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Dav Class 6 Science Chapter 4 Notes – Separation of Substance
| SL.NO | TOPIC |
| 1 | Our Environment |
| 2 | Food |
| 3 | Nature of matter |
| 4 | Separation of Substance |
| 5 | Changes around us |
| 6 | Measurement and Motion |
| 7 | The world of living |
| 8 | Structure and Function of the Living Organism-Plants |
| 9 | Structure and Function of the Living Organism-Animals |
| 10 | Work and Energy |
| 11 | Electric currents and Circuits |
| 12 | Light and Shadows |
| 13 | Magnents |
| 14 | Electric Currents and Circuits |
Dav Class 6 Science Chapter 4 Notes
SEPARATION OF SUBSTANCE
Mixtures and Pure Substances
- Mixtures: Most materials we encounter are mixtures, made up of two or more substances. The components of a mixture are not combined chemically.
- Examples include air (a mixture of gases like oxygen, nitrogen, and carbon dioxide) and milk (a mixture of water, fat, and other substances).
- Pure Substances: A substance made up of only one type of substance.
- Examples include sugar, salt, oxygen, gold, and pure water.
Types of Mixtures
Mixtures are categorized into two types based on the uniform distribution of their components:
- Homogeneous Mixtures: Have the same composition throughout, with components uniformly distributed. Different parts cannot be distinguished from each other.
- Examples: A solution of salt or sugar in water, soft drinks, and alloys like brass.
- Heterogeneous Mixtures: Do not have the same composition throughout. Components are not uniformly distributed and can be distinguished from each other.
- Examples: Mixtures of sand in water, iron nails in sulfur powder, and pebbles in rice.
Dav Public School Class 6 Science Chapter 4 Notes
Methods for Separating Components of Mixtures
The methods for separation are chosen based on the properties of the components.
1. Mixtures of Solids with Solids
- Hand Picking: Used when components are of different colors, shapes, or sizes and the quantity is small. For example, separating pebbles from rice or dal.
- Threshing: Used by farmers to separate grains from stalks. Dried stalks are beaten to release the grains.
- Winnowing: Used to separate lighter husk from heavier grains. The mixture is dropped from a height; wind blows the lighter husk away while the heavier grains fall closer.
- Sieving: Separates components of different sizes using a sieve (a wire mesh with holes). Smaller particles pass through, while larger ones are retained. For example, sieving wheat flour at home or sand at a construction site.
- Magnetic Separation: Used when one component is magnetic, such as iron. A magnet is used to attract and separate the magnetic substance.
- Sublimation: A process where a solid changes directly into its gaseous state upon heating. This method separates solids that sublime (like camphor, naphthalene, or iodine) from those that do not (like sand or salt).
Dav Class 6 Science Chapter 4 Notes
2. Mixtures of Solids with Liquids
- Evaporation: Used to separate a dissolved solid from a liquid. The liquid is heated, causing it to evaporate and leaving the solid behind. This is how common salt is obtained from sea water.
- Crystallization: A process to obtain pure solids in crystal form from a saturated solution. It involves heating a saturated solution and then allowing it to cool without disturbance, leading to the formation of pure crystals.
- Sedimentation and Decantation:
- Sedimentation: The process where insoluble, heavy solid particles in a liquid settle at the bottom when left undisturbed.
- Decantation: The process of gently pouring the clear liquid into another container without disturbing the settled solids (sediments).
- Loading: A method to speed up sedimentation by making light, suspended particles heavier with the help of a chemical like alum. This causes the fine particles to settle down more quickly.
- Filtration: A process that separates insoluble solids from a liquid using a filter. The liquid (filtrate) passes through the porous filter, while the solid impurities (residue) are left behind.
- Centrifugation: A method to separate fine suspended particles from a liquid by rotating the mixture at high speeds. The heavier particles settle at the bottom, and lighter ones stay at the top. Separating cream from milk is a common example.
Separation of Substance Dav Class 6 Science Chapter 4 Notes
3. Mixtures of Liquids with Liquids
- Separating Immiscible Liquids: Used for liquids that do not dissolve in each other (immiscible liquids), which form separate layers. A separating funnel is used, where the heavier liquid is collected from the bottom, leaving the lighter liquid behind. For example, separating mustard oil and water.
Fill in the blanks
- A substance made up of only one type of substance is called a pure substance.
- A mixture where components are not uniformly distributed and can be distinguished from each other is a heterogeneous mixture.
- The process of separating grains from their stalks by beating them is called threshing.
- The method used to separate lighter husk from heavier grains with the help of wind is called winnowing.
- Sieving is a separation method that uses a sieve to separate components of different sizes.
- The process where a solid changes directly into its gaseous state upon heating is known as sublimation.
- An example of a substance that undergoes sublimation is camphor or iodine.
- The process used to separate a dissolved solid from a liquid by heating the liquid is evaporation.
- Common salt is obtained from sea water using the method of evaporation.
- The process of obtaining pure solids in crystal form from a saturated solution is called crystallization.
- When insoluble heavy solid particles settle at the bottom of a liquid, the process is called sedimentation.
- Gently pouring out a clear liquid without disturbing the settled solids is known as decantation.
- To speed up the process of sedimentation, a chemical like alum is sometimes used.
- The solid impurities left behind on a filter paper during filtration are called the residue.
- The clear liquid that passes through the filter during filtration is called the filtrate.
- The method used to separate fine suspended particles from a liquid by rotating it at high speed is centrifugation.
- Separating cream from milk is an example of centrifugation.
- Liquids that do not dissolve in each other are called immiscible liquids.
- A separating funnel is used to separate two immiscible liquids.
- The method of hand picking is used when the components of a mixture are of different colors, shapes, or sizes and the quantity is small.
Dav Class 6 Science Chapter 4 Notes
1.Assertion (A): The method of winnowing is used to separate husk from grains.
Reason (R): Husk is lighter than the grains, and the wind carries it away while the grains fall straight down.
2.Assertion (A): Hand picking is a suitable method for separating small pieces of stones from rice.
Reason (R): This method is effective when the components are of different colors, shapes, or sizes and the quantity is small.
3.Assertion (A): Evaporation is a process used to obtain salt from seawater.
Reason (R): The water evaporates, leaving the solid salt behind.
4.Assertion (A): A sieve can be used to separate sand from pebbles at a construction site.
Reason (R): Sieving is used to separate components of different sizes.
5.Assertion (A): You can use magnetic separation to separate iron filings from sulfur powder.
Reason (R): Iron is a magnetic substance and is attracted by a magnet.
6.Assertion (A): Sedimentation and decantation are used to separate sand from a mixture of sand and water.
Reason (R): Sand is insoluble and heavier than water, so it settles down at the bottom.
7.Assertion (A): The process of sublimation is used to separate a mixture of sand and camphor.
Reason (R): Camphor changes directly from a solid to a gas upon heating, but sand does not.
8.Assertion (A): Filtration is used to separate sugar from a sugar solution.
Reason (R): The sugar particles are retained on the filter paper as a residue.
9.Assertion (A): A separating funnel is used to separate a mixture of mustard oil and water.
Reason (R): Mustard oil and water are immiscible liquids that form separate layers.
10.Assertion (A): Centrifugation is used to separate cream from milk.
Reason (R): Centrifugation separates fine suspended particles from a liquid by spinning at high speeds, causing denser particles to settle.
Answers
- Both A and R are true, and R is the correct explanation for A.
- Both A and R are true, and R is the correct explanation for A.
- Both A and R are true, and R is the correct explanation for A.
- Both A and R are true, and R is the correct explanation for A.
- Both A and R are true, and R is the correct explanation for A.
- Both A and R are true, and R is the correct explanation for A.
- Both A and R are true, and R is the correct explanation for A.
- A is false, and R is false. (Sugar dissolves in water and would pass through the filter paper.)
- Both A and R are true, and R is the correct explanation for A.
- Both A and R are true, and R is the correct explanation for A.