Elements, Compounds and Mixtures PDF

:" Inside the chapter Corr ray Pe tne eeseness wee R es sesteccuene ARETE OC OCOGOCS SOS ASS OICOOM DONNIE: * Elements, Compounds and mixtures: a review * Principles of Separation of mixtures (2) * Separation techniques ce gene A centrifuge is used to separate suspended Particles from a mixture....

:" Inside the chapter Corr ray Pe tne eeseness wee R es sesteccuene ARETE OC OCOGOCS SOS ASS OICOOM DONNIE: * Elements, Compounds and mixtures: a review * Principles of Separation of mixtures (2) * Separation techniques ce gene A centrifuge is used to separate suspended Particles from a mixture. A model , a centrifuge is shown in the figure. Gea In this lesson, you will learn how a real centrifuge works and where it is used. A centrifuge ELEMENTS, COMPOUNDS AND PURE SUBSTANCES MIXTURES: A REVIEW A pure substance can be an element or a You have already learnt about elements, compound. It has a definite composition compounds and mixtures. and fixed chemical properties. For example, Matter is anything that occupies space and copper and aluminium are elements and salt has mass. Matter can exist in two forms, that and sugar are compounds. Elements and is, pure substances and mixtures. compounds are pure substances, Fig. 3.1 Copper and salt are the pure substances The characteristics of a pure substance are given below, © A pure substance has a definite composition. For example, a molecule of salt consists of one atom of sodium and one atom of chlorine. You cannot have a molecule of salt that has a different number of sodium and chlorine atoms. © A pure substance has a fixed melting, point, boiling point and density. Pure water at sea level boils at 100 °C. * A pure substance has a characteristic colour, odour and taste. MIXTURES A mixture is made up of two or more pure substances (elements, compounds or both) that retain their individual properties. The components that make up a mixture are not chemically combined, Lemon juice is a mixture of lemon extract, sugar and water. It has the sour taste of lemon and the sweetness of sugar. We can differentiate between the ingredients by their taste. Air contains a number of gases. Each aS shows its property. Air supports Pause and Do 1. Complete the flowchart: acause OXYZEN is p combustion because OX) : pA orms time WO" ns carbon dioxide. am and wa “4 | ah -_ rater MILKY Dec:z contai 2. Milk is a mixture of cre J i from milk b can separate cream ad f 1 4 Clion: Sugar can be separated Irom a iga solution by evaporating the water = Fig. 3.2 Lemonade is a mixture of lemor extract, sugar and water The characteristics of a mixture are given below. ¢ Ina mixture, the components are present in any proportion. ¢ The components retain their properties A mixture does not have a specific boiling and melting point ora characteristic colour, smell or taste. * Components can be separated by easy physical means. 2. Give two examples of each. (a) Pure substances (b) Mixtures 3. Write one property of Pure substances. Types of Mixtures Different substances in different states may forma mixture. These are given below. - golid-solid Mixture For example, rice and sand; dal and rice; soil, salt, and flour Solid-liquid Mixture For example, sugar syrup, salt solution, starch solution Liquid-liquid Mixture For example, lemon juice, alcohol and water; oil and water; milk and water Gas-solid Mixture For example, smoke and dust particles in air Gas-liquid Mixture For example, aerated drinks, oxygen dissolved in water Gas-gas Mixture For example, air, acid vapours in air, water vapour in air. Depending on the appearance, mixtures can be divided into two types: homogeneous mixtures and heterogeneous mixtures. Homogeneous Mixture Ina homogeneous mixture, the components cannot be differentiated by colour, shape or size. They are evenly distributed. The mixture appears as one single entity. For example, in a salt solution, we cannot see salt particles. The solution appears just as a liquid. Homogeneous mixtures are generally found in the form of solutions and alloys. Solution A solution is a homogeneous mix ture of two or more substances. Components of a solution can be easily separated. For example, solids can be separated from their aqueous solutions by evaporation OF crystallisation. Alloys. Analloy is a homogeneous mixture of two or more metals or a metal and a non-metal. Alloys are obtained by melting the metals together. Brass is an alloy of copper and zinc. Bronze is an alloy of copper and tin. Steel is an alloy of iron and carbon. Alloys are also called solid solutions. Heterogeneous Mixture A heterogeneous mixture is a mixture having a non-uniform composition. The composition varies from one region to another, with at least two phases that remain separate from each other, with clearly identifiable properties. If you examine a sample of a heterogeneous mixture, you can see the separate components. Ice cubes in cola form a heterogeneous mixture. Some other example of heterogeneous mixture are chalk powder in water, iodine and sand, rice and dal, etc. Heterogeneous mixtures are generally found in the form of suspensions and emulsions. Suspension A suspension is a heterogeneous mixture containing solid particles that are sufficiently large for sedimentation. The components can be separated by filtration. It is a mixture in which the solute particles e pe. a @- Emulsion ‘Mm an emMulsio, are not dissolved, but get suspended _ccible liquids fot throughout the bulk of the medium. Twos. one of the components j Particles : ‘el In most case> vse articles of the suspension are visible to the ater. A mixture of oil and water is an f the components naked e “.. n ae ye. Prarie is Ger, en emulsion. When one O cles are left floati ound freely 1n 4 ac ating around y thicker and prese solvent. Some exam nsions are ; ples of suspe ‘aa semi-solid orp shaving creams mulsion. nt in excess, the emulsion, aste-like mass. Face sand in water, chalk in water, dust in and butter are. creams, air, etc. ies examples of € Chalk particles FW) suspended in Fig. 3.4 Oil in water (emulsion) Write T for true and F for false statements. a homogeneous mixture, components can be differentiat r more substances. ed by colour, shape or size. 5 il) _ Asolution is a homogeneous mixture of two o n example of a homogeneous mixture. 1 2 3. Amixture of salt and sugar isa 4. Asuspension is a homogeneous mixture. 5 6. Alloys are obtained by melting metals together. Brass is an alloy of copper and tin. SEPARATION TECHNIQUES For example, seawater is rich in common We need many substances to make our life Slt which is an important ingredient of convenient and comfortable but most of our food to add taste and nutrients. But these substances are available in the form of **4Water. cannot be directly used to get the - mixtures. These mixtures contain unwanted salt. It is necessary to separate salt from substances which may be harmful and may a ter degrade the properties of mixtures. he purpose of separating the components of a mixture is to: {cy Size, shape and colour Boiling point, melting point, density, volatility, solubility, magnetic properties, ability to sublime, ete. A component can be separated from its mixture based on the property it possesses, it techniques of separating which other components do not have, us today. But every This is the differentiator while using a ‘applied to separate separation method. paration technique You have already learnt about several pends upon the separation techniques in the previous class, ponents such as: Some of them, the principles behind them and examples are given below, techniques, their principles and examples Sand separated from gravel at construction sites Stones separated from rice ‘Muddy water separated into mud and clear water on of common salt from sea water tion of iron scrap from waste ize, they can be separated by sieving. ; method is usually preferred when the iponents is small enough to pass les of a sieve. The distillation flask is fitted with a fractionating column, which is connected to the condenser, There is a thermometer inserted into the fractionating column. The temperature across the column varies; it is higher at the bottom and lower at the top. The vapours of the component with a higher boiling point condense at the bottom of the column. The liquid with the lower boiling point vapourises first and rises up. The vapours of the other liquid coming along in small quantities will be condensed and sent back into the flask by the fractionating column. The vapours of the liquid with the low boiling point rig, Are condensed in the condenser, J). C J Us and liquid 1s th all the first component is removed, the. ; ‘ temperature starts rising till the boiling point of the second liquid is reached, [ts vapours are also condensed and collecteg ‘na different container. Crude petroleum oil is refined using this principle. Refining is done ina fractionating tower. The fractions obtainey are petroleum gas, petrol, kerosene, diese lubricating oil and paraffin wax. What is left out is asphalt, used for making roads, Experiment NaCl, or BaSO, and NaC! Procedure: * Pour the mixture in the beaker. some more water. tus, as shown. NaCl is soluble in water. {; « Aim: To separate the components of a mixture of CaCO, and Materials required: Beaker, conical flask, funnel, filter paper, water, and a mixture of CaCO, and NaCl, or BaSO, and NaCl « Add some water in the beaker and stir it throughly until all the salt (NaCl) is dissolved. If required, add * Make acone ofa filter paper, fix it in the conical funnel and set the appara- ¢ Pour the content of the beaker gently into the funnel. ¢ Heat the conical flask to dry up the water. Observation: CaCO, or BaSO, filters out and remains partly in the beaker and partly on the filter paper. The conical flask contains the flakes of NaCl. Conclusion: The combination of filtration and evaporation methods can be used to separate a mixture of CaCO, and NaCl, or BaSO, and NaCl, because CaCO, or BaSO, is insoluble while en collected in a container, 4, IBINATION OF METHODS FOR : ARAT ION ure which has more than two an be separated into omponents by using a ammonium chloride and sand. Iron is attracted by a magnet, so it can be removed by the magnetic separation. Now, we can heat ammonium chloride and sand. The fumes of ammonium chloride are condensed. Ammonium chloride undergoes sublimation. Now, you are left with sand. Separation of salt, sand and grain from their mixture. Grain is separated from the mixture by sieving. Now, you are left with the mixture of salt and sand. Add some water and make a solution. The solution is filtered to obtain sand (residue) and a salt solution. Sand is insoluble in water and can be easily removed by filtration. Salt can be obtained from the salt solution by evaporation. Pees ease eases aseeeseeeeee aeseeeeeeneee Sees eeeeeeeeenweeee stopcock. Mixtures of © Fractional Distillation Bocled emulsions, ut This is used to separate mixtures ae as this comprising miscible liquids like alcohol Be ons is and water. It is based on the difference in the boiling points of the liquids to be separated. Fig. 3.12 shows the set-up for fractional distillation. Thermometer bottomed Water in flask Distillate Bunsen burner Fig. 3.12 Laboratory set-up for fractional distillation SIDER IA IE ER BERIT A A Ma TR om: oa Deeg tena Pigs Procedure: + Tako the mixture Of Wheat and chaff (OF small biti ground, FOF Paper) on A plate, Go te an open * Now, stand on a ais Shaking the plate. Observation: Tho chat OF bits ‘ana MN 8 Of paper form a separate Heap, some ciatanoe away trom whare u grains drop, and 46 thus separated. | ilspiictiair ®d structure ane Grop the Mixture alawly on the HOUNC, CAnatantly ?Froth Floatation The principle behind this me differential Wetting of compe mixture by water. It is used to separate metal ore from mud and othe in the case of ores lighter than the gangue or impurities, For example, sulphide ores such as galena (ore of lead) blende (ore of zine), The impure ore is mixed in water ina tank, to which pine oil and ethy! xanthate are thod is the substances which sublime are separated by ments of a this method "his method ts alse used te purity compounds r impurities For example, a mixture of ammonium chloride and salt ean be separated by sublimation as ammonium chloride and zine sublimes, On heating, ammonium chloride vaporises and gets deposited near the tail end of the funnel, Salt is left in the china dish added. — When air is bubbled through the mixture BE ne i Ss aa from the bottom of the tank, a thick froth Arneronium i is formed. As sulphide ores are insoluble chloride vapours in water and are lighter, they are carried 7 away by the froth to the surface and are: China dish —-Yemr _) skimmed off. Impurities, as they get wet by sebakieh\pa the water, become heavy and settle at the / ia i "a bottom. / Fig. 3.8 Separation ef ammonium chloride and sait Froth Concentrate oDistillation launder If the liquid component is required ina pure form, the solution is subjected to distillation, The principle behind this separation method is the difference between the boiling points Fig. 3.7 Froth Floatation of the components of the mixture, dass » : pee of separation of a liquid from ane ot by first converting the its vapour and then condensing the vapour is called distillation. The distillation apparatus comprises a distilling flask, which is a round-bottomed flask | with a side tube. The side tube is connected to a Liebig condenser and a receiver. A thermometer is inserted into the flask. When heated, the component with the lower boiling point evaporates before the one with the higher boiling point. Vapours Set cooled as they pass through the condenser. The condensed liquid collects in the receiver. The solid component remains in the flask. In evaporation, the liquid component of a mixture turns into vapour and is lost to the atmosphere. In distillation, the liquid component can be recovered. The distilled water used in laboratories and batteries is obtained using this method. Water out Burner Receiving flask Cold water in /|* Distillate Fig. 3.9 Separating mixture by distillatron o Centrifugation Finely suspended solid components ina liquid are separated by spinning the mixture in a closed container at a very high speed. This is called centrifugation. This method is used to separate the components of a mixture based on the difference in density. {uly a solid in lig When a suspension of uig is subj acted toa spin, the heavier oie Cc will settle at the bottom due { substance ee Heavier particle, the centrifugal force. an nce a larger centt ifugation ae experie AS shan the lighter particles. Centr ifugatio, ‘5 used in cases where filtration doesn’; work due to the smaller size of the sojiq particles Best examples are colloids c 5 like blood, separating cream and butte; from milk, etc. This method is used ip hospitals, pathology labs, dairy farms ang industries. Fig. 3.10 Centrifugation A simple laboratory centrifuge has a vertical shaft with two, four or more than four test tube holders. When using a centifuge, the mixture is taken in one test tube and water in the test tube kept just opposite it. This is called the balancing test tube. When the motor works, the shaft rotates. The solid particles settle at the bottom. Separating Funnel A separating funnel is shown in Fig. 3.11. There is a stopcock at the tail end of the funnel. It is used to control the flow of the liquid. A liquid mixture, when poured into the funnel and allowed to stand, separates into different layers. Each laye! can be drawn out into different containe!s