Grade 7 General Science Textbook PDF

Fetena.net : Ethiopian No#1 Educational Resource General Science Student Textbook Grade 7 Fetena.net : Ethiopian No#1 Educational Resource Take Good Care of This Textbook...

Fetena.net : Ethiopian No#1 Educational Resource General Science Student Textbook Grade 7 Fetena.net : Ethiopian No#1 Educational Resource Take Good Care of This Textbook This textbook is the property of your school take good care not to damage or lose it. Here are 10 ideas to help take care of the book 1. Cover the book with protective materials, such as plastic , old newspapers or magazine. 2. Always keep the book in a clean dry place. 3. Be sure your hands are clear when you use the book 4. Do not write on the cover or inside pages. 5. Use a piece of paper or cardboard as a bookmark. 6. Never tear or cut out any pictures or pages. 7. Repair any torn page with paste or tape. 8. Pack the book carefully when you place it in your school bag. 9. Handle the book with care when passing it to another person. 10. When using a new book for the first time, lay it on its back, open a few page at a time. Press lightly along the bound edge as you turn the pages. This will keep the cover in good condition. General Science : Ethiopian No#1 Educational Fetena.net Student Textbook Resource GRADE 7 General Science Student TextBook General Science Grade 7 Student Textbook Authors: Goshu Asab (M.Sc.) Michael Getachew (M.Sc.) Andualem Beka (B.Sc.) Editors and Evaluators: Getahun Getachew (BEd) Muluneh T/Birhan (BEd) Ali Kemal (MEd) Team Leader Getachew Talema (MA) Illustration and Layout Design TMS Addis Ababa City Administration Education Bureau General Science Fetena.net Student Textbook : Ethiopian No#1 Educational Resource GRADE 7 General Science Student TextBook Table of Contents page number Unit 1: Basic Concepts of Science.......................................................... 1 1.1.The Nature of Science and its Branches................................................... 2 1.2. Common Laboratory Equipment, Uses, Safety Rules and Procedures in Science Laboratories.........................................................12 Review Exercise.............................................................................................10 Unit 2: Matter in Our Surrounding..................................................... 20 2.1. Characteristics and Nature of Matter................................................... 21 2.2. Physical and Chemical Properties of Matter....................................... 32 2.3. Classification of Substances.................................................................37 2.4. Changes around us: Physical and Chemical Changes..........................47 2.5. Separation of Mixtures and its Application..........................................52 Review Exercise............................................................................................64 Unit 3: Elements, Compound and Chemical Reaction..................................67 3.1. Elements and their representation.........................................................68 3.2. Compounds and their representation.....................................................71 3.3. Simple chemical reactions and equations............................................. 80 3.4. Uses Of Chemical Reactions in Every Day Situation........................... 88 Review Exercise........................................................................................... 91 Unit 4: Cell as the Basis of Life.......................................................................93 4.1. Microscope...........................................................................................94 4.2. Cell.....................................................................................................103 Review Exercise...........................................................................................118 Unit 5: Living Things and Their Diversity....................................................121 5.1. Living Things.......................................................................................122 5.2. The kingdom of life..............................................................................131 Review Exercise...........................................................................................150 Unit 6: Earth in Space................................................................................... 154 6.1. Shape and Dimensions of the Earth.....................................................156 6.2. Parts of the Earth (Body and Atmosphere)..........................................164 6.3. Earth’s movements...............................................................................171 6.4. Earth System and Cycles.....................................................................176 Review exercise.................................................................................184 Addis Ababa City Administration Education Bureau i  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook Unit 7: Motion, Force, Energy And Energy Resources..............................188 7.1. Definition and Types of Motion............................................................190 7.2. Definition of Force and Gravitational Force.........................................194 7.3. Effects of Force.....................................................................................199 7.4. Measuring Forces..................................................................................202 7.5. Definition of Energy.............................................................................204 7.6. Forms and Conversion of Energy..........................................................205 7.7. Energy Sources......................................................................................208 7.8. Wise use and Conservation of energy....................................................210 7.9. Resource Depletion and Environmental Degradation............................212 Review Exercise.................................................................................... 216 ii  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook c 2021 by Addis Ababa Education Bureau While every attempt has been made to trace and acknowledge copyright, the authors and publishers apologies for any accidental infringment where copyright has proved untraceable. Acknowledgement Above all, Ato Zelalem Mulatu, AAEB Head, should receive the most acknowledgements for his outstanding leadership from the outset to the end of the Textbook and Teacher’s guide preparation. Just to mention his chief roles but a few: he generated valuable ideas, shared his vast experience during most panels, initiated and convinced his conviction to all stakeholders that the Addis Ababa City Government School teachers have to take the lion’s share in the Textbook and Teacher Guide development. His unabated inspiration and urge to the team for diligence, deep sense of patriotism, synergy and true professional ethics has been energy to all actors partaking in the task. The next bottom-heart gratitude has to be extended to the following management members of the bureau: Ato Admasu Dechasa, Deputy Head of the Curriculum Division, Ato Dagnew Gebru, Deputy Head of the Education Technology, Ato Samson Melese, deputy Head of Teacher Development Division, W/ro Abebech Negash, Bureau Head Advisor, Ato Desta Mersha, Bureau Technical Advisor and Ato Sisay Endale, Head of Education Bureau Office. Members of the AAEB management, have to be commended for their painstaking efforts in addressing instantly each issue of challenge, reviewing all drafts and providing immediate feedbacks. Without their unreserved devotion, the timely and successful realization of this huge work would not have been possible. The Last deepest acknowledgement needs to go to the school principals for allowing the textbook writers to be free of their regular job of teaching and to focus on the material preparation. Moreover, their earnest and consistent moral support deserves special words of praise. iii  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook Unit 1 BASIC CONCEPTS OF SCIENCE Learning Outcomes At the end of this unit, you will be able to: define science as a body of knowledge and the processes and practices used to add to that body of knowledge; describe the main branches of science and explain their relationship relate how science and technology affect one‘s beliefs, practices and ways of thinking; appreciate the contributions of outstanding scientists to science and technology; discuss the importance of scientific values in decision making and problem solving; identify the significant contributions of Ethiopian Scientists in science and technology; identify different laboratory tools; demonstrate safe ways of using apparatus in the laboratory; practice precautionary measures in the laboratory; exhibit knowledge of laboratory safety rules and procedures; identify potential hazards and implement appropriate safety procedures when working in the laboratory. 1  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook Main Contents 1.1. The Nature of Science and its Branches - Definition of science - Branches of science - Science and technology - Scientists and ethical discipline 1.2. Common Laboratory Equipment, Uses, Safety Rules and Procedures in Science Laboratories - Common Laboratory Apparatus - Laboratory Safety Rules - Science Laboratory safety symbol and hazard signs, and meanings resources - Steps to write Laboratory report 1.1 The Nature of Science and its Branches By the end of this section you should be able to: Define science; Distinguish between the Indigenous Science and Conventional Science; Describe the main branches of science and explain their relationship; Relate how science and technology affect one‘s beliefs, practices, and ways of thinking; Appreciate the contributions of outstanding Ethiopian scientists to science and technology; Discuss the importance of ethical disciplines in scientific investigations; Solve the issue of environmental problems in their school compound and its surroundings. 2  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook Introduction In the lower grades, you have learnt about science in general. For example, environmental science. In this and next grade you will learn about general science which deals with things related to your day to day life. Activity 1.1 Form a group and discuss the following questions. Then share your ideas to the classmates i. Describe science by your own words ii. Investigate the ways in which the major areas of science are further divided. You can use reference books and the internet to augment your current ideas iii. Differentiate Conventional Science and Indigenous Science The word science comes from the Latin word ‘Scientia’, which means’ Knowledge’. But science is not just about having knowledge: Science is a systematic method of gaining knowledge about the physical and natural world and the social aspect of human society. It provides an ordered way of learning about the nature of things, based on observation and evidence. Science can be indigenous or conventional. Indigenous science is process by which indigenous people build their empirical knowledge of their natural environment. It is knowledge based on the social, physical and spiritual understandings. Conventional science is the system of knowledge which relies on certain laws that have been established through the application of the scientific method to phenomena in the world around us. 3  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook Indigenous Science incorporating local people‘s knowledge and indigenous perspectives, while conventional scientific approaches are commonly recognized as Western science. Activity 1.2 Perform the following activities. Find some practical indigenous knowledge in your community that solves community problems and present your finding to your class Why Do You Learn Indigenous Knowledge In Science? There are two main reasons to include Indigenous Knowledge in the science: firstly, to increase awareness of original culture and identity and secondly, to integrate indigenous knowledge with western science. Ethiopia is one of the countries where a wide variety indigenous knowledge practiced for a long time to solve practical problem that exist in different areas like: extractions of medicinal chemicals from plants to treat disease and fight infections. The common medicinal plants used for treating and curing various disease are: Hagenia Abyssinica (Kosso tree) , Eucalyptus globulus (bahrzaf), and Ocimum lamiifolium Hochst (Damakese)etc preserving meat by adding a salt and smoke drying. 1.1.2. Branches of Science Activity 1.3 Form a group and discuss the following questions. Then share your ideas to the class 1.What are the major branches of science? 2. Give short descriptions of physics, Chemistry and Biology. 4  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook Science has two major categories, which are natural science and social science. Natural science is the study of nature and natural laws. It includes fields such as Chemistry, Biology and Physics. Science Natural science Social Biology Chemistry Physics Figure 1.1. Branches of science Biology is a branch of natural science which studies about living things. Chemistry is a branch of natural science which deals with the properties, composition, structure and transformation of substances. Physics is the branch of natural science. It is the study of the nature of matter, energy and their interactions. There is no clear boarder line between the different branches of natural sciences. Knowledge of natural sciences overlaps with each other. For example, Chemistry and Physics knowledge are studied as a subject called physical science/physical chemistry. It is the study of properties of materials and their interaction. ◊ Biopysics: a combination of Biology and Physics. It is the study of physical phenomena and physical processes in living things, on scales spanning molecules, cells, tissues and organisms. 5  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook ◊ Biochemistry: combination of biology and Chemistry. It is the branch of science that explores the chemical processes within and related to living organisms. It involves the study of chemical reaction in living things. l Biophysics Physics Biology Natural Science Chemistry Physical Chemistry Biochemistry Figure1.2.The relationships between some fields of Natural Science Exercise 1.1 I. Give short answer for the followings questions 1. What is science? 2. List the three branches of natural science 3. Which field of science studies about matter and energy? 4. What is the difference betwen biophysics and biochemistry? 1.1.3. Science and Technology You have already discussed what science is. Now, you will see what a technology is. Technology is the use of scientific knowledge to help human beings work easier and live better as well as enjoy their environment more. It includes the use of materials, tools, techniques, and sources of power to make life easier, more pleasant and work more productive. 6  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook Things such as automobiles, TV sets, radio, bulb, microchip, computer, airplane and home tools (appliances) are the products of technology. Key words Science is a systematic method of gaining knowledge about the physical and natural world. Technology is the use of scientific knowledge to help human bings work easier and live better or putting scientific knowledge intopractice. A person who studies technology is called a technologist. Technologists apply Science and mathematical knowledge and skills to produce a very useful tool. Figure 1.3 Relationship of science and technology Science and technology is integrally connected; but they are different fields driven by different concepts and processes. Science generates knowledge for its own sake, in order to propose and test explanations. Technology, on the other hand, develops human-made solutions to real-world problems. Of course, when science uses technology to generate knowledge, technology uses scientific knowledge to generate solutions. 7  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook Uses of Science and Technology for the Society Science and technology plays an important role in our daily life. They mainly concerned with the production of new materials of desirable properties and qualities to satisfy social needs.They play an important role in agriculture, in production of medicines and drugs, in environment and population control, in construction industry, in manufacturing various products such as cosmetics, textiles, dyes, soaps and detergents, plastics, rubber and a variety of metals, non- metals, alcoholic beverages, dry cells and car batteries, etc. 1.1.4. Scientists and Ethical Discipline Famous Scientists in the World and Ethiopia A scientist is someone who systematically gathers and uses research and evidence, to make hypothesis and test them, to gain and share understanding and knowledge. Some of the world and Ethiopian scientists and their contribution are listed below. Marie Curie (1867-1934), Isaac Newton (1643-1727) Michael Faraday Albert Einstein (1879- won the Nobel Prize for discovered the laws of (1791-1867),discovered 1955) Developed special the discovery of the motion and law of gravity. the generation of relativity theory elements polonium electricity from and radium magnetism. He built the 1st dynamo. Fig1.4 Some World known scientist and their works 8  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook Activities 1.4 Form a group and do the following activity Choose one of the scientists and create a role-play for the press release following the news of his/her discovery. Various roles to consider would include: the scientist; media; fellow scientists; and the general public. Alternatively, you could choose an Ethiopian scientist and create a cartoon strip showing their discovery. Dr.Aklilu Lemma(1935-1997) made his most important scientific discovery very early in his career, in 1964, when he discovered a natural treatment to schistosomiasis,also known as snail Prof.Yalemtsehay Mekonnen fever disease or bilharzia. He found that was born in Asela, Ethiopia on berries from the endod plant, which is May 30, 1955. She work on commonly used to make soap and sham- human physiology, the impact poos in many parts of Africa, is a potent, of pesticides on human health, inexpensive and safe molluscicide, to the use of plants as medicinal prevent the spread of the parasitic worm. against human and animal This discovery made the plant an object of disease and as the first female scientific research in many parts of the world. professor of Addis Ababa university. 9  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook Gebisa Ejeta (born 1950) Dr. Tewolde Berhan Gebre Egziabher is an Ethiopian plant breeder, is an Ethiopian scientist, who has geneticist and Professor at Purdue worked to ensure biodiversity and the University. In 2009, he won the rights of communities to their genetic World Food Prize for his major contributions in the production of resources. sorghum. Fig1.5 Some Ethiopian known scientist and their works Ethical Principle in Science Activity 1.5 Form a group and discuss on the following questions then present your opinion to the class i. Do you think ethical discipline is important for science? ii. List down some ethical disciplines in science Ethics is an integral part of science. Like science, it requires to be consistent and empirically justified in our interpretation the action of scientists. Things are always get in front of us either right or wrong, good or bad, but we have to decide that what we actually want to do through our ethical point of view. The following lists are some of ethical principles that various codes address in science: 10  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook Honesty Responsibility Objectivity Openness Competence Legality Non-Discrimination Carefulness. Exercise 1.2 Choose the best answers for the following questions. 1. The natural science disciplines are A. interacting C. interrelated B. overlapping D. all of the above 2. The branches of natural science studying the composition of compounds and the processes taking place in organisms, respectively, are: A. Chemistry and Biology C. Biology and Physics B. Physics and Geology D. Biology and Geology 3. Which one of the following is true about Science? A. It is the study of physical and natural world. B. It comes from Latin word “Scientia meaning ‘knowledge’ C. It is the system of acquiring knowledge based on scientific method. D. All are correct 4. Which one of the following is true about Indigenous knowledge? A. It is based on scientific method. B. The knowledge derived from western countries. C. It incorporates local people’s knowledge. D. It has universal perspective and commonly recognized as western science. 5. Which one of the following is the World famous scientists who discover law of motion and gravity? A. Michael Faraday B. Marie Curie C. Isaac Newton D. Albert Einstein 11  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook 1.2 Common laboratory Equipment, Uses, Safety Rules and Procedures in Science laboratories At the end of this topic, students will be able to:- Identify different laboratory tools (such as Balance, Beaker; Tongs, Bunsen burner, Test tubes, Petri dishes, etc.), and describe their uses; Prepare some laboratory equipment/tools from locally available materials; Demonstrate knowledge of lab safety rules and procedures; Practice precautionary measures in the laboratory; Identify potential hazards when working in the laboratory; Implement appropriate safety procedures when working in the laboratory; Demonstrate the appropriate use of personal protective equipment for a given laboratory activity. 1.2.1. Common Laboratory Apparatus Activities 1.6 Form a group and perform the following task. From locally available materials produce laboratory tools such as beaker, measuring cylinder, balance, tong, etc. and present its use to the class. Laboratory equipment comprises different sets of apparatus, which are designed to perform various tasks in the laboratory by students, teachers and scientists. The students can conduct laboratory work smoothly and more efficiently only when they are familiar with the apparatus commonly used in the laboratory. Some laboratory apparatus are shown in table 1 below. 12  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook Table 1 Different laboratory tools and their use Name Picture Uses Triple-beam Obtaining the mass of an balance object Beaker Holding water (also used to heat liquid Tongs Transporting a hot beaker; and removing lid from crucible Thermometer Used to measure temperature Test tubes Holds small amounts of liquids for mixing or heating. Petri dish To grow and count bacteria Graduated Marked with milliliter (ml) cylinder scale and is used to measure volume Bunsen burner Heating (flame-safe) contents in the lab Key words Laboratory equipment refers to the various tools and equipment used by students, teachers and scientists working in a laboratory. Laboratory report explains what you did in experiment, what you learnt and what the result mean 13  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook Project work Prepare laboratory tools Dear students, prepare some laboratory equipment’s or tools such as beaker, measuring cylinder, balance, tongs, etc. from locally available materials 1.2.2 Laboratory Safety Rules Activities 1.7 i. List down some laboratory safety rules ii. Discuss hazard symbols on chemical bottles, electrical gadgets and other materials found in the laboratory Laboratory can be considered as a place of discovery and learning. However, by the very nature of laboratory work, it can be a place of danger if proper scientfic precautions are not taken. Follow the followings laboratory safety rules precautions when you perform an activity in laboratory. Dress appropriately (goggles, gloves, shoes and laboratory coats). Tie back loose hair. Know the locations of safety equipment like fire extinguisher. Know what to do in case of an accident. Do not taste or smell chemicals. Do not eat or drink in laboratory. Never add water to concentrated acid solutions. Always add acid into water. Follow the Amharic AW! Not WA! (A-acid, W-water) Carry out only the experiments assigned by your teacher. Dispose of all chemical wastes properly. 14  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook 1.2.3 Science Laboratory Safety Symbols and Hazard Signs, Meanings Depending upon the scientific investigation being conducted, a lab can be filled with dangerous chemicals, Biological specimen, sharp instrument, breakable objects. In order to safe workplace and avoid accidents, lab safety symbols and signs need to be posted throughout the workplace. The following laboratory safety symbols warn of possible dangerous in laboratory user to help keep safe and informed. Toxic materials High voltage hazard Gloves Saftety glasses Flammable materrials boots Face shield Corrosives Electrical hazard Chemical storage area Hand wash Fire extinguisher Biological hazard Health hazard Protective cloth Hearind protection Figure: 1. 6 A) hazard signs B) Laboratory safety symbols 1.2.4 Writig a Laboratory Report Laboratory is a place where experiments in science is performed; therefore, it helps students learn and develop their power of observation, skill in handling apparatus varies kinds and independent thinking. 15  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook A laboratory report is a written composition of the results of an experiment. It should be written precisely and clearly, using good grammar and punctuation. Each report must include: date, title, objective, theory, materials or equipment, chemical used, procedure, observation, result, discussion, and conclusion. Exercise 1.3 Choose the best answers for the following questions 1.Which one of the following is NOT allowed in science laboratory? A. Knowing the hazards of the materials being used B. Reading the labels on the reagent bottle carefully C. Wearing any type of cloth and shoes D. Not using laboratory glassware for eating or drinking purposes. 2. Which of the following laboratory tool is used for the approximate measurements of volume of liquids A. Test tube B. Thermometer C. Measuring Cylinder D. Dropper 3. The type of laboratory equipment categorized under measuring equipment is A. Bunsen burner B. Triple-beam balance C. Tongs D. Stand and clamp Key terms Conventional Science Natural Science Ethics Safety Rules Hazard Signs Science Indigenous Science Scientist Laboratory Technologist Laboratory Equipment Technology 16  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook Unit Summary Science is a systematic method of gaining knowledge about the physical and natural world and the social aspect of human society. Indigenous science is process by which Indigenous people build their empirical knowledge of their natural environment Conventional science is the system of knowledge which relies on certain laws that have been established through the application of the scientific method to phenomena in the world around us. Science has two major categories, which are natural science and social science. Natural science has three branches which are Biology, chemistry and physics. Technology is the use of scientific knowledge to help human beings work easier and live better as well as enjoy their environment more. A person who studies technology is called a technologist. Science and technology plays an important role in our daily life Some famous scientists in Ethiopia are Dr. Aklilu Lemma, Engineer Kitew Ejigu,Dr.Gebisa Ejeta, and Prof.Yalemtsehay Mekonnen Famous scientists from the world are Albert Einstein, Michael Faraday. Marie Curie and Isaac Newton etc. Laboratory equipment comprises different sets of apparatus, which are designed to perform various tasks in the laboratory. Knowing Laboratory safety rule is very important to reduce risks faced during laboratory investigation. 17  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. Natural science is the study of nature and natural laws. 2. Biology, Physics and chemistry do not share common areas of study. 3. Technology makes life easier or more pleasant and work more productive. Part II: Choose the best answers for the following questions 1. The study of living things is the concern of A. Chemistry C. Biology B. Physics D. Geology 2.______ is a branch of natural science which studies the nature of matter, energy and their interaction. A. Chemistry C. Biology B. Physics D. Geology 3. The famous Ethiopian scientist who discovered a natural treatment to Schistosomiasis or bilharzia disease. A. Eng. Kitew Ejigu C. Dr. Gebisa Ejeta B. Dr. Aklilu Lemma D. Prof. Yalemtsehay Mekonen 4. Which of the following is NOT a laboratory safety rule? A. You should tie back loose hair. B. You should add water to Acid. C. Do not suck solution in the pipette by mouth. D. When lighting a Bunsen burner, you should light the match stick before turning on the gas. 18  General Science Fetena.net Grade 7 StudentResource : Ethiopian No#1 Educational Textbook 5._________is a branch of Knowledge and the systematic study of universe and its all encompasses, one that based upon facts, observation and experiments. A. Theory B. Natural law C. Dogma D. Science Part III Match the items in column ‘A’ with items in column 'B' A B 1. Biochemistry A. Combination of Biology and Physics 2. Physical Chemistry B. Combination of Geology and Physics 3. Biophysics C. Combination of Biology and Chemistry 4. Geo-physics D. Combination of Chemistry and Physics Part IV; Fill in the blanks with appropriate terms. 1._____________is the place where experiments in science is performed. 2. A person who study about technology is called ____________. 3.Who is the famous Ethiopian scientist involved in development of African commercial hybrid strains of sorghum_______. Part V: Give short answer to the following questions. 1. Define technology 2. What is the difference between science and technology? 3. Mention the steps to write laboratory report. 4. Why ethics in science is important? 19  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