General Science Grade 7 Textbook PDF

General Science Student text book Grade 7 Southern Nations, Nationalities, and Peoples Regional 1 State Education Bureau  General Science Grade 7 General Science Students Textbook...

General Science Student text book Grade 7 Southern Nations, Nationalities, and Peoples Regional 1 State Education Bureau  General Science Grade 7 General Science Students Textbook Grade 7 Authors: Goshu Asab (M.Sc.) Michael Getachew (M.Sc.) Andualem Beka (B.Sc.) Editors and Evaluators: Getahun Getachew Muluneh T/Birhan Ali Kemal Adopters: Degu Zewdie Getahun Tadese Mulu Waketola Developed by Adiss Abeba Education Bureau, and Adopted by Southern Nations, Nationalities, and Peoples Regional State Education Bureau Students Textbook  General Science Grade 7 Table of Content 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............................................................................................... 22 Unit 2: Matter in Our Surrounding.................................................................. 23 2.1. Characteristics and Nature of Matter....................................................... 25 2.2. Physical and Chemical Properties of Matter............................................ 36 2.3. Classification of substances..................................................................... 41 2.4. Changes around Us: Physical and Chemical Changes............................... 53 2.5. Separation of Mixtures and its Application periods................................. 59 Review Exercise............................................................................................... 72 Unit 3: Elements, Compound and Chemical Reaction.......................................... 76 3.1. Elements and their representation............................................................ 77 3.2. Compounds and their representation........................................................ 81 3.3. Simple chemical reactions and equations................................................. 90 3.4. Uses Of Chemical Reactions in Every Day Situation............................... 99 Review Exercise............................................................................................. 103 UNIT 4: CELLS AS THE BASIS OF LIFE....................................................... 106 4.1. Microscope............................................................................................ 107 4.2. Cell........................................................................................................ 116 Review Exercise............................................................................................. 133 Unit 5: Living Things and Their Diversity......................................................... 137 5.1. Living Things........................................................................................ 139 Students Textbook  General Science Grade 7 5.2. The kingdom of life............................................................................... 149 Review Exercise............................................................................................. 169 Unit 6: Earth in Space.................................................................................... 174 6.3. Earth’s movements................................................................................ 192 6.4. Systems & Cycles (effects, measurement ideas/estimation)................... 196 REVIEW EXERCISE..................................................................................... 206 UNIT 7: MOTION, FORCE, ENERGY AND ENERGY RESOURCES........... 210 7.1. Definition and types of motion.............................................................. 212 7.2. Definition of Force and Gravitational Force.......................................... 216 7.3. Effects of force...................................................................................... 221 7.4. Measuring forces................................................................................... 223 7.6. Forms and Conversion of Energy.......................................................... 227 7.8. Wise use & Conservation of energy....................................................... 233 7.9. Resource depletion and environmental degradation............................... 235 Review Exercise............................................................................................. 240 Students Textbook  General Science Grade 7 Unit 1: Basic Concepts of Science Unit Learning Outcomes At the end of this unit, learners will 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 Main Contents ‘s beliefs, practices, and ways of thinking.  Appreciate the contributions of outstanding 1.1. The Nature of Science and scientists to science and technology. its Branches 1.1.1. Definition of science  Discuss the importance of scientific values in 1.1.2. Branches of science decision making and problem solving. 1.1.3. Science and technology  Relate how science and technology affect 1.1.4. Scientists and ethical one‘s beliefs, practices, and ways of thinking. discipline  Identify the significant contributions of 1.2. Common laboratory Ethiopian Scientists in science and technology. equipment,  Identify different laboratory tools 1.2.1. uses, safety rules and  Demonstrate safe ways of using apparatus in procedures in science the laboratory. laboratories  Practice precautionary measures in the 1.2.2. Common laboratory laboratory apparatus  Exhibit knowledge of lab safety rules and 1.2.3. Laboratory safety rules procedures. 1.2.4. Science Laboratory  Identify potential hazards and implement safety symbol and hazard appropriate safety procedures when working signs, and meanings in the laboratory resources Steps to write Laboratory report Page 1  General Science Grade 7 1.1. The Nature of Science and its Branches Learning Competency: By the end of this section you should 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. 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 our day to day life. 1.1.1. Definition of Science Activity 1.1 Form a group and discuss the following questions. Then share your ideas to the class. You can use reference books and the internet to augment your current ideas i. Describe science by your own words ii. Investigate the ways in which the major areas of science are further divided. iii. Differentiate Indigenous Science and Conventional Science Page 2  General Science Grade 7 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. Through science, we explore our environment, gather knowledge and develop ideas that help us interpret and explain what we see. Science may 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. Indigenous Science incorporating local people‘s knowledge and Indigenous perspectives, while conventional scientific approaches are commonly recognized as Western science. Activity 1.2 Find some practical indigenous knowledge in your community that solves community problems and present your finding to your class Q. Why teach Indigenous Knowledge in science? There are two main reasons to include Indigenous Knowledge in the science: Page 3  General Science Grade 7 Firstly, to increase awareness of original culture and identity Secondly, in modern day environmental problems have social and cultural dimensions which benefit from perspectives other than 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 curing various disease are: Hagenia Abyssinica (Kosso tree), Eucalyptus globulus (bahrzaf), Ocimumlamiifolium 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. 1. What are the major branches of science? 2. 2. Give short descriptions of physics, biology and geology. Science has two major categories, which are natural science and social science. Again, natural science has three branches which are Biology, chemistry and physics. It as shown below in figure 1.1 Natural science is the study of nature and natural laws. It includes fields such as chemistry, biology, physics and geology. These fields of study in natural science are closely interrelated. There are no distinct boundaries between them.  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. Page 4  General Science Grade 7  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.  Biophysics: combination of biology and physics. Biophysics is the study of physical phenomena and physical processes in living things, on scales spanning molecules, cells, tissues and organisms.  Biochemistry: combination of biology and Chemistry Biochemistry 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. Figure1.1. The relationships between some fields of Natural Science Page 5  General Science Grade 7 Key words Science: a systematic method of gaining knowledge about the physical and natural world. Technology: is the use of scientific knowledge to help human beings work easier and live better or putting scientific knowledge into practice. Exercise 1.1 I. Give short answer for the followings questions 1. What is science? 2. List the three branch of natural science 3. Which field of science is study of matter and energy? 1.1.3. Science and Technology You have already seen 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 or more pleasant and work more productive. Things such as automobiles, TV sets, radio, bulb, microchip, computer, airplane and home tools (appliances) are the products of technology. A person who studies technology is called a technologist. Technologists apply Science and mathematical knowledge and skills to produce a very useful tool. Page 6  General Science Grade 7 Figure 1.2 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, proposing and testing explanations. Technology, on the other hand, develops human-made solutions to real-world problems. Of course, science uses technology to generate knowledge and technology uses scientific knowledge to generate solutions. Uses of Science and technology for the society Science and technology plays an important role in our daily life. It is mainly concerned with the production of new materials of desirable properties and qualities to satisfy social needs and plays an important role in agriculture, in the production of medicines and drugs, in environment and population control, in the 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 Activity 1.4 From their background information let them discuss in group about the importance of scientific values in decision making and problem solving. Page 7  General Science Grade 7 Science can and should be important for all major decisions in life. Science is often used to support decisions that have profound economic, social and environmental impacts. Good decision-making follows from having clear favorites for what is to be achieved and using science to evaluate potential means of reaching those aims. Mostly decisions are or should be based on two pillars: beliefs and values. A decision maker’s beliefs are a reflection of his or her perceptions of reality, including facts, opinions, and uncertainties surrounding them whereas its values reflect his or her sense of what to strive for or to achieve, including goals, objectives, and associated negotiations. Obviously, science can help identify unexpected consequences or causal relationships where ethical values or principles are relevant. In addition, individuals need reliable knowledge for making informed decisions. Science is valued by society because the application of scientific knowledge helps to satisfy many basic human needs and improve living standards. At a more general level, science can and should be important for all major decisions in life. For example,  Science can help us learn which products are safe to use or which foods are healthy to eat.  Doctors use science to decide how to diagnose and treat disease(.Finding a cure for disease)  Governments may use science to decide which rules to make and how to enforce them.  Forecasting weather condition (rainy, cloudy, sunny) are some examples. Page 8  General Science Grade 7 1.1.4. Scientists and ethical discipline Famous scientists in 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. Fig1.3 some world known scientist and their works Activities 1.3 Form a group and 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. Page 9  General Science Grade 7 Dr. Aklilu Lemma (1935-1997) made his Prof. Yalemtsehay Mekonnen was most important scientific discovery very early born in Asela, Ethiopia on May in his career, in 1964, when he discovered a 30,1955. She work on human natural treatment to schistosomiasis, also physiology, the impact of pesticides known as snail fever disease or bilharzia. He on human health, the use of plants as found that berries from the endod plant, which medicinal against human and animal is commonly used to make soap and shampoos disease and as the first female in many parts of Africa, is a potent, professor of Addis Ababa university. inexpensive and safe molluscicide, to prevent the spread of the parasitic worm. This discovery made the plant an object of scientific research in many parts of the world. Gebisa Ejeta (born 1950) is an Ethiopian plant breeder, geneticist and Professor at Dr. TewoldeBerhan GebreEgziabher is an Purdue University. In 2009, he Ethiopian scientist, who has worked to ensure won the World Food Prize for his biodiversity and the rights of communities to their major contributions in the production of sorghum. genetic resources. Fig1.3 some Ethiopia known scientist and their works Page 10  General Science Grade 7 Ethical principle in science Activity 1.4 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 same 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 are some of ethical principles that various codes address in science. Those are:  Honesty  Competence  Responsibility  Legality  Objectivity  Non-Discrimination  Openness  Carefulness. Exercise 1.1 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 Page 11  General Science Grade 7 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 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’s D. It has universal perspective and commonly recognized as western science 5. World famous scientists who discover law of motion and gravity A. Michael Faraday C. Isaac Newton B. Marie Curie D. Albert Einstein 1.2. Common Laboratory Equipment, Uses, Safety Rules and Procedures in Science Laboratories Learning Competency: 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. 12  General Science Grade 7 1.2.1. Common Laboratory Apparatus Activities 1.4 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. i. List down some laboratory safety rule ii. Discuss hazard symbols on chemical bottles, electrical gadgets and other materials found in the laboratory 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 apparatuses are shown in tables 1 described here below. Table 1 Different laboratory tools and their use Name Picture Use Practice Triple-beam Obtaining the mass of an Using this tool measure mass of balance object your book, balls, some stones --- etc. Beaker Holding water (also used to heat liquids) Tongs Transport a hot beaker; remove lid from crucible 13  General Science Grade 7 Thermometer Used to measure Using this tool temperature practice how to measure temperature of some body Test tubes Holds small amounts of liquids for mixing or heating. Petri dish Used to grow micro- organisms (like bacteria and fungi) Graduated Marked with milliliter cylinder (ml) scale and is used to measure volume Bunsen burner Heating (flame-safe) contents in the lab Fuse A safety device consisting of a strip of wire that melts and breaks an electric circuit if the current exceeds a safe level. Syringe Used for sucking in and ejecting liquid in a thin stream 14  General Science Grade 7 Key words Laboratory Equipment: refers to the various tools and equipment used by students, teachers and scientists working in laboratory Laboratory Report: is how you explain what you did in experiment, what you learnt and what the result mean Making laboratory equipment/tools from locally available materials Based on the availability of laboratory tools in their locality, encourage to do some Some laboratory tools. Project work Prepare laboratory tools Dear students, prepare some laboratory equipment’s or tools such as beaker, measuring cylinder, balance, tongs, etc. from the locally available materials 1.2.2. Laboratory Safety Rules Laboratory may 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 common- sense precautions are not taken. Follow the followings laboratory safety rules precautions when you perform an activity in laboratory.  Dress appropriately (wear, 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. 15  General Science Grade 7 Basic Safety Rules Basic safety rules for laboratory conduct should be observed whenever working in a laboratory. Many of the most common safety rules are listed below.  Know locations of laboratory safety showers, eyewash stations, and fire extinguishers.  Know emergency exit routes.  Avoid skin and eye contact with all chemicals.  Minimize all chemical exposures.  No play will be tolerated.  Assume that all chemicals of unknown toxicity are highly toxic.  Avoid distracting or upsetting persons working in the laboratory.  All containers must have appropriate labels. Unlabeled chemicals should never be used.  Do not taste or intentionally sniff chemicals.  Use equipment only for its designated purpose.  Combine reagents in their appropriate order, such as adding acid to water.  Avoid adding solids to hot liquids.  Never leave containers of chemicals open.  Never consume and/or store food or beverages or apply cosmetics in areas where hazardous chemicals are used or stored. 16  General Science Grade 7 Points/procedures before starting an experiment.  Know the location of the lab safety equipment and understand how to use it. In particular, know the location of the emergency exit, fire extinguisher, eyewash station, and safety shower.  Read through the experiment before going to the lab. Make sure you understand the steps of the experiment. Jot down any questions you have so that you can ask them before starting the lab.  Understand disposal procedures for the chemicals and other items used in your experiment. Don't throw items in the trash or dump liquids down the drain or in waste disposal containers until you are certain it is acceptable to do so.  Be prepared to take data in the lab. Bring your notebook, a pen, and a calculator.  Have personal safety gear, such as a lab coat and goggles, clean and ready to use before the lab. 1.2.3. Science laboratory safety symbol 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. 17  General Science Grade 7 Figure: 1. 4 A) hazard signs B) Laboratory safety symbols 1.2.4. Writing a Laboratory Report Laboratory is the places where experiments in science performed; students learn and develop their power of observation, skill in handling apparatus varies kinds and independent thinking. 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: title, objective, theory, materials and (equipment) used, procedure, observation, result, discussion, and conclusion. Exercise 1.2 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. Never use laboratory glassware for eating or drinking purposes. 18  General Science Grade 7 2. Which of the following laboratory tools 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. Flask D. Stand and clamp Unit Review Check List Check List Competencies given below are expected to be achieved in this unit by students. You are required to respond by saying Yes or No. Put a tick (√) mark under “Yes” column if you are able to perform the competency or under “No” column if you are unable to perform the competency. This would help to evaluate yourself and you can revise the parts of topics for which the competencies are not met. No. Can I Yes No 1. Define science as a body of knowledge and the processes and practices used to add to that body of knowledge 2. Describe the main branches of science and explain their relationship 3. Relate how science and technology affect one‘s beliefs, practices, and ways of thinking. 4. Appreciate the contributions of outstanding scientists to science and technology. 5. Discuss the importance of scientific values in decision making and problem solving. 6. Relate how science and technology affect one‘s beliefs, practices, and ways of thinking. 7. Identify the significant contributions of Ethiopian Scientists in science and technology. 8. Identify different laboratory tools 9. Demonstrate safe ways of using apparatus in the laboratory. 19  General Science Grade 7 10. Practice precautionary measures in the laboratory 11. Exhibit knowledge of lab safety rules and procedures. 12. Identify potential hazards and implement appropriate safety procedures when conducting laboratory Key terms Science Technology Conventional science Ethics Indigenous science Laboratory equipment Safety rule Laboratory Technologist Scientist Natural science Hazard sign Unit Summary  Science is a systematic method of gaining knowledge about the physical and natural world and the social aspect of human society.  Science may be conventional or indigenous.  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 20  General Science Grade 7  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  Mostly decisions are or should be based on two pillars: beliefs and values. A decision maker’s beliefs are a reflection of his or her perceptions of reality, including facts, opinions, and uncertainties surrounding them whereas its values reflect his or her sense of what to strive for or to achieve, including goals, objectives, and associated compromises.  Some famous scientists in Ethiopia are Dr.Aklilu Lemma, Engineer Kitew Ejigu, Dr.GebisaEjeta, Prof. Yalemtsehay Mekonnen and  Famous scientists from the world 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 21  General Science Grade 7 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 tieback 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 22  General Science Grade 7 5. __________ is a branch of Knowledge and the systematic study of universe and it’s 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 places where experiments in science is performed. 2. A person who study about technology is called___________________ 3. Who is the famous Ethiopian scientist has 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. List and explain the functions of some common laboratory apparatus (equipment’s). 4. Mention the steps to write laboratory report. 5. Why ethics in science is important? 6. Explain the two pillars of science. 23  General Science Grade 7 Unit 2: Matter in Our Surrounding Learning Outcomes At the end of this unit, you will be able to:  Use particles theory‘s postulates to explain properties and behavior of materials.  Classify matter as an element, compound, Main Contents homogeneous mixture, or heterogeneous 2.1. Characteristics and nature mixture with regard to its physical properties. of matter  Describe the structure of solids, liquids and gases in terms of particle separation, 2.2. Physical and chemical arrangement and types of motion. properties of matter  Differentiate between physical and chemical 2.3 Classification of substances properties and changes of matter. (in terms of composition and  Appreciate that matter can be classified based observable properties on physical or chemical properties.  Use properties of matter to identify substances 2.4. Physical and Chemical and to separate them. Changes of Substances  Demonstrate scientific inquiry skills along this 2.5 Separation of mixtures and unit: observing, classifying, comparing and its application contrasting, making mode, inferring, communicating, asking questions, designing experiments, drawing conclusions, applying concepts. 24  General Science Grade 7 Introduction The objects 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. 25  General Science Grade 7  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 Q. 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, smell or weighed. Therefore, various forms of energy such as heat, light, and sound are not considered to be matter. 26  General Science Grade 7 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. Magnetism 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 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. 27  General Science Grade 7 Activity 2.3 Perform the following activities Fill in the blank by using the following words {Increase, less, faster, cold, temperature, water, particles, moving, more, energy} 1. Everything is made of ____________. 2. Particles are always__________________. 3. An increase in ____________makes particles move _________. 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. Scientists find the particle model useful for two reasons. First, it provides a reasonable explanation for the behavior of matter. Second, it presents a very important idea i.e. the particles of matter are always moving. The air you 28  General Science Grade 7 breathe, your books, your desk, and even your body all consist of particles that are in constant motion. Thus, the particle model can be used to explain the properties of solids, liquids, and gases Exercise 2.2 I. Give short answers 1. List the postulates of particle theory. 2. Describe the particulate nature of matter Diffusion Experiment: 2.1 Title: simple experiment on diffusion Objective: To discover what is meant by diffusion Materials: Perfume, ink, beaker, pipette, Water (H2O) Procedure Perfume - 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. Ink – add 2 or 3 drop ink into a beaker of water using a pipette and watch the ink diffuse to color the water. Write your result/conclusion from 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. Concentration is the way of measuring how much or how many particles of a substance in that place. 29  General Science Grade 7 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. When someone opens a bottle of perfume in one corner of room, its smell spreads in the whole room quickly. Diffusion in liquids: is slower than that in gas. This is 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 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. 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. 30  General Science Grade 7 Exercise 2.3 1. Complete the blank space from the word box Diffusion, low, scent, high You can smell 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 increasing order of the rate of diffusion of solids, liquids and gases. 2.1.4. 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 gases I know this is because…. Water liquid I can pour it. 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 stay in the same place. Solids have definite shape and definite volume. Examples of Solids are Stones, wood, metals etc. Pattern of solids Microscopic view of solids Figure 2.1: pattern and microscopic view of solids 31  General Science Grade 7 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. Pattern of liquids Microscopic view of liquids Figure 2.2: pattern and microscopic view of liquids 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 Pattern of gas Microscopic view of gases Figure 2.3 pattern and microscopic view of gases Table Properties of solids, liquids and gases Properties Physical states Gases Liquids Solids -disorderly arranged Less orderly Orderly arranged Arrangement of -particles are very far -Arranged particles are (regular pattern) apart relatively close to each Particles are very particles -almost no attractive other close to each other force between -Have relative attractive particles force between particles 32  General Science Grade 7 Motion of -flow(move) freely flow together in -Do not flow or particles -flow together in random motion move random motion -are known as fluids -Vibrate in a fixed -are known as fluids position compressibility Highly and easily Compressible to a very Not compressible compressible small extent Volume -Have no definite -Have no definite -Have definite and shape Shape and volume Shape Shape and volume -Assume the shape of -Assume the shape of the container and the container entirely fill it. Density Have very low density - Have low density than - Denser than all than liquids and solids solids -Condensed state -Condensed state than all compared to gases Pressure Exert pressure equally Exert pressure towards Exert pressure in all direction depth. towards gravity Diffusion Diffuse spontaneously Diffuse very slowly in Difficult to diffuse in all directions with random motion random motion Diagram Exercise 2.4 I. Give short answers 1. What is the three state 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 cannot have poured? 8. Which state of matter can be compressed easily? 33  General Science Grade 7 II. Multiple choice questions 1. Which state of matter are fluids? A. solid B. Liquid C. Gas D. B and C 2. In which state of matter is 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. Solid liquid gas A B solid liquid gss D C 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 inter-converted without changing the composition of the substance. To change a substance from one state to another, energy must be added or removed. Q. What happens when matter changes state? During a change of state, the motion of the particles changes. Particles can break away from each other and gain more freedom to move, or they may attract each other more strongly and have less freedom to move. During a change of state, a substance gains energy from or loses energy to the environment, but the total amount of energy is conserved. 34  General Science Grade 7 Q. 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 (or fusion). The process of changing a liquid into a solid is called freezing (or solidification). When a liquid is cooled, its particles have less energy, they slow down, and they 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. Q. 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. Q. 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. Deposition is the change in state from a gas directly to a solid. Some common substance under go sublimation are: Iodine, ammonium chloride and solid carbon dioxide (dry ice). When matter changes from one state to another, its physical state changes but its chemical identity does not. During a change of state, the energy of the particles, their movement, and the distance between them change. The mass of a substance 35  General Science Grade 7 does not change when its state changes. Each state contains the same amount of matter. 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? 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. 36  General Science Grade 7 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 therefore, can 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, 37  General Science Grade 7 fruity and odorless. For example, water is odorless, flowers are fragrant, and orange smells fruity. Caution! Care has 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 tastes salty. Caution! Testing 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 are never kind 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 condition 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 100oC, and as a vapor or gas above 100oC. 38  General Science Grade 7 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. Examples are melting point, boiling point, density and electrical conductivity. 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 𝑴𝒂𝒔𝒔 𝒐𝒇 𝒔𝒖𝒃𝒔𝒕𝒂𝒏𝒄𝒆 𝒎 mathematically as: 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; 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 another chemical property of matter. 39  General Science Grade 7 Table 2.2: Comparison between Physical and chemical properties. Physical properties Chemical properties Properties can be measured or Properties that describe how a substance observed without changing the changes (or resists change) to form a new chemical nature of the substance. 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 be substance not change. affected for its chemical properties to be investigated. Examples: color, density, volume, Examples: Flammability and reactivity melting. boiling. Conductivity. Exercise 2.5 1. Classify each of the following properties as a physical property or a chemical property. a. Iron metal rusts in an atmosphere of moist air. b. Mercury metal is a liquid at room temperature. c. Nickel metal dissolves in acid to produce a light green solution. d. Potassium metal has a melting point of 63°C. e. Copper metal possesses a reddish brown color. f. Titanium metal can be drawn into thin wires. g. Beryllium metal, when inhaled in a finely divided form, can produce serious lung disease. h. Silver metal shows no sign of reaction when placed in hydrochloric acid. i. Lead is denser than aluminum. j. Flammability of plastics. 40  General Science Grade 7 2. Classify each of the following properties as intensive property or extensive property. a. boiling point e. density b. length f. volume c. mass g. melting point d. Color 3. Categorize the following physical properties as physical properties recognized by our sense organs or measurable physical properties a. Density d. melting point b. odor e. color c. taste 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. 41  General Science Grade 7 Activity 2.8 Perform the following tasks in groups and present your findings to the rest of the class. 1. Consider 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. 2. Classify them are pure substance or mixture. 3. Among pure substance ,state whether it is an element or a compound 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. Figure 2.5 Matter falls into two basic classes: pure substances and mixtures. 2.3.1. A pure substance 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. 42  General Science Grade 7 Figure 2.6 a pure substance can be either an element or a compound. 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 that are found in liquid state. 43  General Science Grade 7 Figure 2.7: Image of copper, silver & gold Non-metals: non-metal is a chemical element that does not have metal’s properties and are few in numbers as compared to metal. Carbon, oxygen, sulfur, fluorine and phosphorous are some common examples of nonmetal. Activity 2.9 Perform the following activity Which non-metal is essential for our life? They are characterized by the following physical properties. These are They exist in two of the three states of matter at room temperature: gases (oxygen) and solids (carbon). Only bromine exists as a liquid at room temperature. 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 44  General Science Grade 7 Table 2.3: Comparing properties of metals and non-metals. Metals Non-metals These are solids at room These exist in all three states temperature except mercury These are very hard except These are soft except diamond sodium 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 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. Most binary compounds contain metallic and non- metallic elements. Some examples of binary compounds are calcium oxide (lime) from calcium and oxygen, Carbon dioxide from carbon and oxygen, etc. Q. 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. 45  General Science Grade 7 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). Mix the two powders by pouring repeatedly from one piece of paper to the other until a homogeneous mixture (by appearance) is obtained. 2. Note the appearance of the pure elements and the mixture. Demonstrate that iron can be separated from the mixture by physical means. Do this by bring 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 46  General Science Grade 7 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. 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. 47  General Science Grade 7 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 Questions: 1 under a magnifying glass, are the iron filings and sulfur seen separately? 2 Is it possible to attract the iron or sulfur by a magnet? Why? Observations and Analysis I. Which part of the experiment (Part I or II) indicates a compound? Give your reason. II. Which part of the experiment (part I or II) indicates a mixture? 48  General Science Grade 7 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? A mixture is a physical combination of two or more pure substances 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 or 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 are the homogeneous mixture 49  General Science Grade 7 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 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 homogeneous Common examples 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) Figure 2.11: Some common examples of homogeneous mixture 50  General Science Grade 7 Heterogeneous Mixtures Activity 2.12 Perform the following tasks in groups and present your findings to the rest of the class. 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 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 particles remain visible and physically separated. Others 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. Figure 2.12: some common examples of heterogeneous mixtures 51  General Science Grade 7 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. sugarsolution, soft drinks, salt Milk,soil.sand and water, oil and water solution, Exercise 2.6 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. Salt. B. metalloid C. Metal D. non metal 3. Which of the following substance make a homogeneous mixture with water A. benzene B. oil C. sugar D. sulfur 4. Which substance is not a mixture? A. air B. sea water C. pure water D. brass 52  General Science Grade 7 2.4. Changes around Us: Physical and Chemical Changes After completing this section, you will be able to  Describe physical and chemical change  Distinguish the physical and chemical changes using their characteristic  Conduct some simple activities to show physical and chemical changes and write group report.  Observe and describe physical chemical changes that are important in everyday life.  Identify useful and harmful physical and chemical changes. 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 Chemical changes changes Reasons 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 all around us all of the time. Changes are classified as either physical or chemical changes. 53  General Science Grade 7 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. A change in physical state is the most common type of physical change. Melting, freezing, evaporation, and condensation are all changes of state. In any of these processes, the composition of the substance undergoing change remains the same even though its physical state and appearance change. The melting of ice does not produce a new substance; the Figure 2.13: substance is water both before and after the change. melting of ice Similarly, the steam produced from boiling water is still water. 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. Chemical changes always involve conversion of the material or materials under consideration into one or more new substances, each of which has properties and composition distinctly different from those of the original Figure 2.14: burning of candle materials. Consider, for example, the rusting of iron 54  General Science Grade 7 objects left exposed to moist air. Some examples of chemical changes are: Iron nail going rusty, heating magnesium ribbon, Burning candle. photosynthesis,fermentation,etc 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 Experiment 2.3 2. Insert a plug Title: Rusting of iron. of mineral wool (mineral fiber) into the mouth of the test Objective: To investigate the type of change that occurs during rusting of iron tube. Procedure: 1.Put aClamp the shiny few lean, test tube ironasnails shownintoinathe testdiagram tube containing some fresh tap water. The water contains dissolved air. 6. Heat the powder mixture at the base of the test tube – gently at first and then 2.Set the test tube in a rack. After a few days observe the change that has taken more strongly (use a blue flame throughout). Heat until an orange glow is seen place. inside the test tube. Immediately stop heating. Let the students see that the glow continues and moves steadily through the mixture. 7. Allow the test tube to cool down. 8. 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 Questions Figure:It2.15 and mortar. rusting oftoiron is advisable wear protective gloves. 1. What color do you observe on the iron nail? 9. 2.Take Is thethe product change formed physical and powder or chemical? Why? it. Examine the product under a magnifying glass. Bring a magnet over it. 2.4.3. Characteristics of physical and chemical changes Activity 2.14 Discuss the following idea 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 55  General Science Grade 7 Characteristics of physical change  No new substance is formed  The composition of substance not altered  It is easily reversed by physical means  Energy changes are not neccerily  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 physical property 2.4.3. 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 live. a. important physical changes b. important chemical changes c. harmful physical changes d. harmful chemical changes Useful effect of Physical changes Physical changes is useful in the following ways:  Evaporation and condensation create water cycle 56  General Science Grade 7  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 is 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 change 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 & medicine production, Food digestion, Fermentation, food cooking, etc. are also some important chemical change in our live. 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 car, bridges, and ships), souring food, burning of fuel, smoke emission, plastic disposal, dumping of chemicals, etc. are harmful chemical change in our live. 57  General Science Grade 7 Exercise 2.7 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 is a change. d) Straightening a bent piece of iron with a hammer is an example of a change. e) The ignition and burning of a match involve a change 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 C. cyclic change B. Physical change D. none 2. Which of the following statements is correct? A. Evaporation is a chemical change B. Digestion of food is chemical change C. Burning of paper is physical change D. all 3. among the following which is a physical change? A. Burning candle B. fermentation C. making an iron bar magnetic D. all 58  General Science Grade 7 2.5. Separation of Mixtures and its Application periods After completing this section, you will be able to  List methods of separation of mixtures  Give some specific examples of mixtures that can be separated by filtration, decantation, simple distillation, magnetic separation and using separator funnel  Name apparatuses used in decantation, filtration, simple distillation, using separator funnel.  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. 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. mixture of orange, banana and mango 59  General Science Grade 7 2.5.1. Separation Techniques of Mixture Most of the substances around us exist in the form of mixtures. However, these mixtures can be separated into pure substances using various 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. 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 does notattracted. (a) (b) Figure 2.16 (a) the mixture contains iron fillings and sand. (b) A magnet separates the iron fillings from the mixtures. 60  General Science Grade 7 Experiment 2.4 Title: Separation of mixture using bar magnet Objective: To separate a mixture of iron fillings and sand Equipment/ Materials Magnetic bar, Iron fillings, Sand, Petri dish/ plastic plate/bowl Plastic bag/wrapper, Spatula Other requirements: Working bench/table, Open space, Laboratory coat, Eye goggles, Nose mask, and Hand gloves. Experimental Procedure 1. Mix the sand with the iron filings in the plastic plate. 2. Wrap the plastic bag around the bar magnet 3. Suspend the bar magnet over the plate 4. The iron would be collected / attracted to the surface of the magnetic 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 On completion of the experiment, you should answer the following questions 1. Why was the sand not attracted to the magnet? What can you conclude from this experiment? 2. Can the same procedure be used to separate carpenter’s nails from saw dust? Give a reason(s) for your answer. 61  General Science Grade 7 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 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 for e.g. cooking oil and water. When we leave the mixture of cooking oil and water, two separate layers are formed, with 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. 62 Figure 2.19: Decantation of solids from asolid-liquid mixture  General Science Grade 7 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 lighter 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 just the upper layer in the funnel. Collect this liquid into another beaker. Examples: Kerosene and water mixture is separated by Figure 2.20: using separating funnel method. This method is also used Separation of to separate oil and water. immiscible liquids