Separation of Mixtures PDF

# Separation of Mixtures ## Let's Learn - Types of mixtures - Need for separation of components of mixtures - Methods for separation of components of mixtures - **Separation of solids from a solid-solid mixture** - handpicking, sieving, magnetic separation, winnowing, threshing. - **Separation...

# Separation of Mixtures ## Let's Learn - Types of mixtures - Need for separation of components of mixtures - Methods for separation of components of mixtures - **Separation of solids from a solid-solid mixture** - handpicking, sieving, magnetic separation, winnowing, threshing. - **Separation of solids from a solid-liquid mixture** - Sedimentation, decantation, filtration, evaporation. ## Jump Start During transportation, the gunny bags containing broken wheat and rice tore. The contents of both the bags got mixed up with each other. If you were the grocer, would you throw away the grains and incur a loss? What would you do? Why? ## Introduction In the earlier chapter, we have learnt that a mixture is made up of two or more substances mixed together in any proportion such that they do not undergo any chemical change and retain their individual properties. The substances which constitute a mixture are called its components. ## Magnetic Separation The method of separating constituents of a mixture using a magnet is called magnetic separation. This method can be used to separate a magnetic substance from any mixture. Metals such as iron, cobalt, and nickel get attracted to magnets and are known as magnetic substances. A mixture of iron filings and sand can be separated by moving a magnet over the mixture. The iron filings cling to the magnet, and so the particles of sand are left behind. This is how a mixture of iron and sand is separated. Huge magnets held by cranes are used to separate magnetic substances in the junkyard. ## Sublimation The process in which a solid directly changes into a vapour, i.e. its gaseous form on heating, without melting first, is known as sublimation. On cooling, the vapours change back into a solid. The solid substance obtained after the vapours are cooled is known as the sublimate. Sublimation is used to separate a mixture of solids where one solid sublimes and the other does not. Iodine crystals, naphthalene balls, camphor, and ammonium chloride are some substances which sublime on heating. ## Threshing The process used to separate grains of plants such as rice and wheat from their stalks is called threshing. The dry stalks of the crop are beaten to shake off the dried grains. The stalks can be beaten against a rock or hard surface such as a wooden board by hand. This is known as manual threshing. Threshing can also be done using machines. ## Winnowing Threshed grains contain seed coverings or husks and small pieces of leaves and stalk. These impurities are collectively known as chaff. Even though the large stalks can be separated from the grains by threshing, the grains still have chaff. The husk is much lighter than the grain. So, when the grains are gently dropped to the ground, only the grain is collected, while the husk blows away. The chaff is separated from the grains by blowing air. The method of separating husk from grains with the help of wind is known as winnowing. ### Quick Review 1. **Winnowing** is a method of separating husk from grains with the help of wind. 2. **Sublimation** is used to separate a mixture of solids where one solid sublimes while the other does not. 3. **Sieving** is a method used for separating sand from gravel. 4. Iron is separated from a mixture of iron and sulphur using **magnetic separation**. ## Separation of solids from a solid-liquid mixture Solids can be insoluble or soluble. A mixture of insoluble solids in liquids can be separated using methods like filtration, sedimentation and decantation. A solid that is soluble in a liquid can be separated by evaporation. ## Separation of insoluble solids from liquids ### Sedimentation and decantation The process of settling down of heavy solids at the bottom of a liquid is called sedimentation. The particles that settle down are called the sediment. The process of pouring out the clear liquid without disturbing the sediment is called decantation. ## Evaporation The conversion of a liquid into vapour, i.e. its gaseous state is known as evaporation. The process of evaporation can be made faster by heating. We can separate salt and water by the process of evaporation. The same principle is used to obtain common salt from seawater. Seawater is allowed to collect in shallow pits along the seashore. As the heat from the sun slowly evaporates the water, common salt is left behind. This salt is collected and purified for our use. ## Filtration The process of separating insoluble solid components from a liquid by passing it through a filter is called filtration. The insoluble solids left on the filter are called the residue while the liquid which passes through the filter is called the filtrate. ## Learn by Doing 1 **Aim**: To separate a mixture of sand and ammonium chloride by sublimation. **Materials required**: A mixture of sand and ammonium chloride, porcelain dish, filter paper, glass funnel, and cotton. **Procedure**: 1. Take a mixture of sand and ammonium chloride in a porcelain dish and cover it with a perforated filter paper. 2. Now place an inverted glass funnel over the filter paper in the porcelain dish. Plug the open end of the funnel with cotton. Heat the porcelain dish gently. **Observation**: Ammonium chloride changes directly from solid to vapour and gets condensed on the upper cooler surface of the funnel. The sand is left behind in the porcelain dish. **Conclusion**: A mixture of sand and ammonium chloride can be separated by sublimation. Ammonium chloride sublimes and the sand is left behind. ## Learn by Doing 2 **Aim**: To separate brewed tea by the process of sedimentation and decantation. **Materials required**: Pitcher, hot water, sugar, and loose tea leaves. **Procedure**: 1. Take a pitcher half-filled with hot water. Add sugar to the water and stir. 2. Now add two teaspoons of loose tea leaves into the pitcher. 3. Leave the pitcher undisturbed for 5-6 minutes. Decant the top part after 5-6 minutes. **Observation**: When the pitcher is left undisturbed, the tea leaves settle (sediment) to the bottom of the pitcher. The top part can be decanted to get brewed tea. **Conclusion**: Brewed tea can be separated from a mixture of tea leaves and hot water by the process of sedimentation and decantation. ## Learn by Doing 3 **Aim**: To demonstrate evaporation due to the heat of the sun. **Materials required**: Common salt, water, bowl, and marker pen. **Procedure**: 1. Take a mixture of common salt and water in a bowl. Mark the level of water in the bowl with a marker pen. 2. Now keep the bowl in the sun for 5 to 6 hours. Mark the level of water in the bowl at the end of 6 hours. 3. What do you observe? Note down your observation. 4. Keep this bowl out again the next day in the sun. What do you observe? What is the residue that is left behind in the bowl? **Observation**: The level of water in the bowl goes down on the first day. On the second day when the bowl is again left out in the sun, the salt is seen in the bowl. **Conclusion**: Water evaporates due to the sun's heat leaving behind the common salt in the bowl. A mixture of salt and water can be separated by evaporation. ## Learn by Doing 4 **Aim**: To separate a mixture of iron filings, salt and sand. **Materials required**: A mixture of iron filings, salt, and sand; a magnet, a sheet of paper, beaker, stirrer, funnel, filter paper, and evaporating dish. **Procedure**: 1. Spread the mixture of sand and iron filings on the paper. Roll the magnet evenly over the mixture. The iron filings get attracted by the magnet and cling to its ends while salt and sand remain on the paper. Remove the iron filings from the magnet. Repeat the procedure several times until the iron filings are completely removed from the mixture. 2. Mix the remaining mixture of salt and sand in water and stir. Make sure you have used enough water to dissolve all of the salt. Using a funnel and filter paper, filter off the sand from the saltwater solution. Wash the sand with some freshwater to remove traces of the salt from the sand in the filter paper. 3. Allow the funnel to dry in the sun or keep it near the burner. Collect all the saltwater in an evaporating dish and evaporate off the water. **Observation**: The iron filings are separated from the mixture by using the magnet. The sand is separated from the mixture by filtration. The salt is separated from the water by evaporation. **Conclusion**: In this experiment, the three constituent materials in the mixture are solids with significantly different physical properties, which makes separation easier. - Iron is a magnetic solid which is insoluble in water. - Salt is a non-magnetic solid which is soluble in water. - Sand is a non-magnetic solid which is insoluble in water. ## Distillation Distillation is a method in which both the soluble substance as well as the solvent can be recovered in pure form after separation. ## Centrifugation Centrifugation is used to separate mixtures that cannot be separated using filtration and sedimentation techniques. It involves the application of centrifugal force to separate particles from a solution according to their size, shape, density, the viscosity of the medium, and rotor speed. ## Separation of Components of Mixtures | **Solid-Solid** | **Soluble solid / Solid-Liquid** | **Insoluble solid / Solid-Liquid** | |---|---|---| | Handpicking | Evaporation | Filtration | | Winnowing | | Sedimentation and decantation | | Threshing | | | | Magnetic Separation | | | | Sieving | | | ## Word Galaxy - **Homogeneous**: having uniform composition and properties throughout the bulk of matter. - **Heterogeneous**: having non-uniform composition throughout the bulk of the matter. - **Winnowing**: a process done to isolate grain of crops from the lighter particles like chaff, and dirt; especially by throwing it into the air and allowing the wind or a forced current of air to blow away impurities. - **Sedimentation**: a process in which insoluble solid material settles to the bottom of a liquid and forms a solid bed. - **Decantation**: the process of pouring a liquid from one container into the other after the components of a solid-liquid mixture is separated by gravity. ## Types of Mixtures Mixtures are usually classified on the basis of the state of the constituents. If two or more solids are mixed, the resulting mixture is called a solid in a solid mixture, e.g. a mixture of sand and salt. Two or more liquids form what is known as a liquid in a liquid mixture, and two or more gases form a gas in a gas mixture. Besides, we can have solid in liquid, solid in gas and liquid in gas mixtures too. A mixture can be homogenous or heterogeneous. The components of homogenous mixtures such as soaps and chemicals are uniformly distributed throughout the mixture. The components of heterogeneous mixtures such as a fruit salad are not uniformly distributed throughout the mixture. | **Types of mixture** | **Example** | |---|---| | Solid in solid | Alloys like bronze and steel | | Solid in liquid | Salt and water | | Liquid in liquid | Antifreeze solution (ethylene glycol and water) | | Liquid in gas | Soda | | Gas in gas | Air | | Solid in gas | Ash particles mixed with air | ## Did You Know The knowledge of chemical mixtures once prevented a major incident in the London Underground! When an accidental leakage of wet, quick-drying concrete flooded the control room of London’s Victoria underground station, the engineers' quick thinking and chemical knowledge prevented a total disaster. They mixed large amounts of sugar into the concrete, slowing down the setting process. This allowed them the time to clear up the spill. ## Misconception **Myth**: All natural substances are pure, and therefore, milk is a pure substance. **Fact**: On adding vinegar to a sample of milk, a liquid supernatant and a solid precipitate can be seen which proves that all naturally occurring substances are not always pure substances; some of them could also be mixtures. ## Need for Separation of Components of Mixtures Mixtures are separated to obtain one or more useful components. Pure substances (elements and compounds) separated from mixtures are used by scientists to study their properties and carry out experiments. Pure substances are also needed in the manufacture of medicines and industrial chemicals. Certain components cannot be used unless they are separated from the mixtures. For example, petrol, diesel, and kerosene need to be separated and extracted from crude petroleum before use. While making tea, the unwanted components are strained out to get the liquid tea. Separation of components of mixtures removes impurities, harmful substances, and unwanted components. The impurities present in water and food need to be separated and removed so that they do not harm plants, animals, and humans. ## Methods for Separation of Components of Mixtures There are many different methods or techniques for the separation of components of a mixture. The choice of the method of separation depends upon the unique properties possessed by the components of a mixture. For example, a mixture of salt in water can be separated by evaporating the water and recovering the pure salt; a mixture of sand and iron filings can be separated into its components with the help of a magnet. ### Separation of solids in solid mixtures Handpicking, sieving, magnetic separation, and sublimation are some methods of separation of solid in solid mixtures. #### Handpicking The method of separating a mixture into its components by hand is called handpicking. Undesirable substances such as pieces of stones and husk in rice can be separated by handpicking. Handpicking can be used only when the undesired component is present in less quantity and has a different size, shape, or colour to be easily identified and picked by hand. Handpicking is a time-consuming technique, hence is not preferred if the quantity of the mixture to be separated is large. #### Sieving Sieving is a method of separating a mixture of various sized particles by passing them through a suitable sieve. (Sieve is a mesh usually fitted into a frame.) Small and fine sieves are used to separate the bran and other impurities from flour. This method can be used at construction sites to separate stones from sand.