Science Grade 8 Past Paper 2021 PDF

SCIENCE Grade C S CIE NCE | GR A D E 8 M Y CM MY CY CMY K Mauritius Institute of Education under the aegis of © Mauritius Institute of Education - 2021 ISBN: 978-99949-44-96-5 Ministry of Education, Tertiary Education, Science and Technology Based on the National Curriculum Framework: Grades 7, 8 & 9 (2017) - Nine-Year Continuous Basic Education SCIENCE Grade i Professor Vassen Naëck - Head Curriculum Implementation,Textbook Development and Evaluation SCIENCE PANEL MAURITIUS INSTITUTE OF EDUCATION - Coordinator, Associate Professor, MIE Dr Ravhee Bholah - Associate Professor, MIE Dr Fawzia Bibi Narod - Associate Professor, MIE Dr Anwar Bhai Rumjaun - Associate Professor, MIE Mohun Cyparsade - Associate Professor, MIE Dr Sarojiny Saddul-Hauzaree - Educator Wazeela Delawarally-Ahsun - Educator Ajeshwaree Douquia - Educator Mehendra Katwaroo - Educator Maya Mohabeer - Educator Preeya Buchiah-Narayanasawmy - Educator Kiran Saddul-Ramasamy - Educator Maneeshah Ramkurrun - Educator Sandeep Seebaluck - Educator Karuna Baguant Design Kamla Ernest - Chief Technician, MIE Vedita Jokhun - Graphic Designer, MIE Leveen Nowbotsing - Graphic Designer, MIE Rakesh Sookun - Graphic Designer, MIE Acknowledgements The Science textbook panel wishes to thank: - Dhirendra Ramroop (Associate Professor, MIE), Shakeel Atchia (Lecturer, MIE) and Vickren Narrainsawmy (Lecturer, MIE) for vetting. - Rajendra Korlapu--Bungaree (Senior Lecturer, MIE) for proofreading. © Mauritius Institute of Education - 2021 ISBN: 978-99949-44-96-5 Consent from copyright owners has been sought. However, we extend our apologies to those we might have overlooked. All materials should be used strictly for educational purposes. ii FOREWORD As the first cohort to embark on the Nine Year Continuous Basic Education at secondary level, we are pleased to offer you a new series of Grade 8 textbooks. These textbooks have been designed in line with the National Curriculum Framework (NCF) and syllabi for Grades 7, 8 and 9 − documents that offer a comprehensive notion of learning and teaching with regard to each subject area. These may be consulted on the MIE website, www.mie.ac.mu. This set of textbooks builds upon the competencies acquired at Grade 7 level. As per the philosophy propounded by the NCF, the content and pedagogical approach as well as the activities allow for an incremental and continuous improvement of the learners’ cognitive skills. The content is contextual and based on the needs of our learners which is constructed on a spiral basis. The comments and suggestions of a variety of stakeholders have been kept in mind. We are especially appreciative of those made by educators who have been part of our validation panels, and whose suggestions emanate from long standing experience and practice in the field. The production of this series of textbooks continue to be a challenge for the writers who have ensured that the learners’ experience is further enriched. I would therefore wish to thank all those who have been part of the whole process, for the time they devoted to it and their ability to maintaining the high standard and quality of the textbooks, while ensuring that the objectives of the National Curriculum Framework are skilfully translated in the content. Every endeavour involves a number of dedicated, hardworking and able staff whose contribution needs to be acknowledged. Professor Vassen Naeck, Head Curriculum Implementation and Textbook Development and Evaluation, who has provided the guidance with respect to the objectives of the NCF, while ascertaining that the instruction designs are appropriate for the age group being targeted. I also acknowledge the efforts of the graphic artists for putting in much hard work to ensure the quality of the MIE’s publications. My thanks go equally to the support staff who ensured that everyone receives the necessary support and work environment which is conducive to a creative endeavour. I am thankful to all those who provided the support and to the Ministry of Education, Human Resources, Tertiary Education and Scientific Research for giving us the opportunity to be part of the whole reform process. Wishing plenty of joy and success to all students. Dr O Nath Varma Director Mauritius Institute of Education iii PREFACE The Grade 8 science textbook is in compliance with the National Curriculum Framework (NCF, 2017) and the Teaching and Learning Syllabus (TLS, 2017) for science. Designed and constructed over nine units using a spiral approach, the textbook ensures a smooth transition from Grade 7 to Grade 8 by building upon content learnt up to Grade 7. The use of everyday experiences and contexts that students can easily relate to is favoured. The textbook is conceptualised in such a way that it includes a number of inquiry-based activities and accompanying tasks for learners. In line with the constructivist approach, the activities will enable learners to build and reinforce understanding of science concepts. It attempts to develop in students the necessary skills, attitudes and values for scientific inquiry. As such, a conscious effort must be made to actively engage pupils in all activities and to allow them to manipulate specimens, materials, simple equipment and apparatus safely and under supervision. Though many questions are incorporated within the activities, educators are encouraged to prompt learners with additional questions while implementing them in the classroom. In addition to the activities, the textbook includes important features that support effective learning and teaching. The “What I have learnt” icon summarises the concepts learnt through the activities. “Find out” features throughout the textbook and aims at encouraging students to look for information beyond the scope of the textbook and to develop the habit and skills of looking for information from various sources. The “Did you know?” icon is included to trigger students’ interest and curiosity about science. This section not only provides them with interesting information related to the concepts being addressed but it also helps to stimulate their curiosity and stretch their imagination further. “Test yourself” is for formative purposes. The “Dictionary corner” is often included to help students understand new words that may be difficult for them to grasp. Suggestions are made for “Project work” to promote cooperative learning. A “Summary of unit” and “Concept map” are incorporated at the end of each unit to clearly summarise all the key and relevant concepts learnt. With the visual impact that graphic organisers afford, it is hoped that learning is aided, consolidated and eventually a high learning retention rate is ensured. The “End of Unit Exercises” are meant for summative assessment purposes. They provide educators with opportunities to assess learners’ understanding of concepts addressed in the units and to provide timely feedback and support. iv This section comprises a variety of exercises, such as fill-in-the-blanks, multiple choice and structured questions, amongst others. It is recommended to encourage learners to justify their answers as and when appropriate as this promotes critical thinking, analysis and deeper conceptual understanding. By adopting a differentiated approach, educators are expected to develop more assessment exercises to assess learners of different abilities. In the conceptualisation of the textbook, care is taken to incorporate learnercentred strategies like concept cartoons, role-play, project-based learning and concept mapping to actively engage the learners in the learning process. Furthermore, applications of the science concepts learnt in real life situations are highlighted. Additionally, the textbook addresses some of the issues of science, technology and society. This is accomplished through activities, project work and discussions which help learners appreciate how science and technology are related to society. It is expected that educators use the textbook to devise and plan further inquiry-based activities. Students must be given ample time to actively engage in the activities, communicate their findings and observations in multiple ways, discuss with their friends and teachers and think before writing down their answers. It is sincerely hoped that the textbook helps motivate learners, stimulates their interest in science and develops the habits of mind and skills for scientific inquiry. Dr (Mrs) Sarojiny Saddul-Hauzaree Coordinator The Science Panel v Table of Contents UNIT 1 Measurement in Science Pg 1-24 UNIT 2 Food and Nutrients Pg 25-50 UNIT 3 Mixtures and Separation Techniques Pg 51-82 UNIT 4 Forces and Pressure around us Pg 83-120 UNIT 5 Digestive and Respiratory Systems Pg 121 -160 UNIT 6 The Language of Chemistry Pg 161-200 UNIT 7 Work, Energy and Power Pg 201-240 UNIT 8 Acids, Bases and Salts Pg 241-282 UNIT 9 Communicable & Non-communicable Diseases Pg 283-306 vi Measurement in Science Unit 1 Unit Measurement in Science 1 Learning Outcomes At the end of this unit, you should be able to: Express physical quantities in appropriate SI units Recall the use of different instruments to measure volume and mass of solid objects Calculate the volume of regularly and irregularly shaped solids Demonstrate a simple understanding of accuracy in measurements Demonstrate an understanding of density Define density as the mass per unit volume of a substance mass volume State the formula for density = Recall and use the formula for density in calculations Discuss the experimental determination of the density of a solid through the measurement of mass and volume Compare the relative densities of solids, liquids and gases Measurement is something we make in everyday life. In a supermarket, for example, rice is sold by measuring its mass and liquid milk by its volume. In a hardware shop, electric wires are sold by length and tiles are sold by area. A physical quantity has a magnitude and a unit. In Grade 7, you were introduced to physical quantities like length, area, volume, time, mass and temperature along with their SI units. Physical quantities like length, time, mass and temperature are measured directly, using a ruler, a stopwatch, a beam balance and a thermometer respectively. Physical quantities like volume are either measured directly or calculated using appropriate formulae. ACTIVITY 1.1 - Recalling physical quantities and their units You must have seen the following items in shops: (a) Cloth (b) Land (c) Oil 1 Unit Measurement in Science 1 (d) Flour (e) Diesel (f ) Rice Discuss in groups and find out which of these are purchased by mass, volume, area or length. Fill Table 1 and state the unit/s in which they are usually measured. Table 1 Item Purchased by mass, volume, area, length Unit(s) in which it is measured rice flour oil land diesel cloth TEST YOURSELF 1. Which two physical quantities does a pediatrician measure to monitor the growth of a baby? Name the two measuring instruments used and state the units of measurement. Physical quantity Instruments used Unit of measurement 2. You have fever and you are urgently driven to the dispensary. Which measurement does the nurse take? State the instrument used and the unit of measurement. Measurement taken 2 Instrument used Unit of measurement Measurement in Science Unit 1 3. The physical education teacher told you that on the annual sports day, you broke the record at school level for the 100 metre race. Which measurement did your teacher use? Which instrument did he/she use and what was the unit of measurement? Measurements taken Instruments used Unit of measurement 1. 2. DID YOU KNOW… One of the greatest scientists of our time, Lord Kelvin stated that: “When you can measure what you are speaking about and express it in numbers, you know something about it.” The SI unit of temperature honours his contribution to science. Lord Kelvin FIND OUT What are the main scientific contributions of Lord Kelvin? Present your answer in a poster. Measuring volume You learnt in Grade 7 that the volume of a substance is the amount of space it occupies. The SI unit of volume is the cubic metre, m3. Another commonly used unit is cubic centimetre, cm3. Solids have regular or irregular shapes and divided into regular and irregular objects. A regular object has a well-defined shape. Its volume can be calculated using well-known formulae. Examples of regular objects are the cube, cuboid, cylinder and sphere. Cube Cuboid Cylinder Sphere 3 Unit Measurement in Science 1 An irregular object does not have a well-defined shape. It has an irregular shape. Two examples are shown below. Stone Sea shell ACTIVITY 1.2 - Distinguishing between regular and irregular objects Materials you will need: One milk box, a Rubik’s cube, a billiard ball, a cylindrical food can, a stone Procedure: 1. Observe the five objects given to you. 2. Discuss in groups and then complete Table 2 to indicate whether they are regular or irregular objects. What characteristic are you observing? Table 2 Object 1. Milk box 2. Rubik’s cube 3. Billiard ball 4. Food can 5. Stone 4 Regular / Irregular object Measurement in Science Unit 1 3. List two other examples of (i) regular (ii) irregular solids. Regular solids: ______________________________________ , ______________________________________ Irregular solids: , ______________________________________ ______________________________________ WHAT I HAVE LEARNT A physical quantity has a magnitude and a unit. Most physical quantities can be measured. SI units are used for scientific and technical work in many parts of the world. Solids have regular or irregular shapes. A regular solid has a well-defined shape unlike an irregular solid. The space occupied by a solid is its volume. ACTIVITY 1.3 - Calculating the volume of a cuboid Materials you will need: A large box from a supermarket, measuring tape / metre rule Procedure: 1. Place the box on the table. 2. Measure the length (L), width (W) and height (H) of the box. Enter your measurements in the table below. Length of box, L ____________________ cm L Width of box, W W ____________________ cm H Height of box, H ____________________ cm Calculate the volume of the box. FIND OUT How is the volume of a cylinder calculated? TEST YOURSELF 1. A toothpaste box is 3 cm × 4 cm × 15 cm in size. Calculate its volume in (i) mm3 (ii) cm3 (iii) m3. 2. The interior dimensions of a room are 3 m × 5 m × 8 m. (i) Calculate the volume of air in the room. (ii) What assumption did you make in this calculation? (iii) Which instrument will you use to measure the interior dimensions of the room? 5 Unit Measurement in Science 1 3. A cheese crate has interior dimensions of 40 cm × 30 cm × 20 cm. It is completely filled with identical cheese boxes each of size 10 cm × 6 cm × 4 cm (i) Calculate the interior volume of the crate. (ii) Calculate the volume of one cheese box. (iii) Calculate the number of cheese boxes in the crate. 30 cm 40 cm 20 cm Volume of liquids After studying the volume of a regular solid, we now move to the volume of a liquid. Two apparatus commonly used in the physics laboratory for measuring the volume of liquids are the graduated measuring cylinder and beaker. They are available in different “capacities” for measuring small, as well, as large volumes. By “capacity’’, we mean the maximum volume the cylinder or beaker can hold. Measuring cylinder Beaker A measuring cylinder has markings on it to enable us to read the volume. These markings are more accurately known as graduations. Normally, the graduations are in cm3 or in mL. 1cm3 is the same volume as one mL. 1cm3 = 1mL When water is poured into a measuring cylinder or any other container, the liquid forms a curved surface at the edge. This curved surface is known as the “meniscus” of the liquid. While reading volume, the eye must be at the same level as the lower meniscus. 6 Meniscus Eye at same level as the meniscus Measurement in Science Unit 1 Accuracy in measurement A measurement needs to be accurate. By “accurate”, we mean how close our measured value is to the true value. In order to improve accuracy, we need to avoid errors of measurement. Two main errors are: (i) Zero error (ii) Parallax error What is zero error? An instrument has zero error if it gives a non-zero reading when the true reading is zero. Look at this electronic top pan balance in Figure 1(a). It has a zero error. There is nothing on it, but it is not reading zero. Figure 1 (a) Figure 1 (b) Top pan balance with zero error Compression balance without zero error What effect do you think this will have on all the readings? _____________________________________________________________________________ ACTIVITY 1.4 - Using a compression balance with zero error Figure 2 (a): Compression balance with oranges Figure 2 (b): Empty Compression balance Study Figure 2. 1. Write down the mass of the oranges as shown by the balance. _________________ 2. What is the reading of the balance after the oranges are removed? _________________ 3. What is the true mass of the oranges? _________________ 4. How is this error called? _________________ 5. What precaution should be taken when making a measurement with a balance? _____________________________________________________________________________ 7 Unit Measurement in Science 1 ACTIVITY 1.5 - Understanding parallax error The length of the pen is being measured. It is being taken from three different positions by three observers A, B and C. B A C 1. Record the readings by A, B and C. Observer A ____________________ cm Observer B ____________________ cm Observer C ____________________ cm 2. Which observer makes a correct measurement? _________________ 3. Name the error which the other two observers are making. _________________ 4. How can this error be avoided? _______________________________________________ Parallax error in the measurement of volume Parallax error is a common error made in the measurement of volume, for example, when using a measuring cylinder. It occurs when the eye is incorrectly positioned. To avoid parallax error, it is important to place the eye opposite to the graduation mark to be read and the line of sight should be perpendicular to the scale at the graduation mark. Wrong eye position Correct eye position Wrong eye position Scale of a graduating cylinder 8 Measurement in Science Unit 1 While measuring volume, it is important to place the eye level with the meniscus (curved surface) and the line of sight should be perpendicular (900) to the scale of the measuring apparatus. Mercury Water Correct reading at the bottom of the curve Correct reading at the top of the curve WHAT I HAVE LEARNT In the physics laboratory, the volume of a liquid is measured using graduated beakers and measuring cylinders. The curved surface of a liquid is its meniscus. It is important to avoid parallax error in order to increase accuracy of a measurement. FIND OUT Find out the name of a common liquid whose meniscus is curved upwards. Volume of irregular solids Since an irregular solid does not have a well-defined shape, its volume is measured by using the displacement method as learnt in Grade 7. A measuring cylinder is enough if the object is small. However, if the object is large, a displacement can is used along with the measuring cylinder. A displacement can ACTIVITY 1.6 - Measuring volume of a small stone Materials you will need: 250 cm3 measuring cylinder, water, thread tied to a small stone Procedure: 1. Pour some water into the cylinder. Measure its volume V1. 9 Unit Measurement in Science 1 2. Holding the thread, gently lower and immerse the stone. 3. Record the new volume V2. Enter your results in the table below. Final volume of water + stone, V2 /cm3 Initial volume of water, V1 /cm3 Volume of stone = V2 - V1 /cm3 4. Why must the stone be immersed gently? ___________________________________ 5. (a) (b) Which error must be avoided while reading the volume of liquid? ________________ How is this error avoided? _________________________________________________ __________________________________________________________________________ 6. How much water is displaced compared to the volume of the stone? _____________________________________________________________________________ 7. Who discovered the displacement method? (Refer to your Grade 7 textbook). _____________________________________________________________________________ ACTIVITY 1.7 - Measuring the volume of a small paper clip accurately Materials you will need: 100 cm3 measuring cylinder, water and 50 small identical paper clips Procedure: 1. Pour some water into the cylinder. Measure the initial volume, V1. 2. Gently immerse one paper clip. Do you notice any measurable increase in volume of water? _______________ 3. Is it easy to measure the volume of a paper clip using a single paper clip? ______________ 4. Now, gently immerse the remaining 49 paper clips into the cylinder. Measure the final volume, V2. 10 Measurement in Science Unit 1 Results and calculations: Volume of water + paper clips, V2 = ____________________ cm3 Volume of water, V1 = ____________________ cm3 Volume of 50 paper clips = ____________________ cm3 Volume of 1 paper clip = ____________________ cm3 DID YOU KNOW… The different planets in our solar system are of different sizes. The relative size (and volume) of the planets is shown in Figure 3. Figure 3 Measurement of mass ACTIVITY 1.8 - Understanding mass Materials you will need: A: 80-page copybook 80-page copybook,120-page copybook, electronic balance B: 120-page copybook Electronic balance Procedure: 1. Compare the two copybooks, A and B. (a) Which copybook contains more sheets of paper? (b) Which copybook contains more matter (number of sheets)? 11 Unit Measurement in Science 1 Copybook A Copybook B Number of sheets [more / less] Amount of matter [more / less] Mass as recorded by balance [more / less] Since copybook A has fewer pages, it contains less matter. Alternately, copybook B has more pages and hence contains more matter. Mass is a measure of the amount of matter found in a body. Thus, copybook B has more mass than copybook A. Formerly, mass was measured using a beam balance. Nowadays, top-pan and electronic balances are more frequently used. The SI unit of mass is the kilogram (kg). Another commonly used unit is the gram (g). We also have a much smaller unit, the milligram (mg). 1 kg = 1000 g 1 g = 1000 mg 1 mg = The average mass of a Grade 8 boy is 40 kg. The mass of a medium-sized apple is 80 g. One tablet may contain 500 mg [ = 1 g ] of paracetamol. 1 1000 g 2 Beam balance Compression balance Electronic balance FIND OUT The mass of a 120-page copybook is 100 g on Earth. What will be its mass on the Moon? 12 Measurement in Science Unit 1 DID YOU KNOW… Earth has about 80 times more mass than our Moon Mass of Earth = 80 Mass of Moon Relative size of Earth and Moon Density Consider a block of sponge and a block of metal both to be of the same size and shape. Let us now view both under a microscope. Sponge Metal Lots of space More compact Figure 4 In Figure 4, we see that under a microscope, the particles in a sponge are fibre-like with a lot of spaces between the fibres. In a metal, on the other hand, the particles are more compact. So, sponge contains less mass per unit volume as compared to a metal. 13 Unit Measurement in Science 1 ACTIVITY 1.9 - Understanding density Study the sponge and a metal in Figure 4 and fill Table 3. Table 3 Sponge Metal Distance between particles (less / more) Amount of matter (less / more) Mass (less / more) Volume occupied (less / more / same) mass Ratio of volume (less / more) We find that the ratio mass is less for the sponge and more for the metal. volume In physics, this ratio is known as density. The density of a substance is defined as its mass per unit volume. Density = mass volume The SI unit for density is kg/m3. Another commonly used unit is g/cm3. Exercise: A metal cube has sides L=2 cm. The mass of the cube is 64 g. Calculate the density of the metal in (i) g/cm3 (ii) kg/m3 Solution: (i) Volume of metal cube = L3 = 2 cm × 2 cm × 2 cm = 8 cm3 64 g Density = mass = volume 8 cm3 = 8 g/cm3 (ii) To convert g/cm3 to kg/m3, we simply multiply by 1000. 8 g/cm3 = 8 x 1000 kg/m3 = 8 000 kg/m3 1 g/cm3 = 1000 kg/m3 14 Measurement in Science Unit 1 A few common densities are given in Table 4. Table 4 Substance g/cm3 kg/m3 Oil 0.9 900 Ice 0.92 920 1 1 000 Iron 7.8 7 800 Aluminium 2.7 2 700 Mercury 13.6 13 600 Water Question: Iron is stronger than aluminium. Yet, aluminium is used to make aircrafts. Explain why. _____________________________________ _____________________________________ FIND OUT One important property of mercury is its high density. Find out the name of a very useful apparatus which makes use of this property. What is this apparatus used to measure? _____________________________________ ACTIVITY 1.10 - Determination of the density of a solid Materials you will need: A thread tied to a stone, compression or electronic balance, measuring cylinder and water Step 1: Place the stone on the balance. Note its mass. Step 2: Pour water into the measuring cylinder. Note its volume. Step 3: Gently immerse the stone using the thread. Note the new volume. volume of stone Enter your results in Table 5 and complete the table. 15 Unit Measurement in Science 1 Table 5 Mass of stone ____________________ g Initial volume of water ____________________ cm3 Final volume of water ____________________ cm3 Volume of stone ____________________ cm3 Density of stone = mass ____________________ g/cm3 Density of stone ____________________kg/m3 volume TEST YOURSELF 1. Using Table 4, explain why a stone sinks in water. 2. Why is it not advisable to measure the mass of the stone after measuring its volume? _____________________________________________________________________________ 3. How will you avoid parallax error while reading its volume? _____________________________________________________________________________ 4. Comment on the thickness and mass of the string used. _____________________________________________________________________________ DID YOU KNOW… In the times of Archimedes, around 2300 years ago, the king wanted to know if one of his crowns was made of pure gold or not. Archimedes determined its volume by using the displacement method and its mass by using a balance. Then, he calculated its density and proved to the king that the crown was not made of pure gold. Floating and sinking In summer, nothing replaces a glass of water with an ice cube floating on it! Why does ice float on water? It is certainly not correct to say that “the ice cube has a smaller mass”. Note that an iceberg which has a mass of several thousand tons can also float on water. You will remember the wreck of the legendary ship Titanic was due to its collision with a massive iceberg floating on the sea. 16 Measurement in Science Unit 1 Iceberg floating on sea surface Titanic wreck In fact, the answer lies in the difference in densities of ice and water. Ice floats on water because its density is less than the density of water. Conversely, an iron nail, however small it is, will sink in water. This is because iron is denser than water. This does not directly explain why a ship made of steel and having a mass of several tons actually floats on water. Why does a ship float on water? To understand this, let us go through the next activity. ACTIVITY 1.11 - Why does a steel container float on water? Figure 5 shows a steel container floating on water. The mass of the container is 200 g. The volume of the container is 250 cm3. Hence, density of container = mass = 200 g = 0.8 g/cm3 volume 250 cm3 Since the density of the steel container is less than the density of water, it floats on water. This is precisely how a ship floats on water. Its mass is very large but at the same time it is hollow. As a result, the volume occupied is large enough to make its density less than the density of water. Hence it floats. Figure 5 Huge cruise ship floating on water 17 Unit Measurement in Science 1 TEST YOURSELF 1. A metallic object has a mass of 400 g and occupies a volume of 50 cm3. Calculate its density in (i) g/cm3 (ii) kg/m3 2. Calculate the mass of air in a rectangular room of dimensions 10m × 8m x 4m. [Density of air = 1.25 kg/m3] 3. The mass of a bottle is 100 g when empty and 180 g when full of water. When the bottle is filled with cooking oil, the total mass is 172 g. (i) Calculate the mass of water in the bottle. (ii) Calculate the volume of the water. [Density of water = 1 g/cm3] (iii) What is the capacity of the bottle in cm3? (iv) Calculate the density of the cooking oil. 4(a) Observe the huge rock and the smaller one just in front of it in Figure 6. Figure 6 Given that both rocks are made of the same material, guess which one has a higher density, the huge one or the small one. (b) Now calculate the density of each, given the following data. Huge rock mass = 460 000 kg volume = 200 m3 Small rock mass = 1 840 kg volume = 0.8 m3 (c) What conclusion can you draw from your results? __________________________________ 5. The mass of a boat is 2550 kg. What must be the minimum volume occupied by the boat for it to float on water? [Density of water = 1000 kg/m3] 18 Measurement in Science Unit 1 Relative densities of solids, liquids and gases Why do solids, liquids and gases have significantly different densities? To understand this, we first remember the structure of matter from Grade 7. We learnt that solids, liquids and gases are all made up of very large numbers of very small particles. In a solid, the particles are regularly and compactly arranged. There is very little free space between the particles. In a liquid, the particles are arranged in small groups. There is some space between the groups. In a gas, the particles are far apart. There are large spaces between them. Figure 7 summarises the structure of a solid, liquid and gas. Solid Liquid Gas Figure 7 ACTIVITY 1.12 - Deducing relative densities of solids, liquids and gases Observe Figure 7 and fill up Table 6. Table 6 Solid Liquid Gas Volume occupied [same/different] Amount of matter [very large, large, very small] Density [very high, high, very low] In a solid, the particles are most closely packed. Hence, the mass per unit volume is maximum in a solid. As a result, the state of matter having the largest density is a solid. The table below summarises the general trend. Density of solids Density of liquids largest """""""""""""" Density of gases smallest As usual, there are exceptions which you will learn in higher classes. (See Table 4) 19 Unit Measurement in Science 1 Summary of unit 1. A physical quantity has a magnitude and a unit. Length, area, volume, mass, density are a few physical quantities. 2. The volume of a substance is the amount of space it occupies. 3. The mass of a body is the amount of matter it contains. 4. In order to improve the accuracy of a measurement, zero error and parallax error must be avoided. 5. An instrument has zero error if it gives a non-zero reading when the true reading is zero. 6. Parallax error occurs when the eye is not directly opposite to the mark and the line of sight is not perpendicular to the scale. 7. The density of a substance is its mass per unit volume. The “triangle formula” is useful in density problems. D= M V M=DxV V= M D 8. For a solid to float on a liquid, the density of the solid must be less than the density of the liquid. For example, ice floats on water as the density of ice is less than the density of water. 9. A ship floats on water as its average density is less than the density of water. 10. As a general rule, the density of a solid is higher than the density of a liquid, which in turn is higher than the density of a gas. 20 SI unit Mass Density of > Density of > Density of solids liquids gases kg Errors in measurement Parallax error how to avoid? in general D= M V can be calculated using Density SI unit m3 Volume Keep line of sight perpendicular to scale and opposite to the mark MEASUREMENT IN SCIENCE Zero error how to avoid? Check the zero mark. It mustt give a zero reading when the true reading is zero. Unit 1 Measurement in Science Displacement method using measuring cylinder or displacement can can be found by Irregular solid Regular solid can be calculated using Formulae Measurement in Science Unit 1 21 Unit Measurement in Science 1 WORK OUT Multiple Choice Questions 1. The zero end of a half metre rule is damaged. What must you do? A Discard it B Start measuring at the 1 cm mark and subtract 1 cm from the reading C Start measuring at the 1 cm mark and add 1 cm to the reading D Avoid parallax error 2. When reading the volume of a liquid in a measuring cylinder, how do you avoid parallax error? END OF UNIT EXERCISES A By checking the zero mark of the measuring cylinder B By looking opposite to the mark C By looking perpendicular to the scale D By looking opposite to the mark and perpendicular to the scale 3. You have only one small paper clip. Why is it not possible to accurately measure its volume using a measuring cylinder containing water? A A paper clip is a regular solid B The paper clip will be damaged C The rise in volume will hardly be noticeable D Its mass is small 4. Why is the density of a solid normally high compared to a liquid or gas? A A solid contains more particles B The particles in a solid have more mass C A solid contains more particles per unit volume D A solid occupies more volume 22 Measurement in Science Unit 1 5. Match items in the column A to corresponding items in the column B Column A Column B displacement method 2. Error caused by wrong eye position gas 3. A solid of well-defined shape Dead Sea 4. Mass per unit volume of a substance solid 5. Amount of matter a body contains density of iceberg is less 6. Density of iceberg compared to density of sea water mass 7. State of matter having highest density density 8. A person floats in this sea a regular solid 9. State of matter having lowest density parallax error 10. Used to measure volume of an irregular solid zero error END OF UNIT EXERCISES 1. Error caused by a ruler with a damaged zero mark 6. Write True or False 1. An electronic balance is used to measure mass. 2. 1 kg of steel has more mass than 1 kg of cotton. 3. 1 kg of steel occupies more volume than 1 kg of cotton. 4. Volume is the amount of matter a body contains. 5. To convert g/cm3 to kg/m3, multiply by 1000. 6. When using a measuring cylinder, parallax error must be avoided. 7. Parallax error occurs when a ruler has a damaged zero-end. 8. The volume of a needle can be measured by using the displacement method. 9. A ship floats on water because the density of steel is less than the density of water. 10. An ice cube floats on water but an iceberg sinks. 7. Fill in the blanks using appropriate words and symbols. (i) The mass of a body is the amount of ___________________ it contains. The SI unit is ___________________ and another commonly used unit is ___________________. (ii) Volume is a physical quantity which measures the amount of ___________________ occupied by a solid, liquid or gas. The SI unit is ___________________ and another unit is ___________________. 23 Unit Measurement in Science 1 (iii) Density is a physical quantity which is defined as___________________ per unit ___________________. The SI unit is ___________________ and another commonly used unit is ___________________. The density of a substance depends on how closely packed the ___________________ are in it. (iv) In order to obtain a value for the density of a stone, we first measure its mass using a ___________________. Its volume is measured by the ___________________ method. Then the density is calculated by dividing its ___________________ by its ___________________. 8. It is commonly said: “Metal is heavier than cotton.“ Why is this sentence wrong? Rewrite the sentence correctly. ____________________________________________________________________________ END OF UNIT EXERCISES Calculations 9. 50 cm3 of water taken from the Dead Sea has a mass of 62 g. What is its density? Why is the density of water from the Dead Sea higher than the density of normal sea water? 10. A piece of steel has a volume of 12 cm3 and a mass of 96 g. Calculate the density of steel in (a) g/cm3 (b) kg/m3. 11. A rectangular container has a 10 cm square base and contains water to a depth of 12 cm. When a stone of a mass of 600 g is gently lowered into the water, the level rises to 14 cm. (a) Calculate the volume of water displaced by the stone. (b) What is the volume of the stone? (c) Calculate the density of the stone in kg/m3. 12. The pages of a book are numbered 1 to 200 and each leaf is 0.15 mm thick. If each cover is 2.5 mm thick, calculate the thickness of the book. Give your answer in (i) mm (ii) cm (iii) m. 13. A 100 cm3 measuring cylinder contains 50 cm3 of water and has a total mass of 150 g. 30 ball bearings having a volume of 0.5 cm3 each are carefully immersed into the cylinder. The ball bearings are made of steel having density 8 g/cm3. (a) Calculate the final volume of water in the measuring cylinder. (b) Calculate the total mass of the ball bearings. (c) Calculate the final mass of the cylinder and its contents. 24 Food and Nutrients Unit 2 Unit Food and Nutrients 2 Learning Outcomes At the end of this unit, you should be able to: Define nutrients as food substances or molecules that all organisms need for the proper functioning of their body Classify nutrients into carbohydrates, fats, proteins, vitamins and minerals Select and list examples of food sources rich in carbohydrates, fats, proteins, vitamins, minerals and dietary fibres State the main role of carbohydrates, proteins and vitamins (A and D) in our body State that carbohydrates are subdivided into simple and complex carbohydrates, giving examples such as glucose and starch respectively Demonstrate an understanding of starch as a complex carbohydrate made up of many simple sugar units Recognise different examples of food sources rich in glucose and starch State that proteins are large food molecules that are made up of smaller units called amino acids Carry out simple food tests Identify the components of various food samples using the different food tests Define the term ‘balanced diet’ as comprising carbohydrates, fats, proteins, vitamins, minerals, water and dietary fibres in the correct proportion Recognise that malnutrition may be the result of either a lack or an excess of a particular nutrient in the diet State the deficiency diseases of vitamin A, vitamin D, iron and calcium Show an awareness that excess of carbohydrates in the diet can lead to diabetes while excess of fats in diet can lead to obesity and heart diseases You may recall Unit 2 in Grade 7 where you learnt about the importance of food to living organisms. Food provides us with energy, allows us to grow and helps our body fight against diseases. There are different nutrients present in our food, where each nutrient is responsible for its function(s) in our body. Therefore, we need different nutrients for the proper functioning of our body. Let us identify these nutrients. 25 Unit 2 Food and Nutrients Classification of nutrients ACTIVITY 2.1 - Identifying nutrients in food sources List the different nutrients and give three examples of food sources for each. Write your answers in Table 1. Table 1 Name of Nutrient Food Sources ________________________________________ ________________________________________ ________________________________________ ________________________________________ ________________________________________ ________________________________________ ________________________________________ ________________________________________ ________________________________________ ________________________________________ ________________________________________ ________________________________________ Table 2 below shows the different types of nutrients and the main groups under which they are classified based on their particular function in our body. Table 2 Types of Nutrients Group of Nutrients Carbohydrates and fats (lipids) Nutrients (food) for energy Proteins Nutrients (food) for growth/body building Vitamins and minerals Nutrients (food) for health There are two other substances that are equally important to our body; they are water and dietary fibre or simply fibre. Fibre is also known as roughage. The importance of both water and fibre will be discussed later in this unit. 26 Food and Nutrients Unit 2 A. Energy providing nutrients Both carbohydrates and fats are the main enegy-providing nutrients. They are made up of carbon, hydrogen and oxygen. They store chemical energy which is released during respiration. ACTIVITY 2.2 - Comparing energy content of two food nutrients (Teacher Demonstration) Materials you will need: Mounting needle, retort stand, tap water, electronic balance, thermometer, carbohydrate food source, fat food source, boiling tube Figure 1 represents an experiment to measure heat energy released when burning a food sample. Thermometer Burning food on mounted needle Water Figure 1 Procedure: (a) Weigh equal amounts of food sample, one containing a carbohydrate and the other a fat. (b) Pick each food with a separate mounted needle as shown in Figure 1. (c) Label 2 boiling tubes as A and B. (d) Add 5 ml of water in each boiling tube. (e) Record the temperature of the water in boiling tube A. (f ) Heat the carbohydrate food source until it flames. (g) Put the flame under the boiling tube A. Record the final temperature of the water (until the temperature does not rise further). (h) Repeat steps (e) - (g) using boiling tube B and a fat source. 27 Unit 2 Food and Nutrients (i) Figures 2 and 3 show the final temperature readings for burning of the carbohydrate and fat food sources respectively. Figure 2 Figure 3 1. Observe Figures 2 and 3 and record your readings below. Final temperature in Figure 2: _______________________________ Final temperature in Figure 3: _______________________________ 2. Given the initial temperature is 24º Celcius, calculate the rise in temperature when burning a carbohydrate and fat samples. Rise in temperature when burning carbohydrate: _________________________________________ Rise in temperature when burning fat: _________________________________________ 3. Which of the two nutrients gives more energy? _____________________________________________________________________________ WHAT I HAVE LEARNT 28 Both carbohydrates and fats release energy on burning. More energy is liberated when fat is burnt as compared to the same amount of carbohydrate. DID YOU KNOW… Fat is a good energy storage nutrient and is stored under the skin as adipose tissue. Food and Nutrients Unit 2 Carbohydrates Carbohydrates are classified into two groups namely simple and complex carbohydrates as shown in Figure 4. A simple carbohydrate is made up of one sugar molecule. A complex carbohydrate is made up of many simple sugars forming long chains. Simple carbohydrates are small molecules which are soluble in water. Glucose is a simple carbohydrate. Complex carbohydrates are larger molecules such as starch in plants and glycogen in animals. simple carbohydrate complex carbohydrate Figure 4 ACTIVITY 2.3 - Finding the different food sources of glucose and starch The following food sources are rich in glucose. Write down the name of the food source below each given picture. (a) Observe carefully the pictures below and write down the name of the food source rich in glucose. _______________________ _______________________ _______________________ The following food sources are rich in starch. Write down the name of the food source below each given picture. (b) Write down the name of the food source rich in starch. _______________________ _______________________ _______________________ 29 Unit 2 Food and Nutrients (i) State another example of a simple carbohydrate present in the food in part (a). _____________________________________________________________________________ (ii) The simple carbohydrates can be extracted from the food sources in part (a) and used in the manufacture of certain food such as syrup. Give three other examples of such food. (1) _____________________ (2) _____________________ (3) _____________________ (iii) State one example of food that is manufactured from each food source mentioned in (b). (1) _____________________ (2) _____________________ (3) _____________________ DID YOU KNOW… The food manufactured from either simple carbohydrate or starch is termed as processed food. B. Protein – The body building nutrient Proteins are very large molecules made up of small building units known as amino acids. Proteins cannot be stored in the human body. ACTIVITY 2.4 - Identifying proteins from plant and animal sources The pictures below show different sources of proteins. Observe carefully the pictures and answer the questions that follow. 30 Food and Nutrients Unit 2 (b) Write down two examples of food sources under the two categories given below: Animal sources of proteins: (1) _____________________ (2) _____________________ Plant sources of proteins: (1) _____________________ (2) _____________________ Uses of proteins in our body Needed for growth and development Involve in contraction and relaxation of muscles Build cells and repair of damaged tissues PROTEINS Destroy or help in destruction of foreign bodies, such as bacteria (antibodies) Speed up chemical reactions (enzymes) Food Tests Food tests may be carried out to show the presence of simple carbohydrates, starch, proteins or fats in a food sample. Table 3 below gives the nutrient, its respective food test and the reagents used to carry out the food test. Table 3 Nutrient Name of food test Reagent(s) used Simple carbohydrates (glucose, fructose) Benedict’s test Benedict’s solution Starch Iodine test Iodine solution Proteins Biuret test - Sodium hydroxide - Copper (II) sulfate solution Fats Emulsion test Ethanol 31 Unit 2 Food and Nutrients ACTIVITY 2.5 - Testing for simple carbohydrate using Benedict’s solution Materials you will need: Glucose solution as simple carbohydrate, Benedict’s solution, small beaker, test tubes, thermometer, syringe, water Procedure: (a) (b) (c) (d) (e) (f ) Label two test tubes A and B. Add 2 cm3 of glucose solution in test tube A. Then add 2 cm3 of Benedict’s solution in test tube A. Place test tube A in a water bath which is heated to 80 0C or above. Repeat step (b) to (d) using water instead of glucose solution in test tube B. Observe carefully the test tubes and answer the following questions. 1. State the colour of Benedict’s solution. __________________________________________________________________________ 2. What colour is the glucose solution after addition of the Benedict’s solution? __________________________________________________________________________ 3. Does the solution in test tube A remain clear after heating? __________________________________________________________________________ 4. What is formed in test tube A after heating? __________________________________________________________________________ 5. The test tubes below show the changes in colour that occur while heating the test tube. Write down the colour obtained in each test tube. _______________ 32 _______________ _______________ _______________ Food and Nutrients Unit 2 6. What do you observe when Benedict’s test is carried out on water? __________________________________________________________________________ What can you conclude from this experiment? __________________________________________________________________________ ACTIVITY 2.6 - Testing for the presence of starch using iodine solution Materials you will need: Starch suspension, iodine solution, test tubes, a dropper, syringe Procedure: (a) Take 2 test tubes and label them A and B. (b) Add 2 cm3 of starch suspension to test tube A, followed by one or two drops of iodine solution. (c) Add 2 cm3 of water in test tube B, followed by one or two drops of iodine solution. This is the control test tube. Observe carefully Figures 5 and 6 and then fill in Table 4. Figure 5: Test tube A Figure 6: Test tube B Table 4 Test tube Observation of contents after iodine test A (Starch and iodine solution) ____________________________________________________ B (Water and iodine solution) ____________________________________________________ What do you conclude for the test of starch using iodine solution? __________________________________________________________________________ 33 Unit 2 Food and Nutrients ACTIVITY 2.7 - Testing for the presence of protein using the Biuret test Materials you will need: Sodium hydroxide solution, dilute copper (II) sulfate solution, egg albumen, syringe, dropper, test tube, water Procedure: (a) Add 2 cm3 of egg albumen to a test tube labelled A, followed by 2 cm3 of sodium hydroxide. (b) Then add a few drops of dilute copper (II) sulfate solution. Shake after addition of each drop. (c) Take another test tube labelled B and repeat steps (a) and (b) with water instead of egg albumen. Observe Figures 7 and 8 carefully and then fill in Table 5. Figure 7 Figure 8 Table 5 Test tube Observation of contents after Biuret Test A (Egg albumen+ sodium hydroxide and copper (II) sulfate) ____________________________________________________ B (Water+ sodium hydroxide and copper (II) sulfate) ____________________________________________________ Based on your observations, conclude whether protein is present or absent in egg albumen. __________________________________________________________________________ 34 Food and Nutrients Unit 2 Test for fats/lipids When ethanol and cold water are added to a lipid sample, a white emulsion is observed. WHAT I HAVE LEARNT The Benedict’s test produces a green/yellow/orange/brick red precipitate when simple carbohydrate is present but it remains blue when a simple carbohydrate is absent. The iodine test is carried out to identify starch in food samples. A blue-black colour shows the presence of starch and a yellow/brown colour shows an absence of starch. The Biuret test is used to test for the presence of protein in food samples. A purple or violet colour is formed in the presence of protein but when protein is absent the colour remains blue The Emulsion test is used to identify the presence of fats. A white emulsion is formed in the presence of fats. Now that you have learnt how to carry out different food tests, work in groups to find out the nutrient(s) present in each of the following food samples: bread, soaked bean, seeds and milk. ACTIVITY 2.8 - Identifying nutrients in a food sample using food tests A sample of food mixed with water was tested to find out the nutrients present and the results are shown in the table below. Read Table 6 carefully and answer the questions that follow. Table 6 Test Results/Observations Iodine solution added yellow colour Benedict’s solution added and the mixture heated brick red precipitate Mixture shaken with ethanol and poured in water white emulsion Dilute sodium hydroxide solution added, followed by a few drops of dilute copper sulphate (II) solution blue colour 1. Which food nutrients are present in the food sample? __________________________________________________________________________ 2. Which food nutrients are absent in the food sample? __________________________________________________________________________ 3. Suggest a food that may contain similar nutrients as the food sample above. __________________________________________________________________________ 35 Unit 2 Food and Nutrients C. Vitamins and minerals Both vitamins and minerals are needed in very small amount in our diet. There are different types of vitamins and minerals. Each has a particular function in our body. Table 7 gives the different function(s) and sources of iron, calcium, vitamins A and D. Table 7 MINERALS VITAMINS Nutrients Vitamin A Vitamin D Iron Calcium Function(s) Sources 1. Essential for eyesight, especially night vision Egg yolk, oily fish (salmon, sardines), broccoli, yellow or orange vegetables such as carrot and pumpkin 2. Increases our body’s defence against infection Helps in bone and teeth formation - Cod liver oil, tuna and milk. - Produced in the skin on exposure to sunlight Essential for the formation of red blood pigment called haemoglobin Green leafy vegetables, red meat, cashew nuts, pulses and moringa leaves 1. Builds and maintains healthy bones and teeth - Milk and dairy products such as yogurt and cheese - Almonds 2. Helps in blood clotting D. Fibre Fibres or dietary fibres form the indigestible compounds of plants. They are mainly carbohydrates and one example of a fibre is cellulose. In human beings, the alimentary system cannot digest cellulose. Therefore, fibres pass relatively unchanged along the alimentary canal. Some examples of food sources that are rich in fibres are oats, fruits and vegetables. Fibres provide bulk to the undigested food, helping it to move along the large intestine by peristalsis (see Unit 5) and help in the elimination of faeces. Lack of fibres in our diet leads to constipation. 36 Food and Nutrients Unit 2 E. Water You have learnt in Grade 7 that cytoplasm is the jelly-like substance that makes up the cell. The human body consists of about 70% of water. Water has many properties based on which it can have different functions. Therefore, water is important for cells to function properly. Figure 9 shows some properties of water and the relevant functions. Properties of water and their function Water as a good solvent Dissolves toxic substances in our body which are removed as urine and sweat. Water as a reagent - Used in chemical digestion of food Used as raw material in photosynthesis (Plants) Water as a cooling agent Helps to control body temperature. The evaporation of sweat from surface of skin cools the body. Figure 9 You have learnt the different types of nutrients and their importance in our diet. We will now find out about balanced and unbalanced diet. Balanced Diet Balanced diet is the daily intake of food comprising carbohydrates, fats, proteins, vitamins, minerals, water and dietary fibres in the correct proportion, as shown in Figure 10 below. Proteins Fats Carbohydrates Balanced Diet Vitamins Minerals Water Fibres Figure 10 37 Unit 2 Food and Nutrients DID YOU KNOW… According to the National Academy of Medicine in USA, men need 38 grams of fibre and women need 25 grams per day. Factors affecting a balanced diet Some of the factors that affect a balanced diet are: 1. Biological factors such as age, gender, health conditions and genetic make-up of the individual. 2. Climatic factors Individuals living in very cold regions need a diet rich in fat catering for the larger need in energy. Fat stored under the skin acts as an insulator. 3. Occupation Someone who does heavy work will need more energy each day than a person doing light work. ACTIVITY 2.9 - Finding the different factors affecting a balanced diet Based on what you have learnt so far on nutrients: (a) List the appropriate nutrient(s) which will be needed in higher proportion in the diet of the following individuals: (i) An individual living in a cold region: _____________________ (ii) A growing child: _____________________ _____________________ (iii) A pregnant woman: _____________________ _____________________ (iv) A manual worker: _____________________ (b) State the reason to support your answer in part (a). (i) _______________________________________________________________________ _______________________________________________________________________ (ii) _______________________________________________________________________ _______________________________________________________________________ 38 Food and Nutrients Unit 2 (iii) _______________________________________________________________________ _______________________________________________________________________ (iv) _______________________________________________________________________ _______________________________________________________________________ Unbalanced Diet You have already discussed earlier that a healthy eating habit involves the intake of a balanced diet. Now we will find out what will happen if an individual takes an unbalanced diet. An unbalanced diet may lead to malnutrition. Malnutrition can be either undernutrition or overnutrition. An unbalanced diet can be caused by: (i) not having enough food to eat or not eating a nutrient in the right proportion. This condition is known as undernutrition. (ii) overeating, that is eating more than what is required by the body. This condition is known as overnutrition. Malnutrition, that is, both overnutrition and undernutrition may lead to diseases. Undernutrition Deficiency diseases occur as a result of inadequate intake of nutrients such as vitamins and minerals. You will now learn about the deficiency diseases caused by a lack or inadequate intake of vitamin A, vitamin D, iron and calcium in the diet. 39 Unit 2 Food and Nutrients Table 8 gives the deficiency diseases and their respective signs and symptoms resulting from lack of iron, calcium, vitamin A and D. Table 8 Nutrient Vitamin A Vitamin D Iron Deficiency disease Sign(s) and Symptom(s) Night blindness (i) decreased ability to see in dim light Rickets Anaemia (i) bones soften leading to deformity (bowed legs) (ii) bones become weak and brittle and can fracture more easily (i) weakness (ii) fatigue (iii) headaches (iv) shortness of breath (v) poor memory and concentration (i) weak bones and teeth Calcium Rickets Overnutrition You have seen earlier that any nutrient taken in excess in our diet can lead to diseases. Over nutrition often implies an excess of carbohydrate or fat intake that the body cannot use. Excess of carbohydrate can lead to diabetes. Excess fats get stored in our body (under the skin or around organs) and lead to obesity. Obesity increases the risk of heart diseases such as a heart attack. Both diabetes and heart diseases are categorised as non-communicable diseases. You will learn more about non-communicable diseases in Unit 9. Some factors that contribute to heart diseases are as follows: (i) Unhealthy diet (ii) Lack of exercise (iii) Alcohol consumption (iv) Smoking cigarettes 40 Food and Nutrients Unit 2 DID YOU KNOW… Cardiovascular diseases are diseases that affect the heart and the blood vessels in our body. In Mauritius, mortality due to diseases of the circulatory system and diabetes increased from 31% in 1975 to 46% in 1990 and peaked at 59% in 2007. However, during recent years, it has fluctuated between 56% and 57%, indicating a decreasing trend. Reading nutrition facts or information on food packaging Nutrition facts or information are presented on food containers or packaging. The picture below shows nutrition information from a food package. Nutrition Facts Serving Size 2/3 cup (55g) Servings Per Container About 8 Amount Per Serving Calories 230 Calories from Fat 72 % Daily Value* Total Fat 8g12% Saturated Fat 1g 5% Trans Fat 0g Cholesterol 0mg0% Sodium 160mg7% Total Carbohydrate 37mg12% Dietary Fiber 4g 16% Sugars 1g Protein 3g Vitamin A Vitamin C Calcium Iron 10% 8% 20% 45% Use the information given in the above picture to complete Table 9 below. Table 9 Nutrition facts per serving size Start here serving size 55 g Check amount of calories 230 calories Read the different nutrients provided by the food item Total Carbohydrates Total Fat Protein Sodium Vitamin A Vitamin C Iron........... g........... g........... g........... g........... g........... g........... g 41 Unit 2 Food and Nutrients PROJECT WORK Make a list of the different packaged food items that you have eaten during a week. Cut out or collect the nutrition facts from different food packagings. For each food item, calculate the total amount of calories (a unit measuring amount of energy liberated when burning food), the amount of protein, fats, calcium, vitamin A, vitamin D, iron and fibres provided per serving of food. Summary of unit (a) Balanced diet is the daily intake of food consisting of carbohydrate, fat, protein, vitamin, mineral, fibre (roughage) and water, in the right proportion. (b) Nutrients are broadly classified under nutrients for (i) energy, (ii) health and (iii) body building. (c) Carbohydrates and fats provide us with energy. Proteins are used in the building of tissues and the production of important substances such as enzymes and antibodies. Vitamins and minerals protect us from diseases. (d) Carbohydrates can be grouped as simple and complex. (e) Proteins are large molecules made up of small units known as amino acids. (f) Food tests can be carried out to show the presence of a particular nutrient in a food sample. Iodine test is used to show the presence of starch; Benedict’s test shows the presence of simple carbohydrates; Biuret test shows the presence of proteins and Emulsion test is used to test the presence of fats. (g) Vitamin A is important for night vision; Vitamin D and calcium are responsible for bone and teeth formation. Iron is an important component of haemoglobin that carries oxygen in our blood. (h) Fibres provide bulk allowing movement of undigested food along the large intestine and thus prevent constipation. (i) Water is a major composition of cells and is important for many processes occurring in our body. (j) Lack of nutrients in a diet leads to deficiency diseases while eating more than what the body can use is known as ‘overnutrition’. (k) Overnutrition may lead to diabetes and heart diseases. 42 Food and Nutrients Unit 2 Further readings Carbohydrate is stored as starch in the form of starch grains in plant cells. In animals, carbohydrate is stored as glycogen. Some carbohydrates arising from various natural food sources, have been changed during chemical processes to “refine” them. Processing occurs industrially. Examples of refined carbohydrates are white flour and white rice. They are processed from raw grains which naturally contain mainly vitamins and fibres. A food or diet pyramid is a visual guide showing the relative proportion of different types of food to be eaten daily in order to stay healthy. Figure 11 is a diagram illustrating a food pyramid. Oils/fats group Dairy group Meat/beans group Vegetables group Fruits group Grains/cereals group Figure 11 43 44 Green/Yellow/Orange/ Brick Red precipitate positive Blue negative Benedict’s solution using Benedict’s test using Biuret test protein Food tests Purple/Mauve positive Blue negative Sodium Hydroxide & Copper (II) Sulfate simple sugar Unit 2 Food and Nutrients starch Blue black positive Yellow/Brown negative Iodine solution using Iodine test fats White emulsion positive No emulsion negative Ethanol & water using Emulsion test Unit 2 Food and Nutrients Rickets deficiency disease Calcium Form bulk of faeces main function Bone & teeth formation main function Constipation deficiency disease Dietary fibres main function Formation of haemoglobin Anaemia Iron deficiency disease e.g. Minerals H2O Unit 2 Food and Nutrients Night blindness deficiency disease Helps to see in darkness main function e.g. Vitamins Vitamin A Food for health consists of Balanced diet Rickets deficiency disease Vitamin D Bone & teeth formation main function Amino acids made up of Protein Body building food simple Cellulose complex in plants Carbohydrate Starch complex in man Glycogen Fat Energy providing food e.g. Glucose, Fructose Food and Nutrients Unit 2 45 Unit 2 Food and Nutrients WORK OUT Multiple Choice Questions. Circle the correct answer. 1. Action of sunlight on the skin leads to synthesis of _________________. A Vitamin D B Vitamin A C Iron D Calcium 2. Excess _________________ in the human body are stored in the tissue below the skin. A Vitamin D B Carbohydrate C Proteins D Fats 3. Lack of _________________ in the diet causes constipation. A Fat B Fibres C Proteins D Vitamin A END OF UNIT EXERCISES 4. A portion of cooked rice was tested by adding iodine solution to it. Which colour will be seen? A Blue-black B Pale blue C Brown D Green 5. What is calcium used for in the body? A Blood clotting and forming haemoglobin B Forming haemoglobin and preventing anaemia C Preventing anaemia and formation of bone D Formation of bone and blood clotting. 6. What is the main source of protein in the vegetarian diet? A Pulses B Citrus fruits C Green leafy vegetables D Red meat 7. A source of simple carbohydrate is _________________. A Seed B Fruit C Brown rice D Potatoes 8. The risk of obesity and heart disease is increased by a diet high in _________________. A Fat B Protein C Carbohydrate D Both fat and carbohydrate 9. _________________ are high in sugars and lipids. A Fruits and vegetable B Meat, poultry, fish, dry beans, eggs C Milk, yoghurt and cheese D Fats, oils and sweets 10. The only way to get all the nutrients you need is to eat _________________. A More dairy food B A combination of foods C The same foods over and over again 46 D Only fruits Food and Nutrients Unit 2 11. The body’s main source of energy is _________. A Carbohydrates B Iron C Vitamins D Proteins 12. A positive Benedict’s test would be _________. A Blue colour B Purple colour C Blue black coloration D Brick red precipitate 13. Which of the following is not a function of water? A It helps in digestion and excretion B It forms the cytoplasm C It forms body fluids such as blood D It gives energy 12. Biuret test is the food test that is carried out to indicate the presence of _________. A Glucose B Fructose C Starch D Protein 13. State whether each of the following is True or False. END OF UNIT EXERCISES (a) Vitamin is a good source of energy. _________ (b) Glucose and fructose are examples of carbohydrates. _________ (c) Starch is a plant storage carbohydrate. _________ (d) Age and gender affect the diet of an individual. _________ (e) Undernutrition can be described as the lack of energy providing nutrients in the diet. _________ (f ) Carbohydrates cannot be stored in human body. _________ (g) Excess of protein is stored under our skin. _________ 14. Fill in the blanks. (a) Carbohydrates and fats are both _____________ providing nutrients. They both consist of the elements carbon,_____________and_____________. On combustion, fats liberate_____________energy than carbohydrates of same mass. Energy is used by the body for_____________and mental activities. (b) Starch is a_____________carbohydrate made up of_____________sugar units. A food sample containing starch will turn _____________ _____________ with iodine solution. (c) Proteins are needed for_____________of damaged tissues and for_____________. Proteins are _____________ food molecules that are made up of units called _____________ _____________. An example of vegetarian protein food source is _____________. 47 Unit 2 Food and Nutrients (d) Vitamins are needed in _____________ amount in our diet. Vitamin A is important for night _____________. Vitamin D is important for _____________ and _____________ formation. (e) _____________ is important for blood clotting. It is also important for bone formation. When this mineral is lacking in the diet, the deficiency disease _____________ occurs. (f ) Fibres are present in vegetables and fruits. They help food to _____________ along the alimentary canal as they cannot be _____________ by our alimentary system. (g) Water forms a major constituent of the _____________ of cells. Body fluid such as _____________ transport food and oxygen around the body. END OF UNIT EXERCISES (h) A balanced diet consists of all nutrients in the _____________ proportion. (i) Unbalanced diet can result either in _____________ or undernutrition. (j) _____________ and _____________ diseases may be caused as a result of excess intake of carbohydrates and fats respectively in the body. 15. Fats and carbohydrates provide the body with _____________. Excess fats can be stored in the body under the _____________ and complex carbohydrates stored in the liver as _____________. The two types of carbohydrates are _____________ and _____________. Examples of foods rich in starch are _____________ and _____________. Examples of foods that are rich in glucose are _____________ and _____________. Structured Questions 16. Food tests are being carried out on a food sample to determine the presence of different nutrients. (a) Name the reagent(s) needed to show the presence of glucose in the food sample. __________________________________________________________________________ (b) Briefly explain how you would carry out the food test in part (a). __________________________________________________________________________ __________________________________________________________________________ 48 Food and Nutrients Unit 2 (c) What would be your observation if glucose is present? __________________________________________________________________________ (d) Biuret test is being carried out on the food sample. What colour confirms the presence of protein? __________________________________________________________________________ (e) (i) Iodine test is also carried out on the food sample. What nutrient is being tested for? __________________________________________________________________________ (ii) If the above nutrient is present, what colour change would you expect? END OF UNIT EXERCISES __________________________________________________________________________ 17. (a) State three main ways in which the body uses food. 1. _________________________________________________________________________ 2. _________________________________________________________________________ 3. _________________________________________________________________________ 18. Which of the following are not rich in carbohydrates: bread, fish, potatoes, beans, meat, lettuce, sugar, biscuits? __________________________________________________________________________ 19. (a) Name the mineral element(s) important for: (i) bones and teeth , (ii) blood pigment (iii) good night vision (i) ________________ (ii) ________________ (iii) ________________ (b) Which of these elements is (i) present in milk, (ii) lacking in milk? (i) ________________ (ii) ________________ 20. State one benefit of including dietary fibre (roughage) in the diet. __________________________________________________________________________ 49 Unit 2 Food and Nutrients 21. The percentage of different food components present in 100 grams of an individual’s meal is shown below. 60% carbohydrates 15 % fats 18 % proteins 2 % water (a) Name the two nutrients not represented above. __________________________________________________________________________ (b) Give two examples of food sources for each of the nutrients shown above. __________________________________________________________________________ __________________________________________________________________________ (c) Calculate the percentage of the missing nutrients. END OF UNIT EXERCISES __________________________________________________________________________ (d) What type of disease will the individual have if such meal is taken regularly? Explain why. __________________________________________________________________________ __________________________________________________________________________ (e) How can the individual avoid the disease mentioned in part (d)? __________________________________________________________________________ 22. (a) What is a balanced diet? __________________________________________________________________________ (b) Write down one property of a simple sugar. __________________________________________________________________________ (c) Based on the property above, explain how the simple sugar glucose is adapted to its function. __________________________________________________________________________ __________________________________________________________________________ (d) Name a complex carbohydrate present in the cell wall of plant. __________________________________________________________________________ (e) State the function of the carbohydrate mentioned in part (d) above. __________________________________________________________________________ 50 Mixtures and Separation Techniques Unit 3 Unit Mixtures and Separation Techniques 3 Learning Outcomes At the end of this unit, you should be able to: Recall mixtures and their properties Identify solutions and suspensions and give examples of both Distinguish between the properties of solutions and suspensions Explain that differences in properties allow the separation of the components of a mixture Investigate how mixtures can be separated into their respective components by the following techniques: magnetic attraction, filtration, decantation and evaporation Draw labelled diagrams to illustrate the steps involved in separation techniques Explain the principles involved in magnetic attraction, filtration, decantation and evaporation as separation techniques Explain what alloys are and identify alloys as mixtures Identify bronze, brass, steel and stainless steel as alloys and state their respective components and composition Show understanding of the uses of these alloys and relate their uses to their properties In Grade 7, you learnt that matter is found around us, has mass and occupies space. For example, in your daily life, you are surrounded by matter such as metals, sugar, kitchen salt, water and air. You also learnt that matter can be elements, compounds and mixtures. In this unit, you will explore the properties of mixtures and learn how they can be separated into their individual components. Mixtures ACTIVITY 3.1 - Recalling about mixtures and their properties This activity consists of two parts: Part A and Part B. 51 Unit 3 Mixtures and Separation Techniques PART A: Observe the pictures given in Table 1 which represent three different mixtures. Complete the table to list the components present in each mixture. Table 1 Air Fruit salad Sea water Mixture Components present in the mixture PART B: Three sets of mixtures containing red beans and white beans are shown in Figures 1, 2 and 3. Observe carefully and answer the questions that follow. Figure 1 Figure 2 Figure 3 1(a) Count the number of red beans and white beans in each mixture. Write down your answer in Table 2. Table 2 Figure 1 Number of red beans Number of white beans 52 Figure 2 Figure 3 Mixtures and Separation Techniques Unit 3 1(b) The amount of each component in a mixture makes up its composition. From your results in Table 2, what can you conclude about the composition of a mixture? __________________________________________________________________________ 2. Suggest a simple method that can be used to separate the red beans from the white beans. __________________________________________________________________________ 3. After completing Parts A and B, fill in the blanks below by choosing the correct answer. Fruit salad, sea water and air are examples of mixtures. A mixture consists of _______________ (one/several) components are _______________ (physically/chemically) combined (joined) together. The composition of a mixture _______________ (can/cannot) vary. The components of a mixture _______________ (can/cannot) be separated by simple methods. WHAT I HAVE LEARNT A mixture consists of two or more components which are physically combined together. Salads, air and sea water are examples of mixtures. A mixture has the following properties: The composition of the different components in a mixture can vary. Thus a mixture has variable composition. The components of a mixture can be separated by simple methods. DID YOU KNOW… Blood is a mixture consisting of several components including water, sugar, and different types of blood cells. 53 Unit 3 Mixtures and Separation Techniques Solutions and suspensions Some mixtures can exist as solutions or suspensions. In the following activities, you are going to investigate the properties of solutions and suspensions. ACTIVITY 3.2 - Preparing a solution Materials you will need: One beaker containing water, kitchen salt, spoon, glass rod Procedure: Fill ¾ of the beaker with water. Add one spoonful of the kitchen salt in the beaker. Stir the mixture with the glass rod. Carefully observe the contents of the beaker and answer the following questions. Kitchen salt Water Adding kitchen salt to water and stirring Mixture of kitchen salt and water after stirring 1. What happens to the solid kitchen salt when it is added to water? __________________________________________________________________________ 2. Describe the appearance of the resulting mixture in the beaker. __________________________________________________________________________ 3. When the salt is dissolved in water, a solution is formed. The salt is called the solute while water is called the solvent. 54 Mixtures and Separation Techniques Unit 3 (a) Fill in the red box with the appropriate word. solute added to solvent results in formation of a ________________ (b) Can you provide a definition for a: (i) solution? _________________________________________________________ (ii) solute? _________________________________________________________ (iii) solvent? _________________________________________________________ 4. Give 3 other examples of solutions. __________________________________________________________________________ ACTIVITY 3.3 - Preparing a suspension Group Work Materials you will need: One beaker containing water, flour, spoon, glass rod Procedure: Fill ¾ of the beaker with water. Add one spoonful of flour in the beaker. Stir the mixture with the glass rod. Carefully observe the contents of the beaker and answer the following questions. Flour Water Adding flour to water and stirring Mixture of flour and water after stirring 55 Unit 3 Mixtures and Separation Techniques 1. What happens to the flour when it is added to water and the mixture is stirred? __________________________________________________________________________ 2. Describe the appearance of the resulting mixture in the beaker. __________________________________________________________________________ __________________________________________________________________________ 3. When flour and water are mixed, a suspension is formed. Can you provide a definition for a suspension? __________________________________________________________________________ 4. Give three other examples of suspensions. __________________________________________________________________________ ACTIVITY 3.4 - Distinguishing between the properties of solutions and suspensions In this activity, you will compare a solution with a suspension. Materials you will need: Mixtures of solutions and suspensions provided in labelled beakers A, B, C and D Beaker A: Water and sugar Beaker C: Water and powdered chalk A 56 B Beaker B: Water and mud Beaker D: Water and food colouring C D Mixtures and Separation Techniques Unit 3 Procedure: 1. Your class will be divided into groups. 2. Each group will be provided with four sets of mixtures in four beakers A, B, C and D. 3. Observe the mixtures carefully. Discuss with your friends and fill in parts (i), (ii) and (iii) in Table 3 by inserting a tick ( ) or cross (X) in the appropriate columns. Table 3 Properties i The mixture is cloudy. ii When left to stand, solid particles settle to the bottom. A B C D solution suspension iii Fine solid particles can be seen in the mixture. 6. After completing Table 3, what can you conclude about the properties of solutions and suspensions? Write your answers in Table 4. Table 4 Properties of solutions Properties of suspensions WHAT I HAVE LEARNT A solution consists of two components: a solute and a solvent. A solute is the dissolved component in a solution. A solvent is the liquid in which the solute is dissolved. A solution consists of a mixture containing a solute dissolved in a solvent. Examples of solutions include sugar solution, salt solution, caustic soda solution and food colouring dissolved in water. A suspension consists of a mixture of a liquid with undissolved solid particles. Examples of suspensions include muddy water, corn starch and water, water and powdered chalk. 57 Unit 3 Mixtures and Separation Techniques The table below distinguishes the properties of solutions and suspensions. Solution Suspension A solution is clear; we can see through it. A suspension is usually cloudy; we cannot see through it. The solid particles are completely dissolved in the solution. The solid particles are not dissolved in a suspension. The solid particles do not settle to the bottom if a solution is left to stand. The solid particles settle at the bottom if a suspension is left to stand. DID YOU KNOW… A colloid is a mixture in which the dispersed undissolved solid particles are smaller in size than the undissolved solid particles in a suspension. An example of a colloid is mayonnaise. Separation of Mixtures Mixtures form part of our everyday life. The separation of these mixtures into their components is important. The components of a mixture are separated for example in the filtration of muddy water, in the making of filter coffee and in obtaining salt from seawater. In this section, you will investigate how mixtures can be separated by simple physical methods such as magnetic attraction, decantation, filtration, and evaporation. In the following activities, you will explore and investigate magnetic attraction as a separation method. ACTIVITY 3.5 - Explaining that differences in properties allow the separation of the components of a mixture (e.g. magnetic property) Materials you will need: 58 One bar magnet, wooden ruler, plastic cup, 1 clean iron nail, glass, paper, a piece of magnesium ribbon Mixtures and Separation Techniques Unit 3 Procedure: 1. Place the bar magnet close to the wooden ruler. What do you observe? Is the wooden ruler attracted to the bar magnet? 2. Fill in Table 5 by writing [Yes] or [No] in the appropriate column. 3. Repeat the same procedures above with the plastic cup, iron nail, glass, paper and the piece of magnesium ribbon. Table 5 Material [Yes or No] Material Wooden ruler Glass Plastic cup Paper Iron nail Magnesium ribbon [Yes or No] 4. After completing Table 5, answer the following questions. (a) Do all the above tested materials have magnetic property? Explain your answer. __________________________________________________________________________ (b) Do you think that all materials have same property(ies)? __________________________________________________________________________ __________________________________________________________________________ (c) Thus, suggest why the different components of mixtures can be separated? __________________________________________________________________________ 59 Unit 3 Mixtures and Separation Techniques ACTIVITY 3.6 - Separating the components of a mixture using a magnet In this activity, you will be working in groups and you will be testing the following hypotheses: Hypothesis I: A bar magnet can be used to separate magnetic materials from non-magnetic materials. Hypothesis II: A bar magnet cannot be used to separate magnetic materials from non-magnetic materials. DICTIONARY CORNER Hypothesis: an explanation made on the basis of limited evidence and used as a starting point for further investigations Materials you will need: 1 bar magnet, towel, 4 beakers each containing one of the following mixtures. Mixture A: Sulfur and iron filings Mixture B: Iron paper clips and copper turnings Mixture C: Iron nails and zinc powder Mixture D: Chalk powder and sulfur Procedure: 1. Place the bar magnet over the first mixture A. 2. Observe carefully and record your observations for mixture A in Table 6. 3. Wipe the magnet clean with the towel. 4. Repeat the experiment with mixtures B, C and D. Record your observations in Table 6. Table 6 Mixture A Bar magnet Observations 60 Sulfur powder and iron filings Mixture B Iron paper clips and copper turnings Mixture C Mixture D Iron nails and zinc powder Chalk powder and sulfur Mixtures and Separation Techniques Unit 3 5. After completing Table 6, answer the questions below: (a) Which common material is found in mixtures A, B and C? __________________________________________________________________________ (b) What can you deduce about the property of this material? __________________________________________________________________________ (c) Which mixture A, B, C or D does not contain any magnetic material? Explain your answer. __________________________________________________________________________ (d)(i) Which hypothesis is correct (I or II)? Write down the correct hypothesis. __________________________________________________________________________ (ii) Justify your answer. __________________________________________________________________________ 6. Draw labelled diagrams in the boxes I and II to represent the experimental set-up before the separation of mixture A and after the separation of mixture A respectively. Box I: Before separation of mixture A Box II: After separation of mixture B FIND OUT Do all metals have magnetic properties? 61 Unit 3 Mixtures and Separation Techniques WHAT I HAVE LEARNT Different materials have different properties. For example, iron has a magnetic property whereas glass, paper, wood, plastic and some metals like magnesium do not. The differences in the properties of different materials allow the separation of components of a mixture. Different materials can be separated based on their magnetic properties.Therefore, magnetic materials such as iron can be separated from non-magnetic materials using a bar magnet. DID YOU KNOW… One application of magnetic separation is illustrated in the operation of a crane. The crane uses a powerful magnet to lift and separate objects made of iron or steel from other non-magnetic objects. Thus, the iron or steel separated can then be recycled for use. Decantation Most materials around us are mixtures that consist of two or more components. However, at times we may require only one pure component of a mixture. Thus, we must learn how to separate mixtures. Decantation is a quick and simple method to separate a heavy insoluble solid from a liquid. However, it requires some degree of skill to decant liquids effectively. In the following activity, you will investigate decantation as a separation method. ACTIVITY 3.7 - Investigating decantation as a separation method Figure 4 illustrates a conversation about decantation between a little girl, Zariah, her mother and brother Angel. Study the conversation in Figure 4 and answer the questions that follow. 62 Mixtures and Separation Techniques Unit 3 There is a solution inside the mushroom can. How can I get rid of the solution from the mushroom can? This solution is used to preserve the mushrooms in the can, Zariah. Just pour the solution out carefully, the mushrooms will be left behind in the can. Mother Zariah Oh! I’ve just recalled from my chemistry classes that this separating method is called decantation. Decantation is often used in the kitchen. Angel Figure 4: Conversation on decantation mushrooms solution 1. Why did mother use the word ‘carefully’ when she answered Zariah’s question? __________________________________________________________________________ 2. Angel stated that this method is called decantation. Briefly explain how decantation is carried out to separate the mushrooms from the solution. __________________________________________________________________________ __________________________________________________________________________ 3. Explain why the mushrooms can be separated from the solution by decantation. __________________________________________________________________________ 4. Explain why a mixture of sand and water can be separated by decantation whereas a mixture of kitchen salt and water cannot. __________________________________________________________________________ __________________________________________________________________________ 5. Provide a definition for decantation. __________________________________________________________________________ 63 Unit 3 Mixtures and Separation Techniques 6. Angel mentioned that decantation is often used in the kitchen. Give two other examples to support his statement. 1. ________________________________ 2. ________________________________ 7. Figure 5 below illustrates how decantation is carried out in the laboratory to separate a mixture of sand and water. Observe Figure 5 carefully and answer the questions which follow. Step 1: Preparing a mixture of sand and water Step 2: The mixture is allowed to stand and the sand settles at the bottom. Step 3: We carefully pour the liquid from the mixture into another beaker using a glass rod as shown above. Figure 5: Decantation to separate a mixture of sand and water (a) Why is it important to allow the sand to settle down in the beaker before pouring out the water? __________________________________________________________________________ (b) Why should the water be poured slowly and carefully using a glass rod? __________________________________________________________________________ 8. Draw a labelled diagram to illustrate the separation of water from a mixture of sand and water by decantation. 64 Mixtures and Separation Techniques Unit 3 WHAT I HAVE LEARNT Decantation is a method of separating a heavy insoluble solid from a liquid. Decantation is the process of carefully pouring out the liquid from the mixture, leaving the heavy insoluble solid behind in the container. For an insoluble solid to be separated from a liquid by decantation, the solid must not float, but must settle down. Decantation can be used to separate mixtures such as rice and water, sand and water, and baby corn and water. Filtration While decantation is used to separate heavy insoluble solids from liquids, filtration is another separating technique that is used to separate finely divided insoluble solids from a liquid. Activities 3.8 and 3.9 will allow you to explore filtration as a separation technique. The activities will also help you to appreciate the applications of filtration in everyday life. ACTIVITY 3.8 - Exploring filtration as a separation technique Observe Figures 6, 7 and 8 carefully and answer the questions that follow. Figure 6: Vacuum cleaner Figure 7: Air conditioner Figure 8: Tea strainer 1. The vacuum cleaner, air conditioner and tea strainer shown in Figures 6, 7 and 8 respectively, involve a common component that allows separation to take place. Think and suggest a name for this common component. __________________________________________________________________________ 2. Give the name of the separation method involved in the vacuum cleaner, air conditioner and tea strainer by unscrambling the letters below. LT R A F I N I O T Answer: ______________________________________________________ 65 Unit 3 Mixtures and Separation Techniques 3. According to you, what is being separated from air in the vacuum cleaner and air conditioner? __________________________________________________________________________ 4. In Figure 8, what is being separated from tea when it is passed through the tea strainer? __________________________________________________________________________ 5. Observe the badminton racket and the shuttlecock shown below. shuttlecock Badminton racket (a) Explain why the shuttlecock does not pass through the net of the badminton racket. __________________________________________________________________________ (b) The net of the badminton racket acts as a filter. The shuttlecock cannot pass through the net as the holes in the net are too small for it to pass through. Use this information to explain how the tea leaves are separated from the tea in Figure 8. __________________________________________________________________________ __________________________________________________________________________ 6. Give another application of filtration. __________________________________________________________________________ 66 Mixtures and Separation Techniques Unit 3 ACTIVITY 3.9 - Separating a mixture of chalk powder and water by filtration In this activity, you will carry out an experiment to separate a mixture of chalk powder and water. Materials you will need: 250 ml beaker, funnel, filter paper, glass, glass rod, chalk powder, water, retort stand Procedure: 1. Half-fill a 250 ml beaker with water. 2. Add chalk powder to the water and stir with the glass rod. Describe the appearance of the resulting mixture in the beaker. __________________________________________________________________________ __________________________________________________________________________ 3. Fold the filter paper as shown below. Step 1 Step 2 Step 3 Write down the steps for folding the filter paper. Step 1 _______________________________________________________________________ Step 2 _______________________________________________________________________ Step 3 _______________________________________________________________________ 4. Place the folded filter paper in the funnel and moisten it with clean water so that the filter paper sticks to the surface of the funnel. 67 Unit 3 Mixtures and Separation Techniques 5. Set up the apparatus for filtration as shown below. 6. Pour the mixture into the filter paper with the help of a glass rod. 7 (a)The liquid passing through the filter paper is called the filtrate. The solid material remaining on the filter paper is called the residue. Observe and describe the appearance of the filtrate and the residue. Filtrate in beaker Residue on filter paper Appearance of filtrate _________________________________________ Appearance of residue _________________________________________ (b) Filter paper is like a sieve with small holes in it. Explain how the filter paper brings about separation of the chalk powder from water in this experiment. __________________________________________________________________________ __________________________________________________________________________ 8. Explain why filtration is appropriate to separate a mixture of flour suspension in water but not that of a kitchen salt solution. __________________________________________________________________________ __________________________________________________________________________ 68 Mixtures and Separation Techniques Unit 3 9. Label the diagram for the filtration process of chalk powder and water by filling in the empty boxes. ____________________ ____________________ ____________________ ____________________ ____________________ ____________________ ____________________ ____________________ WHAT I HAVE LEARNT Filtration is a method of separating an insoluble solid from a liquid using a filter. Filtration is possible when the size of the insoluble solid particles is larger than the pores of the filter used. For example, insoluble dust particles get trapped into the filter of the vacuum cleaner or air conditioner since the size of the dust particles is larger than the size of the pores of the filter. In laboratories, filtration is usually used to separate a mixture of a liquid and an insoluble solid. The liquid which passes through the filter paper during filtration is called a filtrate. The solid which remains on the filter paper during filtration is called residue. DID YOU KNOW… Hairs in our nostrils trap the dust particles that we breathe in and allow only clean air to pass through the trachea to our lungs. Filtration of blood occurs in the kidneys. The wastes are then excreted via urine. Hairs in nostrils Kidneys 69 Unit 3 Mixtures and Separation Techniques Evaporation as a separating technique After a rainy day, you must have observed that everything outside becomes wet. However, as the sun comes out, everything becomes dry again. Have you ever wondered what happens to the water as the wet things dry up? The liquid water changes state to form gaseous water vapour due to heat from the sun. The water vapour formed mixes with other gases present in air. In fact, this process is called evaporation. Water evaporates easily. Thus, by applying heat, evaporation can be used to remove water from a solution containing dissolved solid. The solid is left behind in the container when all the water has evaporated. The following activities will help you to investigate evaporation as a separating technique. ACTIVITY 3.10 - Separating salt from seawater by evaporation 1. Seawater is a mixture which can be separated into its main components by evaporation. (i) What are the two main components of seawater? __________________________________________________________________________ (ii) Which component is the solute and which component is the solvent? __________________________________________________________________________ 2. Study Figure 9 carefully and fill in the blank. Components of sea water can be separated by ______________________________ Sea water Salt pans Figure 9: Obtaining salt from sea water in salt pans 3. Briefly describe how salt is obtained from sea water in salt pans. __________________________________________________________________________ __________________________________________________________________________ 4. Seawater is pumped into salt pans that are usually situated in hot regions. Suggest why hot regions are preferred to cold ones. __________________________________________________________________________ 70 Mixtures and Separation Techniques Unit 3 ACTIVITY 3.11 - Separating a mixture of copper (II) sulfate and water by evaporation In this activity, you will carry out an experiment to separate a mixture of copper (II) sulfate and water. Materials you will need: Beaker, evaporating basin, copper (II) sulfate crystals, water, Bunsen burner, tripod, wire gauze Procedure: 1. Solid copper (II) sulfate solute is added to a beaker containing water. The mixture is stirred until all the copper (II) sulfate salt has dissolved to form a solution. 2. Pour some of the solution into an evaporating basin. Observe the solution and describe its appearance. ____________________________________________________ 3. Place the evaporating basin on a beaker of water to which heat is applied. Stop heating when most of the water of the copper (II) sulfate solution has evaporated and the volume has been reduced to one quarter of its initial volume. (a) Suggest a reason for not heating the evaporating basin directly over the Bunsen burner. _________________________________________________________________________ (b) Suggest a laboratory safety precaution that should be taken while carrying out heating. _________________________________________________________________________ 71 Unit 3 Mixtures and Separation Techniques 4. Leave the evaporating basin to cool in air for about 1 hour. What do you see remaining in the evaporating basin? Describe its appearance. ____________________________________________________ ____________________________________________________ 5. The diagram below shows the evaporation of copper (II) sulfate solution using a water bath. Label the diagram by filling in boxes. ____________________ ____________________ ____________________ ____________________ ____________________ ____________________ ____________________ WHAT I HAVE LEARNT Evaporation is a method used to separate a solute from a solution. The solution is placed in an evaporating

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