General Science Grade 8 Textbook PDF

General GeneralScience Science Student text book Student text book Grade 7 Grade - 8 Southern Nations, Nationalities, and Peoples Regional State Education Bureau  General Science Students Textb...

General GeneralScience Science Student text book Student text book Grade 7 Grade - 8 Southern Nations, Nationalities, and Peoples Regional State Education Bureau  General Science Students Textbook Grade 8 Authors:  Yonas Nibret (BSc., MA)  Sefiw Melesse (Msc.)  Abebe Habte (Msc) 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 1  Table of Contents UNIT ONE BASICS OF SCIENTIFIC INVESTIGATION................................................................. 7 1.1 Scientific Measurements........................................................................................... 7 1.2 Doing Scientific Investigation................................................................................ 22 Summary.................................................................................................................... 27 Review exercise......................................................................................................... 27 Unit Review............................................................................................................... 29 Check List.................................................................................................................. 29 UNIT TWO COMPOSITION OF MATTER....................................................................................... 30 2.1 Early Thinking about the Composition of Matter................................................... 31 2.2 Inside of an Atom.................................................................................................... 32 2.3 Molecules................................................................................................................ 36 Unit Review................................................................................................................. 1 Check List.................................................................................................................... 1 Summary...................................................................................................................... 2 Review Exercise........................................................................................................... 3 UNIT THREE CLASSIFICATION OF COMPOUNDS........................................................................... 5 3.1 Introduction............................................................................................................... 5 3. 2 Organic Compounds................................................................................................ 7 2  3.3 Inorganic Compounds............................................................................................. 12 3.4 Neutralization Reaction and Salts........................................................................... 31 Unit Review............................................................................................................... 36 Check List.................................................................................................................. 36 SUMMARY............................................................................................................... 38 REVIEW EXERCISE................................................................................................ 39 UNIT FOUR Human Body Systems and Health.................................................................................... 43 4.1 Integumentary systems............................................................................................ 43 4.1.1 Components of integumentary system.............................................................. 44 4.1.2. Functions of integumentary systems................................................................ 48 4.1.3. Major skin diseases and disorders................................................................... 49 4.2 Muscular system...................................................................................................... 55 4.2.1. Components of muscular system..................................................................... 55 4.2.2 Function of muscular systems........................................................................... 57 4.2.3. Major muscle disease and disorders................................................................ 57 4.3. Skeletal System...................................................................................................... 58 4.3.1. Structural components of skeletal system........................................................ 59 4.3.2 Functions of Skeletal system............................................................................ 65 4.3.3 Major diseases of skeletal system..................................................................... 66 4.4. Digestive system.................................................................................................... 68 4.4.1. Structural components of Digestive system.................................................... 68 4.4.2. Functions of Digestive system......................................................................... 69 3  4.4.3. Major diseases of Digestive system................................................................. 73 4.5 Respiratory system.................................................................................................. 75 4.5.1. Structural components of Respiratory system................................................. 76 4.5.2. Functions of Respiratory system...................................................................... 77 4.5.3 Major diseases of Respiratory system.............................................................. 78 4.6 Circulatory system.................................................................................................. 79 4.6.1. Components of Circulatory system.................................................................. 79 4.6.2. Functions of Circulatory system...................................................................... 80 4.6.3 Major diseases of Circulatory system............................................................... 82 4.7 Reproductive system............................................................................................. 83 4.7.1. Male and female reproductive organs.............................................................. 84 4.7.2 Functions of male reproductive structures........................................................ 85 4.7.3 Function of female reproductive structures...................................................... 86 4.7.4 Menstruation..................................................................................................... 88 4.7.5 Reproductive health.......................................................................................... 89 Unit summary............................................................................................................. 92 Review exercise......................................................................................................... 95 Unit Review............................................................................................................... 96 Check List.................................................................................................................. 96 UNIT FIVE Ecosystem and Conservation of Natural Resources........................................................ 99 5.1. Ecosystem and Interactions.................................................................................. 100 5.1.1. Definition and components of ecosystem...................................................... 101 4  5.1.2Trophic (feeding) relationships........................................................................ 106 5.1.3. Food chain and food web............................................................................... 107 5.1.4. Trophic pyramids........................................................................................... 109 5.1.5. Nutrient cycles and energy flow.................................................................... 111 5.2. Conservation of Natural Resources..................................................................... 115 5.2.1. Soil................................................................................................................. 116 5.2.2. Water.............................................................................................................. 121 5.2.3 Air................................................................................................................... 124 5.2.4. Forests............................................................................................................ 128 5.2.5. Biodiversity.................................................................................................... 131 5.2.6. Indigenous knowledge and conservation of natural resources...................... 133 SUMMERY............................................................................................................. 135 Review exercise....................................................................................................... 137 Unit Review............................................................................................................. 139 Check List................................................................................................................ 139 UNIT SIX THE SOLAR SYSTEM................................................................................................. 141 6.1 Family of the Solar System................................................................................... 142 6.2 Formation of the Solar System.............................................................................. 153 6.3 Earth in Comparison with Solar System............................................................... 157 6.4 Our planet’s suitability for life (uniqueness)........................................................ 160 Summary.................................................................................................................. 161 Review Exercises..................................................................................................... 162 5  Unit Review............................................................................................................. 164 Check List................................................................................................................ 164 UNIT 7 PHYSICAL PHENOMENA IN THE SURROUNDING.............................................. 165 7.1 Phenomena of Light (source & properties)........................................................... 166 7.2 Vision and Imaging............................................................................................... 173 7.3 Sound..................................................................................................................... 178 7.4 Heat....................................................................................................................... 186 7.5. Simple circuit....................................................................................................... 191 7.6 Magnetism............................................................................................................. 195 Summary.................................................................................................................. 200 Unit Review............................................................................................................. 203 Check List................................................................................................................ 203 6  UNIT ONE BASICS OF SCIENTIFIC INVESTIGATION Learning Outcomes: At the end of this unit, learners will able to:  Identify the basic and derived units of measurements.  Explain the concept of measuring physical quantities.  Describe the components of a scientific investigation.  Demonstrate ability to work effectively and respectfully with others in performing fair testing. This unit contains two sub units: scientific measurement and doing scientific investigation. Under scientific measurement the indigenous and modern methods of measurement will be discussed first. Then the classification of physical quantities into fundamental and derived quantity will be discussed, followed by the units of these quantities. Finally, the difference between accuracy and precision will be discussed. Under doing scientific investigation, the importance, procedures and ethical issues of a scientific investigation will be discussed. Finally using locally available materials, a simple investigation will be conducted. 1.1 Scientific Measurements At the end of this section, learners 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  Categorize the basic and derived units of measurements (length, mass, time, temperature, volume, area, density, force)  Identify prefixes and perform conversions among units of measurements  Distinguish between accuracy and precision in measurements 7 Key Terms: Fundamental quantity, Derived quantity, Fundamental unit, Derived unit, Prefix, Accuracy and Precision, Scientific method. Introduction In science it is a common experience to make observations and ask basic questions like how big an object is? How tall are you? To answer these questions, measurements have to be made. Measurement is the process of obtaining the magnitude of a quantity relative to an agreed standard. In this section both the indigenous and modern methods of measurement will be discussed. The indigenous method of measurement refers to a measurement practiced locally while the modern method refers to a measurement applied by the scientific community. Indigenous Methods of Measurements An indigenous method of measurement refers to measurement methods that are practiced locally for a long period of time and are passed from generations to generation. In this section, we will pay attention to the measurement of length, mass, and time. A. Length Length is a measure of the distance between two points.In Ethiopia we use different indigenous units of length measurement. The commonly used ones are: 1. Hand-span: The hand-span is the measure from the tip of your little finger to the tip of your thumb when your hand is stretched out, Fig 1.1 (a). 2. Digit (tat):A digit is the width of an adult human male fingertip, Fig 1.1 (b). 3. Cubit (Kind): A measure of distance from the tip of one's elbow to the tip of the middle finger when your arm is extended, Fig 1.1 (c). 4. Foot (Chamma): A measure of distance from the back of the heel to the tip of the big toe, Fig 1.1 (d). 5. Pace (Ermijja): A linear distance measure of a person's extended walk. A pace is a unit of length consisting either of one normal walking step. Pace: The pace is the 8  distance measured from the heel of one foot to the heel of the same foot when it next touched the ground, Fig 1.1 (e). 6. Arm span: Arm span also known as fathom is the distance from the middle fingertip of the left hand to that of the right hand when you stretch your arms out as far as they can reach, Fig 1.1 (f). Figure 1.1 Indigenous Length measurements Activity 1.1: Make a group containing 5 students. Using your hand span, cubit and digit measure the width of a table or a desk in your classroom. Record your measurement in the table below. No Name of the student Measurement result making measurement 1 2 3 4 Question: Did each of you obtain the same measure for that bench? Justify the difference of students’ measurement. 9 Exercise 1.1: By measuring your hand-span, digit, cubit, foot, pace and arm-span write them in order of increasing value. B. Mass The amount of matter present in a substance is called mass. Like length, there is also an indigenous method of measuring mass. The following are some examples of the indigenous unit of mass measurement used in Ethiopia. 1. Weqet - Weqet is a mass measuring unit usually used to measure the mass of powder of gold in local markets. It is approximately equal to ……. gram. 2. Quintal – Quintal (may be taken from the English word quintal) is a bag used to measure the mass of grains. It is approximately equal to a hundred kilogram. Figure 1.2 Indigenous mass measurements Exercise 1.2: Discuss about the reliability of the above two indigenous mass measuring methods. C. Time Time is the measure of the duration for an interval. There is also an indigenous method of measuring time. Our elders were used the shadow of a tree to measure time. As the position of the Sun changes from morning to evening the length of the shadow of a tree varies. In the morning and late in the afternoon, the length of the shadow is high. At noon when the Sun is overhead no shadow will be seen. Using this fact, they could tell the approximate time of the day by just looking at the position of the shadow of a tree found at or near their home. 10 Activity 1.2: Using a long tree found in your school, mark the time at different height of the shadow of the tree. Use this shadow clock for some time. Discuss your observation. Project 1.1: In ancient time three commonly known time measuring devices were used: They are known as sundial, sand clock and water clock. Using internet explore how these devices were used to measure time and report your finding to the class. D. Volume Volume is the measure of the space occupied by an object.In the local markets of Addis Ababa the following tools are used for different size volume measurements. 1. Jog: A plastic cup used for measuring the volume of liquids. 2. Tassa: A large serving can (often for cereals, pulses and liquids). 3. Sini: A small ceramic cup often used for measuring coffee, pulses and spices. 4. Birchiko: A glass often for measuring pulses and liquids. 5. Kubaya: A mug, often used for measuring cereals, pulses and liquids. በጆግ በጣሳ በስኒ በብርጭቆ በኩባያ ተሰፍረዉ የተቀመጡ ነገሮች Figure 1.3: Indigenous volume measurements Exercise 1.3: 1. Discuss about the problems there could be in using the above indigenous volume measuring devices. 2. Discuss in group about the pros and cons of indigenous measurements used in your locality Project 1.2: With the help of your teacher go to the local market found near to your school. Gather information about the indigenous measuring devices used for different 11 measurements in the market. You can also ask your elder family members. Present a report to your class Physical Quantities and Scientific Methods of Measurement In our day to day life, we measure many things such as the mass of vegetables, the volume of liquids, the speed of a car, the temperature of the day etc. Such quantities which could be measured are called physical quantities. A physical quantity is a property of an object that can be measured or calculated from other physical quantity. Examples of physical quantities are: length, mass, time, temperature, area, volume, density, force etc. Fundamental Physical quantities and their units Generally, physical quantities are classified into two types, namely: fundamental quantities and derived quantities. Fundamental quantities, also known as base quantities, are quantities which cannot be expressed in terms of any other quantity. They are the bases for other quantities. There are seven fundamental (basic) physical quantities: length, mass, time, temperature, electric current, luminous intensity and amount of a substance. In this unit we will discuss only about the first four commonly measured fundamental quantities: length, mass time and temperature. The names and symbols of the units of the fundamental quantities in the International system of units (SI) are shown in table 1.1.The International System of Units (SI, abbreviated from the FrenchSystème international (d'unités)) is a system of measurement based on base units. An international system of units (SI) is currently used all over the world. We saw that, measurement is the comparison of an unknown quantity with some known quantity. This known fixed quantity is called a unit. Thus, the result of a measurement is expressed in two parts. One part is a number and the other part is the unit of the measurement. For example, if a student has a mass of 32 kg: the quantity being 12 measured is mass, the value of the measurement is 32 and the unit of measure is kilograms (kg). This tells us that any measurement consists of two parts. The first is the number which indicates the magnitude of the quantity and the second indicates the unit (standard) of that quantity. Units can be classified into two groups: fundamental units and derived units. The units used to measure fundamental quantities are called fundamental units. It does not depend on any other unit. Table 1. 1 Fundamental quantity and their SI units Quantity Name of Unit Symbol of the unit Length Meter m Mass kilogram kg Time Second S Temperature Kelvin K Derived Physical Quantities and their Units Physical quantities which depend on one or more fundamental quantities for their measurements are called derived quantities. Speed, area, volume, density and force are examples of derived quantities. The units used to measure derived quantities are called derived units. It depends on fundamental units for their measurement. SI derived units are described by mathematically combining (dividing, multiplying or powering) the base units. Some of the derived quantities and their units are given in table 1.2. Table 1. 2 Derived quantities and their SI units No. Derived quantity Unit 1 Area m x m = m2 2 Volume m x m x m = m3 13  3 Speed m/s 4 Density Kg/m3 Example 1.1: Show how the unit of (a) area and (b) speed is derived from the fundamental units. Solution: (a) The equation for the area of rectangular surface is Area = length x breadth. Both length and breadth are length measurements. Hence they are measured in meter. Unit of area = unit of length x unit of breadth Unit of area = m x m = m2 (b) The equation for speed is Speed = distance/time Thus the unit of speed is the unit of distance (m) over the unit of time (s) = m/s Activity 1.3: Discuss in group about the importance of scientific measurement to the study of science. Let the representative of your group present what you have agreed to your class. Exercise 1.4: Show how the units of the following derived quantities are derived from the unit of base quantities. (a) volume, (b) density and (c) force. Prefixes and Conversion of Base Units Prefix In science we deal with quantities which are both very large and very small. A short hand form of writing very large and very small numbers is known as a prefix. A few of the prefixes used in the SI system of units are shown in Table 1.3. Table 1.3. SI prefixes Prefix Symbol Name Decimal representation Mega M million 1 000 000 14  Kilo k thousand 1 000 Centi c hundredth 0.01 milli m thousandth 0.001 Conversion of base units It is often necessary to convert between units of measurement. For example, a mass measured in grams may be required to convert into kilogram. To convert from one unit to another within the SI, usually means moving a decimal point. If you can remember what the prefixes mean, you can convert within the SI system relatively easily by simply multiplying or dividing the number by the value of the prefix. Example 1.2: Convert 6.5 kilogram (kg) to gram (g). Solution: Since k is a prefix representing 1000, so: 6.5 kg = 6.5 × (1000) g = 6500 g Example 1.3: Convert 200 meters to kilometers. We know that 1 km = 1000m. Then we will ask if 1000m is 1km then what will be 200m in km? 1 km  200 m 200 km Solution: 200 m    0.2 km Exercise 1.5 1000 m 1000 1. Convert the following: a) 0.6 km to cm b) 500 g to kg c) 30 min to hour d) 50 m to mm e) 0.25 kg to g f) 0.5 hour to second 2. Write the following quantities in units with the appropriate prefixes: a) 3500 m b) 0.0012 sec c) 0.01 g 15 Measuring Physical Quantities The measurement of a physical quantity is done by using measuring instruments. In this section we will discuss how to measure mass, length, time, and temperature using their appropriate devices. Measuring the mass of objects Instruments which are used to measure mass are known as balances. The balance compares the mass of an object with a known mass. Different types of balances are there, see Fig 1.4. A spring scale is also used to measure mass. It work based on the principle that the amount of extension (or compression) of a spring is proportional to the mass of the object attached to it. Figure 1.4: Instruments Used to Measure Mass Note that, before taking measurement check that the balance is on a level surface, and reads zero when no load is placed on it. 16 The SI or base unit of Mass is kilogram (kg). For small mass we use gram (g). To measure the mass of objects less than 1 gram, we can use milligram. To measure the mass of big objects we use quintal and tone. 1 kg = 1000 g. 1 g = 1000 mg 1 quintal = 100 kg 1 tone = 1000 kg Example 1.4: How much is 1200 gram in kilogram? 1 Solution: 1200 g  1200  kg  1.2 kg 1000 Exercise 1.6: Convert the following measurement: (a) 2.5 kg to gram, and (b) 200 gram to milligram. Measuring Length Length is a measure of how long an object is. Depending on the size of the length of the object, we are going to use different types of length measuring instrument, see Figure 1.5. Figure 1.5 Instruments used to Measure Length 17 The SU unit of length is meter (m). When we want to measure larger lengths, we can use kilometers. A kilometer is 1000 meter.If we want to measure small things, we can use centimeters. There are 100 centimeters in one meter.If we want to measure very small things, we can use millimeters. There are 1000 millimeters in 1 meter. 1km = 1000 m 1 m = 100 cm 1cm = 10mm Note that when we are measuring length using these device do not forget to place the zero mark exactly at one end of the thing you are measuring and read the scale at the other end. Example 1.6: How many millimeters are there in a meter? Solution: 1m = 100 cm = 100 x 10 mm = 1000 mm Exercise 1.7: Convert the following into the required measures: (a) 8 meters to millimeter. (b) 5500 meters to kilometer. Measuring time Time is used to quantify the duration of events. Time is measured with a stop watch or clock. 18  Figure 1.6: Time measuring Instruments The SI unit of time is second (s). For longer intervals of time the minute (min) and the hour (hr) are used. Still for bigger units of time we use: day, month , year, decades, century and millennium. 1 hour = 60 minutes 1 minute = 60 seconds 1 day = 24 hours 1 week = 7 days 1 year = 365.25 days Example 1.7: How much is one hour in seconds? Solution: 1 hour = 60 minutes = 3600 seconds (60 × 60) Exercise 1.8: How many (a) minutes, and (b) seconds are there in one day? Measuring Temperature Thermometer is the device used to measure the temperature of an object or place. The SI unit of temperature is Kelvin. Degree Celsius (°C) is the commonly used unit of temperature. The reading you will see after putting the thermometer inside the object whose temperature is going to be determined is the temperature of the object. Thermometers could be analogue or digital, see Figure 1.7 19  Figure 1.7: Temperature Measuring Devices Activity 1.4:Measuring your body temperature.  use the digital thermometer to measure the temperature of two people  Compare the two temperatures using the standard temperature of a body of 37°C  Record your observations Activity 1.5: Measuring the temperature of water.  Using a laboratory thermometer, measure the temperature of a warm water.  Record your observations In using thermometer, hold the thermometer at the top, do not hold the bulb of a thermometer and do not let the bulb touch the glass. Safety Never put a laboratory thermometer into your mouth. Accuracy and Precision in Measurement Accuracy refers to how close a measurement is to its accepted or known value. Activity 1.6: If in a laboratory you obtain a mass measurement of 8.2 kg for a given substance, but the actual or known mass is 10 kg, is your measurement accurate? Answer: This measurement is not accurate, because your measurement (8.2 kg) is not close to the known value (10kg). Precision refers to how close two or more measurements are to each other, regardless of whether those measurements are accurate or not. 20 Activity 1.7: In the above example 1.4, if you measure the mass of the given substance five times, and get 3.2 kg, 3.1 kg, 3.25 kg, 3.3 kg and 3.2 kg. Is your measurement precise? Answer: This measurement is precise, because the values are close to each other but not accurate because it is far from the known value (10 kg). This shows that precision is independent of accuracy. You can be very precise but inaccurate. You can also be accurate but not precise. Activity 1.8: The figure below shows 3 results of a student playing a dart game. In the space provided below each figure, write whether the result is (a) accurate but not precise (c) precise but not accurate (b) accurate and precise (d) neither precise nor accurate Exercise 1.9: What is the difference between Accuracy and Precision? Exercise 1.10: 1. Define the following terms: physical quantity, fundamental quantity, derived quantity, accuracy and Precision. 2. State the various indigenous methods of measurement used in Addis Ababa. 3. What are prefixes? 4. What is the difference between accuracy and precision in measurements? 21 1.2 Doing Scientific Investigation After completing this section, you will be able to:  Describe the components of a scientific investigation;  Demonstrate ability to work effectively and respectfully with others in performing fair testing;  Practice scientific investigation procedures using appropriate contents to their age levels. Introduction to Scientific Investigation Science is, in part, a process of learning about the world through observation, inquiry, formulating and testing hypotheses, gathering and analyzing data, and reporting and evaluating findings.This process is referred as the scientific investigation or scientific method. Scientific Method Activity 1.6 What are the applications of scientific method? All sciences, including the social sciences, employ variations of what is called the scientific method. Scientific methodis the process by which scientists approach their work. The Steps of the Scientific Method Based on the type of question being asked, the type of science being applied and the laws that apply to that particular branch of science, you may need to modify the method and alter or remove one or several of the steps. 1. Ask Questions A scientific investigation typically begins with observations. Observations often lead to questions. This question will include one of the key starters, which are, how, what, 22 when, why, where, who or which. The question you ask should also be measurable and answerable through experimentation. It is often something that can be measured with a numerical result, although behavioral results are part of the scientific method as well. 2. Perform Background Research With your question formulated, conduct preliminary background research to prepare yourself for the experiment. You can find information through online searches or in your local library, depending on the question you are asking and the nature of the background data. You may also find previous studies and experiments that can help with your process and conclusions. 3. Establish your Hypothesis Based on the data that were gathered, the researcher formulated a hypothesis. A hypothesis is a tentative explanation for a set of observations. Your hypothesis should also include your predictions that you can measure through experimentation and research.A hypothesis must be based on scientific knowledge, and it must be logical. 4. Test your Hypothesis Next, test your hypothesis by conducting an experiment. Your experiment is a way to quantifiably test your predictions and should be able to be repeated by another scientist. Assess your scientific process and make sure that the conditions remain the same throughout all testing measures. If you change any factors in your experiment, keep all others the same to maintain fairness. After you complete the experiment, repeat it a few more times to make sure the results are accurate. 5. Analyze the Results and Draw a Conclusion You can now take your experiment findings and analyze them to determine if they support your hypothesis. Drawing a conclusion means determining whether what you believed would happen actually happened. If it did not happen, you can create a new hypothesis and return to step three, and conduct a new experiment to prove your new 23 theory. If what you hypothesized happened during the experimentation phase, the final step is putting together your findings and presenting them to others. 6. Communicating Results The last step in a scientific investigation is communicating what you have learned with others. This is a very important step because it allows others to verify your methods and results. If other researchers get the same results as yours, the hypothesis becomes stronger. However, if they get different results, they may not support the hypothesis. When scientists share their results, they should describe their methods and point out any possible problems with the investigation. Finally, communicating results can be done in a variety of ways including scientific papers, blogs, news articles, conferences, etc. Figure 1.9 Steps in Scientific Method Example: Simple experiment with candle that shows the necessary of air for burning Consider how the scientific method applies in this simple experiment with air necessary for burning under two different conditions. 1. Ask Question: Is air necessary for burning? 24 2. Do back ground Research: From different literatures ‘‘air is necessary for burning.’’ 3. Formulate Hypothesis: The null hypothesis is that there will be no air needs for burning. The alternative hypothesis is that there will be air needs for burning. 4. Test Hypothesis by Experiment and Collect Data: Take a candle and fix it on a table. Light the candle. The candle will continue to burn due to continuously available fresh air providing the required oxygen for combustion. Now cover the burning candle by putting an inverted gas jar over it. After a short time, the candle stops burning and gets extinguished. 5. Analyze the Results and Draw Conclusion: When the burning candle is covered with gas jar, then the candle takes away the oxygen necessary for burning from the air enclosed in the gas jar. After some time, when all the oxygen of air inside the gas jar is used up, then the burning candle gets extinguished. This proves that air is necessary for combustion or burning of substances. Figure 1.10 a) Burning of candle b) Candle stops burning 6. Communicate Results: Report your findings in the form of a written report as an oral presentation. Air is necessary for burning. 25  Activity 1.7 Form groups and conductinvestigations on activities listed below. After investigation present your findings to the class. a. What is the effect of sunlight on the growth of bean plant? b. Does a coiled nail act like a magnet? c. How do plants store their food in their leaf? Exercise 1.13 Describe the components of a scientific investigation. Project Work Conduct some investigations (for example, making injera) using local materials and methods (procedures) in groups by reading different reference books or asking a person who is knowledgeable and experienced in the area. Figure 1.11Injera Figure 1.12 Injera being cooked on a griddle ummary of the unit 26 Summary  Measurement is the process of obtaining the magnitude of a quantity relative to an agreed standard.  Indigenous units of measurement for length: cubit, span, digit, foot and pace, for mass weqet and quntal, for time length of a shadow are used.  Fundamental quantities are a set of physical quantities which cannot be expressed in terms of any other quantities. Their corresponding units are called “Fundamental units”.  The physical quantities which can be obtained by mathematically combining (i.e., multiplying and dividing) the fundamental quantities are known as “Derived quantities”. Their corresponding units are called “Derived units”.  Prefixes are symbols representing very large and very small numbers.  Accuracy refers to how close a measurement is to the accepted value while precision refers to how close measurements are to each other.  Scientific methodis the process by which scientists approach their work. Review exercise I. Choose the correct answer from the given alternative 1. Which of the following quantities is a base quantity? a) Area b) volume c) temperature d) force 2. The difference between a base and derived unit is a) Base units are big in value but derived units are small in value. b) Base units are derived from derived units. c) Derived units are derived from base units. d) There is no difference between them. 3. Which of the following is a derived quantity? 27  a) mass b) area c) time d) length 4. The SI unit of density is a) kg/m2 b) kg/m3 c) kg/m d) g/m3 1 5. The prefix that represents is 1000 a) kilo b) mega c) centi d) milli II. Fill in the blank spaces with an appropriate word. 1. Length, mass, time and temperature are ______________ quantities. 2. Area, volume, density and force are ______________ quantities. 3. One million centimeter is equal to _____________ meter. 4. The prefix for a number 0.01 is _______________. 5. The SI unit of volume is ____________________. II. Match the quantities in column-I to their units in column-II: Column I Column II 1 Area (a) K 2 Temperature (b)m3 3 Density (c ) m2 4 Volume (d)kg 5 Mass ( e) kg/m3 IV. Give short answer 1. Write four fundamental quantities with their units. 2. Write four derived quantities with their units. 3. Write the measurement 0.005 m using prefix. 4. Convert 1000 cm to kilometer. 5. The value of acceleration due to gravity on the surface of Earth is known to be 9.81 m/s2. In an experiment students have found the following results. 12.2 m/s 2, 12.3 m/s2, 12.1 m/s2 and 12.08 m/s2. Is this measurement accurate or precise? 28  6. List the steps used in scientific method. Unit Review 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 Explain the concept of measuring physical quantities? 2 Describe the various indigenous methods of measurement? 3 Distinguish between the basic and derived physical quantities? 4 Categorize the basic and derived units of measurements (length, mass, time, temperature, volume, area, density, force)? 5 Identify prefixes and perform conversions among units of measurements? 6 Distinguish between accuracy and precision in measurements? 7 Describe the components of a scientific investigation? 8 Demonstrate ability to work effectively and respectfully with others in performing fair testing? 9 Practice scientific investigation procedures using appropriate contents to their age levels? 29  UNIT TWO COMPOSITION OF MATTER Learning Outcomes: At the end of this unit, you will 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;  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  Parts of an atom (nucleus and electron Shells)  The Subatomic Particles of the atom  Relative mass, the charge and location of sub-atomic particles  Atomic number and mass number  Determination of the electrons, protons and neutrons 2.3 Molecules  Molecules of elements  Molecules of Compounds 30 2.1 Early Thinking about the Composition of Matter After completing this section, you 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;  Compare earlier conceptions of the structure of matter with their conceptions. Activity 2.1 Form groups and discuss the following and present your opinion to the class. 1. What is matter? 2. What do you think matters made up of? The earliest recorded discussion of the basic structure of matter comes from ancient Greek philosophers, the scientists of their day.Some of them argued that matter is continuous i.e., it could be divided endlessly into smaller pieces. Others believed that matter is discrete; i.e., it cannot be infinitely divided. Democritus (460 - 370 B.C)expressed the belief that all matter consists of very small, indivisible particles, which he named atomos(meaning uncuttable or indivisible). He thought of atoms as moving particles that differed in shape and size, and which could join together. According to Democritus matter is discrete. Aristotle (384 – 322 B.C) argued that matter is divided into smallerand smaller parts, the division continuous forever without any limit. He did not believe in microscopic building particles of matter. Therefore, according to Aristotle, matter is continuous and he believed that matter consisted of the combinations of fire, earth, air, and water. 31  Activity 2.2 Form two groups and debate on one of the following ideas assigned to your group. After discussion present your reasons to the class. 1. If matter is divided and subdivided again and again, what would ultimately be obtained? a. Group 1: According to Aristotle’s believe b. Group 2: According to Democritus’s believe Table 2.1Comparison between the discrete and continuous theory of matter Discreteness Theory Continuous Theory  Proposed by Democritus Proposed by Aristotle  There is a limit to which matter is broken Matter is infinitely divisible  Believed in the existence of atoms Rejected the idea of atoms Exercise 2.1 1. Compare and contrast the continuity and discreteness theory of matter. 2.2 Inside of an Atom After completing this section, you 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;  Determine the number of protons, neutrons, and electrons in an atom. 32 What are the two parts of atom? An atom consists of a tiny dense nucleus surrounded by electrons are spread throughout a relatively large volume of space around the nucleus. The nucleus contains positively charged protons and neutral neutrons, so it is positively charged. The electrons are negatively charged. Because the amount of positive charge on a proton equals the amount of negative charge on an electron, a neutral atom has an equal number of protons and electrons. Protons and neutrons have approximately the same mass and are about 1800 times more massive than an electron. This means that most of the mass of an atom is in its nucleus. However, most of the volume of an atom is occupied by its electrons. Figure 2.1 Diagrammatic representation of the atom The subatomic particles Activity 2.3 Draw a simple sketch of hydrogen atom model on your exercise book by using coloured pen following the instructions listed below. i. Draw a small circle labeled ‘‘nucleus’’. ii. Add a smaller circle labeled ‘‘proton’’ inside the nucleus. iii. Add another circle around the nucleus and add a symbol such as a dot for the electron Atoms possess internal structure; that is, they are made up of even smaller particles, which are called subatomic particles. A subatomic particle is a very small particle that 33 is a building block for atoms. An atom contains three fundamental sub atomic particles: proton, electron and neutron. An atom has a definite number of protons, electrons and neutrons. The structure of the atom describes how these particles are arranged to make an atom. The relative charge of a proton is +1. The electron is assigned a charge of −1. The neutron is assigned zero charge. Since an atom has equal number of protons and electrons, it is electrically neutral. A proton has a mass of 1.673 × 10–24 g, and a neutron has a mass of 1.675 × 10–24 g. Thus, a proton and a neutron have almost the same mass. Since the mass of an electron is very small, 9.109 × 10–28 g, its mass is assumed to be negligible or approximately zero because it is ≈ 2000 times less heavy than both the proton and neutron. Table 2.2Nature and location of sub-atomic particles Particle’ Location Actual Mass Relative Actual Charge Relative Name (g) Mass (amu) (C) Charge Proton Nucleus 1.673× 10-24 1.00728 ≈1 +1.60218×10-19 +1 Electron Outside nucleus 9.109× 10-28 0.00055 ≈ 0 -1.60218×10-19 -1 (shell) Neutron Nucleus 1.675× 10-24 1.00866 ≈ 1 0 0 Project Work Prepare hydrogen model by using locally available materials in groups and present your model to the rest of class.. Atomic Number and Mass Number Activity 2.4 Form groups and discuss the following. Share your opinion with your group members and present your group opinion’s to the class. Determine atomic numbers and mass numbers of common elements by using periodic table. 34 All atoms can be identified by the number of protons and neutrons they contain. The atomic number (Z) of an atom equals the number of protons in its nucleus. The atomic number is also the number of electrons that surround the nucleus of a neutral atom. Atomic number (Z) = Number of protons= number of electrons Mass number (A) is the sum of the number of protons and the number of neutrons in the nucleus of an atom.Except for the most common form of hydrogen, which has one proton and no neutrons, all atomic nuclei contain both protons and neutrons. Mass number (A) = Number of protons + Number of neutrons. = Atomic number + Number of neutrons. The mass and atomic numbers of a given atom are often specified using the notation: Mass number Atomic number A Z x Symbol of element 12 Example: 6 C, mass number = 12, atomic number = 6, and C is the symbol of carbon. Determination of the electrons, protons and neutrons Activity 2.5 Form groups and discuss the following. Share your opinion with your group members. 1. Use a periodic table to tell the atomic number, mass number, proton numbers, neutron numbers and electron numbers of the first 10 elements. Proton is equal to the atomic number of atoms. Number of protons = atomic number (Z) Electron: The atom is neutral therefore the number of electrons is equal to the number of protons. Number of electrons = atomic number (Z) = number of protons 35 The number of neutrons in an atom is equal to the difference between the mass number and the atomic number or proton number. Number of neutrons = Mass number (A) - Number of protons Exercise 2.2 Give the appropriate answers for the following questions. 1. Complete the following table. Particle Location Actual Mass (g) Relative Relative Mass (amu) Charge Proton Electron Neutron 2. A nucleus consists of 9 protons and 10 neutrons. Determine: i. The element by referring periodic table ii. Mass number 3. How many neutrons, protons and electrons are there in an atom of the element 14 7 N? 2.3 Molecules After completing this section, you will be able to:  Define molecules;  Give examples of monatomic, diatomic and polyatomic molecules;  Use models or particles model diagram to represent molecules of elements and compounds. 36  Activity 2.6 Form groups and discuss the following. Share your opinion with your group members. After discussion present your findings to the class. 1. What is molecule? 2. Mention some examples of monoatomic, diatomic and polyatomic molecules. Molecules of Elements A molecule of an element consists of only one type of an element. Molecules of elements can be classified as monoatomic, diatomic and polyatomic. 1. Monoatomic molecules are molecules that contain one atom of the element. Examples: He, Ne, Ar, Kr, Xe and Rn are monoatomic molecules 2. Diatomic moleculesare molecules that contain two atoms of the element. Examples: O2, H2, F2, Cl2, I2 are diatomic molecules. Figure 2.2 Diagrammatical representations of Ne and H2. 3. Polyatomic molecules are molecules that contain three atoms of the element. Examples: O3, P4, S8 are polyatomic molecules. Molecules of compounds A molecule of a compound always contains two or more atoms of different elements combined chemically. Water (H2O), ammonia (NH3), carbon dioxide (CO2), etc. are some examples of molecules of compounds. 37 Exercise 2.3 Give the appropriate answers for the following questions. 1. What is a molecule? 2. Classify the following molecules as monoatomic, diatomic or polyatomic? a) Ar c) S8 e) He b) N2 d) O3 f) Br2 3. Draw the diagram representation of ozone (O3) molecule. 4. Which of the following molecules are molecules of elements? Which of them are molecules of compounds? a) Ne b) H2O c) HCl d) Br2 e) NH3 f) P4 38 Unit Review 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 Give a short history of the concept of the atom? 2 Compare and contrast the continuity and discreteness (discontinuity) theory of matter? 3 Compare earlier conceptions of the structure of matter with their conceptions? 4 Describe the structure of an atom as a nucleus containing protons and neutrons, surrounded by electrons in shells (energy levels)? 5 State the relative charge and approximate relative mass of a proton, a neutron and an electron? 6 Draw hydrogen atoms, including the location of the protons and electrons, with respect to the nucleus? 7 Differentiate between mass number and atomic number? 8 Determine the number of protons, neutrons, and electrons in an atom? 9 Define molecules? 10 Give examples of monatomic, diatomic and polyatomic molecules? 11 Use models or particles model diagram to represent molecules of elements and compounds? 1  Key Terms  Atom  Electron shell  Atomic nucleus  Mass number  Atomic number  Molecule  Continuous theory  Monoatomic molecule  Diatomic molecule  Neutron  Discreteness theory  Polyatomic molecule  Electron  Proton Summary  Democritus (460-370 BC) introduced the idea that matter consists of very small indivisible particles called “atoms”.  The three fundamental subatomic particles are protons, neutrons and electrons.  Protons are positively charged.  Neutrons are chargeless.  Electrons are negatively charged.  A proton and a neutron have approximately the same mass; but the mass of an electron is negligible.  The atomic number of an element is the number of protons in the nucleus of an atom of the element.  An atom is electrically neutral because the amount of positive charge on a proton equals the amount of negative charge on an electron.  The mass number is the sum of the number of protons and the number of neutrons in the nucleus of an atom.  The number of neutrons in an atom is equal to the difference between the mass number and the atomic number or proton number. 2   An atom is represented by the notation, A Z Xin which X is the symbol of an element Z is the atomic number, and A is the mass number.  A molecule is the smallest particle of an element or a compound that can exist freely in nature.  Molecules of elements consist of only one type of atoms and can be classified as monoatomic, diatomic or polyatomic.  Molecules of compounds consist of two or more different type of atoms. Review Exercise I. Write ‘‘True’’ if the statement is correct and write ‘‘False’’ if the statement is incorrect. 1. Nucleus consists of protons and neutrons. 2. Atomic number is the number of protons in the nucleus. 3. Molecules of elements consist of two or more different type of atoms. 4. Proton and electron have approximately the same mass. 5. Different elements have the same number of protons. II. Choose the best answer from the given alternatives. 6. The idea that matter is ‘continuous’ was proposed by A. Democritus C. Dalton B. Aristotle D. None 7. The idea of ‘atoms’ first proposed by the Greek philosopher------- A. Aristotle C. Dalton B. Plato D. Democritus 8. Which of the following particles located in the nucleus of an atom? A. Proton and electron C. Electron and neutron B. Neutron and proton D. Proton, electron and neutron 3  9. The sum of the number of protons and neutrons in an atom is known as A. Atomic number C. Mass number B. Atomic mass D. Number of electron 10.The number of neutrons in 1224Mg are A. 12 B. 11 B. 24 D. 13 11.Which of the following statements concerning the nucleus of an atom is correct? A. Contains only neutrons B. Contains all protons and all electrons C. Is always positively charged D. Accounts for most of the total volume of an atom 12.Which of the following molecule is diatomic molecule? A. O2 B. O3 C. P4 D. S8 13.Which of the following statement is false? A. Molecules of elements consist of only one type of atoms. B. Nucleus is positively charged. C. Molecules of compounds consist of only one type of atoms. D. Neutrons have no charge. 14.Which of the following molecule is molecule of elements? A. H2O C. H2 B. NH3 D. HCl III. Give short answers for the following questions. 15.What are the two main parts of an atom? 16.What are the fundamental sub-atomic particles? 17. Determine the atomic number, number of protons, number of neutrons, number 16 of electrons and mass number for 8 O. 4  UNIT THREE CLASSIFICATION OF COMPOUNDS Learning Outcomes: At the end of this unit, you will able to:  Explain the classification of compounds into organic and inorganic;  Write the formulas and names the first ten alkanes, alkenes alkynes and list the uses 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;  Demonstrate scientific inquiry skills along this unit: Observing, classifying, comparing and contrasting, communicating, asking questions, designing experiment, drawing conclusion, applying concepts and problem solving. Main contents 3.1 Introduction 3.2 Organic compounds 3.3 Inorganic compounds 3.4 Neutralization reaction and salts 3.1 Introduction After completing this section, you will be able to:  Define organic compounds as carbon containing compounds and give examples  Define inorganic compounds as compounds of elements other than carbon. 5  Activity 3.1 Form groups and discuss the following. After the group discussion, choose a group representative to present the group’s opinion to the class. 1. State earlier definitions of organic and inorganic compounds. 2. Do you agree with the notion that says: “organic compounds can be synthesized only from animals and plants”? 3. State modern definitions of organic and inorganic compounds. During the latter part of the eighteenth century and the early part of the nineteenth century, chemists began to categorize compounds into two types: organic and inorganic. Compounds obtained from living organisms were called organic compounds, and compounds obtained from mineral constituents of the earth were called inorganic compounds. During this early period, chemists believed that a special “vital force” supplied by a living organism was necessary for the formation of an organic compound. This concept was proved incorrect in 1828 by the German chemist Friedrich Wöhler. Wöhler heated an aqueous solution of two inorganic compounds, ammonium chloride and silver cyanate, and obtained urea (a component of urine). NH4Cl (aq) + AgCNO (aq) NH4CNO (aq) + AgCl (s) Ammonium chloride Silver cyanate Ammonium cyanate Silver chloride O NH4CNO (aq) Heat (NH2)2CO (s) Or Urea H2N C NH2 Soon other chemists had successfully synthesized organic compounds from inorganic starting materials. As a result, the vital-force theory was completely abandoned. The terms organic and inorganic continue to be used in classifying compounds , but the definitions of these terms no longer reflect their historical origins. 6 All organic compounds contain carbon and hydrogen, along with other possible elements such as oxygen, nitrogen, sulphur, halogens and phosphorus except the oxides of carbon, carbonates, hydrogen carbonates, cyanides and cyanates. Inorganic compounds are the compounds consisting of mineral constituents of the earth or generally found in non-living things. The term inorganic compound refers to all compounds that do not contain carbon. Although, carbon dioxide, carbon monoxide, carbonates and hydrogen carbonates are carbon-containing compounds, which are classified as inorganic compounds. Exercise 3.1 Classify each of the following compounds as organic or inorganic. a. C12H22O11 d. C2H5OH b. NaCl e. CH3Cl c. CaO f. C2H4 3. 2 Organic Compounds After completing this section, you 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 ten members of alkanes, alkenes and alkynes;  Describe a homologous series and its general characteristics;  Name the first eight members of alkanes, alkenes and alkynes;  Identify some common uses of organic compounds. 7 Hydrocarbons Activity 3.2 Form a group and perform the following activity. Share your opinion with your group members. 1. What is hydrocarbon? 2. List the sources of hydrocarbons and indicate their location in Ethiopia. A hydrocarbon is a compound that contains only carbon atoms and hydrogen atoms. Hydrocarbons divided into three large classes:alkanes, alkenes and alkynes. Alkanes Alkanes are hydrocarbons that have the general formula CnH2n+2, where, n is the number of carbon atoms present, n = 1, 2, 3….. For example, the molecular formulas of the first four alkanes are C1H2×1+2 = CH4, C2H2×2 + 2 = C2H6, C3H2×3 + 2 = C3H8, and C4H2×4 + 2 = C4H10, respectively. When we compare the formulas of CH4 and C2H6 or C2H6 and C3H8, they differ by one carbon and two hydrogen atoms or – CH2 – group called the methylene group. A family of compounds in which each member differs from the next by one methylene (- CH2-) groupis called homologous series (homo is Greek for “the same as). The members of a homologous series are called homologues. Exercise 3.2 1. Write the formulas of alkanes that contain 5, 7 and 9 carbon atoms. Alkenes Alkenes are hydrocarbons that have the general formula CnH2n, where, n is the number of carbon atoms present, n = 2, 2, 3….. For example, the molecular formulas of the first three alkenes are C2H2×2 = C2H4, C3H2×3 = C3H6, and C4H2×4 = C4H8, respectively. 8 Exercise 3.3 1. Write the formulas of the alkenes that contain 6, 8 and 10 carbon atoms. Alkynes Alkynes are hydrocarbons that have the general formula CnH2n-2, where n = 2, 3, 4, etc. For example, the formulas of the first three alkynes are C2H2×2-2 = C2H2, C3H2×3-2 = C3H4, and C4H2×4-2 = C4H6, respectively. Exercise 3.4 1. Write the formulas of the alkynes that contain five-eight carbon atoms. Nomenclature (Naming) of Hydrocarbons Activity 3.3 Form a group and perform the following activity. Share your opinion with your group members. 1. How do we give specific name to a hydrocarbon? 2. Are hydrocarbons named based on certain rules or randomly? The name of hydrocarbons is derived from the number of carbon atoms present (prefix) and the ending it contains (suffix).The names of alkanes, alkenes and alkynes end with the suffixes ‘-ane’, ‘-ene’ and ‘-yne’, respectively. i. a prefix- indicating the number of carbon atoms (listed in Table 3.1) and ii. a -suffix indicating the type of the functional group present in the molecule or the type of hydrocarbon. Table 3.1Prefixes commonly used to indicate one to ten carbon atoms. Number of Prefix Number of carbon Prefix carbon atoms atoms 1 Meth- 6 Hex- 2 Eth- 7 Hept- 9  3 Prop- 8 Oct- 4 But- 9 Non- 5 Pent- 10 Dec- Example 1: Write the names of alkanes; CH4 and C3H8. Solution:  CH4 contains one carbon atom. So, we use the prefix ‘meth-’ and adding the suffix ‘-ane’ i.e. meth + ane. Thus the name of CH4 becomes methane.  C3H8 contains three carbon atoms. So, we use the prefix ‘prop-’ and adding the suffix ‘-ane’ i.e. prop + ane. Thus the name of C3H8 becomes propane. Example 2: Write the names of alkenes; C2H4 and C4H8. Solution:  C2H4 contains two carbon atoms. So, we use the prefix ‘eth-’ and adding the suffix ‘-ene’ i.e. eth + ene. Thus the name of C2H4 becomes ethene.  C4H8 contains four carbon atoms. So, we use the prefix ‘but-’ and adding the suffix ‘-ene’ i.e. but + ene. Thus the name of C4H8 becomes butene. Example 3: Write the names of alkynes; C3H4 and C4H6. Solution:  C3H4 contains three carbon atoms. So, we use the prefix ‘prop-’ and adding the suffix ‘-yne’ i.e. prop + yne. Thus the name of C3H4 becomes propyne.  C4H8 contains four carbon atoms. So, we use the prefix ‘but-’ and adding the suffix ‘-yne’ i.e. but + yne. Thus the name of C4H6 becomes butyne. Exercise 3.5 1. Write the formulas and names of alkanes, alkenes and alkynes containing five to ten carbon atoms. Uses of Common Organic Compounds Many organic compounds are very useful in our daily life. Some important organic compounds and their uses are described in the following section. 10 Methane, CH4 Methane is used primarily as fuel for cooking, heating and generating electricity. Methane is the main constituents of biogas that is used as a domestic fuel. Propane (C3H6) and Butane (C4H10) The mixture of propane and butane is compressed at a moderate pressure and stored in steel cylinders. It is marked as bottled gas and commonly known as “butagas”. It is mainly used for cooking and heating. Ethyne (C2H2) One of the main uses of ethyne is to produce oxyacetylene flame, which is used in the cutting and welding of steel and iron. Ethanol (Ethyl alcohol) Figure 3.1 Oxyacetylene torch Ethanol is used in the intoxication ingredient of many alcoholic beverages such as beer, wine, tella, ouzo, teji, etc. Nowadays ethanol mixed with petrol is used as a fuel. It is also used in the production of acetic acid, and in hospitals and clinics for cleaning wounds. Ethanoic Acid (Acetic acid) Activity 3.4 Form a group and perform the following activity. Share your opinion with your group members. Why we add ‘acheto’ or ‘vinegar’ when we eat uncooked vegetables such as salad? Table vinegar contains 4% to 8% acetic acid. Vinegar is used as food flavoring agent. It is also used as a disinfectant. For use in preserving vegetables (pickling) it typically ranges up to 18%. 11 Formalin Figure 3.2Adding vinegar When formaldehyde is dissolved in water it is called formalin. Formalin contains 40%, by volume, of formaldehyde. Formalin is used for the preservation of biological specimens, because it makes proteins hard and insoluble. Exercise 3.6 Give the appropriate answers for the following questions. 1. Classify each of the following hydrocarbons as alkane, alkene or alkyne. a. C5H10 c. C8H14 e. C10H18 b. C10H22 d. C8H18 f. C9H18 2. Write the uses of methane, ethyne, formalin, acetic acid and ethanol. 3.3 Inorganic Compounds After completing this section, you will be able to:  State that inorganic compounds are classified into oxides, acids, base and salts;  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 the laboratory by burning sulphur in air and use moist blue litmus paper to test its acidic nature;  Prepare magnesium oxide in the laboratory by burning magnesium ribbon in air and use red litmus paper to test its basicity in water solution;  Define acid and base;  Describe properties a of acids and bases;  Relate acidic properties to the presence of hydrogen ions and basic properties to the presence of hydroxide ions; 12   Name and write formulas for some common acids (HCl, HNO3, H2SO4) and bases (NaOH, KOH, NH4OH), using the periodic table, a list of ions, and rules for naming acids;  Describe how indicators can be used to classify solutions as acidic or basic;  Investigate properties of bases/alkalis experimentally;  In group, with guidance, prepare their own indicator by extracting the colour from a vegetable, such as beetroot, or flowers and evaluate the indicator;  Investigate household chemicals using locally prepared indicators;  Explain the safety precautions while working with acids and bases;  Create a safety booklet dealing with the handling of acids and alkali. Inorganic compounds can be classified into four groups according to their composition and their properties. These include oxides, acids, bases and salts. Oxides Activity 3.5 Form groups and discuss the following. After the group discussion, choose a group representative to present the group’s opinion to the class. 1. Define oxides and give some examples that are not listed below. 2. Are all compounds containing oxygen oxides? Why? Oxides are binary compounds containing oxygen and any other element. Element + Oxygen → Oxide Some common examples of oxides are water (hydrogen oxide, H2O), carbon dioxide (CO2), lime (calcium oxide, CaO), rust (iron (III) oxide), etc. Exercise 3.7 Give the appropriate answers for the following questions. 13  1. Define oxides. 2. Which of the following compounds are oxides? a. CaCO3 d. rust g. SO3 b. KOH e. H2CO3 h. CO2 c. H2O f. CaO Types of Oxides Most oxides are classified as metallic oxides and non-metallic oxides. i. Metallic oxides are binary compounds containing only metals and oxygen. Metal + Oxygen → Metallic Oxide Examples: CaO, Na2O, Al2O3, MgO, etc. ii. Non-Metallic Oxides are binary compounds containing only non-metals and oxygen. Non-metal + Oxygen → Non-metallic Oxide NO2, H2O, CO2, SO2, SO3, etc are common example of non-metallic oxides. Oxides are also classified as acidic and basic oxides depending on their properties or behaviours. Acidic oxides are oxides that react with water to form acids or acidic solutions. They are mostly non-metallic oxides. Some examples of acidic oxides are SO2, P4O6, CO2, etc. Basic oxides are oxides that react with water to form bases or basic solutions. They are mostly metallic oxides. Some examples of basic oxides are Na2O, Li2O, CaO, MgO, etc. Exercise 3.8 Give appropriate answers for the following questions. 1. Predict whether or not the oxide formed from each of the following elements is a basic oxide and an acidic oxide. a. Calcium c. Sodium e. Sulphur b. Carbon d. Magnesium f. Phosphorus 2. Classify the following oxides as metallic or non-metallic oxides. 14  a. CO2 c. SO3 e. NO2 b. MgO d. CaO f. K2O Properties of Oxides Properties of Acidic Oxides Activity 3.6 Form groups and discuss the following. After the group discussion, choose a group representative to present the group’s opinion to the class. Predict the nature of the oxides formed by some non-metals such as carbon and phosphorus. An acidic oxide or acid anhydride dissolves in water, to form acidic solution or an acid. Acidic oxide + Water → Acid Examples: SO3 + H2O → H2SO4 CO2 + H2O → H2CO3 Acidic oxides react with bases to form salts and water. Acidic oxide + Base → Salt + Water Examples SO3 + Ca(OH)2→ CaSO4 + H2O CO2 + 2NaOH → Na2CO3 + H2O Acidic oxides react with basic or metallic oxides to form salt. Acidic oxide + Basic oxide → Salt Examples CO2 + Na2O → Na2CO3 SO3 + CaO→ CaSO4 15 Properties of Basic Oxides Activity 3.7 Form groups and discuss the following. After the group discussion, choose a group representative to present the group’s opinion to the class. Predict the nature of the oxides formed by some metals such assodium, potassium and calcium.. A basic oxide or basic anhydride reacts with water to produce a base or alkali. Basic oxide + Water → Base (alkali) Examples: CaO + H2O → Ca(OH)2 K2O + H2O → 2KOH Basic oxides react with acidic oxides to form salts. Basic oxide + acidic oxide → salt Examples CaO + CO2→ CaCO3 Na2O + SO3→ Na2SO4 Basic oxides react with acids to form a salt and water. Basic oxide + Acid → salt + water Examples: CaO + 2HCl → CaCl2 + H2O Na2O + H2SO4→ Na2SO4 + H2O Exercise 3.9 1. What are the missing products ‘X’, ‘Y’ and ‘Z’ in the following equations? a. CO2 + H2O → X b. CaO + H2O → Y c. CaO + CO2→ Z Laboratory Preparation of Sulphur dioxide and Magnesium Oxide Sulphur dioxide and magnesium oxide can be prepared in the laboratory by using direct synthesis method. Direct synthesis involves the combination of oxygen with active metals and non-metals. 16 Non-metal + Oxygen → Non-metallic oxide Example: S + O2 → SO2 Metal + Oxygen → Metallic oxide Example: 2Mg + O2→ 2MgO Experiment 3.1 1 Title: Preparation of Sulphur Dioxide Objective: To prepare sulphur dioxide 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. Place a small amount of powdered sulphur in a deflagrating spoon and heat it as shown in Figure 3.3. 2. When it starts burning, put it into a gas jar. 3. When the burning stops, add 5 mL of water to Figure 3.3 Burning of sulphur in air the gas jar and shake it. 4. Put blue and red litmus paper, one after the other, in the jar. 5. Record your observations Observation and Analysis: a. What is the color of the flame when sulphur burns in air? b. What happens to the color of blue and red litmus papers in step 4? c. Write the chemical equation for this combustion reaction. d. Classify the oxide formed by the combustion of sulphur as acidic or basic. Experiment 3.2 1. Title: Preparation of Magnesium Oxide 17 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, sand paper, and goggle. Procedure: 1. Cut about 2-4 cm of magnesium ribbon. 2. Clean the surface of it properly with sand paper. 3. Hold the magnesium ribbon with the help of a pair of tong and burn it over a flame from the Bunsen burner as shown in Figure 3.4. The Figure 3.4 Burning of magnesium in air moment it starts burning, put the burning metal into a crucible and collect the product. 4. Add a small amount of water to the resulting powder in the crucible and shake it. 5. Take red and litmus paper and bring them turn by turn in contact with the solution. 6. Record your observations. Observation and Analysis: a. Why you were cleaned the magnesium ribbon with sand paper? b. What is the color of the flame produced when magnesium burns in air? c. Write the chemical equation for the reaction. d. What happens to the color of the red and blue litmus papers? e. Is the resulting solution basic or acidic? Exercise 3.10 1. Describe how you could prepare each of the following oxides. a. MgO b. SO2 Acids and Bases Acids 18  Activity 3.8 Form a group and perform the following activity. Imagine a taste experiment using orange and lemon. After tasting, present your feeling to the class. 1. What do you feel during tasting lemon? 2. What do you feel during tasting orange? 3. Are they having the same taste? 4. Are they acidic in nature? Why? Acids are a group of substances that release hydrogen ions (H +) when they are in aqueous solution. Acids have sour taste. Examples: lemon juice, vinegar, sour ‘tella’ and milk are some acidic substances in our daily life. HCl, H2SO4 and HNO3 are common laboratory acids. They are also called mineral acids. Bases A base is an oxide or hydroxide of a metal which neutralizes acid to form salt and water. Bases which are soluble in water are called alkalis. An alkali is a substance that releases hydroxide ion (OH–) when dissolved in water. Bases have bitter taste. Examples:NaOH, Ca(OH)2 Naming and Writing Formula of Acids and Bases Activity 3.9 Form groups and discuss the following. After the group discussion, choose a group representative to present the group’s opinion to the rest of class. 1. Write the formulas of hydrochloric acid, sulphuric acid and nitric acid. 2. Write the formulas of sodium hydroxide, calcium hydroxide, potassium hydroxide and ammonium hydroxide. 19 When naming an acid, you can consider the acid to consist of an anion combined with as many hydrogen ions are needed to make the molecule electrically neutral. Therefore, the chemical formulas of acids are in the general form HnX, where X is a monoatomic or polyatomic anion and n is a subscript indicating the number of hydrogen ions that are combined with the anion. The rules that used to named an acid with the general formula HnX. 1. When the name of the anion (X) ends in –ide, the acid name begins with the prefix hydro-. The stem of anion has the suffix –ic and is followed by the word acid. 2. When the anion name ends in –ite, the acid name is the stem of the anion with the suffix –ous, followed by the word acid. 3. When the anion name ends in –ate, the acid name is the stem of the anion with the suffix –ic followed by the word acid. Table 3.2 Naming of common acids Anion Example Acid name Example ending -ide Chloride, Cl- Hydro-(stem)-ic acid HCl (Hydrochloric acid) -ite Sulfite, SO32- (Stem)-ous acid H2SO3 (Sulfurous acid) -ate Nitrate, NO3- (stem)-ic acid HNO3 (Nitric acid) Sulphate, SO42- (stem)-ic acid H2SO4 (Sulphuric acid) Bases are named in the same way as other ionic compounds: the name of the cation is followed by the name of the anion i.e. hydroxide. Examples: NaOH (sodium hydroxide), Ca(OH)2 (calcium hydroxide), NH4OH (ammonium hydroxide) 20 Exercise 3.11 Give the appropriate answers for the following questions. 1. Define the following terms and give some examples for each. a. Acid b. Base 2. Which ion is a characteristic of all acids in water solution? 3. Copy and complete the following table in your exercise book. Name Formula Name Formula Hydrochloric acid Calcium hydroxide HNO3 KOH Sulfuric acid NaOH Acid – Base Indicators Acid-base indicatorsare dyes extracted from plants that show the presence of an acid or a base by undergoing specific color changes when placed in a solution. Litmus, methyl orange and phenolphthalein are common indicators. Properties of acids and bases Properties of Acids Acids generally have the following properties: 1. Acids have a sour taste 2. Acids change the colour of 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 solutions of hydrochloric acid and sulphuric acid. Procedure: 21  1. Label three clean test tubes. 2. Pour about 5 mL of dilute H2SO4 into three test tubes. 3. 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. 4. Add few drops of phenolphthalein in the second and few drops of methyl orange in the third and observe if there is colour change. 5. Repeat the above procedure using dilute HCl and HNO3 solution. Observation and analysis: Record your findings in the following table. Acid Color of the indicator in the acid solution Litmus Phenolphthalein Methyl orange Dilute H2SO4 Dilute HCl Diluted HNO3 Write a laboratory report in groups and submit it to your teacher. 3. Reaction of Acids with metals Dilute acids react with active metals like zinc, magnesium, iron and aluminum to form salts and liberate hydrogen gas. Active Metal + Dilute Acid →Salt + Hydrogen Example Ca + 2HCl →CaCl2 + H2 Mg + H2SO4 → MgSO4 + H2 Experiment 3.4 Title: Reaction of an acid with a metal 22 Objective: To investigate the reaction of zinc metal with hydrochloric acid. Materials required: Test tube, narrow jet test tube, candle, cork, zinc metal, dilute HCl, lighter or match, steel wool, and stand and clamp. Procedure: 1. Set up the apparatus as shown in. 2. Pour about 5 mL of dilute HCl into a Figure 3.5 Reaction of Zn with HCl test tube. 3. Clean a piece of zinc with the steel wool until it is shiny. 4. Add zinc to the test tube containing dilute HCl, close the test tube with a cork, deep narrow jet tube through cork and record your observations. 5. Light a candle using lighter or match and bring near the lighted candle in to the mouth of the narrow jet tube. 6. Repeat the above procedure using dilute sulphuric acid solution. Observation and analysis: a. Why was the piece of zinc cleaned with steel wool? b. What happens when you drop zinc metal into the test tube containing dilute HCl? c. How do you know that a gas is produced in the reaction? d. What is the colour of the gas? e. What happens when the lighted candle is brought near the mouth of the narrow jet tube? f. Write the chemical equation for the reaction between: i. Zinc and hydrochloric acid. ii. Zinc and sulphuric acid. 23 Write a laboratory report in groups and present to the rest of the class. 4. Reaction of Acids with Carbonates and Hydrogen Carbonates Acids react with carbonates and hydrogen carbonates to form salts, water and carbon dioxide gas. Acid + Carbonate → Salt + Water + Carbon dioxide Example 2HCl (aq) + CaCO3 (s) →CaCl2 (aq) + H2O (l) + CO2 (g) Example Acid + Hydrogen carbonate →Salt + Water + Carbon dioxide H2SO4 (aq) + Ca(HCO3)2 (aq) →CaSO4 (aq) + 2H2O (l) + 2CO2 (g) 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: Dilute hydrochloric acid, dilute sulphuric acid, calcium carbonate, sodium hydrogen carbonate, test tubes, test tube rack, lime water (calcium hydroxide solution), spatula, and rubber stopper. Procedure: 1. Using a spatula, add calcium carbonate powder or a lump of calcium carbonate into the first test tube and 5 mL of lime water into the second test tube. 2. Add 5 mL of dilute hydrochloric acid into a test tube containing calcium carbonate cover its mouth with rubber stopper immediately and hold it in inclined position. 3. Bring the mouth of the test tube containing lime water with your other hand holding it in an inclined position closer to that of the test tube which you covered with rubber stopper. 24  4. Remove the stopper so that the gas produced can escape into the test tube containing lime water. Shake the test tube and see if there is any colour change. 5. Repeat the above procedure using sodium hydrogen carbonate and dilute sulphuric acid. Observation and analysis: a. Is there formation of bubbles in step 2? b. If yes, what does the formation of bubbles indicate? c. What happens to the lime water used in step 4? Why is that so? d. Write the equation for the reaction: 1. between hydrochloric acid and calcium carbonate. 2. between sodium hydrogen carbonate and sulphuric acid. 3. that occurs in step 4. 5. Acids neutralize bases. Acids react with bases and basic oxides to form salts and water. Acid + Base →Salt + Water. Examples: 2HCl + Ca(OH)2→CaCl2 + 2H2O H2SO4 + 2NaOH → Na2SO4 + 2H2O The reaction of an acid with a base is called neutralization reaction. Experiment 3.6 Title: Neutralizing effect of an acid on a base. Objective: To investigate the neutralizing effect of sulphuric acid on sodium hydroxide. Materials required: Dilute hydrochloric acid, sodium hydroxide solution, conical flask, phenolphthalein, burette, stand, clamp, measuring cylinder, blue and red litmus papers. Procedure: 1. Set up the apparatus as shown in 2. Fill the burette with dilute hydrochloric acid. 25  3. Measure 20 mL of sodium hydroxide solution, pour it into a conical flask and add about five drops of phenolphthalein. 4. Open the stop cock of the burette; add hydrochloric acid to the sodium hydroxide solution with your one hand, while shaking the conical flask with your other hand. 5. When the colour begins to disappear, add the acid drop by drop shaking the flask continuously. 6. When the colour disappears, completely, close the stop cock of the burette immediately and check the solution in the conical flask using blue and red litmus papers. Figure 3.6 Neutralization reaction of hydrochloric acid with sodium hydroxide Observation and analysis a. What colour appeared when phenolphthalein is added to the solution in the conical flask in step 3. b. Why does the colour disappear in step 6? c. Does the solution obtained in step 6 affect the colour of either blue or red litmus paper? d. Write the balanced chemical equation for the reaction that takes place in this experiment. Write a laboratory report in groups and present your findings to the rest of the class. 26 Properties of Bases 1. Bases have bitter taste. 2. Effect on acid-base indicators Alkalis change the colour of 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, diluted sodium hydroxide (NaOH) solution, test tubes, test tube holder and test tube rack. Procedure: 1. Take four clean test tubes. 2. Add about 5 mL NaOH solution in each of the test tubes and label the test tubes as 1, 2, 3, and 4 as shown in Figure 3.7. 3. Put red litmus paper, blue litmus paper, 2 drops Figure 3.7 Testing the effect of phenolphthalein solution and 2 drops of methyl of a base on indicators orange solution in test tubes 1, 2, 3 and 4, respectively. 4. Observe the colour change and record your observation. 5. Repeat the above procedure using ammonia solution. Observation and analysis: a. Record your findings in the following table. Base Color of the indicator in the base solution Red litmus Blue litmus Phenolphthalein Methyl orange Dilute NaOH NH4OH solution 27  b. What do you conclude from this experiment? Write a laboratory report in groups and present your findings to the rest of the class. 3. Bases neutralize acids. Bases react with acids (acidic oxides) to form salt and water. Base + Acid →Salt + Water Example Ca(OH)2 + H2SO4→CaSO4 + 2H2O Experiment 3.8 Title: Neutralizing effect of a base on an acid Objective: To investigate the neutralizing effect of sodium hydroxide on hydrochloric acid. Materials required: Sodium hydroxide solution, hydrochloric acid, conical flask, phenolphthalein, burette, stand, clamp, measuring cylinder, blue and red litmus papers. Procedure: Figure 3.8 Neutralization reactions of 1. Set-up the apparatus as shown in hydrochloric acid and sodium hydroxide 2. Fill the burette with sodium hydroxide. 3. Measure 20 mL of hydrochloric acid solution, pour into a conical flask and add five drops of phenolphthalein. 4. Open the stop cock of the burette; add sodium hydroxide to the acid solution with your one hand, and shaking the conical flask with the other hand. 5. When the colour begins to appear, add the base drop by drop shaking the flask continuously. 6. When the colour becomes intense, close the stop cock of the burette immediately and check the solution in the conical flask using blue and red litmus papers. 28 Observation and analysis: a. What colour appeared when phenolphthalein is added to the solution in the conical flask in step 3? b. Why does the colour appear in step 6? c. Does the solution obtained in step 6 affect the colour of blue or red litmus paper? d. Write the balanced equation for the reaction that take place in this experiment. Write a laboratory report in groups and present your findings to the rest of the class. Project work Preparation of natural indicator from beetroot How do you prepare your own indicator using beetroot at home? Explain. Hint:- Materials you will need: Beetroot 2-3, knife, water, spoon, boiler, lemon juice (citric acid) Procedure: 1. Take some beetroots, wash them and peel them with the help of a knife. 2. Chop or cut the beetroot into pieces. 3. Put these pieces into a boiler and boil it 30-60 minutes. 4. Filter and collect only juice. 5. Add 5 to 6 drops of beetroot juice to lemon juice and mix it. Observation and analysis 1. What colour is appear in step 5? 2. Why the colour of orange juice changed after the addition of beetroot juice? 3. Is your indicator effective? 4. What do you conclude from this proje