Grade 7 General Science Textbook PDF

General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook Unit 2 MATTER IN OUR SURROUNDING Learning Outcome At the end of this unit, you will be able to: use particles...

General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook Unit 2 MATTER IN OUR SURROUNDING Learning Outcome At the end of this unit, you will be able to: use particles theory‘s postulates to explain properties and behaviour of materials; classify matter as an element, compound, homogeneous mixture, or heterogeneous mixture with regard to its physical properties; describe the structure of solids, liquids and gases in terms of particle separation, arrangement and types of motion. differentiate between physical and chemical properties and changes of matter; appreciate that matter can be classified based on physical or chemical properties; use properties of matter to identify substances and to separate them; demonstrate scientific inquiry skills along this unit: observing, classifying, comparing and contrasting, making mode, inferring, communicating, asking questions, designing experiments, drawing conclusions, applying concepts. Main Contents 2.1. Characteristics and nature of matter 2.2. Physical and chemical properties of matter 2.3 Classification of substances (in terms of composition and observable properties 2.4. Physical and chemical changes of substances 2.5 Separation of mixtures and its application 20  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook Introduction The object around us, called matter, exist in three physical forms or states. These are solids, liquids and gases. For example, water can exist as ice (solid), water (liquid) and steam (gas).The physical state of a given sample of matter depend on temperature and pressure. Energy must be added or removed to change one form or state of substance into another. The idea that matter is made up of tiny particles is called the Particulate nature of matter. Most of the changes that occur in our surrounding are either physical or chemical. A physical change is a change in the form of matter but not in its chemical identity. A chemical change, or chemical reaction, is a change in which one or more kinds of matter are transformed into a new kind of matter. There are two principal ways of classifying matter: by its physical state as a solid, liquid or gas and by its chemical constitution as pure substance and mixture. Mixtures can be separated using a variety of techniques. Some of the methods used to separate mixtures are separation by hand, sieving, filtration, evaporation, magnetic separation, decantation and distillation. 2.1. Characteristics and Nature of Matter After completing this section, you will be able to define matter with examples from day today life; demonstrate that matter is made up of tiny particles; state the postulates of the particle theory of matter; infer the particulate nature of matter from demonstration /investigation; apply particle nature of matter in explaining diffusion and every day effect of diffusion; 21  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook describe and/or make a representation of the arrangement, relative spacing, and relative motion of the particles in each of the three states of matter; describe and explain compression in terms of distance between particles; use the terms melting, evaporating, condensing, and freezing/ solidification to describe changes of state; use the particulate nature of matter to explain: melting, freezing/ Solidification, Evaporation, Condensation. Activity 2.1 Form a group and discuss the following questions and share your ideas with the rest of the class. 1. Describe matter by your own words? 2. Consider the followings: air, light, soil, plant, water, sound, table and heat. Try to classify them as matter and non-matter. 2.1.1. Meaning and Properties of Matter What is matter? Matter is anything that has mass and occupies space. The term mass refers to the amount of matter present in a sample. Matter includes all things both living and nonliving that can be seen (such as plants, water, soil, rocks, table and even this book), as well as things that cannot be seen by our naked eye (such as air and bacteria). Unlike matter, energy is known and recognized by its effect. It cannot be seen, touched, smelt or weighed. Therefore, various forms of energy such as heat, light, and sound are not considered to be matter. Exercise 2.1 1. Classify each of the following as matter or energy (non-matter). a. Air e. Gold i. Silver b. Pizza f. Virus j. Cake c. Sound g. heat k. Water d. Light h. Bacteria l. Magnesium 22  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook 2.1.2 Particulate Nature of Matter. Activity 2.2 Form a group and perform the following activity. Then present your finding to the class. 1. Inflate a balloon and observe its shape in the class room 2. Make observations while wind blowing leaves, or dust in your surroundings. Based on the above activity, work on the given question below a. What do you think that matter is made of? b. How do the particles move around in space The particle model of matter states that all matter is made up of tiny, moving particles with spaces between them. Matter is made of particles too small to be seen that move freely around in space. The inflation and shape of balloon indicates that it is filled with a small particle of gas such as helium, hydrogen, nitrous oxide, oxygen, or air. On other hand, from the effect of wind blowing leaves or dust, it is possible to understand the particle matter is in continuous motion. The idea that matter is made up of tiny particles is called the Particulate nature of matter. Activity 2.3 Perform the following activities Fill in the blank by using the following words {Increase, less, faster, cold, temperature, water, particles, mov- ing, more, energy} 1. Everything is made of ____________. 2. Particles are always__________________. 3. An increase in ____________makes particles move _________. 23  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook 4. An increase in____________ is the same thing as an _________ in energy. 5. The particles in hot water have _________energy than _________water. 6. The particles in ice move ____________ than particles in ___________. 2.1.3 Particle Theory of Matter (Particle Model of Matter) Particulate nature of matter means that all matter is made up of discrete tiny particles. Many years later, scientists came back to Democritus’ idea and added to it. The theory they developed is called the particle model of matter. The followings are main ideas (postulate) in the particle model of matter: 1. All matter is made up of tiny particles. 2. The particles of matter move continuously. 3. The particles have spaces between them. 4. Adding heat to matter makes the particles move faster. 5. There are forces between the particles. 6. Particles of one substance differ from the particles of other substance. Exercise 2.2 I. Give short answers 1. List the postulates of particle theory. 2. Describe the particulate nature of matter. 24  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook 2.1.4. Diffusion Experiment: 2.1 Title: simple experiment on diffusion Objective: To discover what is meant by diffusion Materials and Chemicals: Perfume, ink, beaker, pipette, Water (H2O) Procedure 1. Take a bottle of perfume and open it in one corner of the room and record how long it takes to reach to different students at different distances to smell it. 2. Add 2 or 3 drop ink into a beaker of water using a pipette and watch the ink diffuse to color the water. 3. Record your observation for the above to experment Observation and analysis Write your result/conclusion for the above experiments The mixing and spreading out of a substance with another substance due to the movement or motion of its particles is called diffusion. It is also defined as the net movement of particles from an area of high concentration to an area of low concentration. Diffusion in gases is very fast. This is because the particles move very quickly in all direction. Example: The smell of hot sizzling food reaches us even when we are at considerable distance. Diffusion in liquids is slower that in gas, because the particles in liquids move slower as compared to particles in gases. Example: If a drop of ink is put into a beaker of water, then the color of ink spreads into the whole water of the beaker. Diffusion in solids is very very slow process because the particles of solids are highly restricted to motion. Diffusion in Daily Life Diffusion is everywhere around us in our everyday life. The followings are some common effect of diffusion in day to day activities. 25  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook Tea: A tea bag placed in a cup of hot water will diffuse into the water. Perfume: When perfume is produced in one part of a room, it spreads to the rest through diffusion. There are fewer of the scent-producing chemicals in the further parts of the room, so the molecules naturally spread out. Food Coloring: A drop of food coloring in a glass of water colors the water through diffusion. The dye molecules slowly spread evenly through the liquid, creating one particular shade. Soda: Leave a soda bottle open and the carbon dioxide bubble will diffuse and leave it flat. Air has a lower concentration of that bubbly carbon dioxide than the drink does, so the CO2 molecules depart the beverage and spread into the air. Exercise 2.3 1. Complete the blank space from the word box Diffusion low scent high You can smell deodorant like axe in the classroom after someone sprays it in the hallway because the _____moves from_____ concentration in the hallway to___ concentration in the classroom. This is an example of______ 2. Arrange in an increasing order of the rate of diffusion of solids, liquids and gases. 2.1.5 Properties of Solids, Liquids and Gases Activity 2.4 Copy the table in your exercise book and complete it using objects around you. Discuss your reasons for each decision with your group. Substance solids, liquids and I know this is be gases cause…. Water liquid I can pour it. 26  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook According to Kinetic (particle) theory, all matter is composed of tiny particles (atoms, molecule, and ions).These particles are arranged differently in solids, liquids and gases. Solids In solids, the particles are arranged in fixed pattern. The particles held together strongly and are tightly packed. Particles in solid can vibrate, but, they stay in the same place. Solids have definite shape and definite volume. Examples of Solids are Stones, wood, metals etc. Figure 2.1: pattern of Solids Liquids The particles in a liquid are separated by spaces that are large enough to allow the particles to slide past each other. It takes the shape of its container because the particles can move around more freely than they can in a solid. At room temperature water, ethanol, benzene, oil are liquids. Figure 2.2: pattern of liquids 27  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook Gases The particles in a gas are separated by much larger spaces than the particles in a liquid or a solid. Therefore, a gas is mostly empty space. For example, air, hydrogen, oxygen, carbon dioxide and nitrogen are gases. Figure 2.3: pattern of gas 28  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook Pattern of gas Microscopic view of gases Figure 2.3 pattern and microscopic view of gases Table Table2.1 Properties Properties of solids, of solids, liquids liquids and gases and gases Properties Physical states Gases Liquids Solids Arrangement of -disorderly arranged Less orderly Orderly particles -particles are very far a -Arranged particles arranged(regular apart are relatively close pattern) -almost no attractive to each other Particles are very force between -Have relative close to each other attractive force particles between particles 29 Motion of -flow(move) freely flow together in -Do not flow or move -flow together in random motion -Vibrate in a fixed particles random motion -are known as fluids position -are known as fluids compressibility Highly and easily Compressible to a Not compressible compressible very small extent Volume and shape -Have no definite -Have no definite -Have definite Shape and volume Shape Shape and volume -Assume the shape of -Assume the shape the container and of the container entirely fill it. - have definite volume Density Have very low density -Have low density -Denser than all than liquids and solids than solids -Condensed state than -Condensed state all compared to gases Pressure Exert pressure equally Exert pressure Exert pressure towards in all direction towards depth. gravity Diffusion Diffuse spontaneously Diffuse very slowly Difficult to diffuse in all directions with in random motion random motion Diagram Exercise 2.4 I. Give short answers 1. What is the three state of matter? 29  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook Exercise 2.4 I. Give short answers 1. What are the three states of matter? 2. List the properties of solids 3. Name a property of liquids that do not share with solids 4. Name a property of gas that do not share with liquids 5. Give a characteristic that is the same for liquids and solids 6. Give a characteristic that is the same for gases and liquids 7. Which state of matter can not be poured? 8. Which state of matter can be compressed easily? II. Choose the correct answer for the following questions. 1. Which state of matter is fluid? A. solid B. Liquid C. Gas D. B and C 2. In which state of matter are particles close together? A. solid B. Liquid C. Gas D.all 2.1.6. Changes in State Activity 2.5 Copy the flow chart. The arrows represent the process involved when matter change state. Write the name for each process on the arrow to your flow chart. A B Solid Liquid Gas D C Solid Liquid Gas A change of state is the change of a substance from one physical form of matter to another. A change in physical state is the most common type of physical change. Melting, freezing, evaporation, and condensation are all changes of state. The three states of matter can be interconverted without changing the composition of the substance. To change a substance from one state to another, energy must be added or removed. 30  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook How do solids and liquids change state? When a solid is warmed, its particles gain energy and speed up, and the attraction between them decreases. Eventually they slide past one another. The process in which a solid substance changes into a liquid on heating is called melting (fusion). The process of changing a liquid into a solid is called freezing (solidification). When a liquid is cooled, its particles have less energy, become slow down, and lock into the fixed arrangement of a solid. The temperature at which a liquid substance changes into a solid is the liquid’s freezing point. How do liquids and gases change state? As a liquid is warmed, its particles gain energy. Some particles gain enough energy that they escape from the surface of the liquid and become a gas. The change from a liquid to a gas is called evaporation. The temperature at which a liquid substance changes into a gas is the liquid’s boiling point. As a gas is cooled, its particles lose energy. The attraction between particles overcomes the speed of their motion, and a liquid forms. The change of state from a gas to a liquid is called condensation. How do solids and gases change state? Some solids and gases can change state without ever becoming a liquid. The change from a solid state directly into a gas is called sublimation. Some common substance undergo sublimation are: Iodine, ammonium chloride and solid carbon dioxide (dry ice). 31  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook Deposition is the change in state from a gas directly to a solid. Figure 2.4: Interconversion process of the three state 2.2. Physical and Chemical Properties of Matter After completing this section, you will be able to describe physical Properties; use physical properties of matter to identify substances; conduct experiments to identify properties of substances and make group report; identify chemical properties; distinguish between physical and chemical properties. 2.1.4 Physical properties of matter Activity 2.6 Perform the following tasks in groups and present your conclusions to the class. Given the following physical properties of substances: odor, color, taste, melting point, boiling point and density. 1 Which of these physical properties have constant values under specific condition, such as temperature? 2 Which physical properties can be recognized directly by our sense organs? 32  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook 3 Which of these properties are measured using instruments? 4 What will happen to ice kept in a cup in the classroom? 5. Which sense organs help us to detect color, odor and taste? 6. How do you describe the taste of lemon? Substances are identified by their properties as well as by their composition. A physical property can be measured and observed without changing the composition or identity of a substance. For example, we can measure the melting point of ice by heating a block of ice and recording the temperature at which the ice is converted to water. Water differs from ice only in appearance and not in composition, so this is a physical change; we can freeze the water to recover the original ice. Therefore, the melting point of a substance is a physical property. Other examples of physical property is gold is a shiny yellow metal, lead has a high density. Observations of these characteristics do not change the composition. There are two kinds of physical properties, namely, extensive and intensive physical properties. Extensive physical properties are the properties, which depend on the amount or quantity of sample and they vary from sample to sample. Examples: length, diameter, mass, and volume Intensive physical properties are properties which do not depend on the amount of a substance present. Examples: density, color, melting point, and hardness. Intensive properties are useful in distinguishing between different substances because they do not vary from sample to sample. Some Physical Properties of Substances are Listed Below 1. Physical Properties Detected by Sense Organs Color: The color of a substance results from its interaction with light. Substances can be identified by their colors. For example, chalk is white, water is colorless, and gold is yellow and so on. Odor: refers to the property of a substance perceived by the sense of smell. Terms commonly used to describe the odor of a substance are pungent, fragrant, spicy, fruity and odorless. For example water is odorless, flowers are fragrant, and orange smells fruity. 33  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook Caution! Care has to be taken in smelling substance as they may be harmful Taste: refers to physical properties that can be perceived by the taste buds of the tongue. The taste of a substance is usually described by terms like sweet, bitter, sour, salty, and tasteless. For example honey is sweet, lemon is sour and table salt is salty. Caution! Tasting can be used to identify substances only if the substance to be tasted is not harmful. Activity 2.7 You are allowed to taste some acids in the forms of citric acid that are found in lemon and orange or acetic acid in the form of vinegar at home but you have never been allowed to taste any kind of acids in the laboratory. What is the reason? Discuss your finding in group and present to the class. 2.Physical State: Physical state is the form in which a substance is found under a given conditions such as temperature and pressure. The three physical states of matter are solid, liquid and gas. The same substance may exist in different states at different conditions. For example, water exists in three physical state form as a solid below 0 ºC, as a liquid between 0 oC and 100 oC, and as a vapor or gas above 100 oC. 3. Measurable Physical Properties Measurable physical properties are the properties of a substance that can be measured using an appropriate apparatus. These physical properties have constant values under specific conditions like melting point, boiling point, density and electrical conductivity. 34  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook Melting Point: is the temperature at which a solid substance changes to its liquid state. For example, ice is the solid form of water. Ice melts to liquid (water) at 0°C. Therefore, the melting point of ice is 0°C. Boiling Point: is the temperature at which the vapor pressure of the liquid equals the surrounding atmospheric pressure. At sea level water boils at 100°C. Density: is defined as the mass per unit volume of a substance. It is expressed mathematically as: Mass of substance m Density = or d = Volume of substance V Units of density are kilogram per cubic meter (kg/m3). Electrical Conductivity: Electrical conductivity is the ability of a substance to conduct electricity. This is a physical property mostly characteristic of metallic substances such as copper, aluminum, iron, silver and zinc. 2.1.5 Chemical Properties of Matter A chemical property is a characteristic of a substance that describes the way the substance undergoes or resists change to form a new substance. Chemical properties cannot be determined just by viewing or touching the substance; therefore, the substance’s internal structure must be affected for its chemical properties to be investigated. Flammability is one example of a chemical property. Reactivity between two substances is also another chemical property of matter. 35  substance‘s internal structure must be affected for its chemical properties to be General Science Fetena.net investigated. Grade 7 : Ethiopian No#1 Educational StudentResource Textbook Flammability is one example of a chemical property. Reactivity between two substances is another chemical property of matter. Table 2.2: Comparison between Physical and chemical properties. Physical properties Chemical properties Properties can be measured or observed Properties that describe how a without changing the chemical nature substance changes (or resists change) of the substance. to form a new substance. Easily identified. Cannot be determined just by viewing or touching the substance. The composition or identity of a The substance‘s internal structure must substance not change. be affected for its chemical properties to be investigated. Examples: color, density, volume, Examples :Flammability and reactivity melting. boiling. Conductivity. Exercise 2.5 1. Exercise Classify 2.5 of the following properties as a physical property or each 1. Classify each of the following properties as a physical property or a a chemical property. chemical property. a. Irona. metal rusts Iron metal in inananatmosphere rusts atmosphere ofofmoist moist air.air. b. Mercury metal b. Mercury is is metal a liquid a liquid at roomtemperature. at room temperature. c. Nickel metal c. Nickel dissolves metal dissolvesininacid acid to produce producea light a light green green solution. solution. d. Potassium d. Potassium metal metal has hasa amelting melting point pointofof 63°C. 63°C. e. Copper metal possesses a reddish brown color. e. Copper metal possesses a reddish brown color. f.f. Titanium Titanium metal metalcancan be be drawn into thin drawn intowires. thin wires. g. Beryllium metal, when inhaled in a finely divided form, can produce serious lung disease. h. Silver metal shows no sign of 37 reaction when placed in hydrochloric acid. i. Lead is denser than aluminum. j. Flammability of plastics. 2. Classify each of the following properties as an intensive property or extensive property. a. boiling point b. length c. mass d. Color e. density f. volume g. melting point 36  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook 3. Categorize the following physical properties as physical properties recognized by our sense organs or measurable physical properties a. Density b. odor c. taste d. melting point e. color f. conductivity 2.3 Classification of Substances After completing this section, you will be able to use the particle theory to describe the difference between pure substances and mixtures; differentiate between elements and compounds; classify common elements into metals and non-metals; investigate the properties of metals and non-metals and compile a list of general properties; investigate the properties of non-metals and compile a list of general properties; describe and classify mixtures as homogeneous and heterogeneous. use models/ particles diagrams to show differences between homogenous and heterogeneous; describe the relationship among elements, compounds, mixtures, homogenous mixture and heterogeneous mixtures. Activity 2.8 Perform the following tasks in groups and present your findings to the rest of the class. 1 Conseder the following substances: chalk, bronze, sugar solution, iron, water, milk, oxygen, copper, gold, sugar, table salt, cooking oil, sulfur, air, silver, hydrogen, ink, chlorine and soil. Classify each of them under pure substance or mixture. Among pure substances, state whether it is an element or a compound 37  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook In addition to its classification by physical state, matter can also be classified in terms of its chemical composition into two broad categories: pure substances and mixtures. MATTER Anything that has mass and occupies space PURE SUBSTANCE MIXTURE Only one substance Physical combination of present two or more substances Figure 2.5 Matter falls into two basic classes: pure substances and mixtures. 2.3.1. A Pure Substance A pure substance is a single kind of matter that cannot be separated into other kinds of matter by any physical means. All samples of a pure substance contain only that substance and nothing else. Pure water is water and nothing else. A pure substance always has a definite and constant composition. Some other common examples of pure substances are oxygen, sulfur, copper, silver, gold, sugar, table salt, water and carbon dioxide. Pure substances are classified as elements and compounds. PURE SUBSTANCE Only one substance present ELEMENT COMPOUND Cannot be broken down Can be broken down into into simpler substances by constiiuent elements by chemical,but not physical chemical or physics means means Figure 2.6 a pure substance can be either an element or a compound. 38  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook 2.3.2 Elements and compounds Elements: an element is a pure substance that cannot be broken down into simpler substances by ordinary chemical means. It is composed of only one kind of particle (atoms), which is the smallest particle of an element. At present, 118 elements are known. Among these elements, 92 of them occur naturally on earth while the rest are man- made or artificial elements. Elements might be divided into metals and non-metals. Metals: Many chemical elements are referred to as metals. Some examples of metals are gold, iron, silver, copper, aluminum, sodium and lead. Metals are characterized by the following physical properties They are shiny (lustrous) in nature. They are good conductor of heat and electricity. Their density and melting point is high. Moldable (Malleable): malleability is the ability of a substance to be pressed into sheets when hammered. Ductile: ductility is the ability to be drawn into thin wire. Are solid at room temperature except mercury which is found in liquid state. Figure 2.7: Image of copper, silver & gold Non-metals: non-metal is a chemical element that does not have metallic properties and they are few in number as compared to metals. Carbon, oxygen, sulfur, fluorine and phosphorous are some common examples of nonmetals. 39  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook Activity 2.9 Perform the following activity in groups. Which non-metal is essential for our life? Non metals are characterized by the following physical properties: they exist in two of the three states of matter at room temperature except bromine which exists as a liquid state. they are not shiny (dull appearance), and are non-conductors of heat and electricity they have relatively, low melting points and boiling points. Figure 2.8: Images of carbon and sulfur Table 2.3 Comparison between metals and non-metals. Metals Non-metals These are solids at room temperature These exist in all three states except mercury These are very hard except sodium and potassium These are soft except diamond These are malleable and ductile These are brittle and can break down into pieces These are shiny These are non-lustrous except iodine Electropositive in nature Electronegative in nature Have high densities. Have low density 40  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook Compounds A compound is a pure substance that is made up of more than one type of atom bonded together. A compound can be broken into two or more elements by a chemical means. For example, Water is a compound. By means of an electric current, water can be broken down into the gases hydrogen and oxygen, both of which are elements. The ultimate breakdown products for any compound are elements. Elements can combine with other elements to form compounds. Sodium chloride is formed by the combination of sodium and chlorine elements. Such types of compounds that are formed by the combination of two different elements are called binary compounds. What distinguishes an element from a compound? A compound’s properties are always different from those of its component elements, because the elements are chemically rather than physically combined in the compound. Experiment 2.2 Title: Distinguishing compounds and mixtures. Objective: To investigate the difference between a compound and a mixture. Materials Required: Small bar magnet, iron filings, powdered sulfur, test tube, Bunsen burner, magnifying glass, test tube tong, sand, beam balance, watch glass and test tube made from soda glass tube. Procedure Part I 1. Prepare a mixture containing iron powder and sulfur powder in the ratio 7:4 by mass. Do this by weighing out 7 g of iron powder and 4 g of finely powdered sulfur onto separate pieces of filter paper (or use weighing boats). 2. Mix the two powders by pouring repeatedly from one piece of paper to the other until a homogeneous mixture (by appearance) is obtained. 41  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook Note the appearance of the pure elements and the mixture. 3. Demonstrate that iron can be separated from the mixture by physical means. Do this by bringing one end of a magnet close to the mixture as shown in figure 2.9 Figure 2.9 Separating iron from a mixture of iron and sulfur Questions: i.What did you observe as you bring the magnet close to the mixture? ii. What did you observe under the magnifying glass? Part II 1. Place about 2 g of the mixture into a soda glass tube 2. Insert a plug of mineral wool (mineral fiber) into the mouth of the test tube. Clamp the test tube as shown in the diagram 3.Heat the powder mixture at the base of the test tube gently at first and then more strongly (use a blue flame throughout). Heat until an orange glow is seen inside the test tube. Immediately stop heating. Let the students see that the glow continues and moves steadily through the mixture. 4. Allow the test tube to cool down. 42  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook 5. Once cool, it is possible to break open the test tube to show the appearance of the product, iron (II) sulfide. The test tube can be broken open using a pestle and mortar. It is advisable to wear protective gloves. 6. Take the product formed and powder it. Examine the product under a magnifying glass. Bring a magnet over it. figure 2.10 The reaction between iron and sulfur 2.3.3. Mixtures Activities 2.10 Discuss the following ideas in groups and present your opinion to the rest of the class. 1. Suppose a teaspoon of magnesium filings and a teaspoon of powdered sulfur are placed together in a metal beaker. Would this constitute a mixture or a pure substance? Suppose the magnesium filings and sulfur are heated so they react with each other, forming magnesium sulfide. Would this still be a “mixture”? Why or why not? 2. What is the difference between pure water and a solution of sodium chloride in water? 3. Do you think air is a pure substance or a mixture? Why? 43  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook A mixture is a physical combination of two or more pure substanc- es in which each substance retains its own properties. Components of a mixture retain their identity because they are physically mixed rather than chemically combined. Consider a mixture of small rock salt crystals and ordinary sand. Mixing these two substances changes neither the salt nor the sand in any way. Common mixtures include: Soil- a mixture of different sized particles and plant material. Cooking oil – a mixture of vegetable oils. Ink- contains a mixture of dyes, dissolved in alcohol and water. Milk- contains proteins, carbohydrates, fats, water, minerals. Air- contain oxygen, nitrogen , carbon dioxide. Mixtures are sub classified as heterogeneous and homogeneous. Homogeneous Mixture Activity 2.11 Perform the following tasks in groups and present your findings to the rest of the class. The following substances are given: air, milk, soil, salt solution, brass, chalk, water, cooking oil, gold, silver, sugar solution, Pepsi. Identify which of them are homogeneous mixtures. Homogenous mixtures are a combination of two or more substances that has the same composition throughout and has no visible boundary. A homogeneous mixture also called solution. For example, a mixture of table salt and water (salt solution) is a homogeneous mixture because all the parts of the solution have the same salt-water composition. Homogeneous mixtures (solutions) may exist in one of the three states i.e. solid, liquids and gas. 44  mixture also called solution. For example, a mixture of table salt and Resource water (salt General Science Fetena.net : Ethiopian Grade 7 No#1 Educational Student Textbook solution) is a homogeneous mixture because all the parts of the solution have the same salt-water composition. Homogeneous mixture (solution) may exist in one of the three states i.e. solid, liquids and gas. Table 2.4: state and type of homogeneous mixture (solution) Type of Type homogeneous of homogeneous Common examples mixture(solution) mixture(solution) Gaseous Gas in gas Air, mixture of oxygen and nitrogen Liquids Gas in liquid Soft drinks(Pepsi, Miranda, coca cola),beer Liquid in liquid Alcohol in water Solid in liquid Salt solution, sugar solution Solids Solid in a solid brass (Zn/Cu), Bronze (cu/Sn) Vinegar Steel Sugar solution Figure 2.11 Some common examples of homogeneous mixture Heterogeneous Mixtures Activity Figure 2.11:2.12 Some common examples of homogeneous mixture Perform the following tasks in groups and present your findings to the rest of the class. 46 Consider the following substances: ethanol alcohol, bronze, sugar solution, iron, water, milk, oxygen, copper, gold, sugar, table salt, cooking oil, sulfur, air, silver, charcoal, ink, chlorine and soil. Then identify among the list of substances which are heterogeneous mixture 45  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook Heterogeneous mixtures are a combination of two or more substances that has no uniform composition throughout and contains one or more visible boundaries between the components. The components of a heterogeneous mixture can be identified by our naked eyes or with the help of a microscope or a magnifying glass. For example, a mixture of sulfur and iron filings is a heterogeneous mixture. This is because the sulfur and iron particles remain visible and physically separated. Other Examples of heterogeneous mixture are blood, milk, mixture of sand and water, river water, muddy water, benzene and water, oil and water, dusty air, soil etc. Soup Soil Blood Figure2.12 Figure 2.12:some common examples Some common examplesofofheterogeneous mixtures heterogeneous mixtures Table 2.5: Differences between homogenous and heterogeneous mixtures. Homogeneous mixture Heterogeneous mixture It has a uniform composition It has a non-uniform composition It has only one phase There are two or more phase The constituent cannot be seen easily. The constituent can be seen easily ‗Homo‘ means the same ‗Hetero‘ means different E.g. sugar solution, soft drinks, salt Milk, soil. sand and water, oil and solution, water Exercise 2.6 1. Classify each of the following as a mixture or a pure substance. 46 a. Water b. uranium c. blood d.alcohol e. the oceans f. iron g. table salt  General Science Fetena.net Grade 7StudentResource : Ethiopian No#1 Educational Textbook Exercise 2.6 I Answer the following questions correctly 1. Classify each of the following as a mixture or a pure substance. a.Water b. uranium c. blood d.alcohol e. the oceans f. iron g. table salt h. brass i. hydrogen j. gold k. sugar. l. milk m. honey n. benzene Of the pure substances, which are elements and which are compounds? 2. Define and give four examples illustrating each of the following terms. a. element b. compound c. homogeneous mixture d. heterogeneous mixture II. Choose the best answers for the following questions 1. Which of the following is metallic liquid element at room temperature? A. bromine B. mercury C. sodium D. iron 2. Substance ‘Y’ is hard, lustrous solid which readily conduct heat and electricity. ‘Y’ is likely to be: A.A. air Salt.B. sea B. water Metalloid C. pureC. MetalD.D. water Non-metal brass 3. Which of the following substance make a homogeneous mixture 2.4. Changes around Us: Physical and Chemical Changes with Afterwater? completing this section, you will be able to A. benzene B. oil C. sugar D. sulfur  Describe physical and chemical change 4. Which of the following substances is not a mixture?  Distinguish the physical and chemical changes using their characteristic A. air B. Sea water C. Pure water D. Brass  Conduct some simple activities to show physical and chemical changes and 2.4. Change around Us: Physical and Chemical Changes write group report. After completing this section, you will be able to  Observe and describe physical chemical changes that are important in everyday life. describe physical and chemical change;  Identify useful and harmful physical and chemical changes. distinguish the physical and chemical changes using their Activity 2.13 characteristic; The conduct some followings are simple activities day to day toyour activities in show physical home. Copy andand chemical complete the changes table, and write by identifying group which report; activities represent ―physical change‖ and which one represent observe―Chemical change"physical and describe by giving and reasons for your choice chemical changes that are important in everyday Name of activities life; Physical Chemical identify useful and changesharmful physical and chemical changes. changes Reasons Burning of charcoal 47 Melts of ice  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook Activity 2.13 The followings are day to day activities in your home. Copy and complete the table, by identifying which activities represent “physical change” and which one represent “Chemical change" by giving reasons for your choice Name of activities Physical changes Chemical Reasons changes Burning of charcoal Melts of ice Dissolving sugar in water Fermentation Rusting of nail Evaporation of water Spoilage of food Burning candle Change is happening around us all the time. Changes are classified as either physical or chemical changes. 2.4.1. Physical Change A physical change is a process in which a substance changes its physical appearance but not its chemical composition. A new substance is never formed as a result of a physical change. Figure 2.13 melting of ice 48  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook Melting of ice, Grinding salt, tearing paper into small pieces, Making an iron bar magnetic, evaporation of water, dissolving sugar in water and breaking a stick are common examples of physical changes. 2.4.2. Chemical Change A chemical change is a process in which a substance undergoes a change in chemical composition. Some examples of chemical changes are: Iron nail going rusty, heating magnesium ribbon, burning candle. photosynthesis,fermentation,etc Figure 2.14 burning of candle Experiment 2.3 Title: Rusting of iron. Objective: To investigate the type of change that occurs during rusting of iron Materials and Chemicals: test tube rack, iron nail, test Procedure: 1. Put a few lean shiny iron nails into a test tube containing some fresh tap water. The water contains dissolved air. 2. Set the test tube in a rack. After a few days observe the change that has taken place. Figure: 2.15 rusting of iron 49  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook Observation and analysis 1. What color do you observe on the iron nail? 2. Is the change physical or chemical? Why? 2.4.3 Characterstics of physical and chemical changes Activity 2.14 Discuss the following ideas in groups and present your opinion to the rest of the class 1. List the characteristics of physical and chemical changes you know 2. Compare and contrast the characteristics of physical and chemical changes Characteristics of Physical Change No new substance is formed. The composition of substance is not altered. It is easily reversed by physical means. Energy changes are not necessarily. It is a change in physical property. Characteristics of Chemical change New substances with new properties are formed The composition of substance altered It is accompanied by Energy changes The change is not easily reversed It is a change in chemical property 2.4.4 Useful and Harmful physical and Chemical Changes Activity 2.15 Perform the following tasks in groups and present your findings to the rest of the class. List the important and harmful physical and chemical changes that encounter in our life. a. Important physical changes b. Important chemical changes c. Harmful physical changes d. Harmful chemical changes 50  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook Useful effect of Physical changes Physical changes are useful in the following ways: Evaporation and condensation create water cycle Freezing preserves food, medicine, and other materials Melting, cutting, bending and mould different tools and accessories To get substances in the form, shape or size we want To mix two or more substances together To separate substances from their mixtures Harmful effect of Physical changes Even many physical changes are useful, it may also be harmful in several way: like cutting tree, bad weather condition, oil spills, etc. Useful effect of chemical changes Chemical Changes are useful in the following ways: -Photosynthesis: chemical changes which occur in plants (photosynthesis) produce substances which enable plants to grow We depend on plants for our food. The change which occur in the food we consume are chemical changes. -Energy production: Most of the energy used nowadays, with the exception of wind, water and nuclear energy, is chemical energy. This energy released as heat or electricity when certain chemical change takes place. Food and medicine production, food digestion, fermentation, food cooking, etc. are also some important chemical change in our life to produce new substance. Harmful effect of Chemical changes In contrast to its usefulness, some chemical change has negative impact. For example rusting (rusting of cars, bridges, and ships), souring food, burning of fuel, smoke emission, plastic disposal, dumping of chemicals, etc. are harmful chemical changes in our life. 51  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook Exercise2.7 I Answer the following questions correctly 1.Classify the following as physical changes or chemical changes. a. the cutting of wood b. interaction of food with saliva and digestive enzymes c. The vigorous reaction of potassium metal with water to produce hydrogen gas and potassium hydroxide. d. Straightening a bent piece of iron with a hammer. e. The ignition and burning of a match. f. photosynthesis g. boiling of an egg. h. boiling of water i. dissolution of salt II. Choose the best answers for the following questions 1. Change in size, shape and state of a substance is a____ A. chemical change B. physical change C. cyclic change D. none 2. Which of the following statements is correct? A. Evaporation is a chemical change B. Digestion of food is a chemical change C. Burning of paper is physical change D. all 3. Among the following which one is a physical change? A. Burning of candle B. Fermentation C. Making an iron bar magnetic D. all 2.5. Separation of Mixtures and its Application After completing this section, you will be able to list methods of separation of mixtures; give some specific examples of mixtures that can be eparated by filtration, decantation, simple distillation, magnetic separation and using separator funnel; name apparatuses used in decantation, filtration, simple; 52  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook assemble apparatuses used in decantation, filtration, simple distillation, separator funnel; conduct and report on an investigation that uses physical means such as particle size, density, boiling point, solubility and magnetism to separation; perform simple activities in group, to carry out the separation of mixtures using local materials and write a group report; compare and evaluate the different ways of separating mixtures from products in community. Activity 2.16 Discuss the following questions in groups and present your conclusion to the class 1. Write the common separation methods you know for the following common mixtures from your daily life experiences A. A mixture of Teff and peas B. A mixture of iron filings and sulfur powder C. A mixture of chalk particles in water D. A mixture of cooking oil and water E. Salt solution F. A mixture of alcohol and water G. A mixture of salt and sand H. A mixture of orange, banana and mango 2.5.1. Separation Techniques of Mixture Most of the substances around us exist in the form of mixtures. How- ever, these mixtures can be separated into pure substances using var- ious separation techniques. The process of separating the constituent substances of a mixture by physical methods, taking advantage of the differences in their physical properties is called separation process. Some of the methods used to separate mixtures are Separation by hand, sieving filtration, evaporation, magnetic separation, decantation and distillation. 53  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook Note that the methods for the separation of mixtures into their components depend on the differences in the size, magnetic property, melting point, boiling point, solubility, etc. of the components. We will discuss some of the methods that are used to separate the components of mixtures. I. Magnetic Separation Magnetic separation is used to separate magnetic and non-magnetic substances in a mixture. For example, if sand is mixed with iron filings the mixture is heterogeneous. To separate the iron filings from the sand, you can use a magnet. The iron filings (magnetic component) are attracted by the magnet, while the sand is not attracted. b a Figure 2.16 (a) the mixture contains iron fillings and sand. (b) A magnet separates the iron fillings from the mixtures. Experiment 2.4 Title: Separation of mixture using bar magnet Objective: To separate a mixture of iron fillings and sand Apparatus and chemicals Magnetic bar, Iron fillings, Sand, Petri dish/ plastic plate/bowl Plastic bag/wrapper, Spatula Experimental Procedure 1. Mix the sand with the iron filings in the plastic plate. 2. Wrap the plastic bag around the bar magnet 54  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook 3. Suspend the bar magnet over the plate 4. The iron would be collected / attracted to the surface of themagnetic bar 5. Carefully remove the plastic bag around the magnetic bar and scrape off the iron filings Figure 2.17 mixture of sand and iron fillings Observation and analysis 1.Why was the sand not attracted by the magnet? What can you conclude from this experiment? II.Decantation What type of separation method is used to get a cup of clear coffee as it is poured from coffee pot (“jebena”) as shown in Figure 2.18? Figure 2.18: Separation by decantation 55  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook Decantation is the process of separation of liquid from solid and other immiscible (non-mixing) liquids, by removing the liquid layer at the top from the layer of solid or liquid below. The process can be carried out by tilting the mixture after pouring out the top layer. This process can also be used to separate two liquids that do not mix with each other like cooking oil and water. When we leave the mixture of cooking oil and water, two separate layers are formed, where water at the bottom and oil, being lighter, at the top. We can remove the oil layer from the top by pouring it into another vessel, which leaves us with the water layer at the bottom. Figure 2.19: Decanation of solid from a solid-liquid mixture Separating funnel: When two liquids do not mix, they form two separate layers and are known as immiscible liquids. These two liquids can be separated by using a separating funnel. A separating funnel is a special type of glass funnel, which has a stop-cock in its stem to regulate the flow of liquid. It will separate the immiscible liquids into two distinct layers depending on their densities. The heavier liquid forms the lower layer while the l ighter one forms the upper layer. Remove the stopper and open the tap to run the lower layer into a beaker. You will be left behind with Figure 2.20: Separation of just the upper layer in thefunnel. immiscible liquids using separating Collect this liquid into funnel 56  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook another beaker. Examples: Kerosene and water mixture is separated by using separating funnel method. This method is also used to separate oil and water. III. Filtration: Filtration is a process by which insoluble solids can be removed from a liquid by using a filter paper. A filter paper is a special type of paper which has pores that are tiny enough to let only liquids pass through it. If you pass a solution through filter paper, any undissolved solid particles will get left behind on the paper whereas the liquid will filter through. The liquid that passes through is called Figure 2.21: Filtration the filtrateand the undissolved solid particles are called residue. Example: A mixture of chalk powder and water, soil and water, sand and salt solution, etc. can be separated by this method. In practical application, filtration is a key step in the purification of the tap water you drink. Iv. Evaporation Activity 2.17 Perform the following activity. Dissolve sodium chloride (or any other soluble salt) and water to form a homogeneous mixture (solution). How can you recover the salt again? Figure 2.22: Evaporation of a solution Evaporation is a method used to separate a soluble solid from a liquid in a solution or the process. of vaporizing the solvent to obtain the solute. It is used to separate a mixture containing a non-volatile, soluble solid from its volatile, liquid solvent. We can separate salt from a solution by evaporating the water from the solution. 57  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook. V. Distillation: This method is used for the separation of a mixture containing two miscible liquids that boil without decomposing and have a large difference between their boiling points. It is also used in obtaining pure water from salt solution. Process of conversion of a liquid into vapor by boiling, and then re-condensing the vapor into liquid is called distillation. In simple distillation, a mixture is heated and the most volatile component vaporizes at the lowest temperature. The vapor passes through a cooled tube (a condenser), where it condenses back into its liquid state. The condensate that is collected is called distillate. Figure 2.23 show the simple distillation set up Figure 2.23: simple distillation set up A mixture of two miscible liquids can also be separated by simple distillation. Liquids which mix with each other to form a solution are called miscible liquids. The mixture of alcohol and water, benzene and oil are some examples of miscible liquids. Consider a mixture of alcohol and water. Ethanol, which is an alcohol boils at 78°C, and water boils at 100°C. When the mixture is heated, the alcohol, which has the lower boiling point vaporizes more rapidly than the water. The vapor of alcohol passes through the condenser and then collected as a distillate in the receiver. 58  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook Activity 2.18 Perform the following tasks in groups and present your conclusion to the class. The following mixtures can be separated using a combination of separation techniques. Mention all the possible separation techniques. i Mixture of salt, sand and water ii Mixture of common salt, iron filling and salt iii Mixture of oil, water and sand iv sugar and clay Is one separation method enough when salt and sand is mixed with water? Sometimes to separate such mixture may require combination of two or more techniques. For example, a mixture of common salt and sand can be separated by using the process of dissolving, filtra- tion and evaporation. The first stage of separation is adding water to the mixture. The salt dissolves in water and forms a solution, but not the sand. Then by using filtration, the sand can be separated from the salt solution. Finally evaporation of the filtrate will cause the water to escape leaving the salt behind. Activity 2.19 Perform the following tasks by asking your parents/guardians / grandparents/elders in the neighborhood on the separation tech- niques used in daily lives. Prepare a table of such activities of daily life in which sedimentation, decantation, filtration and evaporation are used/occurs. Then present your findings to the whole class. 59  Perform Science General Fetena.net the : following Ethiopian Grade 7 tasks No#1 by asking your parents/guardians StudentResource Educational Textbook /grandparents/elders in the neighborhood on the separation techniques used in daily lives. Prepare a table of such activities of daily life in which sedimentation, decantation, filtration and evaporation are used/occurs. Then present your 2.5.2. Application findings of Separation Techniques. to the whole class. Table 2.5 application of various separation techniques No. Physical process Application Filtration  River water is potable  Separation of honey from its comb Evaporation  Common salt is obtained from sea water on large scale. Distillation  Alcoholic beverage such as whisky, gin, brandy, areki are manufactured. Magnetic separation  To separate iron and steel from non –magnetic objects such as, glass, plastic, aluminum, etc. Sedimentation followed by  Drink homemade coffee, tella decantation 62 Project Work Separation of mixtures using local materials There is a mixture of table salt, sulfur powder and iron filing inside a beaker. By using any local materials that are found around you, you should try to separate this mixture into their components. Hint: Both sulfur powder and iron filing are insoluble in water whereas sodium chloride (table salt) is soluble in water. Write a group report: In your report indicate the separation techniques and the materials used during the separation processes. 60  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook Exercise 2.8 I. Give short answers for the following questions. 1. How would you separate the following? a. salt solution b. Common salt and sand c. iron and charcoal d. Oil, water and sand e. nitrogen and oxygen 2. Name the separation technique shown in the following diagram A B C D E F 61  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook Key Terms Matter Magnetic Separation Physical Changes Particle Theory Decantation Compounds Diffusion Pure Substance Elements Physical Property Mixture Distillation Chemical Property Non Metal Evaporation Homogeneous Heterogeneous Filtration Mixture Mixture Sublimation Density Freezing Boiling Point Freezing Point Unit Summary Matter is anything that has mass and occupies space. It can exist in three states: solid, liquid, and gas. The idea that matter is made up of tiny particles is called the Particulate nature of matter. Particle theory of matter tell us the particles of matter are always moving. Diffusion is the mixing and spreading out of a substance with another substance due to the movement or motion of its particles. The three states of matter (solids, liquids and gases) can be interconverted without changing the composition of the substance. to change a substance from one state to another, energy must be added or removed. Melting, freezing, evaporation, and condensation are all changes of state. A physical property can be measured and observed without changing the composition or identity of a substance. A chemical property is a characteristic of a substance that describes the way the substance undergoes or resists change to form a new substance. Matter can be classified in terms of its chemical composition into two broad categories: pure substances and mixtures pure substances. 62  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook A pure substance is a single kind of matter that cannot be separated into other kinds of matter by any physical means. Pure substances are classified as elements and compounds. An element is a pure substance that cannot be broken down into simpler substances by ordinary chemical means. A compound is a pure substance composed of two or more elements that are combined chemically in a definite proportion by mass. A mixture is a physical combination of two or more pure substances in which each substance retains its own properties. A homogeneous mixture (also known as solution) has a uniform composition and properties throughout. Heterogeneous mixture is a mixture that does not have a uniform composition throughout. Changes are classified as either physical or chemical changes. A physical change is a process in which a substance changes its physical appearance but not its chemical composition. A chemical change is a process in which a substance undergoes a change in chemical composition. Mixtures can be separated using a variety of techniques. The process of separating the constituent substances of a mixture by physical methods, taking advantage of the differences in their physical properties is called separation process. Some of the methods used to separate mixtures are Separation by hand, Sieving Filtration, evaporation, magnetic separation, decantation and distillation 63  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook Review Exercise Part I. Write ‘True’ for the correct statements, and ‘False’ for the wrong statements. 1. Depending upon the temperature, water can exist in solid, liquid or gas states. 2. A gas has neither a definite volume nor a definite shape. 3. Dust, smoke, bacteria, air born viral particles are components of particulate matter. 4. Elements can be further decomposed by ordinary chemical means. 5. Heterogeneous mixture contains one phase. Part II: Choose the corect answers for the following questions 1. All of the followings are matter except A. plant B. stone C. air D. sound 2. Which of the following decrease during the phase (state) changes of Solids liquids gases A. Degree of order among particles B. Energies of particles C. Speed of particles D. Distance among particles 3. Which of the following is not the property of solids A. Solids have little tendency to diffuse B. Solids are extremely difficult to compress C. Solids are fluids D. Solids have definite volume and definite shapes 4. The particular physical state of substance depends on _ A. temperature B. pressure C. strength of intermolecular force D. all 5. Which of the following has no definite shape and volume? A. Water B. carbon dioxide C. iron D. gold 64  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook 6. The interaction of substance with light results A. taste B. odor C. color D. texture 7. Which of the following is not a physical change? A. sublimation of iodine C. tearing a piece of cloth B. burning of wax in a candle D. dissolving sugar in a tea 8. All of the following are heterogeneous mixtures except A soil C. salt solution B. mixture of water and oil D. blood 9. Which of the following is not a metal A. iron B. sulfur C. copper D. sodium 10. Which of the following has variable composition? A. Water B. salt C. milk D. silver 11. A mixture of sand and sugar can be separated by A. evaporation followed by distillation B. filtration followed by evaporation C. dissolution followed by filtration and evaporation D. dissolution followed by evaporation and filtration. 12. the conversion of a vapor directly to solid without passing through a liquid state is called___________ A. fusion B. evaporation C. sublimation D. deposition 13. Distillation is used in the process of preparation of A. coffee B. areki C.tella D. honey 14. Identify the heterogeneous mixture among the following A. sea water B. blood C. bronze D. air 15. Grade 7 students in a certain school were given the task of separating, iron fillings, sand and salt. Which of the following process is the most appropriate order? A.Evaporation-dissolution - filtration- magnetic separation B. Dissolution –magnetic separation - filtration_ evaporation C. Magnetic separation -dissolution - filtration –evaporation D. Magnetic separation - dissolution – evaporation- filtration 16. I. Physical changes are easily reversible. II. Physical change do not produce new substance III. Physical change do not involve change in mass. 65  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook Which of the above statement are correct? A.I B I and III C.II and III D. I, II and III 17. Which two state of matter are fluids? A. Solid and liquid C. Liquid and gas B. Solid and gas D. Plasma and solid 18. All of the following are same process. EXCEPT A. Condensation C. Crystallization B. Freezing D. Solidification Part III: Match the items in column ‘A’ with items in column ‘B’ A B 1. Melting (fusion) A. process of changing liquid to gas 2. Evaporation B. process of changing liquid to solid 3. Sublimation C. Process of changing solid to gas 4. Freezing D. Process of changing gas to solid 5. Deposition E. process of changing gas to liquid 6. Condensation F. Process of changing solid to liquid Part IV; Fill in the blanks with appropriate terms. 1. Immiscible liquids can be separated by using_________ 2. Separating a solid from a solution by cooling is______ 3. The separation technique that involves heating a solution until the liquid changes into a gaseous state, leaving behind a solid is known as____ 4. When rain falls, this is because the water vapor in the clouds is condensing into liquid _________? 5. I put dirty water into a funnel with a paper lining. Clean water comes out of the funnel into my beaker, and solid dirt gets left behind on the paper. This is an example of___________. Part V: Give short answer to the following questions 1. What is diffusion? 2. Why do solids have fixed shape and volume? 3. Write the difference between extensive and intensive physical properties. 66