Extra 20 important long questions and answers from the Chapter:5 Separation of Substances for Class 6 CBSE Science:

Long Answer Questions

1. Why is it necessary to separate substances?

Ans: We separate substances for the following reasons:

To remove unwanted and harmful substances.

To obtain useful components from a mixture.

To purify substances for safe consumption.

To improve the quality of substances.

To make food items edible and safe.

To prepare substances in their purest form for industrial use.

 

2. Explain the method of hand-picking with examples.

Ans: Hand-picking is the method of manually separating unwanted materials from a mixture.

This method is used when the impurities are large and easily visible.

It is commonly used at home to remove stones from rice or dal.

Farmers use hand-picking to separate weeds from crops.

It is a time-consuming method and requires human effort.

It is suitable for small-scale separation processes.

It is not effective for substances that are mixed thoroughly or in powder form.

 

3. What is winnowing? How is it used in daily life?

Ans: Winnowing is the process of separating lighter particles from heavier particles using wind or air.

This method is used mainly for separating husk from grains.

Farmers use winnowing after threshing the crops.

Lighter husk is carried away by the wind, while heavier grains fall to the ground.

It is an easy and natural method, requiring no machinery.

It is commonly used in rural areas for cleaning grains.

It works best in open spaces where the wind can carry away the lighter materials.

 

4. Explain the process of sieving. Where is it used?

Ans: Sieving is a method used to separate particles of different sizes.

A sieve (a mesh or net) is used to allow smaller particles to pass through while retaining larger ones.

It is used in flour mills to remove husk and large impurities from wheat flour.

Construction workers use sieving to separate fine sand from pebbles.

It helps in filtering tea leaves while making tea.

Different sieve sizes are used depending on the required separation.

It is a simple and effective method used in both homes and industries.

 

5. How is decantation used to separate substances? Give an example.

Ans: Decantation is the process of carefully pouring out a liquid without disturbing the settled solid.

It is useful when the solid is heavier and settles at the bottom.

It is used to remove mud from water by allowing the mud to settle and then pouring the clear water.

It is also used to separate oil and water, as they do not mix.

Decantation is commonly used after sedimentation to improve separation.

It is useful for separating immiscible liquids (liquids that do not mix).

It is a simple and cost-effective method for purification.

 

6. Describe the filtration process with an example.

Ans: Filtration is the process of separating an insoluble solid from a liquid using a filter.

A filter paper, cloth, or fine mesh is used for filtration.

The solid particles are trapped, while the liquid passes through.

It is used in households to filter tea leaves using a strainer.

Water purification plants use filtration to remove dirt from water.

It is also used in chemistry labs to separate precipitates from solutions.

Filtration is an efficient and commonly used purification method.

 

7. Explain the process of evaporation with an example.

Ans: Evaporation is the process of converting a liquid into vapor.

It occurs when a liquid is heated or left in open air.

It is used to obtain salt from seawater by evaporating the water.

Wet clothes dry due to evaporation of water.

It is a natural process that occurs in everyday life.

Sugar solutions can be evaporated to obtain sugar crystals.

It is used in industries to prepare dry substances from liquids.

 

8. What is churning? How is it used in daily life?

Ans: Churning is the process of stirring or beating a liquid to separate substances of different densities.

It is mainly used to separate butter from milk or curd.

When milk or curd is churned, the heavier butter separates from the liquid.

It is done using a churner, blender, or manually with a wooden beater.

It is a traditional method used in villages to make butter.

The liquid left behind after churning is called buttermilk.

Churning is also used in industries to prepare dairy products.

 

9. What is distillation? How is it useful?

Ans: Distillation is the process of separating a liquid from a solution by heating and cooling.

The liquid is heated until it evaporates.

The vapor is collected and cooled back into liquid form.

It is used to obtain pure water from seawater.

It is commonly used in industries to purify chemicals.

It helps in separating different components of crude oil.

Distillation provides pure substances by removing impurities.

 

10. What is the difference between filtration and decantation?

Ans:

Filtration	Decantation
Uses a filter to separate solids from liquids.	The liquid is carefully poured out, leaving the solid behind.
Effective for very fine particles.	Works best when particles are heavy and settle at the bottom.
Used for tea leaves, sand from water, etc.	Used for oil and water separation.
Requires filter paper or a fine mesh.	Does not require any special equipment.
Gives clear and pure liquid.	Some impurities may remain in the liquid.
Commonly used in homes and industries.	Used in simple everyday activities.

 

11. How can we obtain drinking water from muddy water?

Ans: The following steps are used:

Sedimentation

– Allow the mud to settle at the bottom.

Decantation

– Pour out the clear water without disturbing the mud.

Filtration

– Pass the water through a filter to remove fine particles.

Boiling

– Boil the filtered water to kill germs and bacteria.

Chlorination

– Add chlorine to disinfect the water.

Storage

– Store in clean, covered containers for safe use.

 

12. What is the principle of sieving? Where is it used?

Ans: Sieving is a method used to separate particles of different sizes.

A sieve (mesh) allows smaller particles to pass while retaining larger ones.

It is used in flour mills to separate husk and stones from wheat flour.

It is used in construction to separate sand and pebbles.

It helps in removing impurities from grains before cooking.

Different sieve sizes are used depending on the need.

Sieving is a simple and efficient way of separation.

 

13. How is salt obtained from seawater? Explain the process.

Ans: Salt is obtained from seawater using evaporation.

Seawater is collected in shallow ponds.

The water is left in the sun to evaporate.

As the water evaporates, salt crystals are left behind.

The salt is collected and purified before use.

This method is used in coastal areas to produce salt.

The evaporation process helps in separating dissolved solids from liquids.

 

14. What is magnetic separation? Give an example.

Ans: Magnetic separation is a method used to separate magnetic materials from non-magnetic ones.

It works on the principle that magnetic materials are attracted to a magnet.

It is used to separate iron filings from sand.

In industries, magnetic separation is used to remove metal contaminants from grains.

It is helpful in recycling to separate metals from waste.

Magnetic separators are also used in mining.

This method is efficient, quick, and widely used in various fields.

 

15. How is distillation different from evaporation?

Ans:

Distillation	Evaporation
Used to separate liquid from a solution.	Used to separate solids dissolved in liquids.
Involves heating, vaporization, and condensation.	Only involves heating to vaporize the liquid.
Used to obtain pure water from seawater.	Used to obtain salt from seawater.
Needs special equipment like a condenser.	Can be done naturally under the sun.
Used in chemical industries for purification.	Used in salt production and drying processes.
More complex and used in industries.	Simple and used in daily life.

 

16. What is the difference between soluble and insoluble substances? Give examples.

Ans:

Soluble Substances	Insoluble Substances
Substances that dissolve in water.	Substances that do not dissolve in water.
Example: Salt, sugar, lemon juice.	Example: Sand, chalk powder, oil.
They form a uniform solution.	They form a separate layer or settle down.
Cannot be separated by filtration.	Can be separated by filtration.
Found in drinks, medicines, and food.	Found in soil, dust, and certain chemicals.
Used in making solutions.	Used in filtration processes.

 

17. How does filtration help in water purification?

Ans: Filtration is an important step in cleaning water.

It removes solid impurities like dirt and sand.

A filter paper, cloth, or fine mesh is used to trap particles.

Water filters use activated carbon to remove harmful substances.

It is used in households to filter tea and coffee.

Large filtration plants filter drinking water before supplying it.

Filtration ensures clean and safe water for consumption.

 

18. What is threshing? How is it done?

Ans: Threshing is the process of separating grains from harvested stalks.

It is done after crops like wheat and rice are harvested.

The stalks are beaten to free the grains.

It can be done manually by hand or using animals.

Machines like threshers are used for large-scale threshing.

The grains are then separated from husk using winnowing.

Threshing is an essential process in agriculture.

 

19. How is butter separated from milk?

Ans: Butter is separated from milk using churning.

Milk or curd is collected for butter extraction.

It is churned using a blender, machine, or wooden churner.

Churning breaks the fat molecules and allows them to combine.

Butter floats on the surface and is collected.

The remaining liquid is called buttermilk.

This method is widely used in dairy farms.

 

20. What are immiscible and miscible liquids? Give examples.

Ans:

Miscible Liquids	Immiscible Liquids
Liquids that mix completely.	Liquids that do not mix.
Example: Water and alcohol.	Example: Water and oil.
They form a uniform solution.	They form separate layers.
Cannot be separated by decantation.	Can be separated by decantation.
Used in medicines and drinks.	Found in petroleum and cooking oils.
Used in chemistry and industry.	Used in oil separation processes.