) Sediment (c) Filtrate (d) Solution
11. A mixture of oil and water can be separated by: (a) Filtration (b) Churning (c) Evaporation (d) Decantation
12. A filter paper is more effective than a cloth for filtering because it has: (a) Greater strength (b) Larger pores (c) Finer pores (d) A different color
13. Which separation technique relies on differences in size, color, or shape? (a) Winnowing (b) Threshing (c) Handpicking (d) Sieving
14. The material used by farmers in traditional winnowing is a: (a) Sieve (b) Bamboo tray (soop) (c) Thresher machine (d) Wooden log
15. What is left behind after the evaporation of seawater in shallow pits? (a) Pure water (b) Mud (c) A solid mixture of salts (d) Sand
16. Pouring off a liquid after solids have settled is called: (a) Sedimentation (b) Filtration (c) Decantation (d) Churning
17. A thresher machine combines the tasks of: (a) Threshing and handpicking (b) Sieving and winnowing (c) Threshing and winnowing (d) Sedimentation and decantation
18. Iron is an example of a: (a) Non-magnetic substance (b) Filtrate (c) Magnetic substance (d) Residue
19. Which method would be best to separate pebbles from sand at a construction site? (a) Winnowing (b) Handpicking (c) Sieving (d) Magnetic separation
20. Separating tea leaves from tea with a strainer is an example of: (a) Decantation (b) Filtration (c) Sedimentation (d) Evaporation

Answer Keys

Short-Answer Questions Key

1. The principle of handpicking is based on separating components that have visible differences in size, color, or shape. This allows them to be easily identified and removed manually from the mixture.
2. Two examples are separating small stones from grains of wheat and rice, and Malli removing whole black peppers from his pulao.
3. Threshing is the process where farmers beat bundles of harvested stalks against a hard surface, like a wooden log. This action forcibly separates the grains from the stalks.
4. The modern machine is a thresher. Its advantage is that it performs both threshing (separating grains from stalks) and winnowing (separating grains from husk) simultaneously.
5. Winnowing involves letting a mixture of heavy and light components fall from a height in the presence of wind. The wind blows the lighter components (like husk) away, while the heavier components (like grain) fall vertically downwards.
6. A soop is a traditional bamboo tray. In winnowing, a farmer holds the grain-husk mixture in the soop and gently moves it, allowing the mixture to fall so the wind can separate it.
7. Sieving is effective when the components of a solid-solid mixture have different particle sizes. The holes of the sieve must be small enough to retain the larger particles while allowing the finer ones to pass through.
8. In a kitchen, a sieve is used to remove bran from flour. At a construction site, a larger sieve is used to separate pebbles and stones from sand.
9. Common salt is obtained from seawater by collecting the water in large, shallow pits. The water is then left to evaporate under the sun and wind, leaving behind a solid mixture of salts which is then further purified.
10. The process where a liquid turns into its vapor is called evaporation.
11. Sedimentation is the process where heavier, insoluble particles in a liquid settle at the bottom of the container. An example is muddy particles settling at the bottom of a container of water when left undisturbed.
12. Decantation is the process of gently pouring off the liquid from the top of a container after sedimentation has occurred. This is done carefully to avoid disturbing the settled solid layer at the bottom.
13. Decantation is not perfect for tea leaves because some of the smaller or lighter leaves may not have fully settled. When the tea is poured, a few leaves can get carried along with the liquid into the cup.
14. Filtration is a method of separating insoluble solids from a liquid by passing the mixture through a filter. The key difference is that the liquid particles are small enough to pass through the filter’s pores, while the solid particles are too large and get trapped.
15. The solid material left on a filter paper is called the residue.
16. The clear liquid that passes through a filter is called the filtrate.
17. A filter paper is more effective because it has very fine pores. These pores can trap much smaller impurities, like fine mud particles, that might pass through the larger pores in a piece of cloth, resulting in clearer water.
18. Churning involves vigorously agitating curd in a container, often with a churner (mathni). This process causes the lighter butter to separate from the liquid and float to the top, leaving the buttermilk behind.
19. Butter floats to the top during churning because it is lighter than the buttermilk that is left behind in the mixture.
20. Magnetic substances are those that are attracted towards a magnet. Iron is a common example of a magnetic substance mentioned in the text.
21. Magnetic separation was used by moving a magnet through the sawdust. The iron nails, being magnetic, were attracted to the magnet and stuck to it, allowing them to be easily lifted out of the non-magnetic sawdust.
22. In recycling industries, large magnets attached to cranes are used to lift and separate scrap iron and other magnetic materials from large heaps of waste. This allows the iron to be easily collected for recycling.
23. Winnowing requires wind or blowing air to carry away the lighter components of the mixture. In a closed room, there is no wind, so there is no force to separate the lighter husk from the heavier grains.
24. The two properties are that oil does not mix with water (it is immiscible) and it is lighter than water, causing it to form a separate layer on top. This distinct layer can then be carefully poured off (decanted).
25. A fishing net acts like a filter because its mesh has holes that are large enough to let water drain out but small enough to trap the fish. This separates the solid (fish) from the liquid (water) based on size.

MCQ Key

1. (b) Sorting
2. (c) Cream from milk
3. (c) Pore size
4. (c) Threshing
5. (b) Winnowing
6. (c) Sieving
7. (b) Evaporation
8. (c) Sedimentation
9. (b) Magnetic separation
10. (c) Filtrate
11. (d) Decantation
12. (c) Finer pores
13. (c) Handpicking
14. (b) Bamboo tray (soop)
15. (c) A solid mixture of salts
16. (c) Decantation
17. (c) Threshing and winnowing
18. (c) Magnetic substance
19. (c) Sieving
20. (b) Filtration

Essay Questions with Answers (For Teachers)

1. Trace Malli and Valli’s journey across India and describe the different methods of separation they learned about in each location.

Malli and Valli’s journey or ‘Bharat ki Yatra’ was an educational tour where they observed various methods of separation.

• Haryana: At their Nani’s house, they first encountered handpicking, used to remove small stones and husk from grains based on differences in size, color, and shape. They then observed farmers performing threshing, beating wheat stalks to separate the grains. Finally, they witnessed winnowing, where a farmer used wind to separate the lighter husk from the heavier grains.
• Ahmedabad: While preparing food with their Mami before the trip, they learned about sieving to separate bran from wheat flour based on particle size. In Ahmedabad, they learned how evaporation is used to obtain salt from seawater by allowing the water to turn to vapor, leaving the salt behind.
• Puducherry: With their Dada, they learned about three methods while making tea. They discussed sedimentation (tea leaves settling) and decantation (pouring the tea off the leaves). Ultimately, they used filtration with a strainer to perfectly separate the leaves from the tea.
• Madhya Pradesh: At a dhaba, they learned about churning, a method used to separate lighter butter from curd by agitating it.
• Shillong: At their Bua’s house, they helped a carpenter use magnetic separation, employing a magnet to remove iron nails from non-magnetic sawdust.

2. Compare and contrast the separation methods of sedimentation, decantation, and filtration for separating an insoluble solid from a liquid.

Sedimentation, decantation, and filtration are all used to separate insoluble solids from liquids, but they operate differently and have varying levels of effectiveness.

• Sedimentation is the initial step where a mixture is left undisturbed, allowing heavier, insoluble particles to settle at the bottom due to gravity. It does not separate the components but rather arranges them for easier separation.
• Decantation often follows sedimentation. It is the physical act of carefully pouring off the top layer of liquid, leaving the settled sediment behind. It is a simple method but is often incomplete, as some finer particles may remain suspended or be disturbed and poured out with the liquid, as seen with tea leaves.
• Filtration is a more precise method that involves passing the mixture through a filter medium like a cloth or filter paper. The liquid (filtrate) passes through the filter’s pores, while the solid (residue) is trapped. Unlike decantation, filtration can separate even very fine, non-settled particles, making it much more effective for achieving a clear liquid, such as when filtering muddy water.

In summary, sedimentation and decantation are a two-step process based on gravity and careful pouring, while filtration is a single, more thorough process based on particle size and the use of a porous barrier.

3. Explain the agricultural processes of threshing and winnowing. Why are both steps often necessary to get clean grains?

Threshing and winnowing are two crucial, sequential steps in processing harvested grain crops.

• Threshing is the first step, designed to separate the edible grain from the stalk it grew on. This is a mechanical process that involves beating the harvested bundles of stalks against a hard surface to physically knock the grains loose. The result of threshing is a mixture of grains, chaff, and husk.
• Winnowing is the next step, which aims to clean the grains by removing the lighter husk and chaff. This process relies on wind or blowing air. The threshed mixture is dropped from a height; the heavier grains fall straight down into a pile, while the much lighter husk is carried away by the wind.

Both steps are necessary because they solve two different separation problems. Threshing separates the grain from the large, coarse stalk. However, it leaves the grain mixed with the light, flaky husk that covers each individual seed. Winnowing then addresses this second problem by separating the heavy grain from the light husk, resulting in clean grains ready for use.

4. Discuss the role of particle size differences in the separation methods of handpicking, sieving, and filtration.

Particle size difference is a fundamental principle in several separation methods, including handpicking, sieving, and filtration, though it is applied differently in each.

• Handpicking: This method relies on a significant difference in size, as well as color and shape, that is easily visible to the naked eye. The components must be large enough to be physically picked up by hand. For example, picking large stones from smaller rice grains is possible because of the clear size difference.
• Sieving: This method refines the principle of size separation for solid-solid mixtures where handpicking is impractical. It uses a mesh with uniform holes. Particles smaller than the holes (like flour) pass through, while particles larger than the holes (like bran) are retained. The effectiveness is entirely dependent on one component’s particles being larger than the sieve’s pores and the other’s being smaller.
• Filtration: This method applies the principle of size separation to insoluble solids mixed in a liquid. A filter medium with very fine pores is used. The liquid molecules and dissolved substances pass through, but the insoluble solid particles, being larger than the pores, are blocked and collected as residue. This allows for the separation of much finer particles than sieving, such as removing mud from water using filter paper.

5. How is the principle of evaporation used to obtain common salt? Could this method be used to recover both the salt and the water? Explain your reasoning based on the text.

The principle of evaporation is used to obtain common salt by separating it from the water it is dissolved in. Seawater, which is a salt solution, is collected in shallow pits and exposed to sunlight and air. The heat from the sun causes the water, a liquid, to change into its vapor state and escape into the atmosphere. The dissolved salt, being a non-volatile solid, does not evaporate and is left behind as a solid residue. This solid mixture is then collected for further purification.

Based on the text, the simple method of evaporation described (leaving pits under the sun or boiling a solution in an open dish) cannot be used to recover both the salt and the water. This is because the water vapor is allowed to dissipate into the surrounding air and is lost. To recover the water, an additional process, mentioned in the “WISE FISH” game as condensation (conversion of water vapor into its liquid state), would be needed to capture and cool the vapor, turning it back into liquid water. The text itself focuses only on evaporation as a means to recover the solid.

6. Describe the process of making butter from curd using the churning method. What property of butter allows it to be separated?

The process of making butter from curd involves a separation method called churning. The curd is placed in a large pot, and a churner, known as a mathni, is used to agitate the mixture vigorously. This constant, rapid motion causes the fat globules in the curd to clump together and separate from the liquid part.

The property of butter that allows it to be separated is its density. Butter is lighter (less dense) than the remaining liquid, which is buttermilk (chhach). As the churning process separates the butter, its lower density causes it to rise to the surface and float at the top of the buttermilk. It can then be easily skimmed off and collected.

7. Imagine you have a mixture of iron nails, sawdust, and pebbles. Describe a two-step process to separate these three components using methods described in the text.

To separate a mixture of iron nails, sawdust, and pebbles, a two-step process using methods from the text would be effective.

• Step 1: Magnetic Separation. First, a magnet would be passed through the entire mixture. The iron nails are magnetic substances and will be attracted to the magnet, sticking to it. This allows the nails to be lifted out, separating them completely from the non-magnetic sawdust and pebbles.
• Step 2: Sieving. After removing the iron nails, the remaining mixture consists of sawdust and pebbles. These two components have a significant difference in particle size; pebbles are large, while sawdust is fine. This mixture can be separated by passing it through a sieve with holes that are larger than the sawdust particles but smaller than the pebbles. The fine sawdust will fall through the sieve, while the larger pebbles will be retained on top, thus completing the separation.

8. Explain why a modern thresher machine is more efficient than the traditional methods of threshing and winnowing.

A modern thresher machine is more efficient than traditional methods because it combines two separate, labor-intensive processes into a single, automated operation. Traditionally, farmers first had to perform threshing by manually beating stalks to separate the grains, which required significant physical effort and time. Following that, they had to perform winnowing, which involved waiting for windy conditions and manually using a soop to separate the husk from the grain. This second process was dependent on the weather and also physically demanding.

A thresher machine automates both tasks. It mechanically beats the stalks to separate the grains and simultaneously uses an internal fan or blowing mechanism to separate the lighter husk from the heavier grains. This consolidation of tasks makes the process much faster, less labor-intensive, and independent of weather conditions like wind, leading to a significant increase in overall efficiency.

9. Valli’s Mami used a sieve to prepare wheat flour, while Dada used a strainer to prepare tea. Explain how both are examples of filtration and why different “filters” were used.

Both using a sieve for flour and a strainer for tea are examples of the broad principle of filtration, which is separating components based on size by passing a mixture through a porous barrier. In both cases, a substance with smaller particles (fine flour, liquid tea) is allowed to pass through holes, while a substance with larger particles (bran, tea leaves) is held back.

Different “filters” (a sieve and a strainer) were used because the mixtures being separated have very different properties.

• Sieving Flour: This is a solid-solid separation. The goal is to separate fine flour particles from larger, solid particles like bran or small stones. A sieve with a fine metal mesh is appropriate for this dry process.
• Straining Tea: This is a solid-liquid separation. The goal is to separate solid tea leaves from the liquid tea. A strainer’s holes must be small enough to catch the leaves but large enough to let the liquid flow through easily.

The choice of filter depends upon the state of the mixture (solid-solid vs. solid-liquid) and the size of the particles to be removed.

10. Discuss the environmental issue Malli observed during the boat ride and relate it to the theme of separation.

During the boat ride, Malli observed a significant environmental issue: water pollution. When the fisherman, Otukkam, cast his net, it trapped not only fish but also various forms of waste, including plastic bags, broken bottles, food wrappers, and a fish with a straw stuck in its mouth. This highlights how human-generated waste contaminates natural water bodies, harming aquatic life.

This observation relates to the theme of separation in a critical way. The entire chapter focuses on methods to separate desired components from undesired ones (e.g., grains from husk, salt from water). The polluted river presents a far more complex and harmful separation problem. The fisherman’s net, acting as a filter, unintentionally “separates” the waste from the river along with the fish. This demonstrates a negative consequence of having unwanted substances mixed in our environment, where the task of separating pollutants from ecosystems is a massive and urgent challenge for society. The poem in the text further emphasizes the need to “stop plastic pollution at source” to avoid this difficult and harmful separation process later.

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Glossary of Key Terms

Term	Definition
Churning	A process used to extract butter from curd by agitating the mixture, causing the lighter butter to separate and float.
Decantation	The process of removing the liquid from a mixture by tilting the vessel after the heavier, insoluble component has settled.
Evaporation	The process in which a liquid gets converted into its vapor. It is used to separate a solid dissolved in a liquid.
Filtrate	The clear liquid that passes through a filter during the process of filtration.
Filtration	The process used to separate insoluble solid components from a liquid by passing the mixture through a filter.
Handpicking	The method of picking components from a mixture by hand, based on differences in size, color, and shape.
Magnetic separation	The separation of magnetic and non-magnetic substances from a mixture by using a magnet.
Magnetic substances	Substances which are attracted towards a magnet, such as iron.
Mixture	A substance made by combining two or more different materials in such a way that no chemical reaction occurs.
Residue	The insoluble solid particles that remain on the filter after the process of filtration.
Sedimentation	The process of settling down of a heavier, insoluble component at the bottom of a liquid.
Sieving	The process of separating solids from a mixture based on variations in particle size using a sieve.
Threshing	The process in which stalks are beaten to separate grains from them.
Winnowing	The method of separating heavier and lighter components of a mixture by using wind or blowing air.