Preview: Cambridge Lower Secondary Science Teacher Guide 8

Cambridge Lower Secondary

Science STAGE 8: TEACHER’S GUIDE

Gemma Young, Mark Levesley, Beverly Rickwood, Lucy Hawkins, Stuart Lloyd, Louise Smiles 244405 Checkpoint Science_Title page_TG8.indd 1

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Contents

Downloads of editable learning episodes, worksheets, practical notes and answers are available at www.collins.co.uk/CambridgeInternationalDownloads.

Introduction Mapping document

5 9

Chapter 1 ● Obtaining food Chapter overview 1.1 Food from plants 1.2 A balanced diet

23 25 30

1.3 Malnutrition 1.4 Digestion Checking students’ progress

35 38 42

43 45 51 56

2.4 Transport of water and mineral salts in plants Checking students’ progress

59 63

64 65 70

3.3 Foetal growth and development 3.4 Drugs, disease and diet Checking students’ progress

74 77 82

Chapter 2 ● Respiration and circulation Chapter overview 2.1 Human circulatory system 2.2 Human respiratory system 2.3 Smoking and health Chapter 3 ● Reproduction and growth Chapter overview 3.1 Reproductive systems 3.2 Puberty

Chapter 4 ● Elements, compounds and mixtures Chapter overview 4.1 More on changes of state 4.2 Gas pressure and diffusion 4.3 Atoms, elements and the Periodic Table

83 84 87

4.4 Compounds and formulae 4.5 Separating mixtures Checking students’ progress

93 96 99

90

Chapter 5 ● Metals, non-metals and corrosion Chapter overview 5.1 Metals and non-metals

100 101

5.2 Corrosion and rusting Checking students’ progress

104 108

109 111 113

6.3 Reactions with oxygen Checking students’ progress

117 120

121 123 128

7.3 Refraction 7.4 Coloured light Checking students’ progress

133 136 139

Chapter 6 ● Chemical reactions Chapter overview 6.1 Using word equations 6.2 Reactions with acid Chapter 7 ● Light Chapter overview 7.1 Light rays 7.2 Reflection

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Chapter 8 ● Sound Chapter overview 8.1 How sounds are made 8.2 How we hear sounds

140 142 145

8.3 Loudness and pitch Checking students’ progress

148 152

153 155 157

9.3 Distance–time graphs Checking students’ progress

159 162

163 165 169

Checking students’ progress

173

Chapter 9 ● Measuring motion Chapter overview 9.1 Measuring distance and time 9.2 Speed and average speed Chapter 10 ● Magnets Chapter overview 10.1 Magnets and magnetic materials 10.2 Electromagnets Planning guide

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Chapter 4

Elements, compounds and mixtures

Chapter overview

Topic title

Student’s Book pages

Number of 40-minute periods

Overall objectives

Scientific enquiry focus

4.1 More on changes of state

96–100

1–2

To use particle theory to explain the properties of solids, liquids and gases and what happens during changes in state

Communicating explanations clearly

4.2 Gas pressure and diffusion

101–105

2–3

To explain gas pressure and diffusion using particle theory

Planning investigations to test ideas

4.3 Atoms, elements and the Periodic Table

106–109

2

To describe what an element is

Interpreting data from secondary sources

4.4 Compounds and formulae

110–113

2

To describe what a compound is

Interpreting data from secondary sources

4.5 Separating mixtures

114–118

2–3

To describe how to separate a mixture

Identifying hazards and planning how to control risks when carrying out an experiment

End of chapter questions

119–120

1

Check students’ progress

Background science The arrangement and movement of the particles in a substance can be used to explain changes in state, diffusion and gas pressure.

When a substance is heated, heat (thermal) energy is transferred to its particles. This causes the particles to have more movement (kinetic) energy, which changes their motion and arrangement, which may result in a change in state. As a substance is cooled, heat energy is transferred away from the particles and they lose movement energy.

Diffusion is the movement of particles from a high concentration to a low concentration. It happens because of the random movement of particles in liquids and gases.

Particles in a gas randomly hit the sides of their container. The average force over the area of the sides of the container is called the gas pressure. Gas pressure can be increased by increasing the number of gas particles (which increases the number of collisions) or by increasing the temperature (which increases the kinetic energy of the particles and the force with which they hit the container sides).

Stage 8

Elements are pure substances – they only contain one type of particle. They are listed on the Periodic Table in order of atomic number. Elements can react in chemical reactions to form compounds. The atoms in a compound are strongly bonded together; they cannot easily be separated to form their constituent elements. The substances in a mixture can be separated easily by methods that include filtration, evaporation and distillation.

Cambridge Lower Secondary Chemistry

In this chapter students will use their knowledge of particle theory to explain changes in state, gas pressure and diffusion. They will then be introduced to the differences between elements, compounds and mixtures. This chapter builds on the topics Material Changes in Stage 6 of the Cambridge Primary Science curriculum framework and the Chapter 5 in Stage 7.

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4.1

More on changes of state

Topic overview Student’s Book 4.1a

Starting point In this short activity, students work in groups to review what they know about how the particles are arranged in solids, liquids and gases

Page 96 Starting point table

4.1b

Review of particle theory Students review what they know about particle theory; they carry out activities to practise writing explanations using particle theory

Pages 96–98 Questions 1–4

4.1c

Using particle theory to explain changes in state Students use particle theory to write explanations about what happens during changes of state; they consolidate understanding by designing a storyboard

Pages 98–100 Questions 5–6 Activity 4.1

Topic learning objectives • 8Cs1: Show how the particle theory of matter can be used

Cambridge Lower Secondary Chemistry

•

Stage 8

Workbook

to explain the properties of solids, liquids and gases, including changes of state, gas pressure and diffusion 8Ec3: Compare results with predictions.

Downloadable material

Practical notes 4.1b Worksheet 4.1b

Questions 1–8

•

Practical notes 4.1c Worksheet 4.1c

8Ec6: Discuss explanations for results using scientific knowledge and understanding; communicate these clearly to others

Common misunderstandings • Cells and other biological materials are not made of atoms. Remind students that all materials are made up of • • •

atoms. It is the type of atoms, if they are combined with others, and their arrangement that gives rise to so many different types of substance.

During a change in state the mass of a substance changes. This can be challenged by placing some ice on scales, measuring the mass, and showing that the mass does not change as the ice melts.

During a change in mass the particles change size. This can be challenged by using particle diagrams and models The average speed of the atoms or molecules of a substance decreases when the temperature increases, and increases when the temperature decreases, or remains the same with a change in temperature. This misconception can be tackled by using a model such as that shown in 4.1b.

4.1a Starting point Ask students to work in groups of three and give each group an A4 piece of paper. Ask the first student to draw in the top third of the paper a particle diagram to show the particles in a solid. The other students should not look. They should then fold over the paper so the diagram is hidden and pass it to the next student. Tell the class that the solid has been heated so it melts. Ask the next student to draw a particle diagram to show what it now looks like. They fold the paper over and pass it to the final student. Tell the class that the liquid has been heated so it boils. Ask the student to draw the final particle diagram.

Ask the groups to unfold their drawing and discuss how well they think it represents particles in the different states of matter. They can use the diagrams on pages 97–98 of the Student’s Book.

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4.1b Review of particle theory Learning outcomes • To use particle theory to explain the properties of solids, liquids and gases and what happens during changes in state

Scientific enquiry outcomes • Use a scientific model to construct explanations • Communicate explanations clearly Glossary words atom, molecule

Resource preparation For the demonstration: large bottle of carbonated drink (soda), digital scales.

For the activity: a glass of water with spoon/glass rod, a glass of honey/syrup/wall paper paste with spoon/glass rod, sponge/stress ball, block of metal, block of two different metals that have the same volume but a different mass, e.g. aluminium and iron, digital scales, scented candle, unscented candle, piece of paper, piece of thin plastic (from a plastic bag).

Practical notes 4.1b Worksheet 4.1b

• • • • • •

bottle and write it on the board. Cover the display of the scales so the mass can no longer be seen.

Tell the class that the bottle contains materials of each state of matter. Ask them to explain how. (The plastic bottle is a solid, and the drink is a liquid that contains bubbles of gas.)

Challenge: students can draw a diagram showing solid, liquid and gas particles in the bottle of soda.

Tell them that the gas in the bubbles is called carbon dioxide. This consists of molecules made up of one carbon atom and two oxygen atoms. To make particle models easier, we normally draw molecules as single particles. Refer to pages 97–98 in the Student’s Book for diagrams to explain this fully. Ask students to write down the difference between an atom and a molecule.

Ask students to answer questions 1–3 on pages 97–98 of the Student’s Book. These ask students to write explanations using prior knowledge. Go through the answers to check understanding about particle theory before continuing.

Invite students to work in small groups to carry out a series of tasks investigating the properties of different materials. After carrying out each activity, they should write on Worksheet 4.1b what they found out and an explanation for it. This will give students guidance and practice at applying their knowledge to write scientific explanations. Refer to the practical notes for more information.

Refer back to the bottle of soda. Ask students to write down a prediction about what they think the mass is now.

Write a few of the predictions on the board. Reveal the mass; it will have gone down. Ask students to write an explanation that explains why.

Differentiation Less-confident students may need more guidance when writing explanations. For the final task, you may wish to discuss with the class what change would have taken place in the bottle (the gas has escaped the liquid). Some students may have the misconception that if the gas has escaped then the liquid will be heavier because gas is light. This activity gives a good opportunity to correct this.

Homework suggestions

Stage 8

Ask students to write another explanation. They should predict what would happen to the mass of an ice cube as it melts and explain why using particle theory.

Cambridge Lower Secondary Chemistry

Teaching and learning ideas • Place an open bottle of a carbonated drink (soda) onto some digital scales. Ask a student to record the mass of the

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4.1c Using particle theory to explain changes in state Learning outcomes • To use particle theory to explain the properties of solids, liquids and gases and what happens during changes in state

Scientific enquiry outcomes • Use a scientific model to construct explanations • Communicate explanations clearly Resource preparation For the demonstration: large beaker, dried peas.

For Activity 4.1: A4 sheets of paper.

Practical notes 4.1c Worksheet 4.1c

Teaching and learning ideas • Ask students to consider how a thermometer works. Explain that it contains a thin glass tube full of a coloured liquid.

•

• •

Stage 8

Cambridge Lower Secondary Chemistry

• • • • • •

Allow students to work in pairs to study a thermometer and place it in some warm water and then cold water. They should then write down their initial thoughts about how it works.

Ask the class what happens to the particles in a liquid when it is heated. Remind them that they will gain heat (thermal) energy and start to move about faster as they gain movement (kinetic) energy. Model this using some dried peas in a container, such as a large beaker. Shake the beaker and, modelling the transfer of heat energy, the peas move faster. Ask students to describe how their arrangement has changed. They should see that the peas have slightly spread out and are taking up more volume inside the container. Ask them how this links to the thermometer. Students may wish to modify their explanation at this point.

Explain that as particles in a liquid gain energy, the forces between them weaken to allow them to move apart slightly. The liquid expands (gets bigger). Make sure students do not think this happens because the particles have got bigger.

Challenge: Show the class heating and cooling curves. These were introduced in Stage 7 chapter 5. Ask them to consider why the temperature stays constant during melting (the energy being supplied is used to overcome the forces between the particles).

Continue with the model, showing that if you supply the peas with more energy they will start to move more, and some may leave the beaker altogether. Ask the class what this is modelling. (The liquid is boiling to form a gas. The forces between the particles have been broken.)

Demonstrate ice floating in water.

Ask students to read through the information 'Explaining changes in state' on pages 98–99 of the Student’s Book, which explains changes in state in more detail.

Students complete Activity 4.1: Changes in state storyboard on page 99 of the Student’s Book. They design a storyboard to show what happens to the motion and arrangement of particles during changes of state. Students can use their imagination to make their storyboards interesting. For example, the particles can talk and express emotions about how it feels to go through a change in state.

Discuss the problems of burst pipes and how freezing water can protect pond life.

Students answer questions 5 and 6 on page 100 of the Student’s Book.

Differentiation With less confident students you may wish to start the lesson recapping on the names of the changes of state. This content was first taught in Chapter 5 in Stage 7.

Provide less confident students with Worksheet 4.1c, which is a template for the storyboard.

More confident students can tell you how to use the model with peas to show what happens when a gas is cooled.

Homework suggestions Ask students to research into why there are gaps in between the metal rails on a railway track. They should explain this using particle theory.

Ask students to explain why gases and liquids take the shape of their containers, but solids do not in terms of the particle theory of matter.

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