These DAV Class 6 Science Notes and DAV Class 6 Science Chapter 4 Notes – Separation of Substances act as excellent revision resources, particularly in preparation for board exams.
Separation of Substances Class 6 DAV Notes
→ Pure Substance: A substance which is composed of only one type of material is called a pure substance. All the components of a pure substance have similar chemical and physical properties. Mixture: A substance which is composed of more than one type of substance is called a mixture. Different components of a mixture have different chemical and physical properties.
→ Types of Mixtures:
→ Homogeneous Mixture: When the mixture has same composition throughout, it is called homogeneous mixture. The components of a homogeneous mixture cannot be distinguished. Examples: solution of salt and sugar in water, alloys, etc.
→ Heterogeneous Mixture: When the mixture does not have same composition throughout, it is called heterogeneous mixture. The components of a heterogeneous mixture can be distinguished from one another. Examples: mixture of sand in water, iron nails in sulphur powder, pebbles in rice, etc.
→ Types of Mixtures on the basis of physical states of components:
- Mixture of solids with solids
- Mixture of solids with liquids
- Mixture of liquids with liquids
→ Separation Of Components Of Mixtures
→ The components of a mixture can be separated by simple physical methods. These methods are based on difference in properties of components.
→ Separation of mixtures of solids with solids: For this, the following methods are used.
→ Hand picking: This method is used for separating a mixture when the mixture is in small quantity. This method is used when the components are different in sizes, in colour and are fairly big to be picked up by hand. Example: separating pebbles from rice or pulse or separating grass from coriander leaves.
→ Threshing: Threshing is used by farmers for separating grains from stalks. For small amount of harvested crop, threshing is done manually, in which dry stalks are beaten on ground. For bigger amount, threshing machine is used.
→ Winnowing: Winnowing is used for separating lighter objects from heavier objects with the help of wind. This is used by farmers to separate grains from chaff. For this, the mixture is allowed to be dropped from a height. Husk, being lighter, gets blown away, while the grains fall vertically down.
→ Sieving: Sieving is used to separate components of different sizes. A sieve is made up of a wire mesh which is tightly fixed in a frame. The mixture is put in the sieve and the sieve is shaken. The smaller particles pass through the mesh and larger particles remain in the sieve. This method is often used in households to separate impurities from flour. Sieving is also used at construction sites to separate pebbles from sand.
→ Magnetic Separation: This method is useful Then one of the components of a mixture is made of magnetic material. Magnetic separation is used to separate iron articles in scrap-yard.
→ Sublimation: A solid usually changes into liquid before changing into gas. But some solids directly change into gas and its vice-versa is also true. This phenomenon is called sublimation and the substance is called a sublimate. Some solids, which can undergo sublimation, can be separated by using this method. For example, camphor can be separated from a mixture of camphor and sand, by this method. For this, the mixture is heated so that the camphor evaporates by sublimation, leaving the sand behind. The gaseous form of camphor can be cooled down to obtain the camphor in solid form.
→ Separation of mixtures of solids with liquids: Such mixtures can be divided into two categories, viz. solids which dissolve in liquids and those which do not dissolve in liquids.
→ Separating solids which dissolve in liquids: Components of such mixtures can be separated by the following methods:
→ Evaporation: The process by which a liquid changes into gas is called evaporation. By using this method, the liquid component is allowed to evaporate, which leaves the solid component. For example, from a solution of salt in water, salt can be obtained by using this method. In fact, salt is obtained from sea water by using this method.
→ Crystallisation: Crystallisation is used for obtaining pure solid from a solution. For example; the salt obtained from sea water contains many impurities. Crystallisation is used for removing such impurities so that pure salt crystals can be obtained. During crystallisation, pure solid is obtained from a concentrated solution of the given substance.
→ Separating solids which do not dissolve in liquids: Components of such mixtures can be separated by the following methods:
→ Sedimentation and Decantation: The process by which heavy solid particles settle down on their own in a solution is called sedimentation. After sedimentation, the liquid component is carefully poured out without disturbing the sediment. This process is called decantation. Example, sand can be separated from water by using this method.
→ Loading: Sedimentation is a slow process and to hasten this process, loading is employed. For example, during the treatment of water, alum is added to water to initiate precipitation of insoluble impurities in water. Such impurities then settle down at the bottom.
→ Filtration: Filtration is used for separating insoluble solids from a liquid. For this, filter paper is used in laboratory. In households, a tine mesh or cloth is often used. Tea leaves are separated from liquid by this method.
→ Centrifugation: When insoluble particles are suspended in a liquid, they can be separated by this method. For this, the mixture is churned. The lighter particles separate because of centrifugal force. Cream is separated from milk by using this method.
→ Separation of mixtures of liquids with liquids: Such mixtures can be of two types, viz. mixture of immiscible liquids and mixture of miscible liquids.
→ Separation of immiscible liquids: Oil is immiscible with water. When a mixture of oil and water is allowed to settle down, the oil, being lighter, forms a layer at the top. This can be separated by decantation. For better separation, separating funnel is used. The separating funnel is fitted with a tap in its neck. The liquid which forms the bottom layer is slowly poured out through the separating funnel. This leaves the top layer of liquid inside the funnel.
→ Separation of miscible liquids: For separating a mixture of miscible liquids, fractional distillation is used. Different liquids have different boiling points. Fractional distillation works on the difference in boiling points of the component liquids. Petroleum is refined to obtain various petroleum products by using fractional distillation.
→ Combining two or more methods of separation: In real life, many mixtures contain a number of substances. We need to use more than one method of separation in that case.
→ Pure substance: A substance which is composed of only one type of material is called a pure substance. The physical and chemical properties of all the components are same, in case of a pure substance.
→ Mixture: A substance which is composed of more than one type of material is called a mixture. The physical and chemical properties of different components are different, in case of a mixture. Handpicking: In this method, a component from a mixture is separated manually by using hands.
→ Threshing: Separation of grains from harvested stalks is called threshing.
→ Winnowing: Separation of a lighter component from a mixture with the help of wind is called winnowing.
→ Sieving: Separation of solid particles of different sizes through a mesh is called sieving.
→ Sublimation: When a solid changes into gas, without undergoing the liquid phase, it is called sublimation. Similarly, some gases directly change into solid without undergoing the liquid phase.
→ Sedimentation: When insoluble impurities settle down on their own in a liquid, this is called sedimentation.
→ Decantation: When liquid is carefully poured out without disturbing the sediment it is called decantation.
→ Filtration: The process of separating insoluble solid from a liquid with the help of a fine mesh is called filtration.
→ Evaporation: The process of conversion of liquid into vapour is called evaporation.
→ Crystallisation: The process of obtaining pure crystals of a substance from a concentrated solution is called crystallisation.
→ Loading: Using precipitation reaction to hasten the process of sedimentation is called loading.
→ Distillation: The process of obtaining a liquid after evaporation of a mixture is called distillation.