Problem statement What is the difference between the rate of diffusion in solids, liquids and gases? Hypothesis The rate of diffusion increases from to to . Manipulated variable Responding variable Constant variables Temperature and pressure Materials and apparatus Copper(II) sulphate crystals, agar, cork, distilled water, smoke, gas jars, lid, test tube and test tube rack Procedure A Diffusion in solids 1 Pour hot agar (5%) into a test tube until it is almost full. 2 Let the agar cool and solidify. 3 Place a piece of copper(II) sulphate crystal on top of the agar. Close the test tube with a cork and turn the test tube upside down. Agar Copper(II) sulphate crystal 4 Leave the test tube for two days and record your observation. B Diffusion in liquids 1 Fill a test tube with distilled water. 2 Then add copper(II) sulphate crystal into the test tube. Distilled water Copper(II) sulphate crystal 3 Leave the test tube for one hour and record your observation. C Diffusion of gases 1 Fill a gas jar with smoke. Then place a lid on it. 2 Invert another gas jar over it. Smoke Lid Gas jars 3 Remove the lid and observe the changes Experiment 1 Rate of diffusion in solids, liquids and gases 44 ©Praxis Publishing_Focus On Science
Observation Activity Observations A The entire agar turns as the particles of the copper(II) sulphate crystal diffuse into the agar. B The whole test tube of water turns as the particles of the copper(II) sulphate crystal diffuse into the water. C The smoke particles diffuse into the air in the inverted gas jar. Discussion 1 Explain your observation using space-time relationship. (a) Activity A: The rate of diffusion of copper(II) sulphate crystal in solids is because the spaces between the particles in solids are . (b) Activity B: The rate of diffusion of copper(II) sulphate crystal in liquids is because the spaces between the particles in liquids are . (c) Activity C: The rate of diffusion of smoke in gases is because the spaces between the particles in gases are . 2 What is diffusion? 3 (a) Predict the rate of diffusion of copper(II) sulphate crystals in hot water compared to water at room temperature. Does it decrease, increase or remain the same? (b) Give a reason for your answer in 3(a). Conclusion Is the hypothesis accepted? Write down your conclusion. Chapter 2 Matter 45 ©Praxis Publishing_Focus On Science
Changes of State Matter can change from one state to another when it is heated or cooled, that is with a change in temperature. Heat energy is absorbed or released by its particles causing a change in the energy of the particles. As a result, a change in the state of matter occurs. Melting When a solid is heated, heat energy is absorbed by its particles. The heat energy is then converted to kinetic energy and the particles begin to vibrate faster. At the melting point (the temperature when a solid turns into liquid), the particles gain enough energy to overcome the forces of attraction between them and break away from their fixed positions. The particles now move freely and randomly. Hence, the solid turns into a liquid. Freezing When a liquid is cooled, heat energy is released by its particles. The particles lose kinetic energy and begin to move slowly and come closer together. When the particles no longer have enough energy to move freely, the forces of attraction between the particles will pull the particles together to settle in a fixed position. At the freezing point (the temperature when a liquid solidified into solid), the particles can only vibrate about their fixed positions and a solid is formed. Sublimation When solids such as ammonium chloride, iodine crystals, solid carbon dioxide (dry ice) are heated, the particles at the surface of the solid gain enough energy to break away and escape as a gas. When these solids change directly to its gaseous state without going through the liquid state / melting process, the process of sublimation has occurred. Solid 46 ©Praxis Publishing_Focus On Science
Condensation When a gas cools down, heat energy is released by its particles. The particles lose kinetic energy and begin to move more slowly. The forces of attraction between the particles will pull the particles closer to each other. At the condensation point (the temperature when a gas liquefied into liquid), the gas will turn into a liquid. Boiling When a liquid is heated, heat energy is absorbed by its particles. The particles gain heat energy and begin to move faster as the temperature rises. The collisions also occur more frequently. At the boiling point (the temperature when a liquid boils and turns into a gas), the particles gain enough kinetic energy to overcome the forces of attraction between them. The particles now spread apart and move about rapidly in all directions. Hence, the liquid turns into a gas. Evaporation A liquid can also change to a gas through evaporation. When a liquid absorbs heat at any temperature below its boiling point, it changes into gas. It occurs slowly and continuously only on the surface of the liquid where the particles have gained enough kinetic energy to overcome the forces of attraction to escape from the surface of the liquid. Liquid Gas Deposition When a gas is cooled, heat energy is released by its particles. The particles lose kinetic energy and begin to move more slowly. The forces of attraction between the particles will pull the particles closer to each other. In deposition, a substance changes directly from a gas to a solid phase without going through the liquid state. Some examples of this process are the formation of snow from water vapour and the making of dry ice using carbon dioxide. Chapter 2 Matter 47 ©Praxis Publishing_Focus On Science
The temperature of a matter increases when it is heated and decreases when it is cooled. However, the temperature remains constant during a change of state, that is during melting (solid to liquid), boiling (liquid to gas), freezing (liquid to solid) and condensation (gas to liquid). During melting and boiling, the kinetic energy gained by the particles is used to overcome the forces of attraction between the particles. The temperature of the solid or liquid remains the same. On the other hand, during condensation and freezing, the particles release energy to the surroundings, thus enabling them to be pulled closer together. The temperature of the liquid or gas remains the same. Temperature (°C) Boiling point Melting point Ice Water Ice + Water Steam Time (min) Water + C Steam B D A Problem statement Does temperature remain constant during the changes of state? A Temperature during the melting of ice Hypothesis The temperature of ice remains constant during the melting process. Manipulated variable Responding variable Constant variable Quantity of ice cubes Materials and apparatus Ice cubes, thermometer, beaker, Bunsen burner, tripod stand, glass rod and wire gauze Procedure 1 Set up the apparatus as shown in the diagram below. Ice cube Thermometer Glass rod Wire gauze Bunsen burner Experiment 2 Temperature remains constant during changes of state At point A to B, the temperature of the mix of ice and water remains the same, at the melting point. At point C to D, the temperature of the mix of water and steam remains the same, at the boiling point. The change of temperature during the heating of ice 48 ©Praxis Publishing_Focus On Science
2 Record the initial temperature of the ice cubes. 3 Heat the beaker slowly and stir the ice cubes using the glass rod. 4 Observe and record the temperature every three minutes until the temperature remains constant. B Temperature during the boiling of water Hypothesis The temperature of water remains constant during the boiling process. Manipulated variable Responding variable Constant variable Volume of water Materials and apparatus Distilled water, thermometer, flat-bottomed flask, Bunsen burner, tripod stand, glass tube, rubber stopper, retort stand and wire gauze Procedure 1 Measure 100 ml of distilled water and pour it into a flat-bottomed flask. 2 Set up the apparatus as shown in the diagram. Thermometer 100 ml distilled water Bunsen burner Glass tube Flat-bottomed flask 3 Heat the distilled water until its temperature reaches 60°C. Then, record the temperature every three minutes until the temperature remains constant. Result Time (minutes) Temperature (°C) Activity A Activity B Beginning of experiment 3 6 9 12 15 Chapter 2 Matter 49 ©Praxis Publishing_Focus On Science
Discussion 1 (a) Plot a graph of temperature against time for activity A. (b) What happens to the ice cubes as the temperature remained constant? (c) What is the melting point of ice? 2 (a) Plot a graph of temperature against time for activity B. (b) What happens to the water as the temperature remained constant? (c) What is the boiling point of water? 3 Why does the temperature remain constant during the change of state of matter? 4 Draw the changes in the arrangement of water particles before and after reaching the boiling point. Conclusion Is the hypothesis accepted? Write down your conclusion. During the changes of state, only the arrangement and movement of the particles in a matter will change, while the quantity of the particles in a matter remains unchanged. In this case, the mass of a matter remains constant during the changes of state. This is called conservation of mass. Problem statement Does the mass of the matter remain constant during a change of state? A Melting of ice Hypothesis Mass remains constant during the melting of ice. Manipulated variable Responding variable Constant variable Temperature Materials and apparatus Beaker, lever balance and ice cubes Procedure 1 Place the ice cubes in an empty beaker. 2 Weigh and record the initial mass of the beaker filled with ice cubes. Lever balance Ice cube Beaker 3 Allow all the ice to melt into water. Weigh and record the final mass of the beaker with water. Experiment 3 Mass remains constant during changes of state 50 ©Praxis Publishing_Focus On Science
B Dissolution of sugar in water Hypothesis The mass of the sugar remains constant after dissolving in water. Manipulated variable Responding variable Constant variable Temperature / Volume of water Materials and apparatus Distilled water, sugar, beaker, glass rod and lever balance Procedure 1 Prepare a beaker filled with 200 ml of distilled water. 2 Add three spatulas of sugar into the beaker and record the mass. Lever balance 200 ml of water + 3 spatulas of sugar Beaker Scale 3 Stir the solution until the sugar is completely dissolved and record the mass. C Expansion by heat Hypothesis The mass of the metal ball remains constant when heated. Manipulated variable Responding variable Constant variable Heating time Materials and apparatus Metal ball, ring, Bunsen burner, triple beam balance and tongs Procedure 1 Weigh and record the initial mass of the metal ball with its ring. 2 Set up the apparatus as shown in the diagram and heat the metal ball for three minutes. Bunsen burner Metal ball Ring 3 Weigh the metal ball with its ring when it is still hot and record its final mass. Chapter 2 Matter 51 ©Praxis Publishing_Focus On Science
Result Record your result. Activity Mass (g) Beginning of experiment End of experiment A B C Discussion 1 (a) What happened to the mass at the beginning and the end of the experiment in activity A, B and C? Has the mass decreased, increased or remained the same? (b) Give a reason for your answer in 1(a). 2 Which of the following substances will have the same mass after going through changes? Why? (a) A piece of paper is crumpled up (b A potato is diced up (c) Burning of iron powder Conclusion Is the hypothesis accepted? Write down your conclusion. Dew is formed through condensation of water vapour in the air. (Gas ➔ liquid) Wet clothes dry under the sun when water evaporates to become water vapour. (Liquid ➔ gas) Ice cream melts quickly on a hot day. (Solid ➔ liquid) You may or may not be aware that you have observed examples of state changes in your daily life. Consider some of the following examples. 52 ©Praxis Publishing_Focus On Science
After a hot shower, it is likely that you would not be able to see your reflection in the mirror. You have to wipe off the moisture from the mirror’s surface first. This is because condensation occurs when warm water vapour comes into contact with the cooler mirror surface. Have you ever wondered why we can see someone’s breath when he is out in very cold weather? Water exists on Earth in all three states of matter: solid, liquid and gas. Liquid water can be found in the oceans, rivers, lakes and streams, as well as in the soil and underground. Glaciers and snow all contain solid ice. The Earth’s atmosphere contains water vapour which is a gas. Let’s study how water exists in different states in the water cycle. When the warm and moist vapour of his breath comes into contact with the cold and humid air, it condenses into tiny water droplets. We can see these droplets take on a cloud-like appearance. Water cycle Resource Chapter 2 Matter 53 ©Praxis Publishing_Focus On Science
Snow melts into water as a result of the Sun’s heat. This water flows into oceans, lakes and rivers. Water from melting snow and ice also enters the soil, providing water for plants and turning into the groundwater we drink. How does water enter the atmosphere? The Sun’s heat causes water to evaporate from oceans, lakes and rivers. Evaporation occurs when liquid water on Earth’s surface turns into water vapour in our atmosphere. Warm water vapour rises through the atmosphere of the Earth. As it rises higher and higher in the atmosphere, the cool air of the atmosphere causes the water vapour to turn back into liquid water, resulting in clouds. This is known as condensation. When a cloud becomes occupied with liquid water, it falls to the ground as rain or snow. Rain and snow then fill lakes and rivers, and the cycle begins again. 2.2 Physical and Chemical Changes Each substance has unique physical and chemical characteristics. Physical characteristics such as melting point, boiling point, mass, density, solubility and heat conductivity are characteristics that can be observed. Our five senses and scientific instruments have the capacity to detect them. Chemical characteristics such as flammability and rusting are characteristics that change the chemical nature of a substance. This can be observed when a substance combines with other substances or changes into a new substance during a chemical reaction. In the changes of the states of matter that you have learned, no new substance is formed. The particles are of the same kind even though the arrangement and movement of the particles have changed. Therefore, the changes of state affect the physical characteristics of matter, while the chemical characteristics are unaffected. Ice remains as water even after it freezes to a solid state. No new substance is created and the particles are the same before and after the process. Similarly, the melting of a candle as the candle burns does not result in the formation of new products. The materials that make up the candle remain the same. These are examples of physical changes. This means a substance’s composition is unaffected by changes to its physical characteristics. The melting of a candle is a physical change but the burning of a candle is a chemical change. Why? Think About It 54 ©Praxis Publishing_Focus On Science
Chemical changes involve chemical reactions and the creation of new products. It is an irreversible change. How do we know if a chemical change has happened? If you notice a substance change its colour or its temperature, produce bubbles, or a new product is formed, then chemical changes have happened. When wood is burning, the wood reacts with oxygen in the air to transform into carbon dioxide, water vapour and ash. Wood burning is a chemical change, it is not reversible. Rust is a coating that occurs on the surface of iron (e.g. a padlock). Rust and iron are not the same. Rusting on the padlock is a chemical change because a new substance called ‘iron oxide’ is formed during this process. Is it considered physical change if we mix different types of nuts together? Remember that a substance’s physical change is a change in its physical appearance, but its chemical identity remains unchanged. Crushing a can merely alters the shape of the can. The chemical identity remains unchanged. Cutting a tomato into smaller pieces only changes the size of the tomato, not its composition Chapter 2 Matter 55 ©Praxis Publishing_Focus On Science
Burning fireworks results in a chemical change. Fireworks release sound, heat and light energy as they explode. As a result, energy changes are involved in chemical changes. What are the other examples of physical and chemical changes of matter in your daily life? Think About It When you dissolve a vitamin C effervescent tablet in water, gas bubbles form and the water turns orange, indicating that a chemical change has occurred. Activity 3 Aim: To differentiate between the physical and chemical changes in matter Materials and apparatus: Distilled water, sodium chloride powder, iron nail, test tube, beaker, glass rod and spatula Procedure: Activity A 1 Add one spatula of sodium chloride powder to 50 ml of water and stir with a glass rod. Spatula Water Stir Sodium chloride powder 2 Record your observation. Physical and chemical changes in matter 56 ©Praxis Publishing_Focus On Science
Activity B 1 Clean the iron nail with sandpaper and put it into a test tube. Distilled water Iron nail 2 Add 10 ml of distilled water in the test tube as shown in the diagram. 3 Record your observation after seven days. Observations: Activity Observation Type of changes A The sodium chloride powder in water. B The iron nail . Discussion: 1 Give inferences for your observations in Activity A and B. 2 How does iron rust? Iron rusts when it is exposed to and . 3 Complete the table below by identifying the changes in the situations listed. Situation Physical change / Chemical change (a) Bromine exists as liquid at room temperature (b) Wood rots when exposed to rain (c) Iron(III) oxide reacts with strong acids (d) Water boils at 100°C (e) Nickel sticks to a magnet (f) Salts dissolve in water (g) Paper burns when it is lit Conclusion: What is the difference between physical and chemical change? Chapter 2 Matter 57 ©Praxis Publishing_Focus On Science
2.3 Density You are given a Styrofoam cup and a ceramic cup of the same size, which cup is more dense? How do you determine their densities? The density of a material is the amount of mass that fits into a given volume. Study the diagram below, we have two materials of the same volume. Which diagram shows the material tightly packed? Two materials of the same volume with different mass We say that the tightly-packed material has a higher mass and a higher density. We can compare the densities of different objects which have the same volume by comparing their masses. Density of a substance is the mass per unit volume of the substance. The SI unit for density is kilogram per cubic metre (kg/m3 or kg m–3). Another unit that is often used is gram per cubic centimetre (g/cm3 or g cm–3). In Chapter 1, you have learned the measuring tools for mass and volume, this means that if we know the mass and volume of a substance, we can calculate its density by using the formula: A pure substance has the same density when measured under the same condition. For example, pure gold has the density of 19.3 g cm-3. Any gold with the density of higher or lower than this value is impure. Using this idea, Archimedes proved that the crown of King Hiero II was not made of pure gold. Science Facts Density (g cm–3) = Mass (g) Volume (cm3 ) Example 1 A block of lead measuring 10 cm of length, 5 cm of width and 2 cm of height has a mass of 1130 g. What is the density of the lead block? Solution: Density of lead block = 1130 g 10 cm 3 5 cm 3 2 cm = 11.3 g cm-3 58 ©Praxis Publishing_Focus On Science
Activity 4 1 A list of materials is given as below. Air, petrol, rubber, glass, diamond, gold, aluminium, seawater, ice, water, platinum, iron 2 Find out the density of each of the materials from books or the Internet. 3 Based on the information obtained, arrange the density of the materials in increasing order. 4 Identify each of the materials as solid, liquid or gas. 5 Which state of matter has the lowest density? 6 Which state of matter has the highest density in general? Densities of different materials Relationship between Density and Floating or Sinking Take a look at the diagram below. Do you notice that the material with the highest density is positioned at the lowest part of the measuring cylinder? Petrol (0.8 g cm-3) Cork (0.24 g cm-3) Wood (0.9 g cm-3) Glass (2.5 g cm-3) Water (1.0 g cm-3) Mercury (13.6 g cm-3) Arrangement of materials with different densities in a measuring cylinder A material that is less dense than a liquid will float on the liquid while a material that is denser than a liquid will sink in the liquid. This is how the concept of density explains why some materials float, while others sink. Whether a material floats or sinks in a liquid is determined by its density. Let’s explore some examples on how this concept is applied. You may be wondering why, when oil and water mix, they do not dissolve in one another. Oil always floats on top of the water. This is because oil is less dense than water. Oil floats on top of the water. Chapter 2 Matter 59 ©Praxis Publishing_Focus On Science
Activity 5 1 Prepare two raw eggs of similar size and weight, two glasses, water and salt. 2 Fill one glass about ¾ full of water. Predict whether the egg will sink or float in the water. 3 Place an egg carefully in water. Does it sink or float in water? Why? 4 Fill another glass with the same amount of water. Then add 2 tablespoons of salt and stir until it has completely dissolved. 5 Predict whether the egg will sink or float in the salt water. 6 Place the other egg in the salt water. Does it sink or float? Why? Sink or float The density of the water in the Dead Sea is so high that we can easily float on it. Do you know why? Think About It You might believe that all heavy objects sink in water. Is this true? No! All ships would sink into the ocean if this was the case. Density is defined as mass per unit volume, so a bigger volume and smaller mass will result in lesser density. A ship is designed and constructed to be large with a large volume of air in it, and built with different materials so that it has a lower average density. A density lower than water will allow the ship to float on water. An upward force known as upthrust is exerted on an object, when it is partially or completely submerged in a liquid, and pushes it upward. The object floats on the liquid if this force is equal to its weight. When a ship is overloaded with lots of containers, its weight exceeds the upthrust and causes it to sink. Science Facts 60 ©Praxis Publishing_Focus On Science
Activity 6 Aim: To study the relationship between the mass and density of various solids that have the same volume Materials and apparatus: Cubes of copper, iron, glass, cork, lead and digital balance Procedure: 1 Prepare five types of cubes which have the same volumes as the diagram below. Copper Iron Glass Cork Lead 2 Weigh each cube and calculate its density by using the following formula: Density = Mass Volume Note: Volume = length 3 width 3 height 3 Record the results in the table. Result: Cube Volume (cm3) Mass (g) Density (g cm–3) Copper Iron Glass Cork Lead Discussion: 1 Define density. 2 What is the relationship between mass and density if the volume is the same? 3 Arrange the solids above based on their densities in an ascending order. 4 A marble has a density of 2.3 g cm-3 and a volume of 8 cm3 . Calculate the mass of the marble. 5 Complete the statements below to explain the application of the concepts of density in a submarine. Sea water is pumped into the ballast tank causing the submarine to be denser and in the water. Sea water is pumped out from the ballast tank causing the submarine to be less dense and on the surface of sea water. Conclusion: Density when the mass increases for various types of solid materials that have the same . Relationship between mass and density of various solids that have the same volume Chapter 2 Matter 61 ©Praxis Publishing_Focus On Science
Activity 7 Aim: To determine the density of solids using the water displacement method Materials and apparatus: A stone, iron cube, thread, water, digital balance and measuring cylinder Procedure: 1 Weigh a stone using a digital balance and record its mass. 2 Pour 50 ml of water into a measuring cylinder. Record the initial volume of water. 3 Tie the stone with a thread and lower it into the water as shown in the diagram. Record the final volume of water. Stone Thread Water 4 Determine the volume of the stone. Then, calculate the density of the stone. 5 Repeat steps 1 to 4 with an iron cube. Result: Mass of object (g) Initial volume of water (cm3) Final volume of water (cm3) Volume of object (cm3) Density (g cm-3) Stone Iron cube Discussion: 1 What is the formula of density? 2 Water displacement method is a method that is used to measure the volume of an object. Conclusion: Write down your conclusion. Determine the density of solids using water displacement method 62 ©Praxis Publishing_Focus On Science
1 Matter is anything that has and volume. It is made up of tiny and particles that are completely separate from one another with spaces between them. 2 The three states of matter are solid, and gas. 3 The particles in solids are packed closely together in a fixed and pattern. They cannot move around and can only in their fixed position. Solids be compressed because the particles are close together and have very little space to move into. They cannot flow because the particles are closely packed, thus they have a fixed . 4 The particles in liquids are still quite close together but are arranged without a fixed pattern. They are able to move and collide with one another. Liquids be compressed to any extent because the particles are still arranged quite closely and have little space to move into. They flow because the particles are free to move around, thus they take the shape of their container. 5 The particles in gases are from one another. They are able to move freely and randomly in all at high speeds. Gases can be compressed because the particles are far apart and have large spaces to move into. They flow much more than a liquid because the particles move randomly in all directions and spread out as far as they can to occupy the entire space of the container quickly. Thus, they take the shape of their container. 6 Matter can change from one state to another when heat energy is absorbed or by its particles. 7 Melting, freezing, , boiling, , condensation and deposition are processes involved in the changes of state. 8 When a substance’s composition is unaffected by changes to its physical characteristics, it is called changes while changes involve chemical reactions and the creation of new products. 9 The mass per unit volume of a substance is called . Its SI unit is per cubic metre. 10 A material that is less dense than a liquid will on the liquid while a material that is denser than a liquid will in the liquid. RECALL Fill in the missing words. Chapter 2 Matter 63 ©Praxis Publishing_Focus On Science
THINKING CAP Put on your 1 The following table shows the melting points of four substances. Substance Melting point (°C) Nitrogen –210 Mercury –38.8 Iron 1538 Magnesium 650 Which substance has the highest melting point? Explain how the melting point is related to its force of attraction. 2 73.6 cm3 of water freezes into ice with a density of 0.92 g cm-3. What is the volume of the ice? (Note: The mass of ice remains the same when changing state from solid to liquid and vice versa.) 3 How is it possible to say that a fruit’s ripening causes a chemical change? 64 ©Praxis Publishing_Focus On Science
Project Activity objective: Understand the concept of density that allows objects to float or sink in water Problem statement: The object’s ability to float or sink depends on their density. This can be demonstrated by using a submarine model. Concept applied: Density and water displacement method Action plan: 1 Identify various objects that can float or sink in water. 2 Test the ability of objects to float or sink in water. 3 Determine the materials to be used and calculate the total cost of the material. Procedure: 1 Divide the class into groups of four. 2 Each group will brainstorm the concept of density and water displacement method. Search information on materials that float and sink, and on the design of a submarine model from the Internet and books. 3 Identify various objects that can float and sink in water. 4 Test the abilities of objects to float and sink in water. 5 Design a submarine model using the objects identified and tested. 6 Build the submarine model. Discuss how you can make it float and sink. Test it. 7 Redesign and rebuild the model, if necessary. Presentation: 1 Demonstrate to the class how the submarine model can float and sink. Share with the class your experience of designing and building the model. 2 Submit a report that include steps 2 to 7 in the procedure. Build a Submarine Model Chapter 2 Matter 65 ©Praxis Publishing_Focus On Science
When the iron is turned on, the temperature increases gradually until it reaches the point where it may be used to iron clothes. We can feel the warmth of the clothes when we iron them. How does the iron’s heat get transferred to the clothing? Are there any safety measures that can automatically switch off the electricity to the iron if we keep it on for a long time? Temperature and Heat CHAPTER 3 What will you learn? State different temperature scales Describe the various types of thermometers Explain how expansion and contraction of matter can be applied in daily life Define heat capacity, specific heat capacity and specific latent heat of fusion and vaporisation Perform calculation involving heat capacity, specific heat capacity and specific latent heat of a substance Explain the ways of heat transfer Differentiate between heat conductors and heat insulators Explain how living organisms regulate their body temperature ©Praxis Publishing_Focus On Science
3.1 Temperature and Scale Temperature is a measurement of how hot or cold an object is. The thermometer is the tool used to measure temperature. Temperature is measured in Celsius, Fahrenheit, Kelvin or less commonly Réaumur. Temperature Scales We must have a scale with numbers on a thermometer before using it. The temperature scale must be defined. A temperature scale is a way to measure temperature relative to a beginning point (zero) and a unit of measurement. The temperature scale is usually obtained by choosing two temperatures known as fixed points. There are four types of scales which are the Fahrenheit scale, Réaumur scale, Celsius scale and Kelvin scale. TEMPERATURE SCALE TIMELINE The Fahrenheit Scale Daniel Gabriel Fahrenheit, a German physicist and engineer, developed the Fahrenheit scale as a method for measuring temperature. The melting point of ice, which is 32°F, and the boiling point of water, which is 212°F, are used as standards on the Fahrenheit temperature scale. The interval between these two temperatures (212°F and 32°F) is divided into 180 parts, known as degrees Fahrenheit. The Réaumur Scale This is a temperature scale named after René Antoine Ferchault de Réaumur for which the freezing and boiling points of water are defined as 0°R and 80°R respectively. The Celsius Scale In the Celsius scale, the two fixed points are melting point (0°C) of ice and boiling point (100°C) of water. Both temperatures are determined at atmospheric pressure. The Celsius scale was proposed by the Swedish astronomer Anders Celsius. The interval between these freezing and boiling points is divided into 100 equal parts, called degrees Celsius. The Kelvin Scale Kelvin is the base unit of temperature in the International System of Units (SI) and has the unit symbol K. By convention, –273.15°C is used to represent absolute zero on the Kelvin scale. This is the lowest possible temperature at which there is no movement between the particles that make up matter. On the Kelvin scale, the melting point of ice (273.15 K) and the boiling point of water (373.15 K) are used as references. The Kelvin scale divides the range between these two temperatures (273.15 K and 373.15 K) into 100 equal parts. It should be noted that one Kelvin is equivalent to one degree Celsius. 1724 1730 1743 1848 Chapter 3 Temperature and Heat 67 ©Praxis Publishing_Focus On Science
The Fahrenheit, Réaumur, Celsius and Kelvin scales Based on the four scales, their units can be converted from one to another. The following conversion is used to find the temperature in different units. Temperature from Celsius to Kelvin: K = °C + 273.15 Temperature from Celsius to Fahrenheit: °F = ( 9 5 )°C+ 32 Temperature from Celsius to Réaumur: °R = ( 4 5 )°C 3.2 Thermometers There are several types of thermometers that have their respective functions. In general, thermometers must be affordable, simple to use, safe, sensitive and able to measure a wide range of temperatures in order to be effective. The most common thermometer for measuring temperature is the liquid-inglass thermometer. Liquid-in-glass Thermometers The liquid-in-glass thermometer works using the principle of expansion and contraction of liquid when the temperature increases and decreases. Liquid expansion and contraction occur in the capillary tube. The bulb holds a liquid such as alcohol or mercury. When there is an increase in heat, the liquid inside the bulb expands, pushing up into the tube. The temperature can be read from the scale marked on the tube. Mercury Thermometers In a mercury thermometer, the capillary tube is filled with mercury, and the tube is labelled with a standard temperature scale. The mercury expands and contracts as the temperature changes, allowing the temperature to be read from the scale. The temperatures of the body, liquid and vapour can Capillary tube Bulb 212°F 32°F –40°F Boiling point of water Freezing point of water 180 Fahrenheit degrees Fahrenheit 100°C 0°C –40°C 100 Celsius degrees Celsius 373.15 K 273.15 K 233.15 K 100 Kelvins Kelvin 80°R 0°R –32°R 80 Réaumur degrees Réaumur Mercury thermometer 68 ©Praxis Publishing_Focus On Science
all be determined with mercury thermometers. Mercury is used in thermometers because it conducts heat well, is easy to see because it is reflective and this allows the thermometer reading to be determined more easily. Alcohol Thermometers Due to mercury’s toxicity, it has been replaced by alcohol. Alcohol thermometers have functions similar to mercury thermometers. The most popular option is made of ethanol since it is inexpensive and presents a relatively low risk of leakage. Since it is transparent, the liquid is made more visible by the addition of dye. Types of Thermometers Various sizes and shapes of thermometers are available depending on the requirements of the user. Thermometers are divided into two categories based on their functions, clinical thermometers and laboratory thermometers. People use clinical thermometers to check their body temperatures. Digital thermometers, electronic ear thermometers and forehead thermometers are a few examples. In laboratories and during the testing of some samples, laboratory thermometers are used to gauge the temperatures of objects as well as their boiling and freezing points. In addition, maximum-minimum thermometers let meteorologists determine the highest and lowest temperatures at any given location. Examples of laboratory thermometers are pyrometer thermometer and probe thermometer. Digital Thermometers Traditional thermometers have been replaced by more modern thermometers called digital thermometers. These thermometers are regarded as the most accurate when used properly. Digital thermometers provide temperature readings on a display screen and through an electronic circuit. Readings can be obtained from the rectum, under the tongue or under the armpit. Additionally, they are inexpensive, widely accessible and easy to use. Electronic Ear Thermometers Electronic ear thermometers measure body temperature from inside the ear canal using infrared technology. They gauge temperature using the tympanic membrane in the ear. Children benefit greatly from this kind of thermometer as these thermometers can immediately record body temperatures. However, they are pricey and might not be able to detect the body temperature precisely if the thermometer is not inserted correctly. Digital thermometer Electronic ear thermometer Chapter 3 Temperature and Heat 69 ©Praxis Publishing_Focus On Science
Forehead Thermometers Forehead thermometers read temperature using infrared technology. The superficial temporal artery, a branch of the carotid artery, is monitored using infrared sensors. There is no physical contact when taking temperature readings with a forehead thermometer. However, they are not as precise as standard digital thermometers. Pyrometer Thermometers Pyrometer thermometers are remote-sensing tools that allow distance temperature measurement. Typically, the thermal radiation emitted by these thermometers is used to determine the object’s temperature. The fact that these thermometers do not even require you to touch anything is one of their main advantages. Therefore, pyrometers are perfect for keeping track of the temperatures of moving objects or surfaces. They can also be used to measure the temperatures of objects that are too hot to touch or have complex structures. They are employed to gauge temperatures greater than 2000°C. These modern thermometers are widely used to check people’s temperatures in offices, malls, train stations and other public places, particularly during the Covid-19 pandemic. A technician uses a pyrometer thermometer to check the heat of a condensing unit. 70 ©Praxis Publishing_Focus On Science
Probe Thermometers The probe thermometer is one of the most popular types of thermometers. These thermometers are ideal for conducting cleanliness tests in food sector retail stores and laboratories due to their rapid temperature readings. Typically, probe thermometers have a pointed tip that facilitates immersion and penetration. The two types of probes that are available are fixed probe and wired probe thermometers. 3.3 Expansion and Contraction of Matter Most matter expands when heated and contracts when cooled. An example of the effect of heat is thin glass cracking when hot water is poured onto it. The increase in the size of objects when they are hot is called expansion. The decrease in their sizes when they are cooled is called contraction. Expansion and Contraction of Solids The atoms or molecules in a solid vibrate at all temperatures. As its temperature increases, the atoms vibrate more vigorously and these vibrations push the atoms further apart. The volume of the solid increases and the solid expands. When the solid is cooled, the atoms vibrate less vigorously and they become closer together. The volume of the solid decreases and the solid contracts. We can apply the principle of expansion and contraction of matter in making instruments that are useful in our daily life. Bimetallic Strip in a Fire Alarm An automatic fire alarm uses a bimetallic strip to switch on the electric bell when there is a fire. The heat from the fire causes the bimetallic strip to bend towards the contact point. Arrangement of particles in a solid Heated Cooled Cold Hot A probe thermometer is generally used to instantly measure the temperature of food and liquid samples. Chapter 3 Temperature and Heat 71 ©Praxis Publishing_Focus On Science
When the bending strip touches the contact point to complete the circuit, the fire alarm rings. Bimetallic Strip as a Thermostat The bimetallic strip is also used as a thermostat in an electric iron for controlling and maintaining temperature. As temperature rises, the bimetallic strip bends away from the contact point and cuts off the current. When the bimetallic strip cools down, contact is made again and current flows to heat up the iron. The bimetallic strip is made by combining two different metals with different expansion and contraction rates. Science Facts Iron and copper are joined together and fixed side by side. The bimetallic strip will bend when heated, with iron within and copper outside. This shows that at the same temperature, copper expands more than iron. The bimetallic strip bends with copper inside and iron outside when cooled to room temperature. This shows that copper contracts more than iron does. An automatic fire alarm Bimetallic strip Brass Iron Batteries Contact point Electric bell Thermostat in an electric iron Bimetallic strip Temperature control Heating coil Contact point To power supply The bimetallic strip bends upwards Contact point Copper Copper Copper heated cooled Iron Iron Iron Resource 72 ©Praxis Publishing_Focus On Science
Electric Cables Electric transmission cable and the cables of cable cars sag on a hot day and tighten during a cold night. Therefore, allowances have to be made for the expansion and contraction of the cables. Electric cables sag in hot weather and tighten during a cold night. Bridges and railroad tracks have expansion joints to allow them to freely expand and contract with the temperature changes. Concrete Road Bridges are typically made of concrete and steel. These components expand with higher temperatures and contract at lower temperatures. Thus, expansion joints are needed to provide gaps in the bridges. Expansion joints are basically gaps in the bridge that allow the bridge to expand and contract. Without these gaps, the concrete road surfaces may crack due to the forces that build up when the concrete expands during the hot weather. Railroad Tracks When laying railroad tracks, gaps have to be left between successive lengths of rail to allow for expansion on hot days. Without the gaps, the track buckles and this affects the safety of the trains. Expansion joint Chapter 3 Temperature and Heat 73 ©Praxis Publishing_Focus On Science
Expansion and Contraction of Liquids When a liquid is heated, the molecules of the liquid gain more energy and move more vigorously. This allows them to have greater freedom to move. Thus, the liquid expands. Arrangement of particles in a liquid At lower temperatures, the molecules of the liquid have less energy and move closer to each other. This causes the volume of the liquid to decrease and the liquid contracts. This principle is applied in the thermometer we use. Mercury in a Thermometer Mercury is a liquid metal that can expand and contract when there is a change in temperature. This makes it suitable for temperature measurement and it is used in a thermometer. How does the thermometer show the reading of temperature when the bulb of the thermometer comes in contact with a hot object? Explain in terms of expansion and contraction of liquid how this happens. Think About It Heated Cooled Cold Hot (a) Mercury in a laboratory thermometer (b) Mercury in a clinical thermometer -10 0 10 20 30 40 50 60 70 80 90 100 110 120 Mercury Bulb Constriction Capillary tube Linear scale -10 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 Mercury Linear scale Capillary tube Bulb (a) (b) 74 ©Praxis Publishing_Focus On Science
Steam or hot water vapour rise in the air because it expands and becomes less dense than the surrounding air. Expansion and Contraction of Gases The molecules of a gas are farther apart compared with the molecules in a solid and liquid. Gas molecules move at high speeds in all directions. If a gas is confined in an expandable container, the volume of the gas will increase with increasing temperature. The volume will decrease as the temperature drops. Arrangement of particles in a gas When the gas is heated, the molecules become more energetic, move faster and are farther apart. This causes the volume of the gas to increase and expansion is said to have occurred. At a lower temperature, the molecules move very much slower due to less energy. They are closer together, causing the volume to decrease and contraction occurs. Let us take a look at the examples below. What will happen if you leave an inflated balloon in the sun for a while? As the air inside absorbs heat from the surroundings, the balloon will enlarge in size. What will happen if a bottle with an inflated balloon tied to the mouth of the bottle is submerged in ice-cold water? As the bottle cools, the air inside the bottle and balloon contracts, causing the balloon to shrink in size. These are the most visible examples of the expansion and contraction of air due to the change of temperatures. Hot-air Balloons Heat causes air to expand, which makes it less dense than the air around it. This causes the heated air to rise, causing steam and smoke to rise, hot air balloons to float, and other phenomena. Heated Cooled Cold Hot Chapter 3 Temperature and Heat 75 ©Praxis Publishing_Focus On Science
Activity 1 Aim: To study the effect of heat towards the expansion and contraction of solids, liquids and gases A Expansion and contraction of solids Materials and apparatus: Metal ball, metal ring, Bunsen burner, iron bar and gauge (i) Procedure: 1 Drop a metal ball through a ring as shown in the diagram. Ring Holder Metal ball 2 Take out the ball through the ring and heat the ball over a Bunsen flame for a few minutes. Then, drop it through the ring again. What do you observe? 3 Allow the ball to cool down to room temperature and drop it through the ring again. What do you observe? Observation: Write down what you observe. Discussion: 1 Why can’t the metal ball pass through the ring after it is heated? 2 Why can the metal ball pass through the ring after it is cooled down? (ii) Procedure: 1 Place the iron bar in the gauge. Does the iron bar fit in the gauge? Gauge Iron bar 2 Heat the iron bar for a few minutes. Then stop the heating and repeat step 1. 3 When the iron bar is cooled, repeat step 1. Observation: (a) Before heating, the iron bar in the gauge. After heating, it in the gauge. Inference: This is because the iron bar when hot. (b) When cooled, the iron bar in the gauge. Inference: This is because it has to its initial length. Conclusion: Write down your conclusion. Expansion and contraction of solids, liquids and gases 76 ©Praxis Publishing_Focus On Science
B Expansion and contraction of liquids Materials and apparatus: Thermometer, beakers, ice, cold water and hot water (i) Procedure: 1 Rub both of your palms together until your feel the warmth of your palms. 2 Hold a thermometer bulb with both palms and observe the mercury level in the thermometer. Laboratory thermometer 3 Then, place the thermometer in a beaker filled with ice and observe the mercury level in the thermometer. Ice Laboratory thermometer Observation: (a) When both palms hold the thermometer bulb after rubbing, the mercury level in the thermometer . Inference: This is because heat from the palms after rubbing, causes the mercury to . (b) When the thermometer is placed in a beaker filled with ice, the mercury level in the thermometer . Inference: This is because the mercury when it is cooled. (ii) Procedure: 1 Place a thermometer in a beaker of hot water as shown in the diagram. Observe the movement of the mercury column. Chapter 3 Temperature and Heat 77 ©Praxis Publishing_Focus On Science
Thermometer Beaker Hot water 2 Take out the thermometer and place cold water in a beaker. Then place the thermometer again in the beaker. Observe the movement of the mercury column again. Observation: Write down what you observe. Discussion: How does the rise or fall of the mercury column relate to its volume? Conclusion: Write down your conclusion. C Expansion and contraction of gases Materials and apparatus: Basin, conical flask, balloon, hot water, ice, glass tube and coloured liquid droplet (i) Procedure: 1 Set up the apparatus as shown in the diagram. Glass tube Coloured liquid droplet Hot water 2 Pour hot water into the basin and leave the apparatus for 5 minutes. Observe what happens to the coloured liquid droplet. 3 Replace the hot water with ice. What happens to the coloured liquid droplet? Observation: (a) The coloured liquid droplet moves when the flask is placed in hot water. Inference: This is because the air in the flask when heated. (b) The coloured liquid droplet moves when the flask is placed in ice. Inference: This is because the air in the flask when it is cooled. Resource 78 ©Praxis Publishing_Focus On Science
(ii) Procedure: 1 Set up the apparatus as shown in the diagram. Balloon Hot water 2 Pour hot water into the basin and leave the apparatus for 5 minutes. Observe what happens. 3 Then, replace the hot water with ice and leave the apparatus for 5 minutes. Observe what happens. Observation: Write down what you observe. Discussion: 1 Based on your observation, why does the balloon’s size change when the apparatus is placed in hot water? 2 Based on your observation, why does the balloon’s size change when the apparatus is placed in ice? Conclusion: Write down your conclusion. 3.4 Heat Capacity Heat is a form of energy. An object becomes hot when it absorbs heat. Heat is measured in joules (J) and it is transferred from a hot area to a cold area. The heat capacity, C of a substance is defined as the quantity of heat required to raise the temperature of the substance by 1°C or 1 K. The unit for heat capacity is J °C-1 or J K-1. It is expressed using the following equation: C = ( Q ) Q = C or where Q is the heat absorbed or released in joules (J) and is the temperature change in °C or K. Specific Heat Capacity Do you know why the body of a cooking pot is usually made of stainless steel? The specific heat capacity of steel is low. It heats up quickly when only a little heat is applied. When cooking food, this can save energy and time. The specific heat capacity, c of a substance is the amount of heat required to increase the temperature of 1 kg of the substance by 1°C. Different substances have different specific heat capacities. Its unit is J kg–1 °C–1. Take a look at the substances given in the table. Chapter 3 Temperature and Heat 79 ©Praxis Publishing_Focus On Science
Substance Specific heat capacity (J kg–1 °C–1) Substance Specific heat capacity (J kg–1 °C–1) Water 4200 Mercury 139 Copper 387 Gold 129 Glass 840 Iron 452 Water has a specific heat capacity of 4200 J kg–1 °C–1. In order to increase the temperature of 1 kg of water by 1°C, 4200 J of heat is needed. 25°C 1 kg water 4200 J heat 26°C 1 kg water 25°C 1 kg copper 387 J heat 26°C 1 kg copper Copper has a specific heat capacity of 387 J kg–1 °C–1. In order to increase the temperature of 1 kg of copper by 1°C, 387 J of heat is needed. Therefore, water needs almost 10 times more heat than copper of the same mass. Remember that heating substances with high specific heat capacities need a lot of heat energy and a longer time to heat up. They also need a longer time to cool down. For example, land heats up quicker than the sea. This is because the specific heat capacity of seawater is greater than that of land. More heat energy is needed to heat seawater up to reach the same temperature increment as land and so it takes longer. Seawater also takes a longer time to cool down. The quantity of heat gained or lost by an object is given as Q = mc where, Q = heat gained or lost in joules, J m = mass of the object in kg c = specific heat capacity in J kg–1 °C–1 θ = change in temperature in °C Example 1 How much energy must be provided to raise the temperature of 2 kg of water from 25ºC to 35ºC? Solution: Mass, m = 2 kg Specific heat capacity of water, c = 4200 J kg–1 ºC–1 Change in temperature, θ = 35 – 25 = 10ºC Q = mcθ = 2 3 4200 3 10 = 84 000 J 80 ©Praxis Publishing_Focus On Science
Example 2 1 kg of water with a temperature of 15ºC is placed in a refrigerator. What is its temperature after 29 400 J of heat has been removed from it? Solution: Mass, m = 1 kg Specific heat capacity of water, c = 4200 J kg–1 ºC–1 Heat removed, Q = 29 400 J Q = mcθ θ = 29 400 1 3 4200 = 7°C Final temperature = 15 – 7 = 8°C Specific Latent Heat When heat is continuously supplied to an object, the temperature of the object will increase. The temperature will increase to a point where it will remain constant. At this point, the object changes its state of matter. When we boil water, the temperature of the water will increase. When it reaches its boiling point of 100°C, the temperature will remain constant. The water changes into steam. The melting point of ice is 0°C. At this point, the ice is melting, turning into water. The temperature remains constant until all the ice has turned into water. The graph below illustrates the temperature changes of when ice is heated against time. Temperature Time 100°C Solid and liquid Liquid and gas Solid Liquid Gas Heat is absorbed by ice (solid) to raise its temperature Heat is absorded by the melting solid without a temperature change Heat is absorbed by the liquid to raise its temperature Heat is absorbed by the boiling liquid without any changes 0°C in temperature. Chapter 3 Temperature and Heat 81 ©Praxis Publishing_Focus On Science
When 1 kg of a substance is melting and boiling, it absorbs heat without an increase in the temperature. The heat absorbed is known as specific latent heat. Therefore, the specific latent heat of a substance is the amount of heat required to change the state of matter of 1 kg of the substance at a constant temperature. Its unit is J kg–1. During melting or boiling, the temperature of the substance does not change even though the heat is being absorbed by the substance. This is because the heat absorbed does not increase the kinetic energy of the particles but is used to overcome the force of attraction between the particles in order to change its state. The quantity of heat gained or lost when a substance changes its states is given by: Q = mL where, Q = heat gained or lost in joules, J m = mass of the object in kg L = specific latent heat in J kg–1 The specific latent heat of vaporisation of a substance is the amount of heat needed to change 1 kg of the substance from the liquid to the gaseous state without any change in temperature. Take a look at the diagram below. The specific latent heat of fusion of a substance is the amount of heat needed to change 1 kg of the substance from the solid to the liquid state without any change in temperature. Boiling at 100ºC Condensation at 100ºC Freezing at 0ºC Releases latent heat of vaporisation Releases latent heat of fusion Absorbs latent heat of vaporisation Melting at 0ºC Steam Water Ice Absorbs latent heat of fusion 82 ©Praxis Publishing_Focus On Science
The table below shows the specific latent heat of some substances. Substance Melting point (°C) Specific latent heat of fusion (J kg–1) Boiling point (°C) Specific latent heat of vaporisation (J kg–1) Water 0 3.36 3 105 100 2.26 3 106 Mercury –39 1.14 3 104 357 2.96 3 105 Gold 1063 6.28 3 104 2808 1.72 3 106 Copper 1083 2.07 3 105 2566 4.73 3 106 In general, the specific latent heat of vaporisation of a substance is greater than its specific latent heat of fusion because: • more energy is required to break the forces of attraction between liquid molecules in order to change into gaseous state. • extra energy is required to overcome the atmospheric pressure. • energy is used to overcome the surface tension of a liquid when its molecules change into the gaseous state. Example 3 How much energy is required to change 0.65 kg of ice into water at 0ºC? Solution: Mass, m = 0.65 kg Specific latent heat of fusion of water, L = 3.36 3 105 J kg-1 Heat needed, Q = mL = 0.65 3 3.36 3 105 = 2.18 3 105 J Example 4 6.78 3 106 J of heat energy is released from a mass of steam at 100°C to produce water at 100°C. What is the mass of water produced? Solution: Specific latent heat of vaporisation of water, L = 2.26 3 106 J kg-1 Heat released, Q = 6.78 3 106 J Q = mL m = Q L = 6.78 3 106 2.26 3 106 = 3 kg Chapter 3 Temperature and Heat 83 ©Praxis Publishing_Focus On Science
3.5 Heat Transfer Heat transfer, whether in the form of heating a kettle of water or in a natural phenomenon such as a thunderstorm, usually involves the transfer of energy from one location to another. Heat flows from a hotter object or place to a cooler object or place. Heat is transferred by three methods: (a) conduction through solids (b) convection by movement of the liquids and gases (c) radiation by emitting electromagnetic wave directly from a source The heat is transferred from the metallic pan to the food through conduction Conduction Conduction is the process of heat transfer from a hotter region to a colder region through solids, such as metals, when in contact. When a metallic pan is heated, the particles at the bottom part of the pan that received direct heat will vibrate more actively. These particles collide with their neighbouring particles and heat transfer takes place to the whole pan and then from the pan to the food in the pan. Most metals are good conductors of heat. Materials that cannot conduct heat such as glass and wood are insulators. Activity 2 Aim: To study how heat is transferred through solids by conduction Materials and apparatus: Iron rod, thumbtacks, Bunsen burner, wax and retort stand Procedure: 1 Stick a few thumbtacks to an iron rod using melted wax at fixed intervals. 2 Heat the rod with the Bunsen burner at position X. Bunsen burner Wooden block Thumbtack Wax Iron rod Retort stand X 3 Observe the thumbtacks to see the order in which they fall off. Observation: Write down what you observe. Discussion: Why is the wooden block used in this activity? Conclusion: Write down your conclusion. Heat transfer by conduction 84 ©Praxis Publishing_Focus On Science
The circulating movement of fluids that rises and falls continuously is known as the convection current. Activity 3 Aim: To study how heat is transferred by convection in liquid Materials and apparatus: 100 ml beaker, Bunsen burner, tripod stand, wire gauze and a small piece of potassium permanganate(VII) Procedure: 1 Fill a large beaker with water almost to the brim. 2 Using a glass rod, place a small piece of potassium permanganate(VII) crystal into the beaker. 3 Heat the water in the beaker slowly and record the direction of the flow of water. Observation: Draw what you observe. Discussion: Explain what happens when the water is heated. Conclusion: Write down your conclusion. Heat transfer by convection Warm air rises Cool air sinks Convection Convection is the process of heat transfer from a hotter region to a colder region by movement of a heated fluid, such as liquid or gas. When a fluid is heated, the hotter fluid expands, becomes less dense and rises whereas the colder fluid becomes denser and goes down replacing the empty space left by the hot fluid. Sea and land breezes develop as a result of convection. Land warms up more quickly than the sea during the day. The air above the land warms up, expands, becomes less dense and rises. The heated air rising above the land is subsequently replaced by cooler air from the sea. Sea breeze is created when cool air from the sea blows inland. At night, when the land loses heat more quickly than the sea, a land breeze develops. Can you describe the formation of a land breeze? Bunsen burner Beaker Water Potassium permanganate(VII) crystal Hot fluids will rise Cool fluids will go down Sea breeze during the day Chapter 3 Temperature and Heat 85 ©Praxis Publishing_Focus On Science
Radiation Radiation is the transfer of heat in the form of electromagnetic waves directly from a hot object. Why do you feel warm after standing in the sun for some time? How do you receive heat from the sun? Heat transfers from the Sun to the Earth by radiation in the form of electromagnetic waves, even though there is empty space (vacuum) in between the Sun and the Earth. Radiation does not require any medium to transfer heat, and this is different from convection or conduction which requires the movement of a medium from one place to another, or the collisions of particles in a medium. Activity 4 Aim: To study how heat can travel through a vacuum by radiation Materials and apparatus: Bell jar, bulb and vacuum pump Procedure: 1 Fix an electric bulb inside a bell jar as shown. 2 Remove the air in the bell jar using a vacuum pump. Then, switch on the bulb. 3 Feel the side of the bell jar by touching it with both hands. 4 Record your observation. Observation: Write down what you observe. Discussion: Why is it necessary to remove the air from the bell jar? Conclusion: Write down your conclusion. Heat transfer by radiation To switch Bell jar Bulb To vacuum pump Heat radiation travels in all directions. Shiny and bright surfaces emit relatively less heat radiation compared to that of dark, dull surfaces. Surfaces that efficiently emit heat radiation also efficiently absorb heat radiation. Science Facts 86 ©Praxis Publishing_Focus On Science
Alternatively, you can carry out the following activity using different materials from Activities 2 to 4. Activity 5 Aim: To show how heat is transferred Materials and apparatus: Copper / Metal rod, cardboard, candle, paper spiral, rice, metal spoon, toothpick, water, thread, stick, Bunsen burner, 250 ml beaker, tripod stand, wire gauze, retort stand with clamp Procedure: Activity A 1 Set up the apparatus as shown in the diagram. Toothpick Wax Retort stand Copper rod Cardboard A B C D E F Bunsen burner 2 Heat the copper rod for a few minutes. What happens to the toothpicks? 3 Record your observations. Activity B 1 Fill a beaker with water until it is nearly full. 2 Put some rice into the water. 3 Heat the water in the beaker by placing a burning Bunsen burner under the beaker in the middle position as shown in the diagram. Rice Hot water Wire gauze Tripod stand 4 Observe the movement of the rice when the water becomes hot. 5 Describe the movement of the rice. Methods of heat transfer Chapter 3 Temperature and Heat 87 ©Praxis Publishing_Focus On Science
Activity C 1 Set up the apparatus as shown in the diagram. Stick Candle Paper spiral Thread 2 Observe what happens to the paper spiral and record it. Activity D 1 Take a metal spoon and expose it to direct sunlight for 15 minutes. 2 Touch the spoon after 15 minutes. What do you feel? Observation: (a) Activity A: The wax and the toothpick one by one starting with toothpick and finally . Inference: Heat is transferred along the copper rod from the heated end to the end. (b) Activity B: The rice moves to the surface and then moves . The movement repeats forming a convection current. Inference: The hot water below becomes dense and rises to the . water on the surface which is denser moves downwards to replace the space left by the hot water. (c) The paper spiral . Inference: The less dense hot air moves and the dense cold air moves to replace the space left by the hot air. (d) The hand feels . Inference: The spoon becomes after receiving from the sun. Discussion: 1 Identify the method of heat transfer that occurs in each of the activities A to D. 2 State the medium where each method takes place. 3 Compare the rate of heat transfer in each method. Conclusion: Write down your conclusion. 88 ©Praxis Publishing_Focus On Science
3.6 Heat Conductors and Heat Insulators Have you ever tried using a metal spoon to stir a pot of boiling soup? You probably know how rapidly heat energy moves from the hot soup through the spoon and into your hand if you have tried it. This is because the metal spoon is a good conductor of heat. A heat conductor is a substance that allows heat to flow through it easily. Metals like silver, mercury, aluminium, lead, cuprum, iron and zinc are good conductors of heat. Good heat conductors become hot easily when heated and become cold easily when cooled. On the other hand, a heat insulator is a substance that prevents or slows down the rate of heat flowing through it. Back to the example given, you will know how much simpler it is to stir hot soup when using a wooden or plastic-handle spoon. This is because neither wood nor plastic conducts heat easily. Non-metal substances like wood, plastic, asbestos, cork, water, air and polystyrene are good insulators of heat. Good heat insulators are substances that take time to become hot when heated and are slow to cool down when cooled. The bottom of an electric iron is made of metal (iron and steel) that can conduct heat to clothes to remove wrinkles. The handle is made of plastic which is a heat insulator, allowing us to hold the iron. Cooking utensils such as pots are usually made from aluminium or steel. They are good conductors of heat so that the heat can be transferred to the food quickly. However, the handle of utensils is made of plastics so that our hands do not get burnt while holding it. Cork mat is a heat insulator that reduces heat loss from the pot to the table by conduction. Chapter 3 Temperature and Heat 89 ©Praxis Publishing_Focus On Science
Activity A Problem statement Which material is the best insulator of heat? Hypothesis Among insulating materials such as glass, plastic and wood, wood is the best insulator of heat. Manipulated variable Type of insulators Responding variable Time taken for cobalt chloride paper to change color Constant variable Size of materials Materials and apparatus Glass rod, wooden rod, plastic rod, cork, cobalt chloride paper and metal trough Procedure 1 Set up the apparatus as shown in the diagram below. Wooden rod Glass rod Plastic rod Hot water Metal trough Cork Cobalt chloride paper Hot water Metal trough Cobalt chloride paper Plastic rod Glass rod Wooden rod (a) Experimental set-up (b) Top view 2 Insert the rods of different insulators (wood, glass and plastic) through corks at the side of the metal trough. Make sure the length of all the rods inside the trough is the same. 3 Place a piece of moist cobalt chloride paper at the end of each rod. 4 Pour boiling water into the trough so that the end of each of the rods is heated at the same temperature. 5 Record the time taken for the pink cobalt chloride paper at the end of each rod to turn blue. Result Type of insulator Time taken for cobalt chloride paper to change colour Wood Plastic Glass Discussion Which material is the best insulator of heat? Why? Conclusion Is the hypothesis accepted? Write down your conclusion. Experiment 1 Investigating different materials as heat insulators 90 ©Praxis Publishing_Focus On Science
Activity B Problem statement Do different materials act as different heat insulators? Hypothesis Different materials act as different heat insulators. Manipulated variable Responding variable Constant variables Materials and apparatus Cotton wool, paper, aluminium foil, hot water, flat-bottomed flasks, hollow rubber stopper, thermometer, retort stand and clamp, and stopwatch Procedure 1 Take four flat-bottomed flasks. Label them as A, B, C and D. Wrap flask A with cotton, flask B with paper, flask C with aluminium foil and flask D without any wrapping. 2 Fill the flasks with hot water to the top. 3 Close flask A with a rubber stopper inserted with a thermometer as shown. Repeat the same for flask B, C and D. 4 Record the initial temperature of water in each flask. Hot water A B C D Thermometer Cotton wool Paper Aluminium foil Hot water 5 Leave the flasks for 10 minutes. Record the final temperature for each of the flatbottomed flasks. Result Temperature (ºC) Flat-bottomed flask A B C D Initial temperature Final temperature Difference in temperature Discussion 1 Why is flat-bottomed flask D left unwrapped? 2 Arrange the three materials in ascending order based on the ability to release heat. 3 Does cotton act as the best heat insulator compared to paper and aluminium? Give your reason. 4 Based on the activity, which material is suitable to make winter coats? Why? 5 A chick gets protection under the hen's wings which are fluffy. Explain how. Conclusion Is the hypothesis accepted? Write down your conclusion. Chapter 3 Temperature and Heat 91 ©Praxis Publishing_Focus On Science
3.7 How Types of Surfaces Affect Heat Absorption and Emission Have you ever wondered why you feel cooler wearing a white shirt on a hot day? This is because brighter-coloured clothes are poor heat absorbers. People choose to wear brightercoloured clothes in hot weather over dark-coloured clothes. Every object absorbs and emits heat. Its ability to absorb and emit heat is determined by the surface type and colour, as well as the surrounding temperature. Let’s carry out experiments to explore this concept. Activity A Problem statement Which surface absorbs heat better? Hypothesis A dark and dull object absorbs heat better than a white and shiny object. Manipulated variable Responding variable Constant variable Materials and apparatus Dark and dull tin, white and shiny tin, laboratory thermometer, Bunsen burner, wooden block and stopwatch Procedure 1 Set up the apparatus as shown in the diagram. Thermometer Black and dull tin White and shiny tin Wooden block 2 Put the two tins at a distance of 10 cm away from the Bunsen burner. 3 Record the initial temperature of air in each tin. 4 Turn on the Bunsen burner. 5 Record the final temperature after 15 minutes. Result Surface of the tin Temperature of air (ºC) Initial reading Final reading Black and dull White and shiny Discussion Based on the result, which tin absorbs heat better? Why? Experiment 2 Investigating heat absorption and heat emission 92 ©Praxis Publishing_Focus On Science
Activity B Problem statement Which surface emits heat better? Hypothesis A dark and dull object emits heat better than a white and shiny object. Manipulated variable Responding variable Constant variable Materials and apparatus Dark and dull tin, white and shiny tin, hot water, laboratory thermometer, wooden block and stopwatch Procedure 1 Set up the apparatus as shown in the diagram. Thermometer Black and dull tin White and shiny tin Wooden block Hot water at 80°C 2 Fill 250 ml of hot water into both tins. 3 Record the initial temperature of water in each tin. 4 Record the final temperature after 15 minutes. Result Surface of the tin Temperature of water (ºC) Initial reading Final reading Black and dull White and shiny Discussion 1 Based on the result, which tin emits heat better? 2 State the characteristics of the object which is a better heat absorber and heat emitter. Conclusion Is the hypothesis accepted? Write down your conclusion for both Activities A and B. Rough surfaces absorb and emit heat more effectively than smooth surfaces. This is because a polished surface is a good reflector and a poor absorber—it has a low emissivity. Science Facts Chapter 3 Temperature and Heat 93 ©Praxis Publishing_Focus On Science