9th matter.pdf

UNIT 10 MATTER AROUND US Learning Objectives After completing this lesson, students will be able to „„ classify substances as elements, compounds and mixtures based on their chemica...

UNIT 10 MATTER AROUND US Learning Objectives After completing this lesson, students will be able to „„ classify substances as elements, compounds and mixtures based on their chemical composition. „„ group mixtures as homogeneous and heterogeneous. „„ identify suitable method to separate components of a mixture. „„ classify solutions based on the size of the solute particles and compare the true solutions, colloids and suspensions based on their properties. „„ differentiate colloids based on the nature of dispersed phase and dispersion medium. „„ compare o/w and w/o emulsions. „„ discuss some important examples and uses of colloids. Introduction 10.1 Classification of Matter We use the term matter to cover all In class VIII, You have substances and materials from which the universe studied the classification of is composed. Matter is everything around us. The matter on the basis of their air we breathe, the food we eat, the pen we write, physical states. Now let us see clouds, stones, plants, animals, a drop of water how we can classify matter or a grain of sand everything is matter. Samples on the basis of chemical of any of these materials have two properties in composition.Broadly speaking, it has been classified into pure substances and mixtures. common. They have mass and they occupy space. From the point of view of chemistry, pure substances are those which contain only one kind of particles whereas impure substances (mixtures) contain more than one kind of particles. Figure10.1 Examples to show Matter has mass The flow chart given below will help us to understand the chemical classification of matter in detail. Not all things that we see or feel Figure 10.2 Examples to show Matter are matter. For example, sunlight, occupies space sound, force and energy neither occupy space nor have any mass. They are not Thus, we say that matter is anything that matter. has mass and occupies space. 113 IX_SCI_EM_Unit-10_CHE.indd 113 12/12/2021 4:12:06 PM  Matter Pure substances Impure substances (Mixtures) Elements Compounds Homogeneous Heterogeneous Cannot be Can be broken Uniform Non-uniform broken into down into composition composition simpler elements by E.g., sugar + E.g., sand + substances chemical reactions H2O, water + sugar, water + E.g., copper, oxygen, E.g., water, sugar, alcohol oil hydrogen. salt, etc. Building block H, He, Li……. 118 elements of all materials Activity 1 1. Is air a pure substance or Mixture? Robert boyle used the name element Justify for any substance that cannot be broken 2. You must have seen brass statues down further, into a simpler substance. This in museums and places of worship. definition can be extended to include the fact Brass is an alloy made up of approx. that each element is made up of only one kind 30% zinc and 70% copper. Is Brass of atom. For example, aluminium is an element a pure substance or a mixture or which is made up of only aluminium atoms. It compound? is not possible to obtain a simpler substance chemically from the aluminium atoms. You can 10.1.1 Elements only make more complicated substances from it, such as aluminium oxide, aluminium nitrate Most of you may be interested in music, and aluminum sulphate. and some of you may know how it is composed. Music is the combination of a few basic musical notes i.e., Sa, Re, Ga,…Thus, the building blocks Atom: The smallest unit of an element which of music are the musical notes. may or may not have an independent existence, but always takes part in a chemical reaction is Sa, Re, Ga, Ma, Pa... Building blocks of music called atom. Likewise , all substances on earth are made Molecules: The smallest unit of a pure up of certain simple substances called elements. substance, which always exists independently Plants, cats, apples, rocks, cars and even our and can retain physical and chemical properties bodies contain elements. Thus, elements are the of that substance is called a molecule. building block of all materials. Examples: Hydrogen molecule consists of two In the modern periodic table hydrogen atoms (H2) there are 118 elements known Water molecule consists of two hydrogen to us, 92 of which are naturally atoms (H2) and one oxygen atom (O). occurring while the remaining 26 have been artificially created. But from these 118 All elements can be classified according elements, crores of compounds are formed- to various properties. A simple way to do this some naturally occurring and some artificial. is to classify them as metals, non metals and Isn’t that amazing? metalloids. Matter Around Us 114 IX_SCI_EM_Unit-10_CHE.indd 114 12/12/2021 4:12:06 PM  ELEMENT Table 10.1 Difference between elements and compounds. METAL METALLOID NON-METAL Element Compound Made up of only one Made up of more than Copper, Boron, Carbon, kind of atom. one kind of atom. Chromium, Silicon, Oxygen, Gold, Germanium, Neon, The smallest particle The smallest particle that Mercury Arsenic Chlorine that retains all its retains all its properties properties is an atom. is the molecule. 10.1.2 Compounds Cannot be broken Can be broken down down into simpler into elements by When two or more elements combine chemically to form a new substance, the new substances. chemical methods. substance is called a compound. For example, 10.1.3 Mixtures cane sugar is made up of three elements carbon, hydrogen and oxygen. The chemical A mixture is an impure substance. It contains forumula of cane sugar is C12H22O11. two or more kinds of elements or compounds or both A compound has properties that are physically mixed together in any ratio.For example, different from those of the elements from which tap water is a mixture of water and some dissolved it is made. Common salt, also known as sodium salts. Lemonade is a mixture of lemon juice, sugar chloride, is a compound. It is added to give taste and water. Air is a mixture of nitrogen, oxygen, to our food. It is a compound made up of a carbon dioxide, water vapour and other gases. Soil metal, sodium and a non-metal, chlorine. is a mixture of clay, sand and various salts. Milk, ice cream, rock salt, tea, smoke, wood, sea water, blood, tooth paste and paint are some other examples of Activity 2 mixtures. Alloys are mixtures of metals. Make models of the molecules of compounds by using match sticks and clay balls as shown below, Figure 10.3 Mixtures O More to Know O C O H H LPG – Liquefied Petroleum Gas Water molecule Carbon dioxide molecule It is highly inflammable hydrocarbon gas. It contains mixture of butane and propane gases. LPG, liquefied through Compounds of phosphorous, pressurisation, is used for heating, nitrogen and potassium are cooking, auto fuel etc. used in fertilizers. Silicon compounds are of immense 10.1.4 Differences Between importance in the computer industry. Compound and Mixture Compounds of fluorine are used in our There are differences between compounds toothpastes as they strengthen our teeth. and mixtures. This can be shown by the following activity. 115 Matter Around Us IX_SCI_EM_Unit-10_CHE.indd 115 12/12/2021 4:12:07 PM  Table 10.2 Difference between mixtures and Activity 3 compounds. Take some powdered iron filings and mix it Mixture Compound with sulphur. It contains two or It is a single i. Divide the mixture into two equal halves. more substances substance ii. Keep the first half of the mixture as it is, but The constituent may The constituents are heat the second half of the mixture. be present in any present in definite iii.  On heating you will get a black brittle proportion. proportions. compound. They show the They do not show properties of their the properties of the constituents. constituent elements. The components The constituents can may be separated only be separated by Mixture of Iron Sulphide easily by physical one or more chemical iron and Sulphur compound methods. reactions. The black compound is Iron (II) sulphide. heat Activity 4 Iron + sulphur Iron sulphide The Iron sulphide formed has totally Identify whether the given substance is different properties to the mixture of iron and mixture or compound and justify your sulphur as tabulated below: answer. 1. Sand and water 2. Sand and iron filings 3. Concrete 4. Water and oil 5. Salad 6. Water 7. Carbon dioxide 8. Cement Substance Appearance Effect of magnet 9. Alcohol. Iron Dark grey Attracted to it (element) powder 10.2 Types of Mixtures Sulphur Yellow powder None Most of the substances that we use in our (element) daily life are mixtures. In some we will be able Iron + Dirty yellow Iron powder to see the components with our naked eyes Sulphur powder attracted to it but in most others the different components (Mixture) are not visible. Based on this mixture can be Iron sulphide Black solid No effect classified as below. (compound) Mixtures From the above experiment, we can Homogenous Heterogenous summarise the major differences between mixtures and compounds: True Alloys Suspensions Colloids Solutions Blood is not a pure substance. It is a mixture of various 10.2.1 Homogeneous and components such as platelets, Heterogeneous mixture A mixture in which the components cannot be red and white blood corpuscles and plasma. seen separately is called a homogeneous mixture. Matter Around Us 116 IX_SCI_EM_Unit-10_CHE.indd 116 12/12/2021 4:12:07 PM  It has a uniform composition and every part of the when cooled give back the solid substance. This mixture has the same properties. Tap water, milk, process is known as sublimation. Examples: air, ice cream, sugar syrup, ink, steel, bronze and salt Iodine, camphor, ammonium chloride etc., solution (Figure 10.4a) are homogeneous mixtures. Cotton plug A mixture in which the components can be seen Inverted funnel separately is called a heterogeneous mixture. It does Solidified ammonium chloride not have a uniform composition and properties. Soil, Vapours of ammonium chloride a mixture of iodine and common salt, a mixture of China dish sugar and sand, a mixture of oil and water, a mixture Ammonium chloride salt and sand of sulphur and iron filings and a mixture of milk and Burner cereals (Figure 10.4b) are heterogeneous mixture. Figure 10.5 Sublimation The powdered mixture of Ammonium chloride and sand is taken in a china dish and covered with a perforated asbestos sheet. An inverted funnel is placed over the asbestos (a) (b) sheet as shown in Figure 10.5. The open end Figure 10.4 (a) Homogeneous and of the stem of the funnel is closed using cotton (b)Heterogeneous mixture wool and the china dish is heated. The pure vapours of the volatile solid pass through the holes in the asbestos sheet and condense on 10.3  Separation of mixtures the inner sides of the funnel. The non-volatile Many mixtures contain useful substances impurities remain in the china dish. mixed with unwanted material. In order to obtain these useful substances, chemists often have to More to Know separate them from the impurities. The choice of a particular method to separate components The air freshners are used in toilets. The solid slowly sublimes and releases the pleasant of a mixture will depend on the properties of smell in the toilet over a certain period of the components of the mixture as well as their time. Moth balls, made of naphthalene are physical states (as shown in Table 10.3). used to drive away moths and some other 10.3.1 Sublimation insects. These also sublime over time. Certain solid substances when heated Camphor, is a substance used in Indian change directly from solid to gaseous state household. It sublimes to give a pleasant without attaining liquid state. The vapours smell and is sometimes used as a freshner. Table 10.3 Methods of separating substances from mixtures Type of mixtues Mixtures Methods of separation Solid and solid Handpicking, sieving, winnowing, magnetic separation, sublimation. Heterogeneous Insoluble solid and liquid Sedimentation and decantation, loading, filtration, centrifugation Two immiscible liquids Decantation, solvent extraction Soluble solid and liquid Evaporation, distillation, crystallisation Two miscible liquids Fractional distillation Homogeneous Solution of two or more solids in Chromatography a liquid 117 Matter Around Us IX_SCI_EM_Unit-10_CHE.indd 117 12/12/2021 4:12:08 PM  10.3.2 Centrifugation Solvent extraction is an old Centrifugation is the process by which practice done for years. It is fine insoluble solids from a solid- liquid the main process in perfume mixture can be separated in a machine called development and it is also used to obtain a centrifuge. A centrifuge rotates at a very dyes from various sources. high speed. On being rotated by centrifugal force, the heavier solid particles move down 10.3.4  Simple distillation and the lighter liquid remains at the top. Distillation is a process of obtaining pure liquid from a solution. It is actually a combination of evaporation and condensation i.e Distillation = Evaporation + Condensation In this method, a solution is heated in order to vapourise the liquid. The vapours of the liquid on cooling, condense into pure liquid. For example, sea water in many countries is converted into drinking water by distillation. Figure 10.6 Centrifugation This method is also used to separate two liquids whose boiling points differ more than 25 K. In milk diaries, centrifugation is used to separate cream from milk. In washing Steam is Steam condensed machines, this principle is used to squeeze in tube cooled by out water from wet clothes. Centrifugation water is also used in pathological laboratories to Cooling separate blood cells from a blood sample. water out Salt water Cooling water in 10.3.3 Solvent extraction Burner Pure water Two immiscible liquids can be separated by solvent extraction method. This method works on the principle of difference in Figure 10.8 Solvent extraction solubility of two immiscible liquids in a A distillation flask is fixed with a water suitable solvent. For example, mixture of water condenser. A thermometer is introduced into and oil can be separated using a separating the distillation flask through an one-holed funnel. Solvent extraction method is used in stopper. The bulb of the thermometer should pharmaceutical and petroleum industries. be slightly below the side tube. The brackish water (sea water) to be distilled Separating funnel is taken in the distillation flask and heated for boiling. The pure water vapour passes through Keroscene oil (organic layer) the inner tube of the condenser. The vapours on cooling condense into pure water (distillate) Water (aqueous layer) and are collected in a receiver. The salt are left Stopcock behind in the flask as a residue. 10.3.5 Fractional distillation To separate two or more miscible liquids Figure 10.7 Solvent extraction which do not differ much in their boiling Matter Around Us 118 IX_SCI_EM_Unit-10_CHE.indd 118 12/12/2021 4:12:09 PM  points (difference in boiling points is less based on the above basic principles. The than 25 K) fractional distillation is employed. simplest type is paper chromatography. Fractional distillation is used in Paper chromatography petrochemical industry to obtain different This method is used to separate the different fractions of petroleum, to separate the coloured dyes in a sample of ink. A spot of different gases from air, to distill alcohols etc. the ink (e.g. black ink) is put on to a piece of Thermometer chromatography paper. This paper is then set Water out in a suitable solvent as shown in figure 10.10. The black ink separates into its constituent dyes. Fractionating Column As the solvent moves up the paper, the dyes Alcohol and Water Cold Water are carried with it and begin to separate. They Alcohol separate because they have different solubility in the solvent and are adsorbed to different extents Figure 10.9 Fractional distillation by the chromatography paper. The chromatogram shows that the black ink contains three dyes. 10.3.6 Chromatography Before we discuss the technique we will 10.4 Solutions take a look at the difference between the two A solution is a homogeneous mixture important terms: Absorption and Adsorption of two or more substances. In a solution, the Adsorption is the process in which the component present in lesser amount by weight particles of a substance is concentrated only at is called solute and the component present in the surface of another substance. larger amount by weight is called solvent. Absorption is the process in which the In short, a solution can be represented as substance is uniformly distributed throughout follows: solute + solvent solution the bulk of another substance. Example: salt + water salt solution For example, when a chalk stick is dipped in ink, the surface retains the colour of the ink 10.4.1 Types of solution due to adsorption of coloured molecules while Based on the particle size of the solute, the solvent of the ink goes deeper into the stick the solutions are divided into three types. Let due to absorption. Hence, on breaking the chalk us study them through an activity. stick, it is found to be white from inside. Chromatography is also a separation Activity 5 technique. It is used to separate different Take bottles containing sugar, starch and components of a mixture based on their wheat flour. Add one tea spoon full of each one different solubilities in the same solvent. to a glass of water and stir well. Leave it aside for There are several types of chromatography about ten minutes. What do you observe? Which one will mix? Paper Ink spot Water Water Ink Start End Sugar in Starch Flour in water in water water Figure 10.10 Paper chromatography 119 Matter Around Us IX_SCI_EM_Unit-10_CHE.indd 119 12/12/2021 4:12:09 PM  We can see that in the case of sugar we get a different combinations possible (Table 10.4). The clear solution and the particles never settle combination of gas in gas is not possible because down. This mixture is called as true solution. gas in gas always forms a true solution. In the case of starch and water we get a cloudy Brownian movement mixture. This mixture is called as colloidial When colloidal solution are viewed under solution In the case of wheat flour mixed with water we get a very turbid mixture and fine powerful microscope, it can be seen that particles slowly settle down at the bottom after colloidal particles are moving constantly and some time. This mixture is called as suspension. rapidly in zig-zag directions. The Brownian movement of colloidal particles is due to the What are the differences among True unbalanced bombardment of the particles by solutions, colloids and suspensions? the molecules of dispersion medium. The major difference is the particle size of the solute. In fact interconversions of these mixtures are possible by varying the particle sizes by certain chemical and physical methods. Figure 10.11 Brownian movement Tyndall effect Tyndall (1869) observed that when a strong beam of light is focused on a colloidal solution the path of the beam becomes visible. This phenomenon is known as Tyndall effect 10.4.2 Colloidal Solutions and the illuminated path is called Tyndall A colloidal solution cone. This phenomenon is not observed in is a heterogeneous system case of true solution. consisting of the dispersed More to Know phase and the dispersion medium. Dispersed phase The beam of light coming from headlights of or the dispersion medium vehicles is due to Tyndall effect. Blue colour of can be a solid, or liquid or gas. There are eight sky is also due to Tyndall effect. Table 10.4 Classification of colloids based on physical state of dispersed phase and dispersion medium S.No Dispersed Phase (Solute) Dispersion Medium (Solvent) Name Examples 1 Solid Solid Solid sol Alloys, gems, coloured glass 2 Solid Liquid Sol Paints, inks, egg white 3 Solid Gas Aerosol Smoke, dust 4 Liquid Solid Gel Curd, Cheese, jelly 5 Liquid Liquid Emulsion Milk, butter, oil in water 6 Liquid Gas Aerosol Mist, fog, clouds 7 Gas Solid Solid foam Cake, bread 8 Gas Liquid Foam Soap lather, Aerated water Matter Around Us 120 IX_SCI_EM_Unit-10_CHE.indd 120 12/12/2021 4:12:10 PM  Differences between the types of solutions.