NCERT 6th Class (CBSE) Science: Separation of Substances

Question: You are given a simple of water. How will you find out whether it is pure or not. Answer: We will find whether it is pure or not by checking the boiling point. If the boiling point is 100°C it is it is pure and f it is less then 100°C it is impure. Question: Why are objects at a distance seen more clearly after rain? Answer: Objects at a distance are seen more clearly after rain because the light dust particles in the air were settled down by rain and loading and the air becomes clear. Question: List three properties of mixtures. Answer: in a mixture the ratio of components is not same. Components can be separated. The components in mixture retain their properties. Question: Give two situations where it is necessary to separate mixture into its continents. Answer: Two situations where it is necessary to separate mixture into its continents are: Separating tea leaves from tea. Separating oil from water. Question: Why water is an important solvent? Answer: Many things or substance can dissolve in water. That's why it is called an important solvent. It can dissolve gases like oxygen and carbon dioxide. It can dissolve solids like salt and sugar. It can dissolve liquids like alcohol and honey. Question: Sea water has salt dissolved in it. You know that pure water can be obtained from sea water by distillation. However, this method is not used to get drinking water from sea water. What do you think is the reason? Answer: The reason is that because due to the process of distillation all minerals and other substances in water had been removed. This water is not used for drinking thought it pure, it is used in laboratories, car batteries, syringes etc. Separation of two immiscible liquids Question: A battle contains either salt or chalk. How will fined out what it has, without tasting it? Answer: We can get know as salt is dissolved in the water but chalk is never dissolved because it is insoluble. So if we see it is dissolved it is salt and if it dose not dissolve it is chalk. Question: What is the difference between homogeneous and heterogeneous mixture? Give an example of each mixture. Answer: Homogeneous mixture: Mixtures in which constituents are uniformly spread. Each part of the mixture has same properties. Fore example sugar in water, air, soft drinks. Heterogeneous mixture: Mixtures in which constituents are not uniformly spread. Each part of mixture does not has same properties. For example sand, iron, biryani. Question: We always talk about a saturated solution at temperature? Why is the temperature specified? Answer: Saturated solution on heating becomes unsaturated and on cooling it becomes over saturated. So it is necessary to specified the temperature. Question: Under which condition can handpicking be used to separate the constituents of a mixture? Answer: Mixture in small amount Impurity in small amount Difference of colour, shape, size Impurity is big enough to pick by hand Question: How will you separate a mixture of grass, pebbles and sand? Answer: We will separate the mixture by: Sieving: We will separate sand from mixture by sieving. Winnowing: We will separate grass and pebbles by winnowing. Question: Think and write how you will separate a mixture of water, sand, salt and iron fillings. Think- which property of iron can be used for this? Answer: We will separate by: Filtration: We will separate iron fillings and sand from mixture by filtration. Magnetic separation: We will use magnet to separate iron fillings from sand. Distillation: We will separate salt and water by distillation. Question: What is mixture? Answer: When two or more than two substances are mixed together in any ratio then it is called a mixture. Question: Write various methods of separation of components from their mixture. Answer: Handpicking Threshing Winnowing Sedimentation Decantation Filtration Evaporation Condensation Question: Define the term handpicking. Answer: The process used to separate slightly larger particles from a mixture by hand is called handpicking. For example: Stone pieces can be separated from wheat or rice by handpicking. Question: What do you mean by threshing? Where is it used? Answer: Threshing is a process in which we separate grain from stalks. This process is used by farmer to separate gram, wheat, rice, mustard seeds in his field. Question: Write three methods of separation. Answer: Handpicking, threshing and winnowing. Question: How will you separate oil and water from their mixture? Answer: Oil, being lighter than water, will float on it. Two distinct layers are formed and slowly oil is allowed to flow into another container and is separated from water. Separating funnel can also be used to separate the two. Question: What is evaporation? Answer: The process of conversion of water into vapour is called evaporation. This process takes place continuously where water is present. Common salt from sea water is obtained using this method. Question: Define winnowing. Answer: The process is used to separate components from a mixture in which one component is heavier or lighter than other is called winnowing. Winnowing is done with the help of wind or by blowing air. Question: What do you mean by sieving? Give an example. Answer: Sieving allows the fine flour particles to pass through the holes of the sieve while the bigger particles or impurities remain on the sieve. For example, in a flour mill, impurities like husk and stones are removed from wheat before grinding it. Question: What is threshing? Answer: Threshing is a process that is used to separate grain from stalks. In this process the stalks are beaten to free the grain seeds. Sometimes threshing is done with the help of bullocks. Machines are also used to thresh large quantities of grain. Question: Describe the method to obtain salt from sea water. Answer: Sea water contains many salts mixed in it. One of them is common salt, when sea water is allowed to stand in shallow pits, water gets evaporated by sunlight and slowly turns into water vapour. In a few days, the water evaporates completely leaving behind the solid salts. Common salt is then obtained from this mixture of salts by further purification. Question: What is decantation? Answer: Decantation is a process, of separation of insoluble solids from liquid. The suspension of solid particles in liquid is allowed to stand for some time. The solid particles then settle down at the bottom of the container and clean water goes up. Without disturbing the settled particles the clean water is transferred into other container. Question: Where is decantation used? Give two examples. Answer: Decantation is used to separate insoluble solids or liquid from liquid. Rain water is a mixture of mud and water. It is purified by decantation. Oil and water also get separated by this method because oil floats up. Question: How will you prepare cheese (paneer)? Answer: For making paneer, a few drops of lemon juice sire added to milk as it boils. This gives a mixture of particles of solid paneer and liquid. The paneer is then separated by filtering the mixture through a fine cloth or strainer. Question: Explain the method that can be used for separating the following mixture: Sand and husk Wheat, sugar and stalk Water and petrol Rice and salt Sand and salt Answer: Mixture of sand and husk: Sand and husk can be separated by the method of winnowing. Mixture of wheat, sugar and stalk: For separating stalk from the mixture we should follow the winnowing method because milk is lighter than other two components and get separated. Wheat and sugar can be separated by sieving because they are in different sizes. Mixture of water and petrol: Water does not dissolve in petrol. So, it can be separated by the use of separating funnel. Mixture of rice and salt: Rice and salt can be separated by sieving. Mixture of sand and salt: Sand and salt is mixed with water, salt dissolves in water and sand can be separated solution by sedimentation and decantation followed by filtration. After that using evaporation common salt is separated.

Class Notes NCERT Solutions for CBSE Students

NCERT 6th Class (CBSE) Science: Separation of Substances

Question: Sea water has salt dissolved in it. You know that pure water can be obtained from sea water by distillation. However, this method is not used to get drinking water from sea water. What do you think is the reason?

Question: A battle contains either salt or chalk. How will fined out what it has, without tasting it?

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