Cambridge Lower Secondary Science 9 PDF

CAMBRIDGE LOWER SECONDARY SCIENCE 9: TEACHER’S RESOURCE Learner’s Book answers Unit 1 Photosynthesis and the carbon cycle Topic 1.1 Photosynthesis Think like a scientist: Investigating...

CAMBRIDGE LOWER SECONDARY SCIENCE 9: TEACHER’S RESOURCE Learner’s Book answers Unit 1 Photosynthesis and the carbon cycle Topic 1.1 Photosynthesis Think like a scientist: Investigating how light intensity affects the rate of Getting started photosynthesis Learners should see that the plant that has light is 1 This will depend on the results that learners taller and greener than the one kept in the dark. obtain. They are likely to find that the mean They may also see that leaves of the plant in the number of bubbles is greatest when the lamp light are broader and more numerous, and the stems is closest to the test tube. are thicker. Learners may remember that plants make food by photosynthesis, and cannot do this 2 Check that: in the dark, so they do not have enough ‘food’ to the axes are the right way round, with be able to grow well. They may also know that distance of lamp on the x-axis and mean chlorophyll is what makes plants look green, and number of bubbles on the y-axis that this is used to absorb energy from light. With both axes are fully labelled, including units no light, the plant does not make chlorophyll. there are good scales on both axes the points are plotted neatly as small Questions crosses, in exactly the right places 1 carbon dioxide and water a neat line has been drawn; this could be a best fit line, or learners could use a ruler to 2 glucose and oxygen join each point to the next. 3 Photosynthesis transfers energy from sunlight 3 decreases into chemical energy in glucose. The plant can use the glucose to make other substances. 4 increases When the grasshopper eats grass, it takes in Activity: Photosynthesis and respiration some of this energy. The lizard gets some of Similarities: They are both chemical reactions. the energy when it eats the grasshopper. They both happen inside cells. They both involve 4 Plants release oxygen into the air when they energy changes (energy transfers). They both photosynthesise. Animals such as lizards need involve glucose, oxygen, carbon dioxide and water. oxygen for respiration. Differences: Respiration happens in all living cells, but photosynthesis only happens in some plant cells. Activity: Words beginning with photo- (Some learners may also know that photosynthesis Easy words include: photograph, photography, can happen in the cytoplasm in bacterial cells, but photographer, photographing, photocopier, this knowledge is not expected at this level.) photocopying and photocopy. A few learners may Respiration happens in cytoplasm and mitochondria, also know photostat and photogenic. Other less but photosynthesis happens in chloroplasts. likely words for them to think of include photon, Photosynthesis needs sunlight, but respiration photophobia, photocell and photofinish. does not. Think like a scientist: Collecting the gas The reactants in respiration are the products in produced in photosynthesis photosynthesis, and vice versa. 1 So that the gas could be collected over water. In photosynthesis, energy from sunlight is transferred to chemical energy in glucose. 2 So that the water plant could get energy for In respiration, energy in glucose is released for the photosynthesis. cell to use. Cambridge Lower Secondary Science 9 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth 1 © Cambridge University Press 2021  CAMBRIDGE LOWER SECONDARY SCIENCE 9: TEACHER’S RESOURCE Topic 1.2 More about The bubbles contain air. They are likely to contain a lot of oxygen if the leaf has been photosynthesis photosynthesising. Getting started The warm water makes the gases inside the air 1 in the green parts/in the leaves and stem spaces in the leaf expand, which makes them come out of the leaf. 2 because they contain chlorophyll Questions 3 because they are not green/do not receive light 1 The carbon dioxide particles have kinetic energy. Think like a scientist: Planning an They are in constant, random motion. By chance, investigation into the effect of some of them will go into the leaf through the fertilisers on plant growth stomata. Some will also come out. But, overall, more will go in than out because there are more 1 The hypothesis should state a predicted effect of them outside the leaf than inside it. that changing one variable has on another variable. For example: 2 Some of the oxygen diffuses out of the leaf. The more fertiliser the duckweed plants have, Some of the oxygen is used in respiration. the faster they will grow. 3 Plants get their protein by using the There are many other possible hypotheses. carbohydrates they make in photosynthesis Check that the hypothesis is genuinely testable and adding nitrogen to them to make proteins. by experiment. Animals get their protein by feeding on plants and/or other animals. 2 Answers will depend on the hypothesis being tested. It is advisable to have at least five 4 Nitrate and magnesium are both needed for different values of the variable. making chlorophyll, so a shortage of either of them makes leaves go yellow. Nitrate is 3 Learners are likely to suggest counting the also needed for making proteins, but without number of leaves. They could either decide to magnesium the plant cannot photosynthesise, count each set of duckweed just once, after a so it has fewer carbohydrates to make proteins set period of time, or they could count each from. A lack of either nitrate or magnesium one at regular intervals such as every two days. reduces growth. 4 This will depend on which variables are being changed; any other variables that could affect Think like a scientist: Testing a leaf for the rate of growth, such as light intensity and starch temperature, should be kept the same. 1 a Starch is stored in the chloroplasts. 5 This will depend on the learner’s experiment. b Boiling breaks down the cell membranes, They are likely to need Petri dishes, some so the iodine can reach the starch. duckweed plants, some fertiliser and a way of 2 This makes it easier to see the colour change measuring it, and a timer. when iodine solution is added. 6 There are few risks in this experiment. 3 Most learners will get a positive test result, Fertiliser should be handled with care, as it showing that the leaf does contain starch. This would not be good for it to be ingested. Clean was produced from the glucose that was made up any spills quickly. by photosynthesis in the chloroplasts. 7 The predictions should match the hypothesis. 4 Only the green parts contained starch. The Answers to questions 1 and 2 in part 2 will vary white parts have no chlorophyll, which is from learner to learner. needed to absorb energy from sunlight and without which photosynthesis cannot happen. Activity: Which surface of a leaf has most stomata? Topic 1.3 The carbon cycle Learners should see more bubbles emerging from Getting started the lower surface of the leaf because this is where In carbon dioxide in the air, the carbon atom is part most stomata are. of a compound; in photosynthesis it becomes part of a glucose molecule, but is still a carbon atom. Cambridge Lower Secondary Science 9 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth 2 © Cambridge University Press 2021  CAMBRIDGE LOWER SECONDARY SCIENCE 9: TEACHER’S RESOURCE Questions Tube F: Plant photosynthesises and respires, but photosynthesises more than it respires, 1 a The food chain should have a correct and therefore uses up carbon dioxide. sequence of organisms, with one plant Maggots respire, giving out carbon dioxide. and three animals. Arrows should go in The two are likely to balance out. the correct direction. For example: fig tree → wasp → spider → lizard. 6 To make sure that having a platform in place b Yes, the arrows could also indicate how did not cause the differences between the carbon atoms are transferred. Carbon results in the different tubes. is contained in the food that animals Activity: Modelling the carbon cycle eat, in the form of compounds such as 1 No, in the real carbon cycle only some carbon carbohydrates and proteins. atoms will move at any one point in time. 2 Proteins, carbohydrates and fats. Learners Learners could suggest having only one or two could also suggest particular compounds, such atoms moving on each occasion. as haemoglobin. (Note that animals do not 2 Learners should find that stopping contain starch.) combustion results in fewer carbon atoms 3 There would be no (or very little) combustion ending up in the air. of fossil fuels. Topic 1.4 Climate change 4 They take a very long time to form. We are using them up much faster than they are being Questions replenished. A 3; B 1; C 3; D2 Think like a scientist: How do plants Questions and animals affect carbon dioxide 1 An asteroid is a rock, smaller than a planet, concentration? which orbits the Sun. 1 Learners will probably find these results: 2 It produced a lot of heat, which killed plants Tube A: yellow, high carbon dioxide and animals close to the collision site. Tube B: purple, no carbon dioxide It produced a huge tsunami, which killed Tube C: yellow, high carbon dioxide plants and animals on land that were swamped Tube D: yellow, high carbon dioxide by sea water. Tube E: yellow, high carbon dioxide It sent dust high into the atmosphere, so plants died because they could not photosynthesise. Tube F: red, some carbon dioxide Animals then died because there was no food 2 Organisms were respiring in all the tubes. for them to eat. 3 Plants were photosynthesising in tubes B and F. 3 1.3 °C 4 a Carbon dioxide would be used up in tube B. 4 The temperature fell by 0.3 °C between 1880 and b Carbon dioxide would be given out in 1910. It rose by 1.6 °C between 1910 and 2016. tubes A, C, D and E. 5 Multiply the number of years until the end of 5 Tube A: No photosynthesis because no light; the century by 3 mm. plant respires, giving out carbon dioxide. 6 As the mean global temperature increases, Tube B: Plant photosynthesises and respires, more land ice melts and adds extra water to but photosynthesises more than it respires; the oceans. Also, higher temperatures cause carbon dioxide is used up. sea water to expand. Tube C: Maggots respire, giving out carbon Think like a scientist: How do rising dioxide. temperatures affect sea level? Tube D: Maggots respire, giving out carbon dioxide. 1 Learners should find that melting ice on land and increasing water temperature both Tube E: No photosynthesis because no light; increase the water level. Melting ice in the sea plant respires, giving out carbon dioxide. does not increase the water level. Maggots respire, giving out carbon dioxide. 2 They indicate how sea level is expected to rise. Cambridge Lower Secondary Science 9 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth 3 © Cambridge University Press 2021  CAMBRIDGE LOWER SECONDARY SCIENCE 9: TEACHER’S RESOURCE Activity: The carbon cycle and c The wheat plants use the nitrate to make climate change proteins. The proteins can be used to make new cells, some of which will be Respiration and combustion increase the level of used to produce the grains. carbon dioxide in the atmosphere. Photosynthesis decreases it. d In a different place, there might be a different concentration of nitrate in the Learners could suggest: soil before the fertiliser is added. There Plant more trees, because they will might be a lack of other minerals in the photosynthesise and take carbon dioxide out of soil. The soil might be better or worse the air. at holding water. There might be more Stop deforestation (same reason). shade in one place than another. The Stop burning fossil fuels, to reduce combustion. temperature might be different. Stop using so much energy, so that we do not e Magnesium is needed for making need to use as much fuel. chlorophyll. Learners may also be aware of other issues not 1.4 a i D covered here, such as eating less meat (because ii B production and transport of meat uses a lot of iii A energy and produces a lot of carbon dioxide) or iv C reducing air travel. b i 3 Check your progress ii 2 iii 1 1.1 a carbon dioxide c glucose, starch, carbohydrate, protein, b oxygen fat, cellulose or chlorophyll – allow any c soil other correct organic compound. d chlorophyll 1.5 a Sea level will rise. There will be more e stomata extreme weather events, such as typhoons and hurricanes. 1.2 a the type of seaweed b i Many species of organisms are b Any three from: the temperature; completely destroyed. the light intensity; the size of the ii Look for the idea of long-term piece of seaweed; the time for which reduction in photosynthesis the apparatus is left. because of dust thrown up into the c the volume of gas collected (after a set atmosphere, which reduces light period of time). penetration. 1.3 a 4 tonnes per hectare This in turn reduces food for animals. b Adding more than 60 kg per ha gives Other reasons are the immediate only a very small increase in yield. It is results of the impact, including likely that the cost of the extra fertiliser the heat and pressure wave in the would outweigh the small increase in vicinity of the impact, and a income from selling the grain. massive tsunami. Unit 2 Properties of materials Topic 2.1 Atomic structure and may be able to give facts such as the charges on the particles: protons – positive, neutrons – no charge the Periodic Table and electrons – negative. They may be able to Getting started recall the relative masses of the particles: protons and neutrons having more mass than electrons. Answers will depend on what learners can recall. They may be able to recall the arrangement of the You should use this as a form of assessment particles as in the Rutherford model. for learning. Learners should manage to name electrons, neutrons, protons and the nucleus. Some Cambridge Lower Secondary Science 9 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth 4 © Cambridge University Press 2021  CAMBRIDGE LOWER SECONDARY SCIENCE 9: TEACHER’S RESOURCE Questions 9 non-metals 1 6 10 Melting points increase as you go down 2 4 the group. 3 6 11 The colour gets darker as you go down this group. 4 Diagram should have three shells, with electrons structure 2:8:2, and a nucleus with 12 Boiling points increase as you go down 12p and 12n in the centre. the group. 5 Aluminium 13 The melting point of iodine would be higher than −7 °C and boiling point higher than 59 °C. 6 Diagram should have two shells, with electrons structure 2,7, and a nucleus with 9p and 10n in 14 Iodine would be less reactive than bromine. the centre. 15 7 7 The nucleus is made up of protons and neutrons in both models. In the Rutherford 16 The size of the atoms increases as you go model, the electrons are all shown in one cloud down this group. around the nucleus. In the model we use today, 17 The atoms are similar in that they all have 7 the electrons are shown arranged in different electrons in their outer shell. shells or energy levels around the nucleus. In the model we use today, each shell can contain 18 Because the atoms of each element has 7 up to a particular number of electrons. electrons in its outer shell. 19 The melting points increase as you go down Topic 2.2 Trends in groups within this group. the Periodic Table 20 The size of the atoms increases as you go Getting started down this group. Metals in the same group as magnesium: beryllium 21 The outer electron shells are all full and have or calcium. (Accept other metals in this group if 8 electrons (other than helium, which only has you are using a full Periodic Table.) 2 electrons). Metals in the same period as magnesium: sodium or aluminium. 22 The atoms of each element have 8 electrons in Non-metallic solid in the same period as their outer shell. magnesium: silicon, phosphorus or sulfur. Gas in the same period as magnesium: chlorine 23 The melting- and boiling points of krypton or argon. will be higher than those of argon. Questions Think like a scientist: Observation of 1 The metals (except Aluminium) are found on the reactions of Group 1 metals with the left side of the table. water 2 The boiling points decrease as you go down 1 These might include the use of safety glasses the group. and a safety screen; handling the metals with forceps; using only a small piece of each 3 It is lower than 777 °C. metal, and warning students about their 4 eight more electrons position in the room. 5 The size of the atoms increases as you go 2 Descriptions should include any movement down this group. across the water; change in the solid metal; fizzing, any flame and colour of the flame. 6 All have an outer shell containing one electron and an inner shell containing two electrons. 3 lithium + water → lithium + hydrogen hydroxide 7 This group of metals could be called Group 1 because there is one electron in the outer shell. sodium + water → sodium + hydrogen hydroxide 8 The atoms get larger and the reaction with water gets more violent as the size of the atoms potassium + water → potassium + hydrogen hydroxide increase. Cambridge Lower Secondary Science 9 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth 5 © Cambridge University Press 2021  CAMBRIDGE LOWER SECONDARY SCIENCE 9: TEACHER’S RESOURCE 4 This might include the reaction producing from the electrostatic charges between the heat; a gas is released, and the metal moves electrons and the protons. around the water surface. 9 Diagram of calcium atom should have four 5 The differences may include the amount of shells, with electron structure 2,8,8,2, and a movement on the water and the intensity nucleus. of the violence of the reactions. Accept any Diagram of calcium ion should have three observed differences. shells, with electron structure 2,8,8, and a 6 These may include the colour; the fact that nucleus. (Students may or may not write 2+ to they are soft and can be cut; they are all light the top right of the calcium ion diagram.) and float on water and they react to form an 10 2 hydroxide with water. Accept any observed similarities. 11 CaCl2 7 The reaction increases in intensity as you 12 CaO go down Group 1. This would suggest that 13 carbon dioxide, methane, water, rubidium reacts extremely violently and would hydrogen chloride and ammonia. not be safe to use in schools. 14 8 When these Group 1 metals react with water, they produce the alkalis lithium-, sodium- and potassium hydroxide. Topic 2.3 Why elements react to form compounds Getting started 15 An ionic compound, because the compound is The learners’ drawings should match those in the formed from a metal and a non-metal. Learners’ Book in Topic 2.2. The point here is to 16 methane CH4; carbon dioxide CO2; nitrogen N2 focus the learners on getting the details correct by discussing their drawings with their partner. Topic 2.4 Simple and giant Questions structures 1 2,8,1 Getting started 2 2,8 Learners should be able to describe the structure of sodium and chlorine atoms. They might be able 3 Cl to discuss the stability of the two atoms. They 4 Cl− should be able to describe the formation of the ions of these two elements and the formation of 5 Diagram should have three shells, with an ionic bond between them. Suitable diagrams electron structure 2,8,8, and a nucleus. such as those shown in Topic 2.2 could be drawn. 6 Diagram should have two shells, with electron This should not be used simply as a right/wrong structure 2,8, and a nucleus. answer but the idea is to provoke discussion between learners to help them improve their 7 Potassium can lose an electron more easily understanding. because the outer electron is a long way from the nucleus and the positive electrostatic Questions charges on the protons, so it is easier for the 1 An ionic bond is formed when atoms lose or electron to escape from the potassium atom. gain an electron (or electrons) but a covalent The outer electron in the lithium atom is bond is formed when atoms share electrons. closer to the positive electrostatic forces, so it is more difficult for it to escape. 2 ionic bond 8 Fluorine is more reactive than chlorine 3 A molecule is the name given to a particle because it can gain an electron more easily with more than one atom where the atoms because the outer shell of electrons is further share at least one electron in a covalent bond. Cambridge Lower Secondary Science 9 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth 6 © Cambridge University Press 2021  CAMBRIDGE LOWER SECONDARY SCIENCE 9: TEACHER’S RESOURCE 4 A macromolecule is a giant molecule. Examples 5 If a covalent substance were used, there would are silicon dioxide, diamond or graphite. be no conduction of electricity because the forces inside the molecules are strong and 5 Ionic, because it has high melting- and boiling there are no charged particles to carry the points and it is a compound formed from a electricity. metal and a non-metal. 6 A simple molecule with covalent bonds. It has Check your progress low melting- and boiling points. Also credit 2.1 a Below 180 °C and above 63 °C the fact that it is formed from two non-metals b Below 883 °C and above 688 °C so must have covalent bonds. c hydrogen 7 A gas d More bubbles of gas and more heat will 8 They have high melting points because they be generated than with lithium, but less are ionic compounds. The electrostatic forces than with potassium. between the ions in these compounds are very e Lithium 7; sodium 23; potassium 39; strong so, in order to melt the solids, a great rubidium 85 deal of energy is need to break these bonds. f The number of protons plus the number 9 They are composed of simple molecules; the of neutrons. forces within the molecules are strong, but the g Diagram should have a nucleus, three forces between the molecules are weak, so less shells, and the electron structure 2,8,1. energy is needed to melt them. 2.2 a Diagram should be the same as in the 10 Copper sulfate has ionic bonds. It has formed question, but with one additional a giant structure of crystals and is made from cross in the outer shell. a metal and a a non-metal. b A fluorine ion is more stable than a 11 This substance has ionic bonds because it has fluorine atom because the outer (highest very high melting- and boiling points. energy level) shell of electrons is full. 12 Silicon dioxide is hard and has a very high c F− melting point; these are not properties that 2.3 a ionic are expected of a substance with covalent b covalent bonds. We know that silicon dioxide must have covalent bonds because it is formed from two c covalent non-metals so the only explanation can be that d ionic silicon dioxide has a giant covalent structure. e ionic Think like a scientist: Ionic compounds 2.4 CH4 conducting electricity 2.5 a The strong electrostatic forces between 1 The expected answer would be yes, but credit the positive sodium ions and the answers based on the learner’s findings. negative chlorine ions. 2 When ionic compounds dissolve in water, the b The melting- and boiling points of ions are free to move about in the solution sodium chloride will be high because and can carry the electric charge and so the the electrostatic forces are strong. solution can conduct the electricity. 3 The expected answer would be no, but credit answers where learners may have found some conduction if they are based on their results. 4 The ions are held in a strong lattice so they are not free to move to carry the charge and conduct electricity. Learners should explain any conduction they did observe, for example the electrodes were touching or the crystal was wet. Cambridge Lower Secondary Science 9 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth 7 © Cambridge University Press 2021  CAMBRIDGE LOWER SECONDARY SCIENCE 9: TEACHER’S RESOURCE Unit 3 Forces and energy Topic 3.1 Density 7 a A = kerosene; B = water; C = mercury 8 The gas must be less dense than air; the gas Getting started must have a density low enough so that the 1 the (3-dimensional) space occupied by an average density of the balloon, the string and object / length × width × height of an object the gas is less than that of air. 2 1 kg feathers 9 It is cooler at those times, so the surrounding 3 1 cm of iron 3 air will be denser; the difference in density between the balloon and the surrounding air Questions will be greater; the balloon will float more 1a pine wood easily. b i polycarbonate Activity: Densities of some ii The density of polycarbonate is regular objects greater than the density of water. 1 Those objects with calculated densities greater mass _______ than 1.0 g/cm3 should be predictedto sink; 2 a ​​   ​​ volume those that are less, to float. mass 13.5 b density = _______ ​​   ​​ = ____ ​​   ​​ = 2.7 g/cm3 2 If the balance is not at zero, then the volume 5 (recorded / measured) mass of the object will c It will sink because its density is greater be too large or too small. than that of water. 3 a There is material missing from the 3 a 4 × 3 × 6 = 72 cm3 corners, so if measured to where the mass 54 corner should be, then the calculated b density = _______ ​​   ​​ = ___ ​​   ​​ = 0.75 g/cm3 volume 72 volume will be too large. c It will float because its density is less than b The mass should be correct because that of water. damage to the object will not affect the mass 10 300 reading on the balance. 4 density = _______ a ​​   ​​ = ______ ​​   ​​ = 1030 g/cm3 volume 10 c If the calculated volume is too small, then b i The material will float because its the density value will be too large / vice density is less than that of sea water. versa; if the recorded mass is too small ii The material will sink because its density then the density value will be too small / is greater than that of pure water. vice versa. mass Think like a scientist: Densities of some 5 a density = _______ ​​   ​​ volume irregular objects so mass = density × volume 1 The volume is read correctly from the bottom of the meniscus. = 8.96 × 20 = 179.2 g 2 Either: place a heavier object of known mass _______ mass _______ volume on top to make the less dense object b density = ​​   ​​ so volume = ​​   ​​ volume density sink, measure the total volume of the two 4.5 objects by displacement, subtract the volume volume = ​​ ____ ​​ = 0.50 cm3 8.96 of the denser object. 6 a 78 − 50 = 28 cm3 Or: tie a denser object with string to the less dense object, submerge them both in water, mass 84 b density = _______ ​​   ​​ = ___ ​​   ​​ = 3 g/cm3 measure the total volume of the two objects volume 28 by displacement, subtract the volume of the c Any two from: plastic is less dense than denser object and the string (that can also be steel / the result from part b is the average measured by displacement). density of all the materials / the toy is hollow OR contains air. Cambridge Lower Secondary Science 9 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth 8 © Cambridge University Press 2021  CAMBRIDGE LOWER SECONDARY SCIENCE 9: TEACHER’S RESOURCE 3 Use a larger container filled to the very top, 3 The greater the temperature difference, the submerge object, collect water that overflows, greater the rate of thermal energy transfer. measure the volume of the water collected 4 The trend in the learner’s result is correctly using several measuring cylinders. described; this should be a trend rather than 4 The result is likely to be anomalous because only quoting results. wood floats on water, therefore the density of wood is expected to be less than the density of Think like a scientist: Measuring heat water, which is 1.0 g/cm3. and temperature 1 The table should have a column for energy in Topic 3.2 Heat and temperature joules and a column for temperature in °C. Getting started 2 The graph should be drawn with linear scales 1 Any heat source, such as a flame, a hot plate and cover half the grid in both directions. or an immersion heater; it is also acceptable Ideally, the graph should be a straight line. to add more water that is at a higher 3 As the energy supplied to the water increases, temperature. the temperature of the water increases. 2 a The water in the swimming pool. 4 Any three from: volume or mass of water b The temperature increases are the same, / type of container / starting temperature so the larger mass of water requires more of the water / same temperature increase / thermal energy. same quantity of thermal energy from the immersion heater. Questions 5 Any three from: transferred to the cup / to 1 a J the air above the water / to the surface below b °C the cup / to evaporate some of the water / to 2 a The temperatures are the same. the area around the top of the heater (if the heater was not completely submerged). b The thermal energy in the larger block, B, is greater, so B has more heat. 6 Any three from: insulation around the cup / insulation under the cup / ensure the heater is 3 a Thermal energy contained within that completely submerged (if it was not) / put a lid object; the total energy of all the particles on the cup. in the object. b The average energy of the particles in Topic 3.3 Conservation of energy an object. Getting started 4 A → B and A → C and B → C 1 Most should be able to recall at least some 5 The statement will be true only if the from: kinetic, chemical, gravitational substances are the same and have the same potential, elastic potential, electrical, thermal. mass or same number of particles. It is 2 For example, chemical can be changed to possible for an object with a small mass to electrical in a cell or battery. have a higher temperature than an object with larger mass, yet the object with larger mass 3 Where energy spreads out and becomes may have more thermal energy, so has more less useful. heat. Questions Activity: The Mpemba effect 1 a Energy cannot be created or destroyed; 1 The table should have a column for starting energy can be changed or transferred temperature of the water in °C (normally be (statements can be in either order). on the left). There should be a column for b i false time taken to freeze in minutes or seconds, or ii false minutes and seconds. iii true 2 Each temperature difference correctly 2 a 1000 − 500 = 500 J calculated by subtracting −18 °C from each b 100 − 80 = 20 J temperature. Cambridge Lower Secondary Science 9 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth 9 © Cambridge University Press 2021  CAMBRIDGE LOWER SECONDARY SCIENCE 9: TEACHER’S RESOURCE c 1300 + 700 = 2000 J 3 The temperature will increase; the surroundings are at a higher temperature than 3 a 100 − 70 = 30% the ice cream; thermal energy will move from b 55 + 10 = 65; 100 − 65 = 35% the surroundings to the ice cream. 4 Sofia is not correct. The useful energy output 4 Zara is correct; heat, or thermal energy, and the wasted energy cannot add up to more moves but cold does not move, and the gloves than the energy input. 12 + 7 = 19 J, whereas keep the cold air from contacting the skin; energy input is 18 J. So 18 − 7 = 11 J of the the gloves keep the heat of the hands from electrical energy is changed to light. escaping to the colder surroundings. Activity: Conservation of energy 5 a The water is at lower temperature / is 1 The first bottle swings through a smaller colder than the engine; thermal energy distance as the second bottle swings through from the engine moves to the water; heat from the engine is dissipated into the water. a greater distance. The second bottle then swings through a smaller distance as the first b Thermal energy from the water is bottle swings through a greater distance. The dissipated into the air around the radiator cycle repeats. (or dissipated into the radiator); the air at the front of the radiator is at lower 2 Kinetic energy from one bottle is transferred temperature than the water. to the other bottle. Energy cannot be gained (as no additional energy is input), so as one Activity: Hot coffee bottle swings more, the other must swing less. 1 method B 3 Energy is used to overcome friction and air 2 Adding the cold milk to the coffee lowers the resistance; energy is dissipated. temperature of the coffee. Activity: Bottle racers This lowers the temperature difference between the coffee and the surroundings. 1 the (twisted) elastic band The rate of thermal energy transfer (and 2 elastic potential therefore cooling) is lower when the temperature difference is lower. 3 kinetic 3 Same cups; same volume (or mass) of coffee; 4 The bottle racer moves faster / further same volume (or mass) of milk; same starting (depending on their observation) as there is temperature of coffee; same temperature of more elastic potential energy to change to milk; same room temperature; same exposure kinetic energy. to draughts / moving air. Topic 3.4 Moving from hot Think like a scientist: Temperature to cold change from heat dissipation Getting started 1 Table should have a column for time in seconds or minutes and a column for Thermal energy from the room is transferred out temperature of water in °C. through the open window; cold air may enter the 2 Axes should be scaled in a linear way with room but thermal energy moves from the warm air temperature on the y-axis. into the cold air. Line graph should be drawn either with a best Questions fit straight line or a smooth curve. 1 Thermal energy moves from warmer / hotter / 3 The results may show a lag before temperature higher temperature places to cooler / colder / starts to increase and may also show a lower temperature places. decrease in rate of temperature change as time progresses. Learners should describe the trend 2 a The temperature will decrease. shown in their graph. b The food is at a higher temperature than the surroundings; thermal energy will 4 The temperature of the water will stop increasing either when the lamp is switched move from the food to the surroundings; off or when the water reaches the same heat will be dissipated from the food. temperature as the lamp. Cambridge Lower Secondary Science 9 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth 10 © Cambridge University Press 2021  CAMBRIDGE LOWER SECONDARY SCIENCE 9: TEACHER’S RESOURCE 5 The temperature increase of the water will be b Because of convection; hotter water will slower with the LED; the water will not reach be at the top, hotter water is less dense as high a temperature with the LED as it did and will float / rise above cooler water with the lamp. (which will be at the bottom). c Higher up than the first heater; because Topic 3.5 Ways of transferring of convection, the water below the heater thermal energy will not be heated. Getting started Think like a scientist: Conduction of 1 a In a solid, the particles are regularly thermal energy in different materials arranged and in contact. The risk assessment should include keeping paper b In a liquid, the particles are randomly away from the flame; not touching the hot metal rod; arranged and in contact. making sure the candle will not fall over, and allowing c In a gas, the particles are randomly everything to cool at the end of the investigation. arranged and not in contact. 1 Thickness / diameter of rod; distance of rod 2 a Particles vibrate more vigorously, taking from flame; mass of wax; distances between up more space; the solid expands. paperclips; mass of paperclips. b Particles vibrate more vigorously, taking 2 This will vary according to available up more space; the liquid expands. equipment and design of the investigation. c Particles move faster and collide with each other and the walls with more force; the 3 The paperclips closer to the heat source should gas expands. fall first, some of the more distant paperclips may not fall within the allocated time. If Questions different materials have been used, then some 1 a conduction, convection and radiation comparison should be made. For example, the paperclips started to fall off faster from a b conduction and convection; both of these copper rod than from an iron rod. methods require particle movement and there are no particles in a vacuum. 4 The heat source makes particles in the rod c Conduction because the particles in vibrate more vigorously; the vibration is a solid are close together/touching to transferred to neighbouring particles by transfer the energy from vibrations; collisions; this carries on along the rod; if convection cannot occur in a solid different materials have been used then a because the particles are not free to move. comparison should be made – for example, the vibrations are transfered faster in the copper 2 The black T-shirt will absorb thermal radiation than in the iron; transferring thermal energy faster, so Arun will feel hotter sooner. The along the rod, the wax is heated by conduction white T-shirt will reflect more thermal from the rod and will melt when it reaches radiation, so Marcus will feel cooler for longer. its melting point; particles in the solid wax 3 a conduction vibrate more vigorously until they can move further apart and turn to a liquid. b radiation 5 Some materials such as wood will burn; other 4 a The electric heater gets hot (changes materials such as plastic will melt. electrical energy to thermal energy), heat is transferred from the heater to the water Activity: Observing convection by conduction, particles in water around 1 The drawings should, at the very least, show the heater vibrate more vigorously and arrows for the direction of the convection take up more space, water around the current. Arrows should point up from the heat heater expands and becomes less dense, source (which is clearly shown at one side of this hotter water floats to the top of the the base of the beaker), then across the upper tank, cooler water moves to the bottom part of the water, then down the other side of the heater to replace the water that has and back across the bottom to the heat source. risen; this sets up a convection current that heats all the water. Cambridge Lower Secondary Science 9 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth 11 © Cambridge University Press 2021  CAMBRIDGE LOWER SECONDARY SCIENCE 9: TEACHER’S RESOURCE 2 Explanations should refer to particles e.g., every 1 minute (details of the cans need vibrating more vigorously due to being not be given as question asks about these cans, heated. These particles then take up more i.e., the ones that were used in the first part of space, expanding the liquid, decreasing the the investigation). density of the heated liquid and this heated liquid, floating or rising through the denser Topic 3.6 Cooling by evaporation surrounding liquid. Getting started Think like a scientist: Emitting thermal 1 In evaporation, some particles have sufficient energy by radiation energy to leave the surface of the liquid 1 The prediction should be that the water in the and enter the gas state, so evaporation cans will cool at different rates and that this only occurs at the surface. In boiling, all is linked to the colours; the black can should particles have sufficient energy to turn to cool quickest and the shiny silver can should gas, so boiling occurs at all positions in the cool slowest. This should be linked to the liquid at once. Evaporation can occur at any relative ability of each colour to emit thermal temperature whereas boiling only occurs at radiation. one temperature. 2 The table should have one column (at the 2 Particles in a liquid all have different energies. left) for time in minutes, or in minutes and Those at the surface that have sufficient energy seconds. There should then be columns for the can leave the liquid and enter the gas state. temperature in °C for each colour. Questions 3 The graph should have temperature on the 1 The energies of the particles in water at 25 °C y-axis and time on the x-axis. All three (or are different. more) lines should be drawn on the same grid; Particles with the least energy stay in the liquid. each line should be clearly identified using a Particles with the most energy can leave the key for the colour of the can. The lines should liquid. be curves if the results have been recorded correctly. When liquid water turns to gas, the water is said to evaporate. 4 The trend for all cans should be described as the temperature decreasing with time. More 2 C detail can be added, such as the decrease in 3 a The average energy of the particles temperature was faster at the start / when the decreases because the particles with more / water was hotter. A comparison should be the most energy leave the liquid; slower made between the rates of cooling of each moving particles are left behind in the colour of can. liquid. 5 The answer should link the original prediction b The temperature decreases; temperature with the observations. is the average energy of the particles in a substance, so as the average energy 6 Reference to the graph; any point that are decreases, the temperature decreases. further from the line or does not appear to fit with the others. 4 a Evaporation causes cooling; thermal energy from skin is used to evaporate 7 Volume (or mass) of water in each can; the sweat. material / type of can; starting temperature of water; location of cans; none stirred or b There is no loss of thermal energy due to shaken. evaporation. 8 Use of a radiant heat source or placing in 5 When isopropanol contacts the skin, the liquid direct sunlight; if a radiant heater is used then evaporates; evaporation lowers the average all cans to be equal distance from the heat energy of the particles in the liquid, so the source; same volume of water in each; water at temperature of the liquid decreases; thermal same starting temperature in each; cans left for energy from the skin is used to evaporate the the same time; temperature measured at equal liquid. regular intervals which should be specified, Cambridge Lower Secondary Science 9 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth 12 © Cambridge University Press 2021  CAMBRIDGE LOWER SECONDARY SCIENCE 9: TEACHER’S RESOURCE Think like a scientist: Making an air 3.2 B and D cooler 60 3.3 a ​​ ___ ​​= 1.2 g/cm3 1 Thermal energy from your hand will affect the 50 thermometer reading / the thermometer will b It will sink because its density is greater measure the temperature of your hand rather than that of water. than the temperature of the air. (Answer should be specific and not just refer to getting 3.4 a The average energy is the same because better results.) the temperatures are the same. b The heat in beaker Y is greater because 2 There should not be a significant difference there are more particles (with the same between the temperatures measured in steps average energy) / the total energy of all 2 and 3. This is because the air has not the particles is greater. been heated or cooled; the only difference is movement. The temperature from step 7 should 3.5 a °C or degrees Celsius be lower; this is because the water from the b J or joules towel has evaporated, lowering its temperature. Thermal energy from the air around the wet 3.6 a Energy is always conserved, meaning that towel is used to evaporate the water. energy cannot be created or destroyed. 3 The three temperatures from steps 2, 3 and 7 3.7 50 − 5 = 45 J should be the same if a dry towel is used; this 3.8 a The temperature of the ball decreases is because there is no cooling by evaporation. because thermal energy is transferred to the water. The temperature of the water Activity: Feeling the effects of increases because thermal energy is evaporation transferred from the ball. 1 To increase the rate of evaporation. b C 2 The alcohol should feel coldest, the water next 3.9 conduction; thermal energy is transferred and the soap the least cold. Blowing makes from the tea to the spoon; metal is a good each of the liquids (perhaps with the exception conductor of heat of the soap) feel even colder. 3.10 a air is heated; the air becomes less dense; 3 a alcohol the air floats / rises b soap b air cools; the air becomes denser; the air 4 There are no numerical results / no measurements. sinks / falls 5 Either repeat the experiment using a skin 3.11 the black car is hotter inside; black is a thermometer or perform an experiment good absorber of radiation; white is a good similar to that in Main Teaching Activity How reflector / poor absorber of radiation does sweating work. 3.12 evaporation; thermal energy is removed from the skin; the most energetic particles leave Check your progress the sweat, lowering the average energy of the 3.1 B remaining particles Unit 4 Maintaining life 4.1 Plants and water Think like a scientist: Investigating transport in a celery stalk Questions 1 The drawing should show an outline of the 1 The long extension from the cell increases its cut stalk, and coloured spots in the correct surface area. This increases the surface across positions. This will depend on the type of which it can take up water and mineral salts, stalk that has been used in the experiment. so this uptake happens faster. 2 xylem cells 2 Nitrate ions are needed to make proteins. Magnesium ions are needed to make chlorophyll. Cambridge Lower Secondary Science 9 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth 13 © Cambridge University Press 2021  CAMBRIDGE LOWER SECONDARY SCIENCE 9: TEACHER’S RESOURCE 3 a To make sure that the coloured areas in Questions the stalk had appeared because dye had 1 The parts are identified in the diagram in been carried up through the stalk, not Topic 1.2. leaked in from the side. b To remove any dye from the outside of 2 The upper surface is covered with a layer of the stalk, so we could be sure that the wax that stops water passing through. The coloured spots were caused only by dye underside has stomata, which are openings that had been carried up the stalk. leading to the air spaces inside a leaf. Water vapour can diffuse out from the air spaces, 4 The water would move from the soil into the through the stomata. root hairs, then across the root to its centre. There it would enter the xylem vessels, which Think like a scientist: carry it up through the stalk. Investigating transpiration 1 Whether the leaves were exposed to the air Think like a scientist: or not. Planning an experiment 2 The soil was covered in both. Learners should Questions also have tried to keep the temperature the same 1 The water will move up faster, because higher for both plants and to use two plants of the temperatures give more kinetic energy to same size. They should have ensured there was particles. the same quantity of water in the soil in each pot 2 As temperature increases, the speed at which and that the light intensity was the same. water moves up the stem increases. 3 Answers will depend on the learners’ results. 3 The plan should include the idea of changing They are likely to find that the loss of mass the temperature, and measuring how fast was much greater in the plant that did not the dye moves up the stem at different have a bag covering its leaves. temperatures. 4 Water vapour was lost from the leaves of the 4 The apparatus is likely to include a container, plant that did not have its leaves covered, by some coloured water, several stalks, a timer and transpiration. The water vapour that was lost a ruler. Learners may need other apparatus or from the leaves of the other plant was trapped materials, depending on their plan. inside the bag and could not escape. The independent variable is temperature. Think like a scientist: Which side of a The dependent variable is the rate at which leaf loses most water? the coloured water moves up the stalk. This 1 This will depend on the learners’ results. The involves measuring time and distance. most likely sequence (in increasing ability to Variables to keep the same include depth conserve water) is: leaf with no petroleum jelly; of coloured water, size of the stalk and with petroleum jelly on upper surface only; light intensity. with petroleum jelly on lower surface only; with Risk assessment: Cutting the stalk carries a petroleum jelly on both surfaces. risk of harm from the sharp blade. Cut on 2 The upper surface has few (or no) stomata, but a firm, non-slip surface and move the blade the underside has stomata, through which water away from the body. vapour can diffuse out from the air spaces. 4.2 Transpiration 3 It is unlikely that the two leaves would lose exactly the same mass. The leaves were Getting started probably different masses to start with and The particles in the liquid should be randomly contained different quantities of water. One arranged, but with each particle touching at least leaf may have been in a slightly draughtier two other particles. The particles in the gas should place than another. Learners may make other not be touching at all, and should be far apart. suggestions, depending on what happened in When liquid water turns to a gas, the particles their experiment. move faster and spread further apart. Cambridge Lower Secondary Science 9 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth 14 © Cambridge University Press 2021  CAMBRIDGE LOWER SECONDARY SCIENCE 9: TEACHER’S RESOURCE 4 Using two leaves gives more reliable results, as Questions you can avoid the possibility that the one leaf 1 oxygen and any nutrients, such as water, you test might be unusual. Using even more glucose, vitamins, minerals leaves would be much better, as this would then give you the opportunity to identify 2 carbon dioxide and urea any anomalous results. It would increase the 3 Vitamin A for good vision for the mother and likelihood of obtaining reliable data. the fetus, and for their white blood cells to 5 This will depend on the learners’ experiences as fight pathogens. they did their experiment. Do not give credit to Vitamin C for strong skin and blood vessels answers that involving changing another variable. for both the mother and the fetus. Vitamin D for strong bones and teeth for both Activity: Conserving water in the mother and the fetus. the desert 4 protein: meat, fish, pulses, milk and other Answers will vary, depending on the desert dairy products plants studied in Stage 8, and each learner’s own experience. Possible suggestions could include: carbohydrate: bread, rice, potatoes, pasta, small leaves with a thick layer of wax to reduce cereal grains transpiration; very deep or wide-spreading roots to iron: meat, dark green vegetables, fish and increase access to water. shellfish, nuts and seeds calcium: dairy products, nuts and seeds 4.3 Excretion in humans vitamin A: green vegetables, carrots, squash, fruit, dairy products, fish Getting started vitamin C: citrus fruits, potatoes, colourful 1 Yes; they both need water for transport and berries cooling. vitamin D: oily fish 2 We also need water for getting rid of waste materials in urine. Check your progress 3 Plants use water for support and 4.1 a kidney photosynthesis. b ureter Questions c urea 1 renal system d bladder 2 Carbon dioxide diffuses into the blood and is e urethra carried to the lungs. There, it diffuses from the f urine blood capillaries into the alveoli. It is removed 4.2 Plants take up water from the soil into their from the body in expired air. root hairs. 3 Plants make their own proteins, using The water flows through xylem vessels which carbohydrates that they have made in carry it to the plant’s leaves. photosynthesis and nitrates that they absorb In the leaves, a lot of the water changes from from the soil. So they are unlikely to have liquid to gas. excess proteins that they need to get rid of. It diffuses out of the leaf through the 4.4 Keeping a fetus healthy stomata. Getting started 4.3 a balance Description of the nutrients and their functions b 3g are detailed in Stage 8, Topic 7.1. Learners c 945 − 808 = 137 g. may suggest a range of ideas about particular d 137 ÷ 6 = 22.8 g requirements in the diet of a pregnant woman; e From the plant. The plant with no accept all at this stage, and perhaps ask learners to covering over either the plant or the soil revisit them when they have carried out the activity lost a total of 137 g, whereas the plant in Topic 4.4: Display about diet during pregnancy. with the plant covered lost a total of 31 g. Cambridge Lower Secondary Science 9 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth 15 © Cambridge University Press 2021  CAMBRIDGE LOWER SECONDARY SCIENCE 9: TEACHER’S RESOURCE f Water vapour diffused out of the leaves b Accept any correct responses. For of the plant, through its stomata. The example, fish for protein; yoghurt for water vapour condensed to a liquid on calcium; meat for iron. the inside surface of the bag. c Most people’s diets contain more fat 4.4 a There is a wide range of correct answers. than they need, so her normal diet is Credit any answer that includes a correct likely to contain enough fat for herself function of that nutrient. For example: and her fetus. Too much fat can lead to obesity and heart disease. She needs more protein because protein is needed for growth, and the fetus is d Any two of: Carbon monoxide from growing. the cigarette smoke gets into the fetus’s blood and reduces how much oxygen She needs more calcium to help the fetus it can carry. Nicotine also gets into the form strong bones and teeth, as well as fetus’s blood; it is an addictive substance keeping her own bones and teeth strong and can damage the blood vessels. and healthy. Babies born to mothers who smoke She needs more iron so that the fetus can during pregnancy are at increased risk of produce haemoglobin for its red blood having a low birthweight. cells, as well as increasing the number of her own red blood cells. Unit 5 Reactivity Topic 5.1 Reactivity and 5 magnesium + oxygen → magnesium oxide displacement reactions 6 zinc Getting started 7 yes The point of this task is to provoke discussion 8 magnesium rather than to focus on right or wrong answers. 9 no Learners may recall colour changes, new products such as gases being formed, changes in pH when Think like a scientist: Displacing metals chemical reactions take place. They should be 1 If there has been a change in the colour of the able to discuss relevant examples from their solution or the metal, that would show that previous experience such as reactions of Group 1 one metal had displaced another. metals with water, burning magnesium ribbon or neutralisation reactions. 2 This will depend on what you have been able to provide, but it is likely to be magnesium. Questions 3 This will depend on what you have been able 1 a Lithium should be placed below sodium to provide, but it is likely to be copper. and above calcium. b Lithium reacts with water more vigorously Topic 5.2 Using the reactivity than calcium but less vigorously than series and displacement reactions sodium. 2 a Platinum should be placed below gold. Think like a scientist: Identifying Credit a plausible position, such as near a mystery metal – planning the gold. investigation b Platinum is very unreactive, it does not Credit: a logical plan that includes basic react with oxygen at all (it does not observations of the metal burning in air, with tarnish). water and with dilute acid; displacement reactions; an equipment list; safety considerations; a way 3 Metal B is the most reactive. You can tell of recording results; an indication of what might because the most bubbles are given off. be expected in each observation/test and how this 4 zinc + sulfuric acid → zinc sulfate + hydrogen would help to identify the metal. Cambridge Lower Secondary Science 9 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth 16 © Cambridge University Press 2021  CAMBRIDGE LOWER SECONDARY SCIENCE 9: TEACHER’S RESOURCE Think like a scientist: Identifying a fruits, tomato and other savoury sauces, mystery metal – carrying out the pickled vegetables. investigation 2 hydrogen, nitrogen and oxygen 1 This will depend on which metal you provide. 3 hydrogen, sulfur and oxygen; two atoms of 2 Credit comments on the various reactions that hydrogen, one atom of sulfur and four atoms have been used to suggest a metal. of oxygen. 3 This will depend on what results they found 4 a Both formulae contain chlorine, Cl. but they may want to use different salt b The hydrochloric acid contains hydrogen, solutions once they have an idea of which H, but the sodium chloride contains metal it might be. sodium, Na. Questions 5 a sodium citrate 1 No, because iron is less reactive than b Adding sodium citrate to foods such aluminium. as orange jam helps to maintain its 2 The thermite reaction can be carried out a tangy taste and reduces the risk of the long way from a workshop or laboratory; product decaying. (Leaners may refer to molten iron is produced so that it can be used buffering, which appears in many articles to join the two rails together. on the internet; only credit this if they have explained what it means. Learners 3 So that the raw materials for the process, iron should demonstrate engaging with the ore and coal, did not have to be transported information, not just copy and paste it.) very far. This reduced the costs of production. 6 zinc chloride Think like a scientist: Extracting metals 7 sulfuric acid using carbon 1 There will be a reaction between the copper 8 iron + hydrochloric → iron + hydrogen acid chloride oxide and carbon. There should be copper at the interface of the two powders. The copper can be 9 Sodium is very reactive and the reaction identified by its distinctive colour. would be explosive. copper + carbon → carbon + copper Think like a scientist: Making the salt 2 oxide dioxide zinc sulfate 3 It indicates that carbon is more reactive than 1 zinc + sulfuric acid → zinc sulfate + hydrogen copper. 2 The solution may spit when heated, which 4 Carbon should be placed below magnesium could cause burns. and above zinc. The reason given should be 3 Larger crystals will be produced when the that carbon can displace a number of different liquid is left to evaporate slowly, so that is the metals, including zinc, which is the most better way. reactive of the metals given in the list in the text. Credit any ideas that involve placing 4 Credit any sensible suggestions, such as using carbon above the metals iron and copper. the same mass and volume of zinc and acid for two reactions; using two identical evaporating Topic 5.3 Salts basins; heating one evaporating basin with a Bunsen burner as in the experiment in the Questions Learner’s Book, leaving the other evaporating 1 a Credit any properties of acids, such as basin so that the water evaporates very slowly, turning litmus red, turning universal and then comparing the size of the crystals. indicator solution yellow or red, having a pH of less than 7, tasting sour and that Think like a scientist: Making the salt strong acids are corrosive. copper sulfate b Credit anything suitable, such as vinegar, 1 Safety glasses, 250 cm3 beaker, glass stirring fruit juices, lemonade, fizzy drinks, citrus rod, copper oxide powder, dilute sulfuric acid, measuring cylinder, filter funnel, filter paper, Cambridge Lower Secondary Science 9 – Mary Jones, Diane Fellowes-Freeman & Michael Smyth 17 © Cambridge University Press 2021  CAMBRIDGE LOWER SECONDARY SCIENCE 9: TEACHER’S RESOURCE conical flask, evaporating basin, tripod, gauze, 6 Credit properties, such as soapy feel, turns pipeclay triangle, heatproof mat, Bunsen litmus blue, turns universal indicator solution burner, tongs. blue or purple, has a pH greater than 7. 2 The risk assessment should feature each 7 A base is a metal oxide. If a metal oxide process, for example: dissolves in water, it makes and alkaline solution. Step 1: Measuring acid and adding copper magnesium + sulfuric → magnesium + water oxide: risk of getting acid in your eye, so wear 8 oxide acid sulfate safety glasses. Step 2: Heating the copper oxide and sulfuric 9 MgO + H2SO4 → MgSO4 + H2O acid: general risks of heating and not touching 10 Iron oxide could be reacted with hydrochloric hot items, wearing eye protection when using acid to form iron chloride. acids, not boiling the mixture as harmful fumes can be given off. Learners should Think like a scientist: Preparing a salt mention both the risks and how they can from acid and a carbonate attempt to overcome them. 1 This will vary depending on what equipment Step 3: Allowing the mixture to cool: general you have available but is likely to include risks of heating and not touching hot items, safety glasses, copper carbonate, hydrochloric wearing eye protection when using acids. acid, measuring cylinder, beaker, spatula, filter Step 4: Filtering: risk of splashes of the funnel, filter paper, conical flask, evaporating solution getting into the eyes, so wear safety basin, tripod, pipeclay triangle, Bunsen glasses. burner, heatproof mat, tongs. Step 5: Evaporating: risk of solution spitting 2 The risk assessment should feature each and general risk of heating and not touching process, for example: hot items, using tongs to move the evaporating Step 1: Measuring acid: risk of getting acid in basin, wearing safety glasses, taking care your eye, so protect yourself by wearing safety about how close you get to the apparatus. glasses. 3 To remove any unreacted copper oxide powder. Step 2: Adding the copper carbonate to the 4 Use hydrochloric acid instead of sulfuric acid. hydrochloric acid: wear eye protection when using acids. The risk assessment should 5 copper + hydrochloric → copper + water feature each process and learners should oxide acid chloride