Chapter 1 MATTERIN OUR SURROUNDINGS As we look at our surroundings, we see a large variety of things with different shapes, sizes and textures. Everything in this universe is made up of material which scientists have named “matter”. The air we breathe, the food we eat, stones, clouds, stars, plants and animals, even a small drop of water or a particle of sand – every thing is matter. We can also see as we look around that all the things mentioned above occupy space and have mass. In other words, they have both mass* and volume**. Since early times, human beings have been trying to understand their surroundings. Early Indian philosophers classified matter in the form of five basic elements – the “Panch Tatva”– air, earth, fire, sky and water. According to them everything, living or nonliving, was made up of these five basic elements. Ancient Greek philosophers had arrived at a similar classification of matter. Modern day scientists have evolved two types of classification of matter based on their physical properties and chemical nature. In this chapter we shall learn about matter based on its physical properties. Chemical aspects of matter will be taken up in subsequent chapters. 1.1 Physical Nature of Matter 1.1.1 MATTERISMADEUPOFPARTICLES For a long time, two schools of thought prevailed regarding the nature of matter. One school believed matter to be continuous like a block of wood, whereas, the other thought that matter was made up of particles like sand. Let us perform an activity to decide about the nature of matter – is it continuous or particulate? * The SI unit of mass is kilogram (kg). Activity ______________ 1.1 • Take a 100 mL beaker. • Fill half the beaker with water and mark the level of water. • Dissolve some salt/ sugar with the help of a glass rod. • Observe any change in water level. • What do you think has happened to the salt? • Where does it disappear? • Does the level of water change? In order to answer these questions we need to use the idea that matter is made up of particles. What was there in the spoon, salt or sugar, has now spread throughout water. This is illustrated in Fig. 1.1. Fig. 1.1: When we dissolve salt in water, the particles of salt get into the spaces between particles of water. 1.1.2 HOWSMALLARETHESEPARTICLES OFMATTER? Activity ______________ 1.2 • Take 2-3 crystals of potassium permanganate and dissolve them in 100 mL of water. ** The SI unit of volume is cubic metre (m3). The common unit of measuring volume is litre (L) such that 1L = 1 dm3, 1L = 1000 mL, 1 mL = 1 cm3. 2015-16 12.11.14 • Take out approximately 10 mL of this solution and put it into 90 mL of clear water. • Take out 10 mL of this solution and put it into another 90 mL of clear water. • Keep diluting the solution like this 5 to 8 times. • Is the water still coloured ? Fig. 1.2: Estimating how small are the particles of matter. With every dilution, though the colour becomes light, it is still visible. This experiment shows that just a few crystals of potassium permanganate can colour a large volume of water (about 1000 L). So we conclude that there must be millions of tiny particles in just one crystal of potassium permanganate, which keep on dividing themselves into smaller and smaller particles. The same activity can be done using 2 mL of Dettol instead of potassium permanganate. The smell can be detected even on repeated dilution. The particles of matter are very small – they are small beyond our imagination!!!! 1.2 Characteristics of Particles of Matter 1.2.1 PARTICLESOFMATTERHAVESPACE BETWEENTHEM In activities 1.1 and 1.2 we saw that particles of sugar, salt, Dettol, or potassium permanganate got evenly distributed in water. Similarly, when we make tea, coffee or lemonade (nimbu paani ), particles of one type of matter get into the spaces between particles of the other. This shows that there is enough space between particles of matter. 1.2.2 PARTICLESOFMATTERARE CONTINUOUSLYMOVING Activity ______________ 1.3 • Put an unlit incense stick in a corner of your class. How close do you have to go near it so as to get its smell? • Now light the incense stick. What happens? Do you get the smell sitting at a distance? • Record your observations. Activity ______________ 1.4 • Take two glasses/beakers filled with water. • Put a drop of blue or red ink slowly and carefully along the sides of the first beaker and honey in the same way in the second beaker. • Leave them undisturbed in your house or in a corner of the class. • Record your observations. • What do you observe immediately after adding the ink drop? • What do you observe immediately after adding a drop of honey? • How many hours or days does it take for the colour of ink to spread evenly throughout the water? Activity ______________ 1.5 • Drop a crystal of copper sulphate or potassium permanganate into a glass of hot water and another containing cold water. Do not stir the solution. Allow the crystals to settle at the bottom. • What do you observe just above the solid crystal in the glass? • What happens as time passes? • What does this suggest about the particles of solid and liquid? • Does the rate of mixing change with temperature? Why and how? From the above three activities (1.3, 1.4 and 1.5), we can conclude the following: 2015-16 12.11.14 higher than that of solids. This is due to the fact that in the liquid state, particles move freely and have greater space between each other as compared to particles in the solid state. 1.3.3 THEGASEOUSSTATE Have you ever observed a balloon seller filling a large number of balloons from a single cylinder of gas? Enquire from him how many balloons is he able to fill from one cylinder. Ask him which gas does he have in the cylinder. Activity _____________1.11 • Take three 100 mL syringes and close their nozzles by rubber corks, as shown in Fig.1.4. • Remove the pistons from all the syringes. • Leaving one syringe untouched, fill water in the second and pieces of chalk in the third. • Insert the pistons back into the syringes. You may apply some vaseline on the pistons before inserting them into the syringes for their smooth movement. • Now, try to compress the content by pushing the piston in each syringe. We have observed that gases are highly compressible as compared to solids and liquids. The liquefied petroleum gas (LPG) cylinder that we get in our home for cooking or the oxygen supplied to hospitals in cylinders is compressed gas. Compressed natural gas (CNG) is used as fuel these days in vehicles. Due to its high compressibility, large volumes of a gas can be compressed into a small cylinder and transported easily. We come to know of what is being cooked in the kitchen without even entering there, by the smell that reaches our nostrils. How does this smell reach us? The particles of the aroma of food mix with the particles of air spread from the kitchen, reach us and even farther away. The smell of hot cooked food reaches us in seconds; compare this with the rate of diffusion of solids and liquids. Due to high speed of particles and large space between them, gases show the property of diffusing very fast into other gases. In the gaseous state, the particles move about randomly at high speed. Due to this random movement, the particles hit each other and also the walls of the container. The pressure exerted by the gas is because of this force exerted by gas particles per unit area on the walls of the container. Fig. 1.4 • What do you observe? In which case Fig.1.5: a, b and c show the magnified schematic was the piston easily pushed in? pictures of the three states of matter. The • What do you infer from your motion of the particles can be seen and observations? compared in the three states of matter. 2015-16 12.11.14 1.4.1 EFFECTOFCHANGEOFTEMPERATUREuestions Q 1. The mass per unit volume of a substance is called density. (density = mass/volume). Arrange the following in order of increasing density – air, exhaust from chimneys, honey, water, chalk, cotton and iron. 2. (a) Tabulate the differences in the characterisitcs of states of matter. (b) Comment upon the following: rigidity, compressibility, fluidity, filling a gas container, shape, kinetic energy and density. 3. Give reasons (a) A gas fills completely the vessel in which it is kept. (b) A gas exerts pressure on the walls of the container. (c) A wooden table should be called a solid. (d) We can easily move our hand in air but to do the same through a solid block of wood we need a karate expert. 4. Liquids generally have lower density as compared to solids. But you must have observed that ice floats on water. Find out why. 1.4 Can Matter Change its State? We all know from our observation that water can exist in three states of matter– • solid, as ice, • liquid, as the familiar water, and • gas, as water vapour. What happens inside the matter during this change of state? What happens to the particles of matter during the change of states? How does this change of state take place? We need answers to these questions, isn’t it? Activity _____________1.12 • Take about 150 g of ice in a beaker and suspend a laboratory thermometer so that its bulb is in contact with the ice, as in Fig. 1.6. (a) (b) Fig. 1.6: (a) Conversion of ice to water, (b) conversion of water to water vapour 2015-16 12.11.14 are some that change directly from solid state closer? Do you think that increasing or to gaseous state and vice versa without decreasing the pressure can change the state changing into the liquid state. of matter? Activity _____________1.13 • Take some camphor or ammonium chloride. Crush it and put it in a china dish. • Put an inverted funnel over the china dish. • Put a cotton plug on the stem of the funnel, as shown in Fig. 1.7. Fig. 1.7: Sublimation of ammonium chloride • Now, heat slowly and observe. • What do you infer from the above activity? A change of state directly from solid to gas without changing into liquid state (or vice versa) is called sublimation. 1.4.2 EFFECTOFCHANGEOFPRESSURE We have already learnt that the difference in various states of matter is due to the difference in the distances between the constituent particles. What will happen when we start putting pressure and compress a gas enclosed in a cylinder? Will the particles come Fig. 1.8: By applying pressure, particles of matter can be brought close together. Applying pressure and reducing temperature can liquefy gases. Have you heard of solid carbon dioxide (CO2)?It is stored under high pressure. Solid CO gets converted directly to gaseous state 2on decrease of pressure to 1 atmosphere* without coming into liquid state. This is the reason that solid carbon dioxide is also known as dry ice. Thus, we can say that pressure and temperature determine the state of a substance, whether it will be solid, liquid or gas. Fig. 1.9:Interconversion of the three states of matter * atmosphere (atm) is a unit of measuring pressure exerted by a gas. The unit of pressure is Pascal (Pa): 1 atmosphere = 1.01 × 105 Pa. The pressure of air in atmosphere is called atmospheric pressure. The atmospheric pressure at sea level is 1 atmosphere, and is taken as the normal atmospheric pressure. 2015-16 12.11.14 What you have learnt • Matter is made up of small particles. • The matter around us exists in three states— solid, liquid and gas. • The forces of attraction between the particles are maximum in solids, intermediate in liquids and minimum in gases. • The spaces in between the constituent particles and kinetic energy of the particles are minimum in the case of solids, intermediate in liquids and maximum in gases. • The arrangement of particles is most ordered in the case of solids, in the case of liquids layers of particles can slip and slide over each other while for gases, there is no order, particles just move about randomly. • The states of matter are inter-convertible. The state of matter can be changed by changing temperature or pressure. • Sublimation is the change of gaseous state directly to solid state without going through liquid state, and vice versa. • Boiling is a bulk phenomenon. Particles from the bulk (whole) of the liquid change into vapour state. • Evaporation is a surface phenomenon. Particles from the surface gain enough energy to overcome the forces of attraction present in the liquid and change into the vapour state. • The rate of evaporation depends upon the surface area exposed to the atmosphere, the temperature, the humidity and the wind speed. • Evaporation causes cooling. • Latent heat of vaporisation is the heat energy required to change 1 kg of a liquid to gas at atmospheric pressure at its boiling point. • Latent heat of fusion is the amount of heat energy required to change 1 kg of solid into liquid at its melting point. 2015-16 12.11.14 • Some measurable quantities and their units to remember: Quantity Unit Symbol Temperature kelvin K Length metre m Mass kilogram kg Weight newton N 3Volume cubic metre mDensity kilogram per cubic metre kg m–3 Pressure pascal Pa Exercises 1. Convert the following temperatures to the celsius scale. (a) 293 K (b) 470 K. 2. Convert the following temperatures to the Kelvin scale. (a) 25°C (b) 373°C. 3. Give reason for the following observations. (a) Naphthalene balls disappear with time without leaving any solid. (b) We can get the smell of perfume sitting several metres away. 4. Arrange the following substances in increasing order of forces of attraction between the particles— water, sugar, oxygen. 5. What is the physical state of water at— (a) 25°C (b) 0°C (c) 100°C ? 6. Give two reasons to justify— (a) water at room temperature is a liquid. (b) an iron almirah is a solid at room temperature. 7. Why is ice at 273 K more effective in cooling than water at the same temperature? 8. What produces more severe burns, boiling water or steam? 9. Name A,B,C,D,E and F in the following diagram showing change in its state 2015-16 12.11.14 Group Activity Prepare a model to demonstrate movement of particles in solids, liquids and gases. For making this model you will need • A transparent jar • A big rubber balloon or piece of stretchable rubber sheet • A string • Few chick-peas or black gram or dry green peas. How to make? • Put the seeds in the jar. • Sew the string to the centre of the rubber sheet and put some tape to keep it tied securely. • Stretch and tie the rubber sheet on the mouth of the jar. • Your model is ready. Now run your fingers up and down the string by first tugging at it slowly and then rapidly. Fig. 1.10: A model for happy converting of solid to liquid and liquid to gas. 2015-16 12.11.14

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