NCERT Solutions Class 6th Science Chapter – 3 Separation of Substances Notes

April 19, 2022

NCERT Solutions Class 6th Science Chapter – 3 Separation of Substances

Textbook	NCERT
Class	6^th
Subject	Science
Chapter	3^rd
Chapter Name	Separation of Substances
Category	Class 6th Science Notes
Medium	English
Source	Last Doubt

NCERT Solutions Class 6th Science Chapter – 3 Separation of Substances Notes In this Chapter We Will read about Pure Substances, Solution And Solubility, Mixtures, Methods Of Separation, Homogeneous Mixtures, Hand-picking, Sedimentation and Churning etc. and More much. you have provided easy notes which use in your study make progress in education.

NCERT Solutions Class 6th Science Chapter – 3 Separation of Substances

Chapter – 3

Separation of Substances

Notes

Pure Substances – Many substances around us contain only one type of constituent particle. Elements and compounds are pure substances. Some of the pure substances are iron, copper, water, salt, etc.

Impure Substances – Substances containing more than one type of constituent particle are called impure substances. Some of the impure substances are pond water, milk, etc.

Impurities – These are the unwanted particles present in a substance making it impure.

Mixtures – Substances that contain more than one component mixed in any ratio are called mixtures. For example, the air is a mixture of many gases like nitrogen, oxygen, carbon dioxide, dust particles, etc.

Homogeneous Mixtures – The mixtures in which the particles of the substances present cannot be seen are called homogeneous mixtures. For example, solution of sugar and water, air, cold drinks, etc.

Heterogeneous Mixtures – The mixtures in which particles of the substances present can be seen easily are called heterogeneous mixtures. For example, water in oil, and dust in the air.

Need for Separation – We carry out the separation of the components of a mixture of an impure substance for the following purposes:

• To remove the unusual or harmful component.
• To obtain the useful component.
• To remove impurities for getting a pure sample.

Principle of separation – The substances present in a mixture retain their original properties like particle size, density, melting point, boiling point, volatility, etc. We use the difference in any one of these properties in the components of a mixture to separate them.

Methods of Separation – Handpicking, winnowing, sieving, magnetic separation, sedimentation, decantation, loading, filtration, evaporation, sublimation, distillation, churning, etc., are some common methods of Separation.

Churning (or Centrifugation) – It is the process of the separation of the lighter particles of a suspended solid from a liquid. For example, to obtain butter from the curd or milk.

Condensation – The process of conversion of water vapour into its liquid form is called Condensation.

Crystallisation – The process of crystallisation is used for obtaining pure crystalline substance from impure Samples.

Decantation – It is the transfer of clean liquid from one vessel to the other without disturbing the settled (sedimented) particles.

Evaporation – It is the process of removing water (or moisture) from a mixture either by heating on flame or direct sunlight. For example, salt from seawater is obtained by this Method.

Filtration – Filtration is used to separate solid particles from a liquid by passing the mixture through filter paper.

Handpicking – This method is used for separating small particles of dirt, stone, husk, etc., from the grains of wheat, rice, pulses, etc.

Loading – It is the process of faster sedimentation by suspending alum in a liquid.

Sedimentation – It is the process of settling heavy solid particles in a mixture at the bottom of the vessel.

Sieving – Sieving is used when two Components of a mixture have different particle sizes. Sieving allows the fine particles to pass through the holes of the sieve, while the bigger particles remain on the sieve. For Example, sieving of wheat flour, and sieving of sand at construction sites.

Saturated solution – A solution in which no more soluble substance can be dissolved at room temperature is called a saturated solution.

Solution – When a soluble substance is dissolved completely in a liquid (say sugar in water), a homogeneous mixture is formed. It is known as a solution.

Threshing – The process that is used to separate the grain from stalks is threshing.

Winnowing – Winnowing can be used to separate lighter and heavier components of a mixture. For example, to separate the husk from grain with the help of air.

Methods Of Separation – Different methods are used for separating different substances that are mixed together. Let us learn about some common methods that are used.

Threshing – Grains or seeds of plants like rice and wheat serve as sources of food. The flour (atta) that is used for making chapattis is made from wheat grains. After these crops have been harvested or cut, the grains need to be separated from the stalks (the dried stems). This is done by threshing.

• The process of beating harvested crops to separate the grains from the stalks is called threshing. It is done manually (by hand) or with the help of machines. Manual threshing is done by holding a pile of crops and beating it on a rock or a hard surface. This loosens and separates the grain from the stalk. Sometimes, threshing is also done by crushing the harvested stalks using bullocks.
• Threshing is also done with the help of machines like the combine harvester. Threshed grains may still contain seed coverings and tiny pieces of leaves or stems (collectively called chaff). These are separated by winnowing.

Winnowing – The method used to separate the chaff from the grain by wind or blowing air is called winnowing.

• The mixture of chaff and grain is taken in a winnowing basket. The farmer stands at a higher level and lets the mixture fall to the ground.
• The grain, being heavier, falls almost vertically whereas the lighter chaff is carried away by the wind and forms a separate heap away from the grain.
• The separated chaff is used as fodder for cattle. The direction of the wind plays an important role in the process of winnowing.

Hand-picking – Rice, wheat, pulses, etc., that we buy from the market may contain impurities (unwanted or harmful particles) in the form of small stones, unwanted grains, etc.
Often, these impurities look very different from the food item and can be spotted easily. The method of separation used in such a case is hand-picking.

This method is preferred when The quantity of the mixture is small, The unwanted substance is present in smaller quantities, and The size, shape, or colour of the unwanted substance is different from that of the useful one.

Sieving – If the components of a mixture are of different sizes, they can be separated by sieving. The smaller component passes through the pores of the sieve whereas the larger component (stones or husk) is left behind in it. This method is used in some homes to separate wheat bran (the bigger particles) from flour.

• However, sieving wheat flour is not advisable as wheat bran, which is removed during sieving, is very rich in nutrients and is also rich is better to remove visible impurities by handpicking.

• The process of sieving is also used to separate pebbles and stones from sand at construction sites. The stones and pebbles present in the mixture remain in the sieve and the fine sand particles pass through the holes of the sieve.

Sedimentation and Decantation – Have you seen pulses being washed in your home? When pulses are kept in a bowl of water, they settle down as they are heavy. However, dirt, insects, tiny pieces of straw, and other lighter impurities float at the top.

• The water, which contains these impurities, is then poured out and discarded. This process involves two methods: sedimentation and Decantation.
• The process of separating insoluble solids, suspended in a liquid, by allowing them to settle down is called sedimentation.
• The solid particles that settle down during sedimentation are called sediments.
• The process of pouring out the clear upper liquid without disturbing the sediments is called decantation.
• The liquid above the sediments is called a supernatant.
• A mixture of sand and water can also be separated by sedimentation and decantation.
• The mixture is left undisturbed for some time.
• Sand, being heavier, settles down and water is poured out into a separate container.

Filtration – The process by which two substances (an insoluble solid and a liquid) are separated by passing the mixture through a filtering device is called filtration.

• Filtration is commonly used in our homes. For example, after preparing tea, we filter out the tea leaves using a strainer. Filtration is also done to remove the pulp from fresh fruit juice. Water may also contain solid impurities, which can be removed by filtration.

• During filtration, the insoluble solid is retained in the filtering device whereas the liquid passes through it. It is important that the particles of the insoluble solid are bigger than the holes in the filtering device for them to be retained in it. A filter paper is a filtering device that has very fine pores in it.

condensation – The process in which gas changes into liquid is called condensation. Condensation is the opposite of evaporation. In nature, water vapour in the air condenses to form its liquid form, the dew. Condensation takes place only when water vapour hits a cold surface.

Q. 1. Why do we need to group materials? Give one reason.

Ans – We often group materials for our convenience. It helps to describe their properties.

Q. 2. Suggest two bases on which we can group objects.

Ans – (i) Material used in making the object, e.g. wood or metal/plastic.
(ii) Material of the object is soft or hard, or substance is soluble or insoluble in water.