Grade 8 General Science Textbook PDF

GENERAL SCIENCE Grade 8 Student Textbook Federal Democratic Republic of Ethiopia Sidaama National Regional State Ministry of Education Education Bureau 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 material, such as plas- tic, old newspapers or magazines. 2. Always keep the book in a clean dry place. 3. Be sure your hands are clean 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 pages with paste. 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 only a few pages at a time. Press lightly along the bound edge as you turn the pages. This will keep the cover in good condition. GENERAL SCIENCE Student Textbook Grade 8 Writers and Editors: Abraham Hailu (M.Sc.) Argiso Nemesa (M.Sc.) Demissie Shimelis (M.Sc.) Hablewongel Desalegn (M.Sc.) Reviewer Abraham Hailu (M.Sc.) Team Leader Daniel Tona (M.Sc.) Advisory and Quality Demissie Shimelis (M.Sc.) Assurence Team Legesse Burako (M.Sc.) Lewtayehu Legesse (M.Sc.) Illustrator Anteneh Million (B.A.) Designer Geda Hoka (M.A.) Federal Democratic Republic of Ethiopia Sidaama National Regional State Ministry of Education Education Bureau Acknowledgement This book is prepared by the Sidama National Regional State Education Bureau based on the textbook preparation documents prepared by the Ministry of Education in accordance with the recommendations of the Education and Training Roadmap. The cost of preparation and publication is covered by the Sidama National Regional State and the FDRE Ministry of Education General Education Certification Program-E (GEQIP-E). Therefore, the Education Bureau would like to thank all those who directly or indirectly supported the preparation of the book in terms of funding, manpower and materials, providing the necessary information, approving their institution, sharing their experience and knowledge, and so on. ©The book is the official copyright of the Sidama Regional Education Bureau. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means (including electronic, mechanical, photocopying, recording or otherwise) either prior written permission of the copyright owner or a license permitting restricted copying in Ethiopia by the Federal Democratic Republic of Ethiopia, Federal Negarit Gazeta ,Proclamation No. 410/2004 Copyright and Neighbouring Rights Protection Proclamation, 10 th year, No. 55, Addis Ababa, 19 July 2004. 2014 E.C. Hawassa, Sidaama, Ethiopia Table of Contents UNIT ONE 1 1. BASICS OF SCIENTIFIC INVESTIGATION 1 1.1. Scientific Measurements 2 1.2. Doing Scientific Investigation 12 UNIT SUMMARY 22 REVIEW EXERCISE 23 UNIT TWO 25 2. COMPOSITION OF MATTER 25 2.1. Early thinking about the composition of matter26 2.2. Inside of an atom 30 2.3. Molecules 36 UNIT SUMMARY 40 REVIEW QUESTIONS 41 UNIT THREE 43 3. CLASSIFICATION OF COMPOUNDS 43 3.1. Introduction to Compounds 44 3.2. Organic Compounds 45 3.3. Inorganic Compounds 51 3.4. Neutralization Reaction and Salts 72 UNIT SUMMARY 77 REVIEW EXERCISE 78 UNIT FOUR 80 4. HUMAN BODY SYSTEMS AND HEALTH 80 4.1. Integumentary System 82 4.2. Muscular System 88 4.3. Skeletal System 92 4.4. Digestive System 98 4.5. Respiratory System 106 4.6. Circulatory System 111 4.7. Reproductive System 118 UNIT SUMMARY 126 REVIEW EXERCISE 128 UNIT FIVE 131 5. ECOSYSTEM AND CONSERVATION OF NATURAL RESOURCE 131 5.1. Ecosystem and Interactions 133 5.2. Conservation of Natural Resources 146 UNIT SUMMARY 169 REVIEW EXERCISE 170 UNIT SIX 173 6. THE SOLAR SYSTEM 173 6.1. Family of the Solar System 174 6.2. Formation of the Solar System 185 6.3. Earth in comparison with Solar system 192 6.4. Our planet’s suitability for life (uniqueness) 194 SUMMARY196 REVIEW EXERCISE 197 UNIT SEVEN 201 7. PHYSICAL PHENOMENA IN THE SURROUNDING201 7.1. Phenomena of Light (source and properties) 202 7.2. Vision and Imaging 207 7.3. Sound 214 7.4. Heat 220 7.5. Simple circuit 225 7.6. Magnetism 226 SUMMARY232 REVIEW EXERCISE 233 Grade 8 UNIT ONE 1. BASICS OF SCIENTIFIC INVESTIGATION Learning Outcomes At the end of this unit, students will be able to: ♻ identify the basic and derived units of measurements; ♻ explain the concept of measuring physical quantities; ♻ describe the components of a scientific investigation; and ♻ demonstrate ability to work effectively and respectfully with others. Main Contents 1.1. Scientific Measurements 1.2. Doing Scientific Investigation Introduction Internationally, the most promoted skills in learning science are through investigation. Scientific investigation is a universal approach to learning science through practical work. Its aim is to provide students opportunities to use concepts and skills to solve problems. In grade 7 you learned about basic concepts of science, indigenous knowledge and people’s perspectives, and about procedures in science laboratories where science investigation are conducted. In this, unit you will study about scientific measurements and scientific investigation. UNIT ONE: BASICS OF SCIENTIFIC INVESTIGATION 1 General Science | Student Textbook 1.1. SCIENTIFIC MEASUREMENTS At the end of this section, students will be able to: ♻ explain the concept of measuring physical quantities; ♻ describe the various indigenous methods of measurement; ♻ distinguish between the basic and derived physical quantities; ♻ identify prefixes and perform conversions among units of measurements; and ♻ distinguish between accuracy and precision in measurements. In this section you will learn about indigenous and modern methods of measurements, prefixes and conversion of physical quantities, accuracy and precision in measurements. Activity 1.1. Discuss the following questions in group and present to the class. 1. What is science? 2. What is measurement? 3. How quantity being measured and expressed in terms of value and unit? Science is a systematized knowledge arising from observation, study and experimentation. The determination of the size or magnitude of something “or” the comparison of unknown quantity with some standard quantity of the same rates is known as measurement. Measurements are made every day in our day to day activities in buying products, sports activities, cooking, and weather forecasting. Scientific measurements are a process of observing and recording objects or events with accuracy, clarity, without ambiguity and reported as a value. 2 Scientific Measurements Grade 8 Activity 1.2. Perform the following activities in group and present to the class. 1. Measure the time taken to cover 50m distance by one of your friends. 2. Measure the height of your friend, and let your friend measure your height also. What instruments did you use? 1.1.1. Modern and Indigenous methods of measurements Activity 1.3. Discuss in group with your class mates and present to the class. 1. What is the difference and similarities between modern and indigenous methods of measurements? 2. What are the common terms that are used interchangeably to refer to the concept of indigenous methods of measurements? Measurement is an integral part of human race, without it there will be no trade, no statistics. Depending on the type of instruments we can classify methods of measurements as: 1. indigenous methods of measurements, and 2. modern methods of measurements UNIT ONE: BASICS OF SCIENTIFIC INVESTIGATION 3 General Science | Student Textbook 1. Indigenous methods of measurements Activity 1.4. In group, list some of the indigenous methods of measurements (length, mass, volume, time) the people use in your locality and present it to the class. Indigenous (traditional or local) methods of measurement are the methods of measurements that an indigenous community accumulates over generations of living in a particular environment. Indigenous methods of measurements are unique to a particular culture and society; and our country Ethiopia, has also its own knowledge in this field. Some of the common units of measurements are given below. I. Mass (m): Some of indigenous methods of mass measuring instruments are: dawulla: A measure of mass approximately equal to 50 kg. quintal: a measure of mass equals to 100 kg. 🔄 How many kilograms are 4 dawulla? II. Length (l): Some of Indigenous methods of measurements of length are described below with figures. i. Azq (in Amharic) ii. “Sinzer” in Amharic (“Taakko in Sidaamu Afoo) A measure of distance about an inch long. People in the countryside use the A measure of distance from the tip of distance from the tip of their thumb finger the middle figure to the tip of the thumb to the first fold (angua in Amharic). while the hand is fully extended. Figure1.1 Azq Figure 1.2 Sinzer 4 Scientific Measurements Grade 8 iii. “Kend” in Amharic (“Cigile” in iv. “Aarb” in Amharic (“Hanqafo” Sidaamu Afoo): It measures a distance in Sidaamu Afoo): A measure of from the tip of one’s elbow to the tip of length approximately about a yard. middle finger. Figure 1.4 Aarb Figure1.3 Kend v. “Chamma” in Amharic vi. “Ermijja” in Amharic (“Qaafo” (Ha’ruma” in Sidaamu Afoo): A in Sidaamu Afoo): A linear distance measure of a distance from the back of measure of about a yard of a person’s the heel to the tip of the big toe. extended walk. Figure 1.5. Chamma Figure 1.6. Ermijja III. Time (t): Time describes the duration between the beginning and end of an event. Traditionally people use the sunrise and sunset as a way to measure time. IV. Volume (v): Some of the indigenous methods of volume measuring instruments are: i. “tassa”, “ensira”, “gerewoina” and “gan” (in Amharic): these are containers of liquids which are also used to measure volume. ii. “enqib” (in Amharic): A measure of volume used to measure grains. 2. Modern methods of measurements 🔄 Can you list some of the modern measuring instruments of Length? Physical quantity can be measured by different measuring instrument; some of the common are measuring length, mass, time and volume. UNIT ONE: BASICS OF SCIENTIFIC INVESTIGATION 5 General Science | Student Textbook I. Measuring Length Activity 1.5. Perform the following activity in group and present to the class Using any available measuring instruments in your school or locality, measure the height and width of your table and classroom door. 🔄 What types of instruments do you use to measure the distance of a place? Length is the distance between two objects. Meter stick and different taps can measure up to 0.1mm accurate. Figure 1.7. Length measuring instruments: (A) meter rule, (B) measuring taps used in sewing, (C) measuring tapes in construction II. Measuring Mass 🔄 What types of instruments do you use to measure the mass of an object? The followings are some of the instruments used for measuring mass: ✅ double beam balance, we can measure up to 1gm accurate. ✅ triple beam balance, we can measure up to 0.1gm accurate. ✅ electron beam balance, we can measure up to 0.001gm accurate. 6 Scientific Measurements Grade 8 Figure 1.8. Different types of Balances: A) Double beam balance B) Triple beam balance C) Electronic balance III. Measuring Time 🔄 What types of instruments do you use to measure the duration of an event? The followings are some of measuring instruments of time: Figure 1.9 Watches: A) digital stop watch B) analog stop watch C) digital watch D) analog watch IV. Measuring Volume 🔄 What types of instruments do you use to measure the volume of a liquid? Volume is the amount of space occupied by an object. It is expressed in cubic units. Some of the common measuring instruments of volume are measuring cup used in the kitchen, measuring cylinders burette and pipette. UNIT ONE: BASICS OF SCIENTIFIC INVESTIGATION 7 General Science | Student Textbook Figure 1.10. Volume measuring instruments 1.1.2. Physical quantities Activity 1.6. Discuss the following questions in groups and present to the class What are physical quantities? How are they classified as basic and derived? A physical quantity is a property of a material or system that can be quantified by measurement. A physical quantity can be expressed by a numerical value and a unit. Physical quantities are categorized into basic and derived physical quantities. Basic and Derived physical quantities In science, we have seven basic physical quantities. All other physical quantities (other than the seven basic quantities) can be expressed in terms of these basic quantities. These are called derived physical quantities. In 1960 an international agreement was reached specifying a particular choice of metric unit in scientific measurement. These preferred units are called SI unit (the International System of Unit). 8 Scientific Measurements Grade 8 Table 1 Physical quantities Fundamental ( basic ) Derived SI unit (Basic Quantity Quantity Units units) Length Meter (m) Area m2 Mass Kilogram (kg) Volume m3 Time Second (s) Density kg/m3 Temperature Kelvin (K) Force kgm/s2 (N) Electric current Ampere (A) Speed m/s Amount of substance Mole (mol) Acceleration m/s2 Luminous intensity Candela (cd) Energy J The units of derived physical quantities are called derived units. They are combinations of the basic units. 1.1.3. Prefixes and Conversion of basic units Table 2: Selected prefixes used in the basic system Basic Standard form Prefix Symbol Example numeral 1.0 x 106 1,000,000 Mega M 1Ms = 1 x 106s 1.0 x 103 1,000 Kilo k 1kg = 1 x 103g 1.0 x 102 100 Hector h 1hm = 1 x 102m 1.0 x 10 10 Deca da 1daL = 10L 1.0 x 0.1 0.1 Deci d 1dL = 0.1L 1.0 x 0.01 0.01 Centi c 1cm = 0.01m 1.0 x 0.001 0.001 Milli m 1ms = 0.001s 1.0 x 0.000001 0.000,001 Micro µ 1μs = 1 x 10-6s Relationship between Units of length ✅ 1 meter (m) = 1000 millimeters (10 mm) 3 ✅ 1 meter (m) = 100 centimeters (10 cm) 2 ✅ 1 kilometer = 1000 meters (10 m) 3 ✅ 1 centimeter (1cm) = 10 millimeter (10mm) UNIT ONE: BASICS OF SCIENTIFIC INVESTIGATION 9 General Science | Student Textbook Relationship between units of mass ✅ 1000 kilogram (1000kg) = 10 quintal = 1 ton ✅ 100 kilogram = 1 quintal ✅ 1 kilogram = 1000 grams Relationship between units of time ✅ 1 hour = 60 minutes; 1minute = 60 seconds ✅ 1 day = 24 hours ✅ 1 month = 30 days; 1 year = 365.25 days (365 and 1/4 days) Relationship between units of volume ✅ 1 liter(l) = 1,000 milliliters(1000ml) = 1000cm 3 Example How many centimeters are there in 0.5m? Given Required Solution L=0.5m L in cm 1m = 100cm 0.5m = x x = 0.5m1cm x 100cm = 50cm Check Point 1.1 Answer the following questions. 1. What is the name given to the unit that equals (a) 103gram? (b) 10-6second? (c) 10-3meter? 2. a. What decimal fraction of a second is a millisecond, ms ? b. Express the measurement 6.0 x 103m using a prefix to replace the power 10. 3. Use power of ten to express 3.76 mg in grams. 10 Scientific Measurements Grade 8 1.1.4. Accuracy and Precision in measurements 🔄 What is the difference between Accuracy and Precision? Precision is a measure of how closely individual measurements agree with one another. Accuracy refers to how closely individual measurements agree with the correct, or, “True” value. Figure 1.11 The distribution of darts on a target illustrates the difference between accuracy and precision From the figure 1.11 (A) shows high accuracy and high precision since it is bunched in the centre of the target and figure 1.11 (B) indicates low accuracy and high precision form a tight off-centre cluster. But figure 1.11 (C) illustrates, the measurements of low accuracy and low precision are scattered and off- centre. UNIT ONE: BASICS OF SCIENTIFIC INVESTIGATION 11 General Science | Student Textbook Exercises 1.1 Give answers to the following Questions. 1. Write examples of indigenous measurements of length and mass. 2. Give example of modern instruments of measurement of length. 3. Write two modern instruments of measurements of mass. 4. What power of ten do the following prefix symbol represents? i. d ii. c iii. μ iv. M v. k vi. M 5. What name of prefixes do you use to write the following measurements without use of exponents? a. 4.56 x 10-2 L b. 9.5 x 10-6s c. 1.0 x 10-3m 6. Convert the following unit from: a. 4.0 cm to m. b. 4.0 m to cm. c. 40 mm to m. d. 4.0 cm to mm. e. 10 ms to second. f. 1 μs to s. 7. What is meant by accuracy and precision? 1.2. DOING SCIENTIFIC INVESTIGATION At the end of this section, students will be able to: ♻ state the importance of scientific investigation; ♻ describe the basic procedures of a scientific investigation; ♻ explain the ethical issues that to be respected in scientific investigations; ♻ conduct, with guidance, simple investigations using inquiry approach; ♻ demonstrate the ability to work effectively and respectfully with others;and ♻ conduct simple investigations using local materials and procedure. 12 Doing Scientific Investigation Grade 8 1.2.1. Introduction to Scientific Investigation Activity 1.7. Form a group and perform the following activity; and present to the class. How can the scientific investigation be used to answer questions about daily life? Think of a question in your life that you could answer using the scientific method. Then describe each step of the scientific method as you move toward answering your question. Investigations are at the heart of science. Scientific investigation is a systematic way of gaining scientific knowledge. Scientific investigations produce evidence that helps to answer questions. Scientific investigation is a quest to find the answer to a question using the scientific method. Everything you do and encounter during your daily activities involves scientific investigation. Humans can acquire knowledge and understanding of the natural world through observation, experimentation, and reflection. Making coffee, cooking eggs, and baking bread involve the different methods. The products you use like soap and shampoo, the fabrics you wear, the electronics that keep you connected to your world, the gasoline that propels a car, etc; all of these and more are a result of scientific investigation. 🔄 In which activities do you use scientific investigation? Can you give examples? Scientific investigation generally involves some or all of the following basic components: ask a question, form a hypothesis, testing hypothesis, gather and analyze evidence, support the hypothesis with evidence, draw conclusions, and communicate results. UNIT ONE: BASICS OF SCIENTIFIC INVESTIGATION 13 General Science | Student Textbook Exercise 1.2 Answer the following questions. 1. What is scientific investigation? 2. Describe the components of a scientific investigation. 1.2.2. Scientific Method and Ethical Discipline Scientific Method Science is a study of the natural environment. It is a body of organized knowledge obtained about nature through observation, explanation, interpretation and rationalization of certain types of information. Scientific method is a systematic approach to problems. It is a process that is used to find answers about the world around us. The steps in scientific method includes making careful observations, asking questions, identifying the problem, forming a hypothesis, test the hypothesis with experiment, analyze data, make conclusion, and communicate results. Step 1: Making careful observations: The first step of the scientific method involves making an observation about something that interests you. It is a critical look through of natural world by using our sense organs. Step 2. Ask question (Identifying the problem): First the problem has to be identified before proceeding to the next steps. Beginning the question with ‘what,’ ‘how’ or ‘why’ is a good start. State the problem as a question. An example of a good question is, “How does fertilizer affect plant growth?” This is simple, measurable and can be done in the lab. Step 3. Form a hypothesis: 14 Doing Scientific Investigation Grade 8 Hypothesis is an explanation for an observation. It is basically an educated guess that can be tested based upon a thorough review of the existing knowledge of the subject. It is important to note that a hypothesis is tentative and must be testable. Step 4. Experimentation (Testing Hypothesis): Helps us to test our hypothesis by carrying out experiments using the collected data. Step 5. Analyze and interpret the data: Analysis of data means studying the organized material in order to discover the essential facts. After the experiment, results are recorded carefully and systematically organized in the form of data, charts or graphs in addition to verbal explanations and the interpreted data accordingly. Step 6. Drawing conclusion: Conclusions or generalizations require careful and objective analysis of the data gathered. The conclusion may or may not support the hypothesis. Step7. Communicate results (Theory, principles, facts and laws): When a given hypothesis has been tested many times and found to be acceptable it is no longer a hypothesis, but it becomes a theory. A theory is a tested explanation of hypothesis and facts. For example, Dalton’s atomic theory, modern atomic theory etc. A concise verbal statement or a mathematical equation that summarizes a broad variety of observations and experience is known as scientific law. A familiar example is the law of gravity. 🔄 Can you give other examples that are scientific theory and scientific law? Make observations Ask questions Form hypothesis Analyze Communicate Draw and Test the results conclusion interpret hypothesis with data Experiment Figure 1.12 Basic steps in scientific method UNIT ONE: BASICS OF SCIENTIFIC INVESTIGATION 15 General Science | Student Textbook Check Point 1.2 Each sentence below describes a step of the Scientific Method. Match each sentence under column “A” to the correct step of the Scientific Method under column “B”. Column “A” Column “B” 1. A student said, “If I fertilize my A. Recognize a problem plants, they will blossom”. B. Form a hypothesis. 2. Student’s experiment proved that C. Test the hypothesis earth worms move away from light. with an experiment 3. A student read about growing plants D. Draw conclusions in water; and he wanted to know E. Making observation how plants could grow without soil. 4. A student grew bacteria from the mouth on plates. She placed drops of different mouth washes on the bacteria of each plate. Ethical Discipline 🔄 Why it is necessary to follow ethical discipline in scientific investigations? Ethics is a set of moral obligations that define right and wrong in our practices and decisions. Doing science with principles of ethics is the bedrock of scientific activity. Scientific investigations must be guided by ethical rules. The following are some of the common ethical disciplines across scientific investigations. ✅ Duty to society: contribute to the well-being of society. ✅ Beneficence: help others and yourself; and maximize benefits. 16 Doing Scientific Investigation Grade 8 ✅ Conflict of interest: what is the right thing to do? ✅ Informed consent: follow procedures and know the risks. ✅ Integrity: demonstrate honesty and truthfulness; moral soundness. ✅ Non discrimination: be fair and treat equally. ✅ Non exploitation: do not harm others or yourself. ✅ Privacy and confidentiality: be faithful, keep promises and agreements. ✅ Professional competence: being adequate or well qualified. ✅ Professional discipline: respect truth, do not lie, cheat or deceive. 1.2.3. Semi-guided investigations In this section, students are asked to perform Semi-guided investigations to answer the following questions: (a) does a coiled nail act like a magnet? (b) is air necessary for burning? (c) do plants store their food in their leaf? Experiment 1.1 Objective: To investigate a coiled nail act like a magnet. Apparatus: A big nail , an insulated copper wire about 0.25m long, one or two cell, pin or paper clips Procedure: 1. Wind some turns of an insulated copper wire round an iron nail core. 2. Connect it to a battery (dry cell) as in the fig.1.13 (A). 3. Place some pins on a paper and bring them to the nail. UNIT ONE: BASICS OF SCIENTIFIC INVESTIGATION 17 General Science | Student Textbook Figure 1.13 (A) Pins are attracted when switch is closed (B) Pins fall when switch is open Observations and Analysis: 1. What do you observe when the switch is closed and bring pins to the nail? 2. What do you observe when the current is switched off? See Fig.1.13(B) 3. What do you conclude from this demonstration? Write a laboratory report in groups and present your to the rest of the class. 18 Doing Scientific Investigation Grade 8 Experiment 1.2 Objective: To investigate if air is necessary for burning. Materials: three gas jars (glasses or beakers) of different size, three equal sized candle pieces, match and a table of smooth surface Procedure: 1. Attach three candles on smooth surface of a table. 2. Strike a match and lit fire to each candle. 3. Simultaneously invert the gas jars on each candle. 4. Observe what happens and record all your observations/data in writing. Caution: This experiment requires supervision and safety considerations!! Figure 1.14 An inverted jar and a burning candle Observations and Analysis: 1. What happens to the fire after some time? 2. Which gas jar candle fire is extinguished first? Why? 3. How does the amount of oxygen affect the burning time of a candle? 4. Discuss the conditions essential for combustion to take place. 5. What do you conclude from this experiment? Write a laboratory report in groups and present to the rest of the class. UNIT ONE: BASICS OF SCIENTIFIC INVESTIGATION 19 General Science | Student Textbook Experiment 1.3 Objectives : To demonstrate if plants store their food in their leaf. Materials : Green leaf of plant, Beaker, Test tube, Test tube holder, Boiling water, Ethanol, Bunsen burner/Hot plate or stove, Tripod stand, Petri-dish, Dropper, Matches and 0.05N iodine solution. Procedures 1. Take a green leaf from a plant which has been exposed to sunlight. 2. Heat a beaker half filled with water on the stove or hot-plate/Bunsen burner. 3. Place the leaf in boiling water and keep it there for about 15-20 minutes. This step kills the cells and renders them highly permeable.Take out the boiled leaf from the beaker and immerse it in a test tube containing ethanol. 4. Place the test tube in the hot water and keep it there until the leaf is decolorized. The alcohol is kept warm in a water bath. 5. Remove the test tube from the hot water. 6. Remove the decolorized leaf from test tube and place it back to the hot water in the beaker. 7. Pull out the leaf from the beaker and put it in a petri dish. 8. Add a drop of 0.05N iodine solution and allow the leaf to remain in the iodine solution for 5 minutes, and then wash it with water. Observation and Analysis: 1. What do you observe in the leaf? 2. Why does it happen? 3. Do plants store their food in their leaf? Write a laboratory report in groups and present to the rest of the class. 20 Doing Scientific Investigation Grade 8 1.2.4. Indigenous action: Using local materials and methods (procedures) to conduct investigation Project work The objectives of this project is to relate indigenous units of measurements to metric unit, either an SI unit with appropriate prefix or a non-SI unit that is accepted to use with SI unit. You should bring and present the local names of indigenous measurement units in your locality by asking parents, elders and the community. To convert from indigenous methods of measuring instruments (unit) into metric unit, or SI unit you can use modern methods of measurements. Your teacher may guide you how to convert indigenous units of measurements to metric unit. Exercise 1.3 Write the answer for the following questions (a) 1. Why scientific investigations must be guided by ethical rules? 2. What are the common ethical disciplines in scientific investigations? 3. The process of obtaining information by using the senses is known as _____ 4. Describe the last step of the scientific method. UNIT ONE: BASICS OF SCIENTIFIC INVESTIGATION 21 General Science | Student Textbook 🔒 🔑🔑 Accuracy KEY TERMS 🔑 Modern methods of 🔑🔑 Basic physical quantities 🔑🔑 measurement Physical quantities Basic units (SI unit) Derived physical 🔑🔑 Precision Prefixes 🔑🔑 quantities Derived units 🔑 Scientific Investigation 🔑 Ethics in scientific Indigenous methods 🔑 Scientific Measurements 🔑 of measurements Investigation Scientific methods UNIT SUMMARY ʯ Measurement is the process of observing and recording objects or events. ʯ SI system means the international system of units, containing seven basic units. ʯ Mass is a measure of the quantity or amount of matter present in an object. ʯ Accuracy indicates how close a measurement is to the true value. ʯ Precision indicates how close the measurements are to each other. ʯ Investigations produce evidence that helps answer questions. ʯ The scientific method is a systematic approach to solve problems. ʯ A hypothesis is a possible explanation for the phenomenon you observed. ʯ Scientific investigations must be guided by ethical rules. ʯ The steps of scientific method include observation, question, hypothesis, experiment, results and conclusion. 22 Doing Scientific Investigation Grade 8 REVIEW EXERCISE I. Write true or false for the following questions. 1. Every measurement expressed interms of a number and a unit. 2. The mass of an object is measured with the help of a beam balance. 3. Forming a hypothesis is the first step of the scientific method. 4. A hypothesis always leads to the formulation of a law. 5. Scientific law is well-tested explanation for experimental results. II. Choose the correct answer from the given alternatives for each of the following questions. 1. The symbols for units of length in order from largest to smallest are A. m, cm, mm, km C. km, mm, cm, m. B. mm, m, cm, km. D. km, m, cm, mm. 2. Scientific measurements are communicated using____. A. a unit B. both a numeric value and unit C. either a numeric value or unit D. a numerical value 3. The SI base unit for time is the: A. day. C. minute. B. hour. D. second. 4. Which of the following is not a fundamental quantity? A. Length C. Density B. Mass D. Time 5. Which of the following is a derived unit? A. Meter C. Kilogram B. Newton D. second UNIT ONE: BASICS OF SCIENTIFIC INVESTIGATION 23 General Science | Student Textbook 6. A student asks a question: How fast does the average person’s hair grow? Which step of the scientific method did he just complete? A. Step 1 - ask a question B. Step 2 - gather background information C. Step 3 - make a hypothesis D. Step 4 - do an experiment 7. One micrometer is equal to: A. 10-6 m C. 10-9 m B. 10-8 m D. 10-12 m 8. Which of the following measurements are NOT equivalent? A. 25 mg = 0.025 g C. 150 ms = 0.150 s B. 24 dL = 2.4 L D. 84 cm = 8.4 mm 9. The amount of space taken up by an object is known as its ___________. A. mass C. length B. area D. volume 10. How many grams are in a milligram? A. 1,000,000 C. 1,000 B. 0.001 D. 0.01 III. Answer the following questions. 1. An explanation for a broad range of observations, facts, and tested hypotheses is called _____________________________. 2. Change the following length, mass or volume measurements to the units shown in brackets. a) 3.6m (cm) d) 0.325km (mm) g) 2 905 mg (kg) b) 4500m (km) e) 8550 kg (g) h) 1.25 g (kg) c) 8500mL (L) f) 1.6 µL (L) 3. Change each of the following measurements to one in which the unit has an appropriate SI prefix. a) 3.76 × 103 m b) 6.34 × 10–6 s c) 1.09 × 10–3 g 24 Doing Scientific Investigation Grade 8 UNIT TWO 2. COMPOSITION OF MATTER Learning Outcomes At the end of this unit, learners will be able to: ♻ narrate the historical development of the atomic nature of substances; ♻ appreciate that atoms are the building blocks which make up all substances; ♻ demonstrate understanding of the idea that the identity of a substance is determined by its atomic structure; ♻ differentiate molecules of elements from molecules of compounds; and ♻ demonstrate scientific inquiry skills along this unit: communicating, asking questions, drawing conclusions, applying concepts. Main Contents 2.1. Early thinking about the composition of matter 2.2. Inside of an atom 2.3. Molecules UNIT TWO : COMPOSITION OF MATTER 25 General Science | Student Textbook Introduction Can you 1. What is meant by matter? recall? 2. What do you think matter is made up of? In grade seven general science textbook, you learned about matter and particulate nature of matter, thus you are familiar with the concept of matter. Do you think matter is the stuff that is all around you? Yes, you are right. Those all things you see and touch every day are matters and consist of small particles. These small particles do have some mass. But one never can see these small particles with eyes, even not with the best microscopes. However, the structure and behavior of small particles is the key for understanding both the physical and chemical properties of matter. Therefore, in this unit, you will learn the fundamental concepts of composition of matter in exploring the early thinking about an atom, the subatomic particles of the atom, atomic number and mass number, and molecules. 2.1. EARLY THINKING ABOUT THE COMPOSITION OF MATTER After completing this section, the learners will be able to: ♻ give a short history of the concept of the atom; ♻ compare and contrast the continuity and discreteness (discontinuity) theory of matter, and ♻ compare earlier conceptions of the structure of matter with their conceptions. 26 Early thinking about the composition of matter Grade 8 Activity 2.1. Perform this activity in group, and present your opinions to the class. 1. Prepare an aluminum foil and cut it into two halves and continue cutting. 2. How long could you continue cutting? Is there a limit or could you infinitely divide into smaller and smaller pieces? What do you conclude from this? 3. What is the fundamental building block proposed by the ancient Greek philosophers? 4. Debate on one of the following ideas assigned to your group. Idea 1: Matter is continuous. Idea 2: Matter is discrete About 2500 years ago, the Greek philosophers thought about the nature of matter and its composition. They described matter as continuous or discrete. The Greek philosopher, Democritus (460-370 B.C.) argued that matter is made of small indivisible particles. He called these small particles ‘atomos’, meaning indivisible. Democritus also thought that matter is discrete (discontinuous). On other hand, Aristotle (384-322 B.C) argued that matter can be divided endlessly into smaller and smaller pieces; and he concluded matter is continuous. The ancient debate about matter is illustrated in Figure 2.1 below. Figure 2.1 Ancient debates about the nature of matter UNIT TWO : COMPOSITION OF MATTER 27 General Science | Student Textbook Based on the above debate, basic difference on the idea of continuity and discreteness of matter is summarized in Table 2.1 below. Table 2.1 Comparison between the discrete and continuous theory of matter Discreteness of Matter Continuity of Matter (Democritus) (Aristotle) Matter is discrete Matter is continuous There is a limit to which matter is Matter is infinitely divisible broken Believed in the existence of atoms Rejected the idea of atoms Although, Democritus’ idea was not accepted by many of his contemporaries (notably Plato and Aristotle), somehow it suffered. Therefore, Democritus philosophy about matter was assumed to be “wrong” and Aristotelian view of the composition of matter were succeeded until John Dalton disproved Aristotelian view by experimental investigation. This confirmed that science- based ideas are continually being tested, modified and improved as new knowledge and explanations supersede existing knowledge and explanations. An atom is the smallest individual particle of an element and does not exist freely in nature. The idea that matter is made up of fundamental particles were explained by atomic theory of matter. You will discuss more about atomic theory in grade 9 Chemistry. 28 Early thinking about the composition of matter Grade 8 Exercise 2.1 I. Choose the best answer from the given alternatives. 1. Among the following things, the one is a matter. A. Water C. Shadow B. Sound D. Light 2. Which of the following is not true about Democritus philosophy of matter? A. Matter is discrete C. An atom is indivisible B. Matter is continuous D. None of the above 3. One of the following agreed on continuity of matter. A. Democritus C. John Dalton B. Aristotle D. J.J. Thomson II. Give short answer to the following questions. 1. According to Democritus, what is “atomos”? 2. What do you mean by a matter is “continuous?” 3. What is an atom? UNIT TWO : COMPOSITION OF MATTER 29 General Science | Student Textbook 2.2. INSIDE OF AN ATOM After completing this section, the learners will be able to: ♻ describe the structure of an atom as a nucleus containing protons and neutrons, surrounded by electrons in shells (energy levels); ♻ state the relative charge and approximate relative mass of a proton, a neutron and an electron; ♻ draw hydrogen atoms, including the location of the protons and electrons, with respect to the nucleus; ♻ differentiate between mass number and atomic number; and ♻ determine the number of protons, neutrons, and electrons in an atom. Activity 2.2. Discuss the activity within a group and present your response to the class. 1. How could you describe the structure of an atom? 2. Draw the picture if you imagine what an atom look like? 2.2.5. Parts of an atom 🔄 Is there any particle smaller than an atom? An atom has two regions such as the atomic nucleus and the electronic shells (energy levels or orbits). Atoms are made of even smaller particles called electrons, protons and neutrons. 🔄 How are these particles arranged in an atom? The central part of the atom is called the nucleus. Protons and neutrons are present in the nucleus. Electrons revolve in shells around the nucleus like planets move around the sun. Note that shells are paths of the electrons take as they move around the nucleus. 30 Inside of an atom Grade 8 Project work Perform the project work in a group and present your work to the class. First draw the diagrammatic representation of the structure of hydrogen atom on paper and next obtain atomic model of hydrogen atom by using locally available material. (Hint: hydrogen atom has 1 electron, 1 proton only; draw a circle around the nucleus and add a symbol such as a dot for the electron). Surrounding the nucleus, there is a region occupied by electrons. This region is very large compared with the size of the nucleus. A) B) Figure 2.2 Diagrammatic representation of the structure of A) hypothetical atom (not to scale) and B) hydrogen atom 2.2.6. The Subatomic Particles 🔄 What are protons, electrons and neutrons? An atom has a definite number of protons, electrons and neutrons. A proton is a positively charged subatomic particle in the atomic nucleus. The positive charge of the nucleus is due to the proton in it. An electron is a tiny negatively charged particle found outside the nucleus of an atom. Since, electrons are found outside the nucleus they are always available at the surface an atom. A neutron is electrically neutral particle located in the nucleus of an atom. UNIT TWO : COMPOSITION OF MATTER 31 General Science | Student Textbook Relative mass, the charge and location of subatomic particles Activity 2.3. Explain the following questions. 1. How protons, neutrons and electrons are alike and different? 2. Is an atom neutral? Why? When you compare the masses of electrons, protons and neutrons, what you find is that electrons have an extremely small mass, compared to either protons or neutrons. Proton has a mass 1837 times greater than that of electron. The mass of proton and neutron is approximately equal. Therefore, most of the mass of an atom is concentrated in the nucleus, assuming the mass of an electron to be negligible or almost zero compared with the masses of protons and neutrons. Hence the nucleus is a heavy part of an atom. But the nucleus occupies a very small space as compared to the volume occupied by the electrons. Compare, the relative mass, charge and location of sub-atomic particles in Table 2.2 below. Table 2.2 Nature and location of sub-atomic particles Actual Relative Electric Particle mass (in atomic mass Location charge gram) (amu) Electron(e-) 9.109x10-28 1/1840 Negative Outside the nucleus Proton (P+) 1.673x10-24 1 Positive Inside the nucleus Neutron(on) 1.675x10-24 1 Neutral/Zero Inside the nucleus You know that electrons are negatively charged and protons are positively charged, but what is amazing is that the positive charge on a proton is exactly equal in magnitude to the negative charge on an electron. Negative and positive charges of equal magnitude cancel each other out, and neutron is neutral. Therefore, an atom is neutral. 32 Inside of an atom Grade 8 Atomic Number and Mass Number 🔄 What makes an atom of one element different from an atom of another element? The significant difference on among atoms of different elements is in their subatomic composition. It is possible to distinguish between different elements by counting the number of protons. If an atom has only one proton, we know it is a hydrogen atom. An atom with two protons is always a helium atom. 🔄 What is the difference between atomic and mass number? How they can be represented with symbol of an element? Indeed, the number of protons in the nucleus of an atom of any particular element is called the element’s atomic number. It is also equal to the number of electrons around the nucleus if the atom is neutral. The physical and chemical property of the elements depends on proton number in atom of element. Z = p+ or Z = e– (in a natural atom) The mass number of an atom is the total number of protons and neutrons in its nucleus. Mass Number (A) = Number of protons + Number of neutrons A = p+ + n° Mass number is designated by the letter ‘A’ whereas atomic number is designated by the letter ‘Z’. However, both mass number and atomic number is always given in whole number. UNIT TWO : COMPOSITION OF MATTER 33 General Science | Student Textbook Check point 2.1 Answer the Following Questions 1. Using the periodic table, write the symbolic notation and determine their number of protons, neutrons and electrons for the following elements. (hint: in a periodic table, mass number is approximately equal to atomic mass). a) Lithium c) Carbon e) Oxygen b) Beryllium d) Nitrogen 2. Determine the atomic number, mass number, and number of protons for the following elements: a) 115 B b) 1020 Ne c) 19 9 F For example, 42He is symbolic notation of helium and its atomic number is 2 and its mass number is 4. Determination of the Electrons, Protons and Neutrons 🔄 How number of electrons, protons and neutrons can be determined? We have seen how atomic number and mass number is determined in the above section. Since, the mass number is total number of protons and neutrons in an atom; then the number of neutrons is therefore the difference between the mass number and the atomic number. The number of neutrons in an atom is calculated by: Number of neutrons = Mass number (A) – Atomic number (Z) 34 Inside of an atom Grade 8 Example: 🔄 How many protons, electrons, and neutrons are in an atom of 19 9 F? Solution No of neutrons= mass number - No of protons, or mass number – atomic number. Thus, No of neutrons= A-Z or A- No of protons= 19-9=10 If an atom is not neutral, the number of electrons and protons are not equal. Check point 2.2 Answer the Following Questions. 1. How many protons, electrons, and neutrons are in an atom of 2311 Na ? 2. How many neutrons are in atom having 14 protons with mass number 28? Exercise 2.2 I. Label each of the following statements as true or false. 1. All the mass of an atom is concentrated in the nucleus. 2. An atom is electrically neutral. 3. In an atom, number of electrons is necessarily equal to number of neutrons. 4. The nucleus is one of the fundamental particles of an atom. UNIT TWO : COMPOSITION OF MATTER 35 General Science | Student Textbook II. Match terms under column ‘A’ to column ‘B’. Column A Column B 1. Proton A. Negatively charged 2. Electron B. Neutral 3. Neutron C. Positively charged III. Fill the blank spaces. 1. Electron, proton, neutron are the types of_____________in an atom. 2. Atomic number is the number of____________in an atom. 3. The central dense part of an atom is called _____________. 2.3. MOLECULES After completing this section, the learners will be able to: ♻ define molecules; ♻ give examples of monatomic, diatomic and polyatomic molecule;and ♻ use models or particles model diagram to represent molecules of elements and compounds. Activity 2.3. Discuss the following questions in a group and present your opinion to the class. 1. What is a molecule? 2. How molecule is differ from an atom? A molecule is the smallest particle of an element or a compound that can exist freely in nature. Only a few elements, such as the gases helium, neon, argon etc. consist of a collection of individual atoms that move about independently of one another. In nearly all molecules, two or more atoms are bonded together in very small, discrete units (particles) that are electrically neutral. 36 Molecules Grade 8 2.3.1. Molecules of elements 🔄 What are molecules of elements? Molecules of elements consist of single atom. They can be classified as monatomic, diatomic and polyatomic. Atoms of some elements such as helium (He), neon (Ne), argon (Ar) contain a single atom and are monatomic molecules. Other molecules are formed with two atoms of an element and called diatomic molecules. Examples: hydrogen (H2), oxygen (O2), and nitrogen (N2). Hydrogen molecule is formed with combination of two hydrogen atoms as follows. Hydrogen atom + Hydrogen atom → Hydrogen molecule H + H H2 🔄 Can you list other monatomic and diatomic molecules? Sometimes, more than two atoms of an element combine to form molecules of that element and called polyatomic atomic molecules. Example: ozone (O3), Phosphorus (P4), and sulphur (S8). Therefore, the molecules which are formed with similar atoms, like hydrogen molecule (H2) are called molecules of elements. These three kinds of molecules of element are illustrated in figure 2.3. Helium, (He) Hydrogen, (H2) Ozone, (O3) Monoatomic molecule Diatomic molecule Triatomic molecule Figure 2.3 Diagrammatic representations of molecules of element UNIT TWO : COMPOSITION OF MATTER 37 General Science | Student Textbook 2.3.2. Molecules of Compounds 🔄 What is a molecule of compound? How it differ from molecules of element? When atoms of different elements combine with each other, the molecules of compounds are formed. A molecule of a compound contains at least two atoms. Water exists in molecular form and formed when an atom of oxygen combine with two atoms of hydrogen as shown in chemical equation and figure 2.4 below. Hydrogen + Oxygen → Water 2H2 + O2 2H2O Figure 2.4 Schematic representations of a) structure of individual water molecule b) water molecules in steam. Here, the atoms of oxygen and hydrogen are different because hydrogen and oxygen are different elements. Therefore, the molecules which are formed from two or more different atoms are called molecules of compound. Other molecules such as ammonia (NH3), glucose (C6H12O6) and carbon dioxide (CO2) are molecules of compounds. 🔄 Can you list some other examples of molecules of compound? 38 Molecules Grade 8 Exercise 2.3 Give short answer to the following questions. 1. Define a molecule. 2. Consider the molecules shown below. i. Ar ii. CO2 iii. N2 iv. O3 v. S8 vi. H2O vii. Cl2 viii. HCl a) Classify the molecules as monatomic, diatomic or polyatom- ic molecules of element? b) Which of these molecules are molecules of elements? c) Which of them are molecules of compounds? 3. What is the difference between H and H2? UNIT TWO : COMPOSITION OF MATTER 39 General Science | Student Textbook 🔒 🔑🔑 Atom KEY TERMS 🔑🔑 Molecules 🔑🔑 Atomic number Electron 🔑🔑 Neutron Nucleus 🔑🔑 Mass number Matter Matter discontinuity 🔑 Proton Subatomic particles UNIT SUMMARY ʯDemocritus suggested that all matter in the universe was made up of tiny, indivisible particles. ʯAn atom is the smallest individual particle of an element and does not exist freely in nature. ʯElectrons are a negatively charged, protons are a positively charged and neutrons are neutral. ʯAn atomic number is a number of protons. The mass number of an atom is the sum of the protons and neutrons in the atom. ʯA molecule is the smallest particle of an element or a compound that can exist freely in nature. ʯThe molecules which are formed with similar atoms are called molecules of elements. Molecules formed with two or more different atoms are called molecules of compound. 40 Molecules Grade 8 REVIEW QUESTIONS I. Label each of the following statements as true or false. 1. Neutral atoms must contain the same number of neutrons and protons. 2. An element’s atomic number is equal to the number of protons. 3. A neutral atom with 4 protons must have 4 electrons. 4. O3 is a molecule of compound. 5. According to Aristotle an atom is indivisible. 6. All matters are made up of an atom. II. Choose the best answer from the given alternatives. 1. Which of the following has the smallest mass? A. Proton C. Neutron B. Electron D. None of them 2. The atomic number and mass number of Aluminum is 13 and 27, respectively. The number of proton, electron, and neutron respectively are:- A. 13, 13 and 13 C. 27, 13 and 14 B. 13, 13 and 27 D. 13, 13 and 14 3. Identify the one which is not a molecule. A. H2SO4 D. Cl2 B. O E. He C. S6 4. The atomic number of an atom is based upon the number of_________. A. neutrons C. electrons B. protons and neutrons D. protons 5. The central portion of an atom is called a/an____________. A. electron C. nucleus B. proton D. Neutron UNIT TWO : COMPOSITION OF MATTER 41 General Science | Student Textbook III. Fill in the blank space in the following questions. 1. ______ and neutrons have approximately the same mass. 2. A molecule containing two or more different type of atoms is called______. 3. A molecule containing more than two similar atoms is called__________. IV. Give short answers for the following questions. 1. Compare the Democritus and Aristotle philosophies about atom. 2. What are the two main parts of an atom? 3. What is the difference between atomic number and mass number? 4. What are the fundamental sub-atomic particles? 5. Complete the following table. Z A Number of Neutron Number of Proton 14 7 15 31 27 14 6. Distinguish between molecules of element and compounds. Give at least three examples for each. 7. The atomic number and mass number of calcium are 20 and 40 respectively. Deduce the number of neutron present in the calcium nucleus. 8. Explain the following molecules and give examples for each. a) Monatomic molecules b) Diatomic molecules c) Polyatomic molecules 42 Molecules Grade 8 UNIT THREE 3. CLASSIFICATION OF COMPOUNDS Learning Outcomes At the end of this unit, learners will be able to: ♻ explain the classification of compounds into organic and inorganic; ♻ write the formulas and name the first eight alkanes, alkenes and alkynes and list the uses of some important common organic compounds; ♻ classify oxides into different groups and give examples of each group; ♻ develop skills in identifying acidic, basic and neutral solutions; ♻ define, and apply the concept of neutralization; ♻ explain the safety precautions while working with acids and bases;and ♻ demonstrate scientific inquiry skills along with this unit: observing, classifying, comparing and contrasting, communicating, asking questions, designing experiment, drawing conclusion, applying concepts and problem solving. UNIT THREE : CLASSIFICATION OF COMPOUNDS 43 General Science | Student Textbook Main Contents 3.1 Introduction 3.2 Organic Compounds 3.3 Inorganic Compounds 3.4 Neutralization Reaction and Salts Start-up Activity Form groups and discuss the following and present to the class. Assume that you are given two compounds (water and alcohol) in two different containers. Explain how you could distinguish between these two compounds. Introduction In Grade 7, you have learned about elements, compounds and chemical reaction. You have distinguished elements from compounds and how they are represented by symbols and formulae. You are also familiar with naming compounds and writing their formulas. In this section you will learn about compounds and their classifications. 3.1. INTRODUCTION TO COMPOUNDS After completing this section, you will be able to: ♻ define organic compounds as carbon containing compounds;and ♻ define inorganic compounds as compounds of elements other than carbon. Compounds are classified into two classes; organic and inorganic. Compounds obtained from living things (plants and animals) are organic compounds and compounds obtained from the constituents of the earth are inorganic compounds. Organic compounds are carbon containing compounds where as inorganic compounds are compounds of elements other than carbon including carbonates (CO32-), hydrogen carbonates (HCO3-), carbonmonoxide (CO) and carbon dioxide (CO2). 44 Introduction to Compounds Grade 8 Activity 3.1. Perform the following research activity and present to the class. From different science books, discuss the historical origins of organic and inorganic; and their relationship between organic chemicals and living things. Exercise 3.1 Answer the Following Questions 1. What are the differences between organic and inorganic compounds? 2. Classify each of the following compounds as organic or inorganic. a) Common salt (NaCl) b) Sugar ( C12H22O11) c) Carbon dioxide (CO2) d) Alcohol (C2H5OH) 3.2. ORGANIC COMPOUNDS After completing this section, learners will be able to: ♻ define hydrocarbons and mention at least one source of hydrocarbons; ♻ write the general formula of alkanes, alkenes and alkynes; ♻ write the specific chemical formulas of the first eight members of alkanes, alkenes and alkynes; ♻ describe a homologous series and its general characteristics; and ♻ identify some common uses of organic compound. UNIT THREE : CLASSIFICATION OF COMPOUNDS 45 General Science | Student Textbook 3.2.1. Hydrocarbons and its sources Activity 3.2. Form a group and perform the following activity. Share your opinion to the class. 1. Which elements are constituents of hydrocarbons? 2. How hydrocarbons are named? Is it based on certain rules or randomly? Hydrocarbons are organic compounds containing only hydrogen and carbon. The natural sources of hydrocarbons include coal, petroleum and natural gases which are formed from the remains of living organisms. The three major classes of hydrocarbons are alkanes, alkenes and alkynes. The name of a hydrocarbon is derived from the number of carbon atoms present (prefix) and the ending (suffix) that relate to their names. To find the base name of hydrocarbons (alkanes, alkenes and alkynes) use the following prefixes. Table 3.1 Prefixes of the first eight hydrocarbons No carbon atoms 1 2 3 4 5 6 7 8 Name Meth- Eth- Prop- But- Pent- Hex- Hept- Oct- Nomenclature of Alkanes, Alkenes and Alkynes Nomenclature of Alkanes Alkanes are hydrocarbons with the general formula of CnH2n+2, where n = 1, 2, 3, etc. and stands for the number of carbon atoms in each alkane. For example, if n=1, the formula of alkane is C1H2×1+2 = CH4. Any consecutive group of hydrocarbon differs from the next one in a series by a CH2 unit called homologues series. CH2 CH2 CH2 CH 4 C 2 H6 C 3 H8 C 4 H10 The names of alkanes end with the suffixes ‘-ane’. For instance, the formula of the alkane containing one carbon atom is CH4. Therefore, n=1 prefix is ‘meth-’ 46 Organic Compounds Grade 8 and we add the suffix ‘-ane’ to the prefix. Thus, the name of the alkane becomes methane. 🔄 What is the formula and name of an alkane containing three carbon atoms (n=3)? Check point 3.1 Answer the Following Questions. 1. Write the formula and name of an alkane containing 2, 4, 5, 6 and 8 carbon atoms. 2. Give the formula and name for the alkane homologues coming before and after C7H16 and find their difference in the number of carbon and hydrogen atoms. Nomenclature of Alkenes Alkenes are hydrocarbons with the general formula of CnH2n, where n = 2, 3, 4, etc. For example, if n=5, the formula of the alkene is C5H2×5 = C5H10. The names of alkenes end with the suffixes ‘-ene’. The first member of alkene starts with two carbon atoms (n=2), C2H4. The prefix is ‘eth-’ and we add the suffix ‘-ene’ to the prefix. Thus, the alkene named as ethene. Similarly, the name of C5H10 is pentene. 🔄 What is the formula and name of an alkene containing three carbon atoms (n=3)? UNIT THREE : CLASSIFICATION OF COMPOUNDS 47 General Science | Student Textbook Check point 3.2 Answer the Following Questions. 1. Write the formula and name of an alkene containing 4, 5, 7 and 8 carbon atoms. 2. Give the formula and name for the alkene coming before and after C6H12; and find their difference in the number of carbon and hydrogen atoms. Nomenclature of Alkynes Alkynes are hydrocarbons with the general formula of CnH2n-2, where n = 2, 3, 4, etc. For example, if n = 4, the formula is C4H2×4-2 = C4H6. The names of alkynes are obtained by changing the suffix ‘-ane’ of alkanes to ‘-yne’. For example, the formula of alkyne containing four carbon atoms is C4H6. The prefix is ‘but-’ and the suffix is ‘-yne’. Combining the prefix and suffix gives butyne. 🔄 What is the formula and name of the first member of alkyne homologous series? Check point 3.3 Answer the Following Questions. 1. Write the formula and name of an alkyne containing 3, 4, 5, 6 and 8 carbon atoms. 2. Give the formula and name for the alkyne coming before and after C7H12; and find their difference in the number of carbon and hydrogen atoms. 48 Organic Compounds Grade 8 Uses of Common Organic Compounds Activity 3.3. Perform the following activity in group and present your opinion to the class. List the sources of hydrocarbons that are found in Ethiopia and report to the class; and explain how they have made life more comfortable for human beings. Methane: Methane (CH4) is mainly used as a fuel gas for cooking, heating and generating light. Methane is the major component of natural gas (~85%), commonly called Biogas, which is used as a domestic fuel. Propane and butane: Both propane and butane are gaseous alkanes marked as bottled gas and commonly known as “buta gas”. It is mainly used for cooking and heating. Ethyne: One of the main uses of ethyne is to produce oxyacetylene flame, which is used in the cutting and welding of steel and iron at high temperature. Figure 3.1 Ethyne produces oxyacetylene flame UNIT THREE : CLASSIFICATION OF COMPOUNDS 49 General Science | Student Textbook Ethanol: is used in alcoholic beverages. Nowadays, ethanol is mixed with petrol for an automotive fuel. It is used in hospitals and clinics for cleaning wounds; and as a solvent for many substances and in making perfumes and paints. Ethanoic acid (Acetic acid): Vinegar (Ethanoic acid) is used as food flavoring agent and preserving vegetables. Formalin: is used for preservation of biological specimens. It is also commonly used as an industrial disinfectant, and as a preservative in homes and medical laboratories as antiseptics, medicines, and cosmetics. Exercise 3.2 Write your answers to the following questions. 1. Classify each of the following hydrocarbons as alkane, alkene or alkyne and write their names. a) C5H10 c) C4H10 e) C6H10 b) C3H4 d) C8H18 2. Write the molecular formulas of the following hydrocarbons and indicate their differences. a) Butane, butene and butyne b) Propane, propene and propyne 3. List common organic compounds and explain their uses. 50 Organic Compounds Grade 8 3.3. INORGANIC COMPOUNDS After completing this section, students will be able to: ♻ classify oxides into metallic and nonmetallic; ♻ describe the properties of acidic oxides and basic oxides; ♻ predict the nature of common oxides; ♻ prepare sulphur dioxide in laboratory by burning sulphur in air; ♻ prepare magnesium oxide in laboratory by burning magnesium in air; ♻ define acid and base and describe their properties; ♻ name and write formulas for some common acids and bases; ♻ describe how indicators can be used to classify solutions as acidic or basic; ♻ investigate properties of bases/alkalis experimentally by preparing their own indicator by extracting the colour from a vegetable or flowers; ♻ investigate household chemicals using locally prepared indicators; ♻ explain the safety precautions while working with acids and bases;and ♻ create a safety booklet dealing with the handling of acids and alkali. Activity 3.4. Perform the following activity and share your opinion with your group. List some elements and inorganic compounds with which you are familiar in your daily activities. Inorganic compounds are compounds consisting of mineral constituents of the earth or generally found in non-living things. Inorganic compounds are mostly found in nature as oxides (O2-), carbonates (CO32-), sulphides (S2-), sulphates (SO42-), chlorides (Cl-) and nitrates (NO3-). Inorganic compounds can be classified into four groups according to their composition and their properties. These include oxides, acids, bases and salts. UNIT THREE : CLASSIFICATION OF COMPOUNDS 51 General Science | Student Textbook 3.3.1. Oxides Oxides are binary compounds containing oxygen and any other element. Binary compounds are those consisting of only two elements. Element + Oxygen → Oxide Some examples of oxides are calcium oxide (CaO), aluminium oxide(Al2O3), sulphur dioxide (SO2), carbon monoxide (CO), hydrogen oxide (water or H2O), etc. Types of Oxides Most oxides are classified as metallic oxides and non-metallic oxides. Metallic oxides are binary compounds containing only metal and oxygen. Some examples of metallic oxides are Calcium oxide (CaO), Sodium oxide (Na2O), Aluminium oxide (Al2O3), Magnesium (MgO), etc. Non-Metallic Oxides are binary compounds containing only non-metals and oxygen. Some examples of non-metallic oxides are Nitrogen dioxide, (NO2), hydrogen oxide (H2O), carbon dioxide (CO2), sulphur dioxide (SO2), etc. Based on their chemical behaviour oxides are classified in to acidic oxides and basic oxides. Acidic oxides: Acidic oxides are oxides of non-metals. They are also called acid anhydrides. Acid anhydride means acid without water. Most non-metals form oxides that exhibit acidic properties and dissolve in water to give acidic solutions. Examples of acidic oxides include; sulphur dioxide (SO2,) nitrogen dioxide (NO2,) carbon dioxide (CO2), etc. It is important to note that all non-metal oxides are not necessarily acidic oxides. 🔄 What is the nature of phosphorous pentoxide, P O ? 2 5 52 Inorganic Compounds Grade 8 Basic oxides: Basic oxides are oxides of metals. They are also called basic anhydrides. Basic anhydride means base without water. Some metals form oxides which exhibit basic properties and dissolve in water to give alkaline (basic) solutions. Some examples of basic oxides are sodium oxide (Na2O), calcium oxide (CaO), magnesium oxide (MgO), etc. All metallic oxides are not necessarily basic oxides. 🔄 What is the nature of potassium oxide, K O? 2 Properties of oxides i. An acidic oxides (acid anhydride) reacts with water to form an acid. Acid oxide + Water → Acid Example: SO3 + H2O → H2SO4 Sulphur trioxide Water Sulphuric acid CO2 + H2O → H2CO3 Carbondioxide Water Carbonic acid ii. A basic oxide or basic anhydride reacts with water to produce a base (Alkaline). Basic oxide + Water → Base Example: CaO + H2O → Ca(OH)2 Calcium oxide Water Calcium hydroxide K2O + H2O → 2KOH Potassium oxide Water Potassium hydroxide Preparation of Oxides The common method for preparing oxides is direct combination of elements with oxygen. The following practical activity shows the preparation of oxides. UNIT THREE : CLASSIFICATION OF COMPOUNDS 53 General Science | Student Textbook Experiment 3.1 Title: Preparation of Sulphur Dioxide Objective: To prepare SO2 and test whether it is an acidic oxide or a basic oxide. Materials required: Sulphur, litmus paper (blue and red), gas jar, bunsen burner, deflagrating spoon. Procedure: 1. Put some powdered sulphur in a deflagrating spoon and ignite. 2. When it starts burning, put it into a gas jar. 3. When the burning stops, add 5 mL of water to the gas jar and shake. 4. Put blue and red litmus paper, one after the other, in the jar. 5. Record your observations. Figure 3.2 Burning sulphur in air Observation and Analysis: (f) What is the color of the flame when sulphur burns in air? What happens to the color of blue and red litmus papers in step 4? (g) Write the chemical equation for this combustion reaction. (h) Classify the oxide formed by the combustion of sulphur as acidic or basic. Write a laboratory report in groups and present your findings to the class. 54 Inorganic Compounds Grade 8 Experiment 3.2 Title: Preparation of Magnesium Oxide Objective: To prepare magnesium oxide and test whether it is an acidic oxide or a basic oxide. Materials required: Magnesium ribbon, red and blue litmus papers, bunsen burner, tongs, crucible. Procedure: 1. Cut about 2 cm of magnesium ribbon. 2. Hold the ribbon with a tong and burn it over a flame from the Bunsen burner. 3. After burning, put the burning metal into a crucible and collect the product. 4. Add small amount of water to the resulting powder in the crucible and shake it.Test the solution with red and blue litmus paper and record your observations Observation and Analysis: (a) What is the color of the flame produced when magnesium burns in air? (b) Write the chemical equation for the reaction. (c) What happens to the color of the red and blue litmus papers? (d) Is the resulting solution basic or acidic? Figure 3.3 Burning of magnesium in air Write a laboratory report in groups and present your findings to the class. UNIT THREE : CLASSIFICATION OF COMPOUNDS 55 General Science | Student Textbook Exercise 3.3 Answer the Following Questions 1. Classify the following oxides as acidic or basic oxides. Give reasons for your classifications. a) SO3 c) N2O5 e) P2O5 b) K2O d) BaO 2. Complete the following reaction. a) CO2 + H2O → ? b) Na2O + H2O → ? 3. Identify the anhydrides of the : a) HNO3 c) H2SO4 b) Mg(OH)2 d) KOH 4. What products are formed when the following metals react with an excess Oxygen? a) Magnesium b) Zinc c) Lithium 3.3.2. Acids Activity 3.5. Form a group and perform the following activity. Imagine a taste experiment using orange, lemon, tomato and grape fruit. They all taste alike. In what way would they taste alike, and why? What is the name of the acid in lemon and orange? Acids are among the most familiar of all chemical compounds that we encounter every day. Citric acid in lemons, sour ‘Tella’ contains acetic acid, human 56 Inorganic Compounds Grade 8 stomach contains hydrochloric acid and some insects such as bees and ants contain formic acid. It is important to remember that not all acids are harmful. 🔄 Can you mention the acids found in milk and soft drinks? Acids are compounds that release hydrogen ions (H+) when they are in aqueous solution. H2O Example: HCl (g) H+ (aq) + Cl– (aq) Hydrochloric acid, HCl, nitric acid, HNO3 and sulphuric acid, H2SO4 are the three common laboratory acids. These acids are called mineral acids. Rules for writing and naming common acids Acids are named based on their anion or the ion attached to the hydrogen. In simple binary acids, one ion is attached to hydrogen. Names for such acids consist of the prefix “hydro-“, the first syllable of the anion, and the suffix “-ic”. These anions usually have the ending “-ide”. For example, HCl, which is hydrogen (H) and chlorine (Cl), is called hydrochloric acid (HCl). Hydro + Base name of non-metal + ic acid Example: HBr, contains the anion bromide named as hydrobromic acid. 🔄 How do you name HI? Acids containing polyatomic ions are named as follows. If the polyatomic ion ends in –ate, change the ending to –ic acid If the polyatomic ion ends in –ite, change the ending to –ous acid Examples: a. HNO3, contains the polyatomic ion nitrate, is called nitric acid. b. HNO2, contains the polyatomic ion nitrite, is called nitrous acid. UNIT THREE : CLASSIFICATION OF COMPOUNDS 57 General Science | Student Textbook Check point 3.4 Answer the Following Questions. 1. Name the following acids. a) HF b) H2SO4 c) H2CO3 2. Write the formula of the following acids. a) Sulfurous acid b) Phosphoric acid c) Nitric acid. Acid- base Indicators An indicator tells us whether a substance is acidic or basic in nature by showing changes in colour. The common indicators available in laboratories are litmus, phenolphthalein, methyl orange or methyl red and universal indicators. The pH Scale Substances can be classified as acidic, basic, or neutral based on their pH values. pH (Power of hydrogen) is a measure of acidity or basicity of a solution. pH scale is ranging from 0 (very acidic) to 14 (very basic/alkaline). Acids have a pH value less than seven and bases have a pH value greater than seven. The pH of a neutral solution equals seven. Figure 3.4 The pH scale 58 Inorganic Compounds Grade 8 Properties of Acids i. Acids have a sour taste: The sour taste of many unripe fruits, lemon, vinegar and sour milk is caused by the acids present in them. Never taste mineral acids because they are corrosive. ii. Acids change the colour of indicators: Indicators show the presence of an acid or a base with specific color changes when placed in a solution. Acids change blue litmus and methyl orange solution to red and in phenolphthalein becomes colourless. The following practical activity shows the effect of acids on indicators. Experiment 3.3 Title: Effect of acids on acid-base indicators Objective: To investigate the effect of dilute hydrochloric acid and sulphuric acid on the colors of litmus paper, phenolphthalein and methyl orange. Materials required: Blue and red litmus papers, phenolphthalein, methyl orange, test tubes, test tube rack, dilute HCl and H2SO4. Procedure: 1. Pour about 5 mL of dilute HCl into three test tubes. 2. Hold the first test tube in inclined position and put blue and red litmus papers turn by turn into it and see if there is any colour change. 3. Add few drops of phenolphthalein in the second and few drops of methyl orange in the third and observe if there is colour change. UNIT THREE : CLASSIFICATION OF COMPOUNDS 59 General Science | Student Textbook 4. Repeat the above procedure using dilute H2SO4 solution. Observation and analysis Record your findings on table. Write a laboratory report in groups. Table 3.2: Effects of acid on Indicators Color of the indicator in the acid solution Acid Litmus Phenolphthalein Methyl orange Dilute HCl Dilute H2SO4 iii. Reaction of Acids with metals: Dilute acids react with active metals like zinc, magnesium and aluminum to form salts and liberate hydrogen gas. Very active metals like sodium, potassium, and calcium react very violently with dilute acids, so care should be taken. Active Metal + Dilute Acid → Salt + Hydrogen Example: Ca(s) + 2HCl(aq) → CaCl2(aq) + H2(g) Calcium Hydrochloric acid Calcium chloride Hydrogen gas The following practical activity demonstrates the reaction of acids on metals. Experiment 3.4 Title: Reaction of an acid with a metal Objective: To investigate the reaction of zinc metal with hydrochloric acid. Materials required: A test tube, zinc granules, dilute hydrochloric acid, match box rubber stopper and a test tube holder. 60 Inorganic Compounds Grade 8 Procedure: 1. Add a few zinc granules in a test tube. 2. Pour about 5 mL of dilute HCl into a test tube as shown in Figure 3.2. Figure 3.5 Reaction of zinc with hydrochloric acid 3. Remove the rubber stopper and introduce the lighted splint in to the mouth of the test tube and record your observations. Caution! Note that you should hold the test tube and the lighted splint away from Yourself and others! Observation and analysis: (a) What happens when you drop zinc metal into the test tube containing dilute HCl? (b) What is the colour of the gas? (c) What happens when the lighted splint is held inside the mouth of the test tube? (d) Write the chemical equation for the reaction between zinc and hydrochloric acid. Write a laboratory report in groups and present to the rest of the class UNIT THREE : CLASSIFICATION OF COMPOUNDS 61 General Science | Student Textbook iv.Reaction of Acids with Carbonates and Hydrogen Carbonates: Acids react with metal carbonates and hydrogen carbonates to form salts, water and carbon dioxide gas. Acid + Carbonate → Salt + Water + Carbon dioxide Example: 2HCl (aq) + Na2CO3(s) → 2NaCl (aq) + H2O(l) + CO2(g) Hydrchloric acid Sodium carbonate Sodium chloride Carbon dioxide Acid + Hydrogen carbonate → Salt + Water + Carbon dioxide Example: HCl (aq) + 2NaHCO3 (aq) → Na2CO3 (aq) + 2H2O (l) + 2CO2(g) Hydrchloric Sodium bicarbonate Sodiom carbon- Water Carbon diox- acid ate ide The following practical activity demonstrates the reaction of acids with carbonates and hydrogen carbonates. Experiment 3.5 Title: Reactions of acids with carbonates and hydrogen carbonates Objective: To investigate the reactions of carbonates and hydrogen carbonates with dilute hydrochloric acid and sulphuric acid. Materials required: test tube, boiling tube fitted with cork, thistle funnel, delivery tube, sodium carbonate, sodium hydrogen carbonate, dilute HCl and freshly prepared lime water (calcium hydroxide solution). 62 Inorganic Compounds Grade 8 Procedure: 1. Take the boiling tube and add about 0.5 g sodium carbonate to it. 2. Take about 2 mL of freshly prepared lime water in a test tube. 3. Add about 3 mL dilute HCl to the boiling tube containing sodium carbonate. 4. Immediately fix the cork filled with a delivery tube. 5. Dip the other end of the delivery tube in the lime water. 6. Observe the lime water carefully. 7. Repeat the above procedure for sodium hydrogen carbonate and dilute H2SO4. Observation and analysis: (a) When dilute HCl is added to sodium carbonate or sodium hydrogen carbonate, what gas is evolved? (b) What happens to the lime water the gas passing to it? Why is that so? (c) Write the chemical equation that occurred on the reactions. Write a laboratory report in groups and present to the rest of the class. v. Acids neutralize bases: Acids react with bases to form salts and water. This reaction is called neutralization reaction. Acid + Base → Salt + Water Example: HCl + NaOH → NaCl + H2O Hydrchloric acid Sodium hydroxide Sodium chloride Water The following practical activity demonstrates the neutralizing effect of an acid on a base. UNIT THREE : CLASSIFICATION OF COMPOUNDS 63 General Science | Student Textbook Experiment 3.6 Title: Neutralizing effect of an acid on a base. Objective: To investigate the neutralizing effect of HCl on sodium hydroxide. Materials required: A test tube, dropper, methyl orange or phenolphthalein solution indicators, solution of sodium hydroxide and dilute hydrochloric acid. Procedure: 1. Take about 2 mL solution of sodium hydroxide in a test tube. 2. Add a drop of phenolphthalein indicator to it and observe the colour. 3. With the help of a dropper add dilute hydrochloric acid drop wise and stir the solution constantly till the colour disappears. 4. Now add a few drops of NaOH solution. The colour of the solution is restored. Figure 3.6 Reaction between NaOH and HCl 64 Inorganic Compounds Grade 8 Observation and analysis (a) What colour appeared when phenolphthalein is added to the solution of NaOH? (b) Why does the colour disappear on adding HCl? (c) What will happen when sodium hydroxide has reacted with hydrochloric acid? (d) Write the balanced equation for the reaction that takes place in this experiment. Write a laboratory report in groups and present your findings to the class. Exercise 3.4 Write the Answer for the Following Questions. 1. Which ion is a characteristic of acids in water solution? 2. What will happen if you add the following on hydrochloric acid, HCl? a) Phenolphthalein b) Blue litmus c) Methyl orange 3. An acid reacts with a substance Z with the liberation of CO2 gas. What can be the nature of Z? 4. List the properties of acids. 5. Complete the following reaction a) Zn(s) + HCl (aq) → ? b) HCl (aq) + CaCO3 (s) → ? c) HNO3 (aq) + KOH(aq) → ? UNIT THREE : CLASSIFICATION OF COMPOUNDS 65 General Science | Student Textbook 3.3.3. Bases Activity 3.6. Perform the following activity and share your opinion with the class. When plants are partly burned, ash is formed. When the ash is dissolved in water, it gives a solution which tastes bitter and feels slippery when rubbed between the fingers. Why do you think this happens? Bases are chemical compounds that we encounter every day and used in industry and at home. Sodium hydroxide, NaOH, used in washing soaps and detergents; potassium hydroxide, KOH in bathing soaps, calcium hydroxide, Ca(OH)2 neutralizes acidic soil, etc. Bases are substances that react with acids to form salts. Bases which are soluble in water are called alkalis. An alkali is a substance that releases hydroxide ion (OH–) when dissolved in water. H2O For example: NaOH (aq) Na+(aq) + OH–(aq) Sodium Hydroxide Sodium ion Hydroxide ion Some of the example of bases include sodium hydroxide, potassium hydroxide, calcium hydroxide and magnesium hydroxide. 🔄 What is the name of the base used to neutralize excess acidity in our stomach? Naming Bases The names of bases end with hydroxide. Start with name of the cation (metal ion or ammonium ion, NH4+) followed by name of the anion (hydroxide ion). Metal (cation) name + hydroxide (OH-) Example: Na+ + OH- → NaOH Sodium ion Hydoxide ion Sodium hydroxide 66 Inorganic Compounds Grade 8 Check point 3.6 Answer the Following Qustions. 1. Name the following bases. a) Mg(OH)2 b) Al(OH)3 c) Ca(OH)2 2. Write the formula of the following bases. a) Potassium hydroxide b) Iron(III) hydoxide c) Ammonium hydroxide Properties of Bases i. Bases are slippery to the touch and have a bitter taste in aqueous solutions: Strong bases such as NaOH and KOH are very corrosive. So they should be neither brought in to contact with the skin nor tasted. ii. Bases change the colour of indicators: Bases turn red litmus to blue, methyl orange solution to yellow and Phenolphthalein to pink. The following practical activity demonstrates the effect of a base on indicators. Experiment 3.7 Title: The effect of a base on indicators Objective: To study the effect of a base on indicators Materials required: Red and blue litmus papers; phenolphthalein solution, methyl orange, calcium hydroxide, test tubes, test tube holder and rack. UNIT THREE : CLASSIFICATION OF COMPOUNDS 67 General Science | Student Textbook Procedure: 1. Take four clean test tubes. 2. Add about 5 mL calcium hydroxide solution in each of the test tubes and label the test tubes as 1, 2, 3, and 4 as shown in Figure 3.4. Figure 3.7 Testing the effect of base on indicator 3. Put red litmus paper, blue litmus paper, 2 drops of phenolphthalein solution and 2 drops of methyl orange solution in test tubes 1,2,3 and 4 respectively. Observe the colour change and record your observation. Observation and analysis: What happens to the colours of the red litmus paper, blue litmus paper,phenolphthalein and methyl orange solutions after the addition of calcium hydroxide (Lime water) solution? Write a laboratory report in groups and present your to the rest of the class. iii. Bases neutralize acids: Bases react with acids to form salt and water.

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