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Science units Grade 8

Contents

8L.1 Gas exchange 161 8M.1 Atoms and molecules 197 8P.1 Energy 223

8L.2 Circulation 167 8M.2 Metals 203 8P.2 Electromagnetism 241

8L.3 Micro-organisms and food 173 8M.3 Uses of metals 211 8P.3 Heat and temperature 247

8L.4 Photosynthesis 179 8M.4 Salts 219 8P.4 Light 257

8L.5 Feeding relationships 185 8E.1 The Solar System 227

8L.6 Digestion 191

Science scheme of work: Grade 8 units 135 hours1st semester67 teaching hours

Unit 8L.0: Preliminary unitIntroduction to grade and revision ofkey ideas from previous grades.1 hour

Life science: 22 hours Materials: 17 hours Physical processes: 19 hours

Unit 8L.1: Gas exchangeStructure and function of lungs. Effectof smoking. Red and white blood cells.8 hours

Unit 8L.2: CirculationStructure and function of heart.Circulation and blood vessels.8 hours

Earth and space: 9 hours

Unit 8M.0: Preliminary unitIntroduction to grade and revision ofkey ideas from previous grades.1 hour

Unit 8M.1: Atoms and moleculesAtoms and molecules. Elements andcompounds. Chemical symbols andequations.7 hours

Unit 8P.0: Preliminary unitIntroduction to grade and revision ofkey ideas from previous grades.1 hour

Unit 8P.1: EnergyForms of energy. Energytransformation. Measuring energy.10 hours

Unit 8M.2: MetalsReactivity series. Corrosion. Action ofacids and the properties of hydrogen.9 hours

Unit 8P.2: ElectromagnetismElectromagnets and motors.8 hours

Unit 8L.3: Micro-organisms and foodMicro-organisms in food, wine and beerproduction.5 hours

Unit 8E.0: Preliminary unitIntroduction to grade and revision ofkey ideas from previous grades.1 hour

Unit 8E.1: The Solar SystemThe Sun, stars and planets.8 hours

Science scheme of work: Grade 8 units 135 hours2nd semester68 teaching hours

Unit 8L.R: Review unitRevision of key ideas from firstsemester.1 hour

Life science: 23 hours Materials: 20 hours Physical processes: 25 hours

Unit 8L.4: PhotosynthesisChlorophyll and chloroplasts. Processof photosynthesis.7 hours

Unit 8L.5: Feeding relationshipsPyramids of number and biomass.Accumulation of toxins in a food chain.7 hours

Earth and space: 0 hours

Unit 8M.R: Review unitRevision of key ideas from firstsemester.1 hour

Unit 8M.3: Uses of metalsMetals and non-metals. Properties anduses of metals. Occurrence andextraction of metals.10 hours

Unit 8P.R: Review unitRevision of key ideas from firstsemester.1 hour

Unit 8P.3: Heat and temperatureTemperature scales. Heat capacity.Conduction, convection and radiation.12 hours

Unit 8M.4: SaltsPreparation and uses of common salts.9 hours

Unit 8P.4: LightLight intensity. Reflection, refractionand dispersion. Colour.12 hours

Unit 8L.6: DigestionStructure and function of digestivesystem. Process of digestion. Role ofenzymes in digestion.8 hours

161 | Qatar science scheme of work | Grade 8 | Unit 8L.1 | Life science 1 © Education Institute 2005

GRADE 8: Life science 1

Gas exchange

About this unit This unit is the first of six units on life science for Grade 8.

This unit is designed to guide your planning and teaching of lessons on life science. It provides a link between the standards for science and your lesson plans.

The teaching and learning activities should help you to plan the content and pace of lessons. Adapt the ideas to meet your students’ needs. For extension or consolidation activities, look at the scheme of work for Grade 9 and Grade 7.

You can also supplement the activities with appropriate tasks and exercises from your school’s textbooks and other resources.

Introduce the unit to students by summarising what they will learn and how this builds on earlier work. Review the unit at the end, drawing out the main learning points, links to other work and 'real life' applications.

Previous learning To meet the expectations of this unit, students should already know the position in the body and function of the lungs. They should know that smoking can damage health. They should know that cells form tissues and organs. They should already be able to relate the functions of specialised cells to their structures.

Expectations By the end of the unit, students know the basic anatomy of the lungs and describe the role of the lungs in breathing. They know that inhaled air has more oxygen and less carbon dioxide than exhaled air, and that these gases are carried to and from the body’s cells in blood vessels. They know why smoking affects health. They know the difference between red and white blood cells. They make working models to illustrate scientific ideas and solve scientific problems.

Students who progress further explain and give equations for aerobic and anaerobic respiration and fermentation, and know how conditions affect respiration. They describe the features of the gaseous exchange system and relate these to function.

Resources The main resources needed for this unit are: • model torso to show structure of lungs, or fresh lamb’s lungs • plastic bottle, straw, rubber band and two balloons to make model lungs • equipment to measure lung capacity (e.g. spirometer (long plastic bag),

round balloons, 2 litre plastic bottle, plastic tubing and water trough) • gas jars, candles, limewater, mirrors, anhydrous cobalt chloride paper • data on the gaseous composition of arteries and veins • photographs of lungs from a smoker and a non-smoker • simple smoking machine (see text for details)

Key vocabulary and technical terms Students should understand, use and spell correctly: • gas exchange • trachea, bronchi, bronchioles, alveoli, diaphragm • oxygenated, deoxygenated, haemoglobin, antibody, plasma, platelets

UNIT 8L.1 8 hours


Standards for the unit

8 hours SUPPORTING STANDARDS CORE STANDARDS

Grade 8 standards EXTENSION STANDARDS

7.7.1 …know that cells are the basic building blocks of organisms and form tissues and organs.

8.7.1 Know the basic structure of the lungs and their role in gas exchange (breathing).

11F.8.1 Explain the structure, anatomy and function of the human lungs and related structures for gaseous exchange and the muscle and skeletal systems that enable breathing.

8.7.2 Know that inhaled air has more oxygen than exhaled air, and that exhaled air has more carbon dioxide than inhaled air.

9.7.2 Explain diffusion and osmosis as mechanisms for the movement of substances into and out of cells.

8.7.3 Know that oxygen and carbon dioxide are carried round the body to and from cells in blood vessels.

8.7.4 Know that smoking damages the lungs and reduces the efficiency of gas exchange.

7.7.2 Recognise and know the function of the cell nucleus, cell membrane, cytoplasm, vacuole and cell wall, and relate the overall structure of some specialised cells (e.g. nerve cells, sperm cells, xylem cells, palisade cells) to their functions.

8.7.5 Compare and contrast the similarities and differences between red and white blood cells and their functions.

9.8.1 Give the word and formula equations for aerobic respiration; explain the process as a cellular biochemical reaction in animals and plants in which food acts as a respiratory substrate and reacts with oxygen to release energy and produce carbon dioxide and water.

8.1.3 Make working models to illustrate scientific concepts and applications.

2 hours

Structure and function of lungs

4 hours

Differences between inhaled and exhaled air; effect of smoking

2 hours

Red and white blood cells

7.1.4 Understand the importance of accuracy and use techniques such as repetition of measurements to ensure it.

8.1.4 Take representative samples during large investigations and decide how many measurements are required for the results to have an acceptable reliability.

Unit 8L.1


Activities

Objectives Possible teaching activities Notes School resources

Review with students what they consider to be the function of the lungs. Clarify potential misconceptions by asking students what they would say to Grade 7 students who said ‘Your lungs help you to breathe’ and ‘Your lungs breathe in oxygen and breathe out carbon dioxide.’ Introduce the term gas exchange to describe the function of the lungs.

Show students a model or diagram of the lungs and name the structures: trachea, bronchi, bronchioles, alveoli and diaphragm. If appropriate, show them fresh lamb’s lungs. Give them a diagram to label that they can cut out into three layers – internal structure of lungs, external structure and ribs. Use a model of balloons in a bell jar or show students an animation to demonstrate how air moves in and out of the lungs. Get students to make their own model from a plastic bottle, straw, rubber band and two balloons. Ask them to try breathing with just their diaphragm and keep their ribs still and visa versa to see that both movements are needed for a deep breath.

Ask students to draw a flow chart of air moving in and out of the lungs, including the difference in air pressure that causes this movement.

A simple model lung

Enquiry skill 8.1.3

Use this column to note your own school’s resources, e.g. textbooks, worksheets.

Students can measure their lung capacity by blowing into a spirometer, round balloon or displacing water from a 2 litre plastic bottle. Tell them to collect three measurements and discuss why you repeat measurements when you cannot measure exactly.

Safety: Students with asthma should not do this practical. Any student should stop the experiment if they start to feel dizzy.

Enquiry skill 8.1.4

2 hours

Structure and function of lungs Know the basic structure of the lungs and their role in gas exchange (breathing). Make working models to illustrate scientific concepts and applications. Take representative samples during large investigations and decide how many measurements are required for the results to have an acceptable reliability.

Extension activity Look for patterns in the class results of lung capacity – is there a correlation between lung capacity and fitness, height or circumference of the chest? Ask students to research on the Internet how athletes increase their lung capacity.

ICT opportunity: Use of the Internet

Unit 8L.1



Ask students to carry out four experiments to show the differences between inhaled and exhaled air. The experiments should show that exhaled air contains: • less oxygen (by measuring the length of time a candle burns in a gas jar of inhaled and

exhaled air); • more carbon dioxide (by bubbling inhaled and exhaled air through limewater); • more moisture (by breathing onto a cold mirror and testing the moisture with cobalt chloride

paper); • more heat (by breathing on to a thermometer).

Tell students to summarise the results of their experiments in a table. Define the term respiration and use the results of these experiments to draw out the word equation for respiration.

Remind students of the internal structure of the lungs and show a diagram of an alveoli surrounded by capillaries. Ask students individually to label their own copies of the diagram with arrows to show the direction in which oxygen and carbon dioxide move. Ask students why the lungs have such a good blood supply and a surface area as big as a tennis court.

Safety: Wear safety glasses when blowing through a straw into limewater.

4 hours

Differences between inhaled and exhaled air; effect of smoking Know that inhaled air has more oxygen than exhaled air, and that exhaled air has more carbon dioxide than inhaled air.

Know that oxygen and carbon dioxide are carried round the body to and from cells in blood vessels.

Know that smoking damages the lungs and reduces the efficiency of gas exchange.

Return to the function of the lungs for gas exchange and ask students what happens next? How does dissolved oxygen leave the lungs and where does it go? Discuss the importance of a circulatory system to carry oxygen to cells and carbon dioxide back to lungs. Describe the difference in colour between oxygenated and deoxygenated blood and explain that, apart from the pulmonary artery, oxygenated blood is carried in arteries. Compare data on the gaseous composition of arteries and veins.

Ask students to investigate how exercise affects breathing rate. They should do this by measuring their breathing rate at rest, then during moderate exercise. They should notice they breathe deeper as well as faster during exercise. Ask students to write a conclusion to this investigation that clearly explains that more oxygen is needed for muscles to get energy from respiration.

Students will obtain a more accurate measure of breathing rate if they raise their hand up and down in time to their breathing for another student to count, rather than trying to count their own breathing rate.

Show students photographs of lungs from a smoker and a non-smoker. Discuss the different components of tobacco smoke that damage the lungs. Ask students to write their own explanations of how nicotine, carbon monoxide and tar reduce the efficiency of gas exchange in the lungs.

Demonstrate using a smoking machine to collect the residues produced by a burning cigarette.

A simple smoking machine

A smoking machine can be made using simple apparatus, such as a 20 ml syringe connected to a short length of wide glass tubing, which has a bung at the other end fitted with a piece of plastic tubing to act as a cigarette holder. Pack a small ball of absorbent cotton wool inside the wide glass tubing.

Demonstrate the smoking machine in a fume cupboard or by an open window.



Ask students to describe the composition of blood; remind them of the specialised red and white blood cells they looked at in Grade 7. Mention plasma and platelets as other important components of blood.

Explain how oxygen is carried by haemoglobin in red blood cells and ask students why they think that red blood cells are biconcave in shape and do not have a nucleus. Show software animation or a video clip of red blood cells squeezing through the smallest capillaries. Discuss with students that there are 5 million red blood cells in a cubic millimetre of blood, they live about 120 days and a constant new supply of red blood cells is needed to replace old cells that break down.

Remind students that smokers carry some carbon monoxide instead of oxygen in their blood and ask students why smokers have more red blood cells than non-smokers.

2 hours

Red and white blood cells Compare and contrast the similarities and differences between red and white blood cells and their functions.

Briefly describe the function of white blood cells engulfing micro-organisms or producing antibodies as part of the body’s defences against disease. Show students diagrams of these two types of white blood cells destroying micro-organisms.

Let students use high-power microscopes to look at prepared slides of red and white blood cells. Ask them to draw and label diagrams of a few of each type of cell. Challenge students to construct a table to summarise the similarities and differences between red and white blood cells (e.g. where made, number per cubic millimetre, shape, nucleus, life span and function).


Assessment

Assessment Examples of assessment tasks and questions Notes School resources a. Label the diagram of the lungs.

b. Look at the diagram of the model lungs below. Which parts of the lungs do the following items in the model represent?

i. glass tube

ii. balloon

iii. bell jar

iv. stretched balloon

c. When you pull the stretched balloon down, air moves down the glass tube and inflates the balloon. Explain why this happens.

Provide students with a diagram of the lungs, diaphragm and ribs to label.

Aisha used a spirometer to measure the volume of air she breathed in and out of her lungs before and during exercise. The graphs represent the volume of air Aisha breathed in and out with each breath before and during exercise.

Set up activities that allow students to demonstrate what they have learned in this unit. The activities can be provided informally or formally during and at the end of the unit, or for homework. They can be selected from the teaching activities or can be new experiences. Choose tasks and questions from the examples to incorporate in the activities.

a. During exercise, Aisha breathed more air in and

out of her lungs than before exercising.

i. How much more air did Aisha breathe in with each breath during exercise?

ii. Explain fully why Aisha needed to breathe in more air during exercise.

b. As Aisha exercised, the volume of air she breathed in and out increased.

i. Give one other way Aisha’s breathing changed during exercise.

ii. How does the graph show this other change?

Adapted from QCA Year 9 science test, 2004

Unit 8L.1


Grade 8: Life science 2

Circulation

About this unit This unit is the second of six units on life science for Grade 8.





Previous learning To meet the expectations of this unit, students should already know the position in the body and the function of the heart. They should know that cells form tissues and organs. They should be able to relate the functions of specialised cells to their structures. They should be able to recognise that our understanding of science has developed over time and is the work of many countries.

Expectations By the end of the unit, students know the basic structure and function of the human heart and the names and locations of the major blood vessels. They can relate the structure of arteries, veins and capillaries to their functions. They know that scientific work is often done collaboratively, sometimes with colleagues in other countries and they assess the contributions of specific scientists.

Students who progress further describe the structure and function of the human circulatory system.

Resources The main resources needed for this unit are: • model of the heart • software animation showing blood flow through the heart • fresh lamb’s heart (or similar), scalpel and surgical gloves • microscopes and prepared slides of capillaries, veins and arteries • Internet access

Key vocabulary and technical terms Students should understand, use and spell correctly: • atrium, ventricle, capillary, vein, artery • pulmonary artery, pulmonary vein, aorta, vena cava • arteriosclerosis

UNIT 8L.2 8 hours





7.7.1 … know that cells are the basic building blocks of organisms and form tissues and organs.

8.8.1 Know the basic structure of the heart and relate this to its function. 11.7.2 Describe the external and internal structure of the heart. Relate features to functions in pumping blood round the body and maintaining separation of oxygenated and deoxygenated blood.

8.8.2 Know the different valves of the heart and how they function.

8.8.3 Know the positions, functions and names of the major blood vessels.

8.8.4 Recognise the differences between arteries, veins and capillaries, and relate their structure to their function.

11.7.5 Differentiate between arteries, veins and capillaries in terms of wall thickness and valves, and relate their structure to their function.

8.8.5 Explain blood pressure and why high blood pressure is an indicator of circulatory problems.

3 hours

Structure and function of heart

3 hours

Circulation and blood vessels

2 hours

Blood pressure

7.2.3 Know that our understanding of science has accumulated and changed over time and is the result of work in many countries.

8.2.2 Assess the importance of the work of specific scientists in developing our understanding of science.

9.2.6 Trace the historical development of some key scientific models and understand the roles of specific scientists in their development.

Unit 8L.2


Activities


Review with students that the function of the heart is to pump blood. Ask students where this blood is pumped to. Explain that the heart is in fact two pumps joined together, with one side supplying the lungs and the other side supplying the other body organs. Show students a model of the heart and name the four chambers. Hold a diagram of the heart next to a volunteer to show why the left side of the heart is labelled on the right side of the page.

Ask students ‘Why does blood flow one way through each side of the heart?’ Point out the valves between atria and ventricles, and those where blood empties into arteries. Show students an animation or video clip of a heart beating and the direction of blood flow. Provide students with a cross-section diagram of the heart and ask them to label the chambers and valves, and which side has oxygenated and deoxygenated blood.

Prepare student worksheets.


If appropriate, dissect a fresh lamb’s heart (or similar) to show the valves attached by strong tendons and the different thickness of different parts of the heart. Ask students why the walls of the ventricles are thicker than the walls of the atria. Ask too why the left ventricle wall is three times as thick as the right ventricle wall and why we can feel our heartbeat on the left side of our chest when it is in the centre. Name the veins and arteries that bring blood to and take it from the heart and ask students to add these labels to their heart diagram.

Ask students to write a set of sentences describing blood flow through the heart, or to put a set of prepared sentences into the correct sequence (e.g. right atrium contracts, right ventricle contracts, blood leaves heart through pulmonary artery, etc.)

Extension activity Ask students to use the Internet to research congenital heart defects and their symptoms and treatment (e.g. hole in the heart, malfunctioning valves).

ICT opportunity: Use of the Internet.

3 hours

Structure and function of heart Know the basic structure of the heart and relate this to its function.

Know the different valves of the heart and how they function.

Assess the importance of the work of specific scientists in developing our understanding of science.

Challenge students to research how our understanding of circulation has developed over time and who they think should be credited with working out how the circulation of the blood works. Tell them to search the Internet using key words such as ‘Ancient China’, ‘Galen’, ‘Ibn Al-Nafis’, ‘Servetus’ and ‘Harvey’. Ask students to consider which scientists based their ideas on evidence and how they collected that evidence. Referring particularly to Ibn Al-Nafis, explain that, even with evidence, it can be difficult to change the accepted explanation of something.


This website provides a useful summary: www.timelinescience.org/resource/students /blood/blood.htm

Unit 8L.2



Provide students with information and diagrams about veins, capillaries and arteries to label. Ask students to write their own explanations of why capillary walls are so thin, artery walls are elastic and veins have valves. Provide students with a diagram of the double circulation and the names of major veins and arteries.

Encourage students to make up quiz questions to test each other about the names and positions of different arteries and veins (e.g. Which artery carries deoxygenated blood?)

Provide students with diagrams to label.

Ask students to examine prepared slides of capillaries, veins and arteries under a microscope using high and low magnification, or project images of blood vessel structure and discuss as a whole class. Challenge students to construct a table to summarise the similarities and differences between veins, arteries and capillaries (e.g. position in body, function, thickness of wall).

Discuss with students how to recognise the three different types of bleeding that occur depending on what type of blood vessel is injured (e.g. bright red blood spurts from an artery) and what first aid to follow (e.g. apply pressure, elevate injured limb or use a tourniquet).

3 hours

Circulation and blood vessels Know the positions, functions and names of the major blood vessels. Recognise the differences between arteries, veins and capillaries, and relate their structure to their function.

Make sure students appreciate that the pulse is the heart rate and that you can feel your pulse when an artery is near the surface of your skin. Discuss with students why you count your pulse using two fingers rather than your thumb. Encourage students to try to find their own pulse points. Describe several pulse points for students so they can practise finding and counting their pulse (e.g. side of neck, temple of head, wrist and ankle).

Ask students to count their pulse over one minute and then calculate how many times their heart beats in one hour, one day and one year.

2 hours

Blood pressure Explain blood pressure and why high blood pressure is an indicator of circulatory problems.

Define blood pressure as the pressure of the blood against the elastic walls of the arteries. Explain that blood pressure has two values. The higher number represents the pressure while the heart contracts to pump blood to the body. The lower number represents the pressure when the heart relaxes between beats. Blood pressure in a healthy person is normally below 120 over 80 mm Hg.

Provide students with information about high blood pressure, or let them search the Internet for it. Ask them to work in groups to produce a poster that includes: • a definition of high blood pressure; • possible causes (e.g. narrowing of arteries caused by arteriosclerosis); • symptoms; • associated risks (e.g. increased chance of a stroke); • diet and lifestyle changes that can reduce blood pressure.

Challenge each group to deliver a one-minute presentation to the class without hesitation, deviation or repetition. Ask students in the audience to judge whether the group achieved the task and to provide constructive feedback on their presentation.



Assessment

Examples of assessment tasks and questions Notes School resources

a. Label the diagram of the heart.

b. Match the blood vessel to the correct description:

Blood vessel Description

Aorta Carries deoxygenated blood from the heart to the lungs

Pulmonary artery Carries deoxygenated blood from the body to the heart

Vena cava Carries oxygenated blood from the lungs to the heart

Pulmonary vein Carries oxygenated blood from the heart to the body

c. Circulation in mammals is called a ‘double circulation’. Explain what this term means and why a double circulation is needed.

Provide students with a diagram of the heart to label.

Assessment Set up activities that allow students to demonstrate what they have learned in this unit. The activities can be provided informally or formally during and at the end of the unit, or for homework. They can be selected from the teaching activities or can be new experiences. Choose tasks and questions from the examples to incorporate in the activities.

a. The diagram represents the flow of blood to and from a muscle.

i. What type of blood vessel is B?

ii. In the table, tick one box in each row to compare the concentrations of oxygen, glucose and carbon dioxide in blood vessels A and B.

Substance A higher concentration in A than in B

The same concentration in A and in B

A lower concentration in A than in B

Oxygen

Glucose

Carbon dioxide

Unit 8L.2



b. Blood flows into and out of all organs.

i. Name the organ represented in the diagram below.

ii. A different organ is represented in the diagram below. Name this organ.




Micro-organisms and food

About this unit This short unit is the third of six units on life science for Grade 8.

This unit is designed to guide your planning and teaching of lessons on life sciences. It provides a link between the standards for science and your lesson plans.




Previous learning To meet the expectations of this unit, students should already know that individual micro-organisms are too small to see with the unaided eye. They should already be able to name the major groups of micro-organisms. They should already understand the importance of micro-organisms in nitrogen fixation, decomposition and nutrient recycling.

Expectations By the end of the unit, students give examples of the use of micro-organisms in food production. They plan, collect data and make observations in a systematic way, identify patterns, consider the validity of evidence, the extent to which it supports a prediction, and draw conclusions.

Students who progress further know that fermentation by micro-organisms produces alcohol.

Resources The main resources needed for this unit are: • samples of food made using micro-organisms (e.g. blue cheese, vinegar) • live yoghurt, sterilised milk, tap funnel • slices of bread, sample of fresh yeast • active yeast and sugar suspension or bread dough

Key vocabulary and technical terms Students should understand, use and spell correctly: • bacteria, fungi, yoghurt • yeast, fermentation

UNIT 8L.3 5 hours





8.11.1 Know that micro-organisms are used in making foods such as bread, cheese and yoghurt.

7.10.2 Know that micro-organisms in soil decompose organic matter and dead organisms and help to recycle nutrients. 8.11.2 Know that micro-organisms are used to make beer and wine. 9.12.4 Give the word equations for anaerobic

respiration; explain the process as a cellular biochemical reaction in which a respiratory substrate reacts without oxygen to release energy and produce carbon dioxide and alcohol or lactic acid; know that when carried out by micro-organisms, this is termed fermentation.

4 hours

Micro-organisms in food production

1 hour

Micro-organisms in wine and vinegar production 8.1.1 Plan investigations, controlling variables and collecting an appropriate

range of evidence, using appropriate techniques to ensure accuracy, identify patterns in observations and data, draw generalised conclusions and test predictions.

Unit 8L.3


Activities


Recap with students what they remember about the major groups of micro-organisms from Grades 6 and 7. Ask students to work in small groups to produce a list of how micro-organisms are harmful and how they are helpful (using their prior knowledge). Take feedback from the groups to build up a balanced picture of micro-organisms as having a huge impact on all our lives – both positive and negative.

Explain that fungi and bacteria are the two groups of micro-organisms used in food production. Provide a number of cards with names of foods on and ask students to sort them into food made using bacteria and food made using fungi (e.g. yoghurt, cheese, vinegar, bread, wine, soy sauce and blue cheese). Show students samples of some foods made using micro-organisms (e.g. blue cheese) to look at with a hand lens.

Prepare word cards in advance.


Let students make yoghurt. Provide a starter culture of live yoghurt and sterilised milk. Ask students to add a spoonful of yoghurt to several test-tubes of milk and keep these test-tubes at different temperatures for 8 hours or overnight to see how temperature affects yoghurt production.

Milk thickens as yoghurt is made; ask students to measure changes in viscosity by timing how long it takes the yoghurt to pass through a tap funnel. Alternatively, ask them to measure changes in pH as the yoghurt is made, using electronic datalogging equipment.

Safety: Do not allow students to taste the yoghurt they make in the laboratory. If you can arrange to use a food preparation area, students could make and taste their yoghurt.

ICT opportunity: Use of datalogger.

Enquiry skill 8.1.1

4 hours

Micro-organisms in food production Know that micro-organisms are used in making foods such as bread, cheese and yoghurt.

Plan investigations, controlling variables and collecting an appropriate range of evidence, using appropriate techniques to ensure accuracy, identify patterns in observations and data, draw generalised conclusions and test predictions.

Show students microscopic images of yeast and a sample of fresh yeast. Explain that yeast is single celled and that this is unusual for a fungus. Ask students how yeast is used in bread-making and clarify that it makes the dough rise. Remind students that yeast is a living thing (a microscopic image will show new yeast cells budding from mature ones) and ask them what yeast might need to live. Ask students what gas yeast produces that makes bread dough rise (bearing in mind that yeast is a respiring, living thing). Challenge students to design a technique for testing this gas and let them try out and refine their ideas.

Let students investigate what affects how much carbon dioxide yeast produces (e.g. amount of sugar, temperature, pH). Students could either measure the height of bread dough or collect bubbles of carbon dioxide from a yeast and sugar suspension.

Collect all the class’s results and ask students to present them as line graphs and describe any patterns they can see. Ask students to consider whether there was sufficient evidence to draw conclusions and if there are any surprising results (e.g. too much sugar may reduce carbon dioxide production).

If using dried yeast, mix it in advance of the lesson and make sure it is active before you start the investigation.

Enquiry skill 8.1.1

Unit 8L.3



1 hour

Micro-organisms in wine and vinegar production Know that micro-organisms are used to make beer and wine.

Explain that carbon dioxide is not the only product when yeast respires and define fermentation. Ask students what they think happens to the alcohol produced when yeast is used to make bread dough rise. Show students diagrams that illustrate wine and beer production and explain that grapes ferment because yeast is found naturally growing on grape skins.

Challenge students to research how vinegar is made using reference books and the Internet. In their report students should include: • the history of vinegar making; • the type of micro-organism used to make vinegar; • different raw materials for making vinegar; • a step-by-step description of vinegar production; • an explanation of why vinegar is not alcoholic.



Assessment


Complete the table below by putting a tick in one or both columns:

Food Made using fungi? Made using bacteria?

Yoghurt

Cheese

Soy sauce

Bread

Wine

Vinegar

Assessment Set up activities that allow students to demonstrate what they have learned in this unit. The activities can be provided informally or formally during and at the end of the unit, or for homework. They can be selected from the teaching activities or can be new experiences. Choose tasks and questions from the examples to incorporate in the activities. Here are instructions for making blue cheese:

1. Add rennet to 1 litre of milk so that it curdles and drain the curds.

2. Sprinkle 2 teaspoons of salt into the curds.

3. Mix 1 teaspoon of blue cheese with 50 ml of clean water.

4. Add this to the curds, mix thoroughly and place in a sterile handkerchief.

5. Press overnight.

6. Use a sterile steel rod to make holes in the cheese every 3 cm.

7. Place on a rack at 10 °C for 50 days.

a. What type of micro-organism makes cheese blue?

b. At which step is this micro-organism added in the instructions above?

c. Why is it important to sterilise the handkerchief and steel rod used in the instructions?

d. Suggest a reason why holes are made in the cheese.

Unit 8L.3



Photosynthesis

About this unit This unit is the fourth of six units on life science for Grade 8.





Previous learning To meet the expectations of this unit, students should already know that green plants make their own food and that the cells of the green parts of a plant contain chloroplasts. They should already know that light is needed for photosynthesis to take place. They should already be able to use secondary evidence and information critically.

Expectations By the end of the unit, students describe the structure and function of plant cells involved in photosynthesis. They know that green plants make their own food by photosynthesis, which requires light and the chlorophyll in chloroplasts, together with water and carbon dioxide, and that oxygen is produced. They identify patterns, consider the validity of evidence, the extent to which it supports a prediction, and draw conclusions. They use word equations to represent chemical reactions.

Students who progress further explain and give the formula for photosynthesis. They evaluate evidence before drawing generalised conclusions. They represent simple chemical reactions with symbol equations.

Resources The main resources needed for this unit are: • photographs or video clips, including time-lapse sequences, showing

plants growing to enormous size • carbonated water and a block of wood, plants growing in water • data on the carbon dioxide and oxygen concentration around leaves over

a 24-hour period • prepared microscope slides of transverse section of a leaf, Elodea, moss

leaves, microscopes with high-power objective lenses. • variegated plant (e.g. geranium (pelargonium), ethanol and iodine

solution) • set of cards, each with H, C or O on them, or a molecular model kit

Key vocabulary and technical terms Students should understand, use and spell correctly: • photosynthesis, chlorophyll, chloroplasts, palisade cells • biomass, variegated leaf

UNIT 8L.4 7 hours



7 hours SUPPORTING STANDARDS

Including Grade 6 and 7 standards

CORE STANDARDS Grade 8 standards

EXTENSION STANDARDS Including Grade 9 standards

8.10.1 Describe the structure and function of plant cells involved in photosynthesis.

6.6.3 Know the parts of flowering plants that are responsible for anchorage (roots), circulation (xylem and phloem), gas exchange (stomata), food production (leaves and stems), reproduction (flowers) and waste removal (stomata).

8.10.2 Know that green plants make their own food by photosynthesis and that water and carbon dioxide are required and oxygen is produced.

9.11.1 State the word and formula equations for photosynthesis; explain the process as a biochemical reaction in chloroplasts that involves the absorption of light energy, which causes water and carbon dioxide to react to generate glucose and oxygen.

8.10.3 Know that light energy and chlorophyll contained in chloroplasts are requirements for photosynthesis.

8.10.4 Construct the chemical equation for photosynthesis in words and symbols.

7.1.2 Use secondary evidence and information selectively and critically.

8.1.2 Consider the extent to which the evidence justifies a conclusion or supports a prediction or hypothesis, and identify further investigations that might be needed.

9.1.2 Evaluate the strength of evidence and assess the validity of conclusions before arriving at a viewpoint.

2 hours

Structure and function of palisade cells

3 hours

Chlorophyll and chloroplasts

2 hour

Equation for photosynthesis

8.3.4 Express chemical reactions in the form of word equations. 9.3.5 Use symbol equations to represent simple chemical reactions and physical relationships.

Unit 8L.4


Activities


Review what students already know about photosynthesis. Define biomass as the mass of living matter. Show students a range of photographs or video clips, including, if possible, time-lapse sequences, illustrating that new biomass is formed as plants grow and that they can grow to an enormous size. Ask them to suggest where the new material in plants comes from. A common misconception is that plants get food from the soil; show students images that challenge this (e.g. plants growing without soil, plants growing in pots where the soil is not used up). Explain that plants make new biomass through the process of photosynthesis using the energy from sunlight and the raw ingredients water and carbon dioxide.

Hold up a bottle of carbonated water and a block of wood to illustrate how amazing it is that plants can convert a gas and water into solid biomass.


2 hours

Structure and function of palisade cells Describe the structure and function of plant cells involved in photosynthesis.

Know that green plants make their own food by photosynthesis and that water and carbon dioxide are required and oxygen is produced.

Review students’ knowledge of plant cell structure by asking them to draw and label a typical plant cell. Provide them with a prepared microscope slide of a transverse section of a leaf so that they can see the internal structure. Ask students to compare the leaf cells close to the upper surface with other cells and to suggest how palisade cells are adapted for photosynthesis (e.g. palisade cells are arranged in rows so that chloroplasts get maximum exposure to light that only passes though one cell wall).

Ask students to draw a diagram of a leaf and annotate it with information about how the leaf is designed for its function to photosynthesise.

Students will need prepared slides and microscopes.

Remind students that plants need light as well as carbon dioxide and water in order to grow well. Establish that the chlorophyll contained in the chloroplasts of plant cells enables them to absorb light, which is necessary for photosynthesis. Provide data on the carbon dioxide and oxygen concentration around leaves over a 24-hour period. Ask students to find patterns in this data and to relate these to night and day. Establish that the evidence supports photosynthesis taking place in the presence of light.

Enquiry skill 8.1.2

Ask students to prepare their own slides of Elodea or moss leaves using a microscope with high-power objective lens. If you light the slide from the side, students may observe the chloroplasts moving to maximise their exposure to light.

Encourage students to find video clips of Elodea cells on the Internet


Video clips are available at www.sciencefix.com/video/elodea_1.mov

3 hours

Chlorophyll and chloroplasts Know that light energy and chlorophyll contained in chloroplasts are requirements for photosynthesis.

Consider the extent to which the evidence justifies a conclusion or supports a prediction or hypothesis, and identify further investigations that might be needed.

Explain to students that the glucose formed in photosynthesis is usually stored as starch and ask them about a test for starch. Students will carry out a series of experiments testing for starch in Grade 9. For this unit, demonstrate testing for starch in a variegated leaf (e.g. geranium (pelargonium)). Before you test the leaf, take a digital photograph or draw a sketch of the distribution of chlorophyll in the variegated leaf. Boil the leaf in ethanol in a hot water bath to remove the chlorophyll, and then test the leaf for starch with iodine solution. Ask students to compare the distribution of starch with the distribution of chlorophyll.

Enquiry skill 8.1.2

Unit 8L.4



Extension activity Challenge students use the Internet or reference materials to find out about plants that do not have green leaves and ask: ‘Do they still have chlorophyll?’ and ‘Why are their leaves dark red?’


Review what students have learnt about photosynthesis and write up the word equation for photosynthesis on the board or OHP. Ask students for the chemical formulae of water, carbon dioxide and oxygen and write these symbols below the word equation. Explain to students that, in a chemical reaction, the reactants react to make new substances and whatever elements are in the reactants will also be in the products. Ask students to work out the three elements that glucose is made of, and then provide them with the formula for glucose to complete the symbol equation.

To show students how to balance the symbol equation, provide groups of students with pieces of card with the letter H, C or O written on them, or a molecular model kit. Students will need six C, twelve H and eighteen O. First ask students to make six molecules of water and six molecules of carbon dioxide. Then tell them to use these reactants to make the products; one molecule of glucose and six molecules of oxygen.

Enquiry skill 8.3.4 2 hours

Equation for photosynthesis Construct the chemical equation for photosynthesis in words and symbols.

Express chemical reactions in the form of word equations.

Remind students that glucose is the first product of photosynthesis and that this is often converted into other substances. Explain that a plant’s biomass consists of many different substances that have been made from glucose. Ask students to suggest some foods made of plant products (e.g. vegetable oil, flour, lentils) and ask them to use their knowledge of the components of a balanced diet to say what types of food are found in these products (i.e. fats, carbohydrates, proteins, fibre). Explain that, to make proteins, plants need more than just the three elements carbon, oxygen and hydrogen; ask students where plants get additional elements from. They should recall from Grade 7 that plants get nitrogen and other elements as nutrients from the soil.


Assessment


In 1637, a Belgian scientist, Van Helmont carried out an experiment with a tree. He measured the mass of a small tree and a pot of soil, then he planted the small tree in the pot of soil and watered the tree for 5 years, he did not add anything else to the pot. At the end of 5 years he measured the mass of the tree and the pot of soil again.

Here are the results of his experiment:

Mass of tree (kg) Mass of soil (kg)

At the start of the experiment 2 90.6

After 5 years 76.7 90.5

a. What was the increase in mass of the tree? Explain this increase in mass.

b. What was the decrease in mass of the soil? Explain this decrease in mass.

c. Describe a similar experiment you could carry out that would provide evidence in 5 weeks rather than 5 years. Include in your plan the detail of what plants you will use, what you will do and what you will measure.

Match the following terms to the definitions in the table below. Chloroplast, chlorophyll, palisade cell, variegated and biomass.

Term Definition

Upper layer of a leaf and main site of photosynthesis

Pigment that traps light energy

Amount of living material

Plant with green and white patches

Part of cell responsible for photosynthesis


There is a useful assessment activity for photosynthesis on the website www.psionica.co.uk/biology/KS3Biology/questions/photoquestions.htm.

Unit 8L.4



Feeding relationships

About this unit This unit is the fifth of six units on life science for Grade 8.


The teaching and learning activities should help you to plan the content and pace of lessons. Adapt the ideas to meet your students’ needs. For extension or consolidation activities, look at the scheme of work for Grade 10F and Grade 7.



Previous learning To meet the expectations of this unit, students should already be able to construct food chains and food webs and should already know why human and environmental change can alter a food web. They should already be able to manipulate observations and data and use tables and graphs.

Expectations By the end of the unit, students construct and interpret a pyramid of numbers and biomass. They understand why toxins increase in concentration along a food chain. They express qualitative and quantitative information through a range of techniques, including graphs and scale diagrams.

Students who progress further understand how energy flows through an ecosystem. They relate pyramids of numbers, biomass and energy to food chains and food webs. They communicate their results using a variety of techniques.

Resources The main resources needed for this unit are: • data on the populations of a predator and prey over time (e.g. snowshoe

hare and lynx at www.bbc.co.uk/schools/gcsebitesize/biology/ livingthingsenvironment/0habitatsandpopsrev8.shtml)

• video clip of snowshoe hare and lynx • data on the effect of DDT on population of a bird of prey

Key vocabulary and technical terms Students should understand, use and spell correctly: • pyramid of numbers, pyramid of biomass • pesticide, insecticide, toxin, mercury, DDT, accumulate, biodegrade

UNIT 8L.5 7 hours





10F.13.1 Describe how the organisms in a pyramid of numbers relate to their biomass and to energy flow through food chains and food webs.

7.6.1 Construct food chains and food webs.

8.5.1 Relate changes in numbers of organisms in a habitat to their feeding relationships.

10F.13.2 Draw energy-flow diagrams to illustrate how energy flows through an ecosystem.

8.5.2 Interpret pyramids of numbers and biomass representing the organisms linked in a food chain.

7.6.2 Know why human action and environmental change can alter a food web.

8.5.3 Explain why toxins increase in concentration along a food chain.

3 hours

Changing populations in feeding relationships

2 hours

Pyramids of number and biomass

2 hours

How toxins build up in a food chain

7.3.1 Use a range of methods, such as description, diagrams, pictures, tables, graphs and calculations, using ICT methods where appropriate, to communicate observations, data, results and conclusions.

8.3.1 Present qualitative and quantitative data using a range of methods, such as descriptions and tables and through pictures, graphs and diagrams, using ICT methods where appropriate, and draw conclusions from them.

Unit 8L.5


Activities


Review students’ understanding of food chains and food webs from Grade 7 by providing them with some examples of food webs to study. Ask them to identify producers and consumers, and predators and prey, and to draw food chains from the food web. Ask students to predict what would happen to the populations of other organisms if one organism were removed from the food web.


Introduce students to a simple food chain (e.g. snowshoe hare eats plant leaves in the conifer forests of Canada). Snowshoe hares can produce three litters of eight young on average per year. Ask students what will happen as the population of hares increases; can the population continue to increase indefinitely or will it reach a maximum? Ask students to list the factors that could stop the population rising (e.g. shortage of food or nesting sites, or disease). Extensive data shows that the hare population rises and falls in a 10-year cycle. Now introduce a predator into this food chain (e.g. lynx). If possible, show students a video clip of these animals in their habitat. Provide information about the population size of each animal. Ask what will happen to the population of predators as the population of prey increases. Ask if the population of predators can keep increasing; if not, what will limit their population growth?

3 hours

Changing populations in feeding relationships Relate changes in numbers of organisms in a habitat to their feeding relationships.

Show students a predator–prey graph in which populations rise and fall over and over again. Ask students to explain the pattern of the graph, including why the prey’s population changes happen after those of the predator.

You can find data for populations of hare and lynx on the Internet, e.g. www.bbc.co.uk/ schools/gcsebitesize/biology/livingthingsenvironment/0habitatsandpopsrev8.shtml

Provide students with a simple food chain (e.g. grass, grasshoppers, toads) and the numbers of each type of organism in 5 m2 (e.g. 1000 grass plants, 20 grasshoppers and 2 toads). Explain that this is very simplified data and does not take into account other feeding relationships. Ask students to represent the data as a pyramid of numbers in which the size of each block represents the number of organisms. Students could draw a sketch of this pyramid or make a scale diagram using squared paper.

Ask students why there are fewer grasshoppers than grass plants and why there are fewer toads than grasshoppers. Repeat this activity for a number of different food chains so that students can see the pattern is repeated. Ask them to explain another general pattern of food chains – the size of animals increases as you go up a food chain.

Mathematics: Drawing scale diagrams.

Enquiry skill 8.3.1

Provide data on two food chains whose pyramid of numbers is not pyramid shaped (e.g. 1 Acacia tree, 20 caterpillars, 2 robins, or 1000 grass plants, 10 rabbits, 100 fleas). Ask students why some pyramids of numbers are not pyramid shaped.

Introduce students to pyramids of biomass for these unusual food chains. Explain that biomass is the mass of living matter, and that it is estimated for an ecosystem by taking small samples rather than trying to weigh everything! Ask students why pyramids of biomass are always pyramid shaped.

2 hours

Pyramids of number and biomass Interpret pyramids of numbers and biomass representing the organisms linked in a food chain.

Present qualitative and quantitative data using a range of methods, such as descriptions and tables and through pictures, graphs and diagrams, using ICT methods where appropriate, and draw conclusions from them.

Extension activity Ask students to find data about a food web on the Internet and to add up the total number of all producers, herbivores and carnivores to produce a food web pyramid of numbers.

ICT opportunity: Use of the Internet. Suitable data can be found at coexploration.org/bbsr/ coral/lessons/lyndsey1.html

Unit 8L.5



Explain to students that some substances (toxins) are not broken down in the body and so the more you eat them, the more they accumulate in your body. Use the example of mercury, which can damage the developing nervous system of babies and young children. Show students the food chain for tuna in the sea and discuss the fact that tuna is a tertiary consumer and at the top of the food chain. Now show them a health warning that we should not eat too much tuna because of the risk that it contains mercury. Explain that mercury is released into the environment from burning fossil fuels, industrial processes, waste disposal and mining. Ask students to explain why tuna may contain an unsafe amount of mercury and why other fish like sardines or anchovies do not.

Ask students to draw a diagram to show accumulation of mercury in tuna – tell them to draw the food chain of plants and animals and add red dots to represent the mercury. Plant and animal plankton have just one or two dots, small fish have a few more, then tuna have lots of dots.

2 hours

How toxins build up in a food chain Explain why toxins increase in concentration along a food chain.

Explain to students that pesticides and insecticides are used worldwide to kill insects that destroy crops or carry disease. Some of these insecticides cannot be broken down in the body and accumulate in the same way that mercury does. At a high dose, insecticides can cause health problems for top consumers, including humans.

Provide students with data about the effect of the insecticide DDT on birds of prey and ask them to interpret this data. Discuss why many parts of the world have banned the use of DDT but some still use DDT to kill the mosquitoes that carry malaria, despite the health risks. Also explain that not all toxins used as herbicides or pesticides are passed onto animals that feed on them. Many biodegrade over very short periods; it is only those containing persistent substances that accumulate.

Encourage students to find out more about accumulation of toxins from the Internet.

ICT opportunity: Use of the Internet. Several websites have useful information (e.g. an activity on the loss of Indian vultures can be downloaded from www.upd8.org.uk/activity.php?actid=66)


Assessment



Scientists measured the concentration of the insecticide DDT in three animals and a microscopic plant called chlamydomonas.

a. The food chain for these four organisms is shown below.

Draw a pyramid of numbers for this food chain.

b. The bar chart shows the concentration of DDT in the four organisms.

Give one reason for the difference in the concentration of DDT in these organisms.


Unit 8L.5



In the left-hand column there are descriptions of four food chains. In the right-hand column there are four pyramids of numbers, which are not drawn to scale. Draw a line from each description to the correct pyramid of numbers.




Digestion

About this unit This unit is the sixth of six units on life science for Grade 8.





Previous learning To meet the expectations of this unit, students should already be able to describe the overall anatomy of the human digestive system.

Expectations By the end of the unit, students know the structure of the digestive system and understand the functioning of enzymes. They distinguish between digestion and absorption of food. They know about diabetes and obesity.

Students who progress further explain and give equations for aerobic and anaerobic respiration and fermentation, and know how conditions affect respiration.

Resources The main resources needed for this unit are: • visking tubing, 1% commercial amylase solution, 1% starch suspension,

iodine solution, ‘clinistix’ or Benedict’s solution • netting bag and pieces of card • starch agar plates with four wells made using a heat-sterilised cork borer

and solutions of amylase, boiled amylase, protease and lipase • jelly with gelatine or agar, fresh pineapple, tinned pineapple • Internet access (or reference material about obesity and diabetes)

Key vocabulary and technical terms Students should understand, use and spell correctly: • mouth, oesophagus, small intestine, large intestine, colon, stomach, liver,

gall bladder, pancreas • enzyme, visking tubing, amylase, protease, lipase • digestion, absorption, insulin, diabetes, obesity

UNIT 8L.6 8 hours



8 hours SUPPORTING STANDARDS

Including Grade 6 and 7 standards

CORE STANDARDS Grade 8 standards

EXTENSION STANDARDS Including Grade 9 standards

6.8.1 Identify and describe the general structure of the human digestive system and know how the mouth, salivary glands, oesophagus, stomach, liver, gall bladder, pancreas, large and small intestine, and anus are connected.

8.6.1 Recall the general structure of the human digestive system and explain the functions of the digestive organs (mouth, oesophagus, small and large intestines and colon, stomach, liver, gall bladder and pancreas).

8.6.2 Explain digestion as the breakdown of large insoluble food molecules into smaller soluble molecules that can be absorbed into the blood stream for transport round the body.

9.8.1 Give the word and formula equations for aerobic respiration; explain the process as a cellular biochemical reaction in animals and plants in which food acts as a respiratory substrate and reacts with oxygen to release energy and produce carbon dioxide and water.

8.6.3 Relate the digestive enzymes amylase, protease and lipase to their substrates and products, and explain how secretions of enzymes, stomach acid and bile control digestive processes.

2 hours

Structure and function of digestive system

2 hours

Process of digestion

2 hours

Role of enzymes in digestion

2 hours

Metabolic health problems

8.9.1 Know the symptoms, causes and problems of diabetes and obesity.

Unit 8L.6


Activities


Review what students already know about the parts of the human digestive system from Grade 6. Provide groups of students with a large piece of paper and ask them to draw a life size outline of the human torso and to draw the digestive tract and the organs associated with digestion. Provide a list of the organs to include: mouth, oesophagus, stomach, small and large intestines, colon and anus, stomach, liver, gall bladder and pancreas.

Ask students to discuss and annotate their diagram with what happens to food in each part of the digestive tract and the functions of the associated organs. When most groups have almost completed their diagrams, explain that they can learn from each other by carrying out an activity called ‘expert and envoy’. One student from each group stays with their poster as expert to explain the diagram; the other members of the group visit the posters of other groups as envoys to find out information. Envoys then return to their home group to update and improve their diagram. Some groups may want to check their facts in a textbook and envoys could also do this.

Let students look at a display of all the groups’ diagrams and give constructive comments about how to improve each other’s work.


2 hours

Structure and function of digestive system

Recall the general structure of the human digestive system and explain the functions of the digestive organs (mouth, oesophagus, small and large intestines and colon, stomach, liver, gall bladder and pancreas).

Give students some individual work to reinforce what they have learnt as a group (e.g. a diagram of the digestive system to label and a list of organs and functions to match together).

Explain that several processes happen to the food we eat and encourage students to develop a list of these in the correct sequence: feeding, digestion, absorption and elimination of faeces. Ask them to identify the specific organs and parts of the digestive tract involved in these four processes.

Encourage students to find out more about digestion on the Internet.

ICT opportunity: Use of the Internet. There is an interactive digestive system at www.open2.net/everwondered_food/science/science_digestion.htm

2 hours

Process of digestion Explain digestion as the breakdown of large insoluble food molecules into smaller soluble molecules that can be absorbed into the blood stream for transport round the body.

Explain to students that digestion is the breakdown of large molecules of food into small molecules; ask why food needs to be in small soluble molecules – where does it go next? Introduce students to the visking tubing experiment below and carefully explain each step so that they understand what this experiment is trying to show. Ask students what type of food starch is and ask them to name some foods that contain a lot of starch. Explain that starch is a large molecule – too large to be absorbed – and that it must be broken down into small, simple sugar molecules before it can be absorbed. Introduce students to amylase and explain that it is an enzyme found in saliva that breaks down starch. Explain to students that they are going to use pieces of visking tubing to represent the small intestine; visking tubing, like the digestive tract, has very small holes in it, so small that starch cannot pass through but simple sugars can. Remind students what the food test is for starch.

Provide students with two pieces of visking tubing – one containing starch solution and the other containing starch solution plus amylase. Tell them to place each piece of visking tubing into a separate beaker of warm water and immediately test the contents of each tube for starch by adding a drop of the contents to a spotting tile with iodine solution. Tell them to repeat this every 2 minutes until the visking tubing containing starch and amylase shows a negative test for starch. Ask students to record their observations in a table and discuss what their results show.

Take a sample from the warm water surrounding the visking tubing and demonstrate testing it for starch and simple sugars. Ask students what these results show.

Enquiry skill 8.1.2

Unit 8L.6



Use a model to help explain what happened inside the visking tubing containing starch and amylase. Use a netting bag to represent the visking tubing and large pieces of card to represent the starch; scissors represent the enzyme amylase. Show students that the large pieces of card will not fit through the holes of the bag. Cut the starch card up into small pieces that will fit through the netting bag. Make sure students are clear which part of the model represents which part of the experiment and in turn what the visking tubing and water bath represent. Ask students to write a description of what digestion is in their own words.

Enquiry skill 8.1.3

Use simple diagrams of molecules to help explain that for each major food group (carbohydrates, fats and proteins) there are specific enzymes (amylase, protease and lipase) that break down large molecules into small molecules so that they can be absorbed.

Get students to carry out experiments that show that enzymes are specific. For example, provide students with a prepared Petri dish of starch agar that has four wells in it made with a cork borer. Ask them to add 2 drops of a different enzyme (amylase, protease and lipase) to each of three wells and 2 drops of boiled amylase to the fourth. After 24 hours, ask them to add iodine solution to the starch agar. They will observe a clear area around the amylase where the starch has been digested but not around the other two enzymes. The boiled amylase also has no effect on the starch agar, showing that enzymes are destroyed by heat.

Safety: Prepare the starch agar plates aseptically and heat-sterilise the cork borer to prevent contamination by micro-organisms.

Remind students of the role of enzymes in digestion and explain that, in addition to enzymes, the conditions inside the digestive tract assist the breakdown of large molecules (e.g. body temperature). Ask students to discuss what other substances are found in the stomach. They may know that the stomach lining produces hydrochloric acid, which makes conditions in the stomach around pH2. This is a hostile environment for any micro-organisms swallowed with food; it also helps stomach enzymes to digest proteins.

Students will have drawn the liver, gall bladder and pancreas on their diagrams of the digestive system at the start of this unit. Check that everyone appreciates that the pancreas secretes digestive enzymes and the liver secretes bile, which is stored in the gall bladder. Bile helps the enzyme lipase to digest fats by breaking down fats into small droplets.

2 hours

Role of enzymes in digestion Relate the digestive enzymes amylase, protease and lipase to their substrates and products, and explain how secretions of enzymes, stomach acid and bile control digestive processes.

Extension activity

This activity encourages students to think through a problem. Present students with two bowls of jelly, one containing a fresh piece of pineapple, the other containing a piece of tinned pineapple. The fresh pineapple jelly will not have set. Ask students to discuss and come up with their own explanation for this. (Fresh pineapple contains a protease that digests the protein gelatine (or agar) that makes the jelly set. Tinned pineapple has been heated, which destroys the enzymes in the pineapple.) Ask students why people who handle raw pineapples wear gloves.



2 hours

Metabolic health problems Know the symptoms, causes and problems of diabetes and obesity.

Explain to students that as well as secreting digestive enzymes, the pancreas also secretes the important hormone insulin. Allow time for students to discuss in groups what they already know about insulin, what it controls and what it means to be diabetic. Gather together the views of the class and correct any misconceptions. Students may not realise there are two forms of diabetes, one that requires insulin injections and one that does not; both are serious conditions. Provide students with graphs of blood sugar level and insulin level to interpret. Ask why it is not a good idea to eat too many sugary foods.

Discuss with students the health problems associated with being overweight or obese. Obesity is a growing worldwide health issue, particularly in developed countries, as is diabetes. Challenge students to find out more about obesity and diabetes using the Internet or reference material. For example: • Is there a link between obesity and diabetes? • What percentage of the Qatar population is obese? What percentage have diabetes? • What are the symptoms and treatment of type 1 and type 2 diabetes? • What are the risk factors associated with developing diabetes? • What are the health problems associated with obesity? • Why is the number of obese people increasing? What can be done to prevent this?

Enquiry skill 8.1.2

ICT opportunity: Use of the Internet. There are many websites with useful information, e.g. www.diabetes.org.uk/. For data on diabetes in Qatar visit www.arabmedicare.com/diabetesfacts.htm and for data on obesity in Qatar visit www.who.int and search Qatar+obesity.


Assessment


Tarik is representing his school at an athletics event. Tarik needs energy from the food he eats for his leg muscles to work. Just before the 200 m race he is competing in, what do you recommend he eat – bread or glucose tablets? Explain your answer.

Biological washing powder contains enzymes that breakdown dirt and food stains on clothing. Biological washing powders work effectively for low temperature washes but some are less effective when the clothes are washed at 95 °C. Explain why.


After food containing starch is digested, a person’s blood sugar level rises. The body responds by producing a hormone called insulin. Insulin lowers the blood sugar level again. The graph below shows how a person’s blood sugar level changes after eating two different samples of food.

a. Use the graph to help you to explain why less insulin would be produced one hour after eating pasta than one hour after eating white bread.

b. Suggest the normal blood sugar level in this case.

Adapted from QCA Year 9 extension science test, 2001

Unit 8L.6

197 | Qatar science scheme of work | Grade 8 | Unit 8M.1 | Materials 1 © Education Institute 2005

GRADE 8: Materials 1

Atoms and molecules

About this unit This is the first of four units on materials for Grade 8. This unit builds on all the units in Grade 7, providing a theoretical background for the observations made in them. This theoretical background is expanded further in Unit 9M.1 ‘Atomic and molecular structure’; teachers of more advanced students may wish to anticipate some of the Grade 9 work in this unit.

Work begun in this unit (such as representing reactions by equations and relating reactivity to the periodic table) should be continued and expanded throughout the other three materials units in this grade.

The unit is designed to guide your planning and teaching of lessons on materials. It provides a link between the standards for science and your lesson plans.




Previous learning To meet the expectations of this unit, students should already be aware that all matter is made up of particles, the behaviour of which depends on the state of the matter. They should also know that the simplest forms of matter are the elements and that these combine to make more complex forms called compounds.

Expectations By the end of the unit, students know that the smallest particle of an element is an atom and that atoms of one element are different from atoms of every other element. They know that compounds are formed from elements and that a molecule is the smallest particle of a compound. They represent elements by symbols and compounds by formulae, and use word equations to represent chemical reactions. They classify elements according to whether they are solids, liquids or gases, and whether they are metals or non-metals. They know where the metallic and the non-metallic elements occur in the periodic table.

Students who progress further distinguish elements from each other in terms of their atomic and electronic structures. They grasp the concept of valency and use it to represent simple reactions by balanced equations. They distinguish between ionic and covalent bonding.

Resources The main resources needed for this unit are: • modelling clay, modelling building bricks, atomic model kits • collection of elements • powerful demonstration burner • tared balance accurate to 1 mg (preferably) or 10 mg • display copy of the periodic table • A3 student copies of the periodic table outline (without elements) • Internet access

Key vocabulary and technical terms Students should understand, use and spell correctly: • atom, molecule, element, compound • names of common elements referred to • symbol, formula, equation, valency • metal, non-metal, periodic table

UNIT 8M.1 7 hours





7.12.7 Know that all matter is made from a small number of elements and that they can be classified as solids, liquids or gases, metals or non-metals.

8.12.1 Know that the smallest particle of an element is an atom and that atoms of one element are of one kind and are different from atoms of every other element.

9.13,1 Know that atoms are made up of a nucleus consisting of protons and neutrons surrounded by electrons in specific orbitals or shells.

7.12.8 Know that elements combine to form compounds and that the properties of compounds are different from the properties of their constituent elements.

8.12.2 Know that elements join together chemically to form compounds, that the smallest particle of a compound is a molecule, and that all molecules of a compound are made up of the same fixed number of atoms of the constituent elements.

9.13.6 Know how atoms combine using ionic (electrovalent) or covalent bonds.

8.12.3 Know that all elements can be represented by a symbol, compounds by formulae and reactions by equations.

9.13.11 Know what is meant by the valency of an element and how to use this in determining the formulae of its compounds.

8.12.4 Know that mass is conserved during a chemical reaction and that the number of atoms of each element taking part in the reaction remains unchanged.

8.12.5 Recognise Mendeleev’s periodic table as a means of classifying elements according to their properties. Identify where the more reactive and the less reactive metals occur on the periodic table and where the metals and the non-metals occur.

2 hours

Atoms, elements, molecules, and compounds

4 hours

Chemical reactions

1 hour

Classification of the elements

8.12.6 Know that elements with similar properties are arranged in columns in the periodic table and that the properties of elements change gradually along the rows.

8.3.4 Express chemical reactions in the form of word equations.

Unit 8M.1


Activities


Atoms and elements Prepare a display of some elements showing their names and some of their physical properties (e.g. name, symbol, metallic/non-metallic character, melting point). Use the display to recall work done on elements in Grade 7 to ensure that students understand that they are the materials from which all other materials are made. Have a periodic table on the wall throughout the unit; refer to it but do not explain its full significance until the end of the unit


Recall work on particles in Grade 7. Use several identical children’s modelling building bricks joined together to represent a small piece of a solid element. Demonstrate how elements are made of particles that we call atoms by pulling apart the individual bricks.

Refer to the early atomic theories of Democritus (2500 years BP) and Dalton (published 1807), noting particularly the use of symbols by Dalton to represent atoms.

Enquiry skill 8.2.2 (the legacy of Dalton)

Assign three or four different elements to each student and ask them to make a cardboard cube for each element showing six of its properties (name, symbol, state at 20 °C, metal/non-metal, and two other properties to be decided by the teacher). They can obtain the data on the elements from the Internet. Tell them to use different colour card for metallic and non-metallic elements and for the different states of the non-metals (these will be used again later). The class as a whole should make examples of all the elements up to calcium plus the more common transition elements.

Print and cut out the templates of the cardboard cubes before the lesson.


Enquiry skill 8.1.6

Teach more advanced students about the atomic structure of the simpler elements and how they differ from each other in terms of numbers of protons and electrons and the arrangement of the electrons.

Compounds and molecules Ask students to use the element cubes from the activity above to show how atoms of elements can combine to form molecules, the smallest building blocks of compounds. Give them examples of the formulae of some simple compounds (e.g. MgO, CuO, H2O, CO2, CH4) and also some larger ones (e.g. C6H12O6, H2SO4). Ask them what they think these might mean. Ask them to make representations of them using their cubes. Make and show models of molecules from modeling clay or from atomic model kits.

Use your discretion at this stage about whether to show ionic compounds such as MgO and CuO as simple molecular models.

2 hours

Atoms, elements, molecules, and compounds Know that the smallest particle of an element is an atom and that atoms of one element are of one kind and are different from atoms of every other element.

Know that elements join together chemically to form compounds, that the smallest particle of a compound is a molecule, and that all molecules of a compound are made up of the same fixed number of atoms of the constituent elements.

Know that all elements can be represented by a symbol, compounds by formulae and reactions by equations.

Establish that students are able to use the words atom, molecule, element and compound correctly by simple means such as true/false statements or sentence completion exercises.

Unit 8M.1



Combining elements Divide the class into groups and ask each to carry out one reaction involving the combination of elements following instructions given. Examples include:

• burning steel wool;

• burning magnesium;

• burning sulfur

• burning hydrogen;

• heating iron and sulfur

• heating copper and sulfur.

Recall others from earlier work or demonstrate some such as:

• sodium and oxygen;

• magnesium and sulfur;

• aluminium and iodine.

Ask each group to report its reaction and to name the product, describe what atoms the molecule of the product contains and write a word equation for the reaction on the board.

Safety: Burn sulfur in a fume cupboard

Safety: Take appropriate precautions when demonstrating these vigorous reactions. The reaction between aluminium and iodine should be done in a fume cupboard.

Ask each group to model what happened using element cubes and write a symbol equation for the reaction underneath the word equation. In some cases the numbers of atoms combining is not 1:1; provide the class with the correct ratio, explaining that later they can look for patterns in the numbers of atoms that combine to form compounds.

At this stage, the symbol equations for reactions with gases will be incorrect. Return to them and correct them after the next activity.

4 hours

Chemical reactions Know that elements join together chemically to form compounds, that the smallest particle of a compound is a molecule, and that all molecules of a compound are made up of the same fixed number of atoms of the constituent elements.

Express chemical reactions in the form of word equations.

Know that mass is conserved during a chemical reaction and that the number of atoms of each element taking part in the reaction remains unchanged.

Elements that form molecules Explain that many gaseous elements exist naturally not in the form of uncombined atoms but as diatomic molecules. List the common ones (H2, O2, N2, Cl2). Ask each group to return to the equations on the board (or in their books) from the previous activity and correctly balance them. Many students may find this difficult. Provide them with coloured modelling clay from which they can make atoms of the elements and then make a model of a balanced equation. At this stage, do not expect all students to be able to write balanced symbol equations. However, you can give more advanced students homework exercises writing word and balanced symbol equations for simple reactions.

Recall from work on air and combustion in Grade 7 the family of elements called the inert gases. Explain that these do not form diatomic molecules because they do not take part in any chemical reactions.

Introduce more advanced students to the concept of valency at this stage. If they need help mastering these ideas, ask them to make a series of valency cards for all common elements, two or three for each. These should be rectangular with one side being 1×, 2× or 3× the length of the other, according to the valency of the atom. They can then work out formulae by putting cards representing the two elements together in two rows in such a way that the rows are of minimum but equal length.



Conservation of mass Recall or repeat the demonstration from Grade 7 on the burning of iron wool in a silica tube. Ask students to recall what happens to the mass of the iron as it burns and why. Challenge them to design an experiment using magnesium that will show that there is an increase in mass when it burns.

Demonstrate the complete burning of magnesium ribbon in a crucible covered with a lid to show the increase in mass. From this experiment, the mass of oxygen that combines with a given mass of magnesium can be calculated by the more advanced students.

Enquiry skill 8.1.2

This is technically not easy and requires very clean magnesium, a powerful burner and practice.

Ionic and covalent bonding Introduce advanced students to ionic and covalent bonding at this stage (see Unit 9M.1 ‘Atomic and molecular structure’).

Ask students to find out, from the Internet or an encyclopaedia, about the work on the properties of elements carried out by three scientists in the mid nineteenth century: Johan Döbereiner in Germany, John Newlands in England, and Dmitri Mendeleev in Russia. Ask them to do an activity that is similar to the work of these scientists by grouping element cubes (see above) with similar properties together. Give assistance where needed by suggesting properties (e.g. metals with a high melting point, gases, solid non-metal).

Then give out an A3 sheet (or bigger) with an outline of Mendeleev’s table, which need only show the five main groups of elements (groups I and II, transition metals, ‘B’ metals, non-metals and rare earth elements). Ask students to place their groups of cubes on the table in roughly the correct place according the display periodic table. Ask them whether they had to split up any of their groups to do this.

Ask students to list the main characteristic properties of the four areas of the period table (excluding the rare earths) from the properties on their cubes.


Ensure that a copy of the periodic table is on display

Enquiry skills 8.2.1, 8.2.2

Prepare worksheets with an outline of Mendeleev’s table in advance.

1 hour

Classification of the elements Recognise Mendeleev’s periodic table as a means of classifying elements according to their properties. Identify where the more reactive and the less reactive metals occur on the periodic table and where the metals and the non-metals occur.

Know that elements with similar properties are arranged in columns in the periodic table and that the properties of elements change gradually along the rows.

Provide each student with an A3 copy of the periodic table outline showing only the main areas without the elements included. List on the table the main characteristic properties of the four areas discussed. Have the table ready to add additional properties of groups of elements in Units 8M.2 and 8M3 when trends across and down the table will emerge.


Assessment


Methane is the main component of the natural gas found in Qatar. It boils at –162 °C and its melting point is –183 °C. The formula of methane is CH4. Methane is flammable and, when it burns, one of the products is carbon dioxide.

a. What is the physical state of methane at (i) –175 °C, (ii) 175 °C?

b. What are the names and symbols of the elements that are present in methane?

c. Give the name and formula of the second product that forms when methane burns.

Sharifa heated some copper powder until it turned black. When she allowed it to cool, it did not turn back into copper. She added the black substance to some dilute sulfuric acid. A blue solution was formed but a little of the black solid remained at the bottom. She separated the blue solution from the black powder and left it for some days in a shallow dish

a. Is copper an element, a compound or a mixture?

b. Is the black substance formed when the copper was heated an element, a compound or a mixture? Give a reason for your answer.

c. Is the blue substance formed when acid was added an element, a compound or a mixture? Give a reason for your answer.

d. How did Sharifa separate the blue liquid from the black solid?

e. What two changes would Sharifa observe in the shallow dish after several days?

The list below shows some of the substances present in air.

Ar CO2 H2O N2 O2

a. Is air a mixture, a compound or an element? Give reasons for your answer.

b. Name the five substances in the list and state whether they are mixtures, compounds or elements.

c. When magnesium burns in air, which element does it combine with? State the name of the product of the reaction.

From a study of the position in the periodic table of the following elements – zinc powder, iron filings, copper powder, sulfur, oxygen – predict which pairs of these elements might react with each other if they are mixed and heated. Name the compound that might be formed in each case.

Enquiry skill 8.1.2.

Students may be allowed to test those predictions that can be safely tested in the laboratory.


Predict the following properties of the elements cobalt, strontium, bromine, selenium and krypton from their position in the periodic table:

a. good or bad conductor of electricity;

b. likely physical state at room temperature;

c. whether the element is likely to burn in air and the physical state of the product of burning.

Unit 8M.1



Metals

About this unit This is the second of four units on materials for Grade 8. This is one of many units in Grades 7 and 8 that explore patterns in chemical reactivity and provide the necessary background knowledge for the understanding of the theoretical basis of chemistry that is introduced in Unit 9M.1 ‘Atomic and molecular structure’.





Previous learning To meet the expectations of this unit, students should already know that metals are a group of elements with specific common physical and chemical characteristics. They should understand the nature of the change when a substance burns and also when a substance reacts with an acid.

Expectations By the end of the unit, students identify reactivity trends for metals in the periodic table. They arrange metals in order of reactivity based on their reactions with air, oxygen, water and dilute acids, and know the products of these reactions. They know that reactive metals can displace less reactive ones from their compounds. They test for hydrogen. They know that we use a variety of methods to prevent iron from rusting, according to the use we make of the metal.

Students who progress further write symbol equations for reactions of metals. They place an unknown metal in the reactivity series according to its properties. They understand why aluminium often does not show behaviour expected from its position in the reactivity series.

Resources The main resources needed for this unit are: • transparent sandwich boxes with a good seal • an investigation planning poster that will help to identify and control

experimental variables • oxygen and hydrogen gas in cylinders • safety screen • samples of different metals

Key vocabulary and technical terms Students should understand, use and spell correctly: • metal • names of common metals used • acid, oxygen • displacement, reactivity series, reactivity order • corrosion, tarnishing, rusting, protection

UNIT 8M.2 9 hours





7.14.2 Know that some acids and alkalis can be corrosive and hazardous, and be aware of the use of hazard symbols to describe this.

8.13.1 Deduce a reactivity series for common metals based on their reactions with air, oxygen, water and dilute acids.

8.13.2 Know that the test for hydrogen is that it explodes when mixed with air and ignited.

7.13.3 Know that when a substance burns, it combines chemically with the oxygen in the air and that the overall mass of the product(s) is greater than the original mass of the material.

8.13.3 Know that when metal reacts with air, oxygen or water, an oxide or hydroxide is formed and that if this is soluble in water, the solution is alkaline.

9.13.6 Know how atoms combine using ionic (electrovalent) or covalent bonds.

8.13.4 Correctly place a metal in the reactivity series based on experimental evidence.

8.13.5 Account for the anomalous behaviour of aluminium in its reactions with air, water and dilute acids.

3 hours

Corrosion

1 hour

Properties of hydrogen

5 hours

Metal reactivity series

8.13.6 Know that iron will rust in the presence of air and water, and that it can be protected from rusting by oiling, painting, galvanising, coating with plastic, electroplating and tin plating.

8.13.7 Understand that reactive metals can displace less reactive ones from their compounds.

Unit 8M.2


Activities


Corrosion Bring some everyday examples of corrosion (e.g. rusted steel objects, tarnished copper or silver) into the classroom. Ask students to give examples of others. List them on the board or OHP. Ask for ideas about what causes corrosion and tarnishing of metals. Some will say it just happens, others will suggest that water is important. Many may observe that seawater is very corrosive.

Challenge them, in groups, to design an experiment to test their ideas. It should use several common metals and several conditions: dry air, moist air, water, salt water. The conditions can be created in well-sealed sandwich boxes. One idea that should be suggested is that all samples should be clean and free from grease. Some students may suggest including some polluting gases, such as sulfur dioxide. There are many possible variables in this activity; try to organise the groups to work together so that the effects of all of them can be tested.

After several days, encourage group and class discussion of the results. Develop a table of results that shows all the metals used and the presence or absence of all the possible variables. The results will show that tarnishing does not happen readily in dry pure air but that all the other factors contribute to it, particularly if the metals are in contact with salt water (or any electrolyte).

Through group discussion decide which metals corroded the most and which were most resistant. Determine also the conditions that caused the least and the most corrosion. Were these conditions the same for all metals?

The correct conditions in the boxes can be created as follows: • use lumps of calcium oxide to absorb water

from the air; • use moist cotton wool to make the air moist; • use crystals of a sulfite add some sulfur

dioxide to the atmosphere; • use alcohol to degrease metals.

Use the investigation planning poster to help plan the experiment.

Water that is largely free from dissolved air may be required. This can be made by boiling the water and then covering it with cooking oil or candle wax to stop the air re-entering. However, it is impossible to make water that is entirely free of dissolved air in a school laboratory.

Enquiry skill 8.1.1


3 hours

Corrosion Know that iron will rust in the presence of air and water, and that it can be protected from rusting by oiling, painting, galvanising, coating with plastic, electroplating and tin plating.

Protecting steel from rusting Ask students to list all the ways that they know of protecting steel from corrosion (rusting). They may suggest painting, oiling, galvanising, electroplating, tin plating, coating in plastic. Ask them to devise a fair test to discover which is most effective.

Use ready prepared examples of galvanised, tin-plated or plastic coated steel. If salt water is used to make the steel rust, the results will be visible quickly.

Discuss the advantages and disadvantages of different forms of protection. Ask students to list in a table when each form of protection is the most appropriate and why. Give help if necessary by putting some of the details on the board or OHP.

Terminology: Be clear about the distinction between iron and steel. Pure iron is very rare. It is a soft metal that does not rust easily. The addition of small quantities of carbon makes steel, which is harder but more susceptible to corrosion. Common objects that we often describe as being made of iron (e.g. ‘iron’ filings) are in fact made of steel. It is, however, the element iron in the steel that corrodes.

Unit 8M.2



Hydrogen Demonstrate safely how hydrogen burns or explodes. This is easier if a cylinder of hydrogen is available. Soap bubbles blown with hydrogen rise rapidly and can be ignited. Demonstrate the hydrogen and air explosion in a test-tube as an example that students can copy. Note the formation of condensation when hydrogen burns; this can be shown to be water using cobalt chloride paper.

Ask students to write word and symbol equations for all reactions. They may need assistance.

Safety: If using a hydrogen cylinder, make sure that it cannot fall over and that the prescribed valve is fitted. Hydrogen is very explosive when mixed with air or oxygen. Always test a small sample before lighting it to ensure it is not mixed with air. Students should not prepare hydrogen in anything larger than a test-tube.

1 hour

Properties of hydrogen Know that the test for hydrogen is that it explodes when mixed with air and ignited.

Ask students to work in groups to prepare and test hydrogen. Tell them to generate the hydrogen from granulated zinc and dilute acid, and ensure they follow instructions to collect hydrogen in a separate tube and identify it by the characteristic explosion with air. Suggest that they add a small quantity of copper sulfate solution to the acid; they will find that this speeds up the reaction. Discuss this as an example of catalysis.

Action of metals on water and acid Recall the corrosion activity at the beginning of the unit. Ask which metals corroded most and which the least. Students have seen that zinc will react with acid to produce hydrogen – ask them to predict what might happen if other metals are added to dilute acid.

Ask groups to test the reaction of a range of metals with water and with dilute acid. Tell them to clean metal samples with emery paper or steel wool and place the samples in test-tubes containing about 2 cm of the liquid. Ask them to test any gas evolved for hydrogen. Allow all samples to stand for at least 1 hour, preferably until the next lesson. Ask students to look carefully to see whether a reaction has occurred and, when it has, to test the residual solution with litmus paper. Careful observation is needed with some samples; there is a reaction between magnesium and water, for example.

Demonstrate the reaction between sodium and water and potassium and water.

Ask students to summarise the results in a table and draw valid conclusions. Is it possible to arrange the metals in order of reactivity, and is the order the same for both experiments?

1 M sulfuric acid can be used. Suggested metals are Ca, Mg, Al, Cu, Fe, Zn, Pb.

Safety: Take appropriate precautions when handling sodium and potassium. Use very small samples, cover the trough with a glass lid and use a safety screen. Students must not handle these metals and should stand a distance away from the demonstration.

Enquiry skills 8.1.1 and 8.1.2

The reaction of metals with oxygen Students may have seen these reactions demonstrated as part of Unit 7M.4. The demonstration may be recalled or repeated. The metal should be very hot or burning before it is lowered into the gas jar containing oxygen. The gas jar should have a little water in it which can be mixed with the smoke and tested with litmus paper. Ask students to write their observations in the table used in the previous activity and to draw valid conclusions about the reactivity order.

The reactivity order for all experiments is the same; it reflects the general reactivity of the metals. Ask the class to write down the symbols of the metals in reactivity order. Then ask them to note where in the periodic table the metals appeared and make some general conclusions about the reactivity of metals in the different blocks of the table.

Safety: If possible, use an oxygen cylinder. Make sure that the cylinder cannot fall over and that the prescribed valve is fitted. Other methods of making oxygen all carry hazards. So, if oxygen has to be prepared, do it before the lesson.

Demonstrate Na, Mg, Fe (wool), Zn, Cu.

5 hours

Metal reactivity series Deduce a reactivity series for common metals based on their reactions with air, oxygen, water and dilute acids.

Know that when metal reacts with air, oxygen or water, an oxide or hydroxide is formed and that if this is soluble in water, the solution is alkaline.

Correctly place a metal in the reactivity series based on experimental evidence.

Understand that reactive metals can displace less reactive ones from their compounds.

Account for the anomalous behaviour of aluminium in its reactions with air, water and dilute acids.

Placing an unknown metal in the reactivity series Provide students with samples of unknown metals and ask them to investigate the reactivity of the metals in several different ways and then place them on the reactivity series.

Suitable metals include Li, Ni and Sn.



Aluminium Draw the attention of more advanced students to the anomalous behaviour of aluminium. In many of the experiments, it may appear unreactive. Sometimes it may appear unreactive to start with and then suddenly begin to react vigorously. Ask students to carry out some tests by cleaning a piece thoroughly and watching it. It will tarnish rapidly. Then ask them to clean another piece and quickly add it to acid. They should see evidence of immediate reactivity.

Describe the resistant oxide coating that is normally present on the metal. This allows it to be used for many purposes even though it is as reactive as magnesium underneath the coating. The reactivity shows when the coating is disrupted. This will be followed up in Unit 8M.3.

Displacement series Show the class that, when a piece of zinc is placed in some copper sulfate solution, it rapidly becomes coated with a deposit of copper. Ask them where the copper must have come from. Ask them to suggest a reaction. Show the displacement reaction on the board or OHP as a word equation.

Split the class into groups and allow each group access to several different metals and to solutions of a salt of each metal. Ask them to place pieces of one metal in solutions of salts of all the others and to look carefully for a reaction (which may be quite slow). Tell them to tabulate the results in a grid. Ask for conclusions. It is quite easy to see that a metal will displace from a solution of its salt any other metal that is below it in the reactivity series.

Ask students to write word equations for any reactions they observed.

Less advanced student may find this activity difficult.

Possible metals include Mg, Cu, Pb, Zn, Al, Fe.

Use 1 M solutions of soluble salts of the metals.

Additional spectacular displacement reactions can be demonstrated by heating oxides of less reactive metals with powdered magnesium or zinc. The thermit reaction between iron oxide and powdered aluminium may be demonstrated.

Safety: Demonstrations that involve heating metal oxides with magnesium or aluminium powder should only be done in class after practice outside lessons. Appropriate safety precautions should be taken. The thermit reaction should be done outside with students standing well clear.


Assessment



Rashid was investigating the rusting of iron. He set up five experiments as shown below, and left the test-tubes for three days.

He wrote the following observations in his book.

Test–tube Observation

A

B

C

D

E

nail slightly rusty

nail still shiny

nail still shiny

nail very rusty

nail slightly rusty, bubbles of gas seen

a. Explain why the nails had not rusted in test-tubes B and C.

b. Is vinegar acidic, alkaline or neutral? When the iron reacted with the vinegar, bubbles of gas were formed. What gas was formed?

[continued]

Unit 8M.2



[continued] c. Before putting the iron nail in test-tube D, Khadija weighed the nail. After three days she dried

and weighed the nail and the rust which had formed. How did the total mass of the nail and rust compare with the mass of the nail at the beginning? Give the reason for your answer.

d. Rashid concluded that the presence of salt in the water made the nail rust more quickly. Explain why he drew that conclusion from his experiments.

QCA Key Stage 3, 2001, level 6

a. Consult the metal reactivity series constructed by investigating the action of metals Na, Mg, Al, Zn, Fe, and Cu with air, water and acids. Where in the reactivity series would you place the following metals?

i. Lithium, Li, reacts vigorously with acids and bubbles are produced rapidly when it is put in water.

ii. Nickel, Ni, tarnishes very slowly when heated in air and does not react with dilute acids.

b. Calcium comes between Na and Mg in the reactivity series. Predict its action with water.

c. Cobalt comes below iron in the reactivity series. Predict what would happen if you placed some zinc into a solution of cobalt chloride.

Enquiry skill 8.1.2

These reactions may be tried out to test the predictions

The diagram shows the production of hydrogen.

a. Name a metal that can be used for this reaction and one that cannot.

b. What does this experiment tell you about the solubility of hydrogen in water?

c. If you took a test-tube of the gas and opened it near a flame, what would you see and hear happening? Condensation will be seen on the inside of the tube; where does this come from?



Uses of metals

About this unit This unit is the third of four units on materials for Grade 8.

It is desirable that students should have studied Unit8P.3 on heat and temperature before they embark on this one.


The teaching and learning activities should help you to plan the content and pace of lessons. Adapt the ideas to meet your students’ needs. For extension or consolidation activities, look at the scheme of work for Grade 10 and Grade 8, (Unit 8M.2)


Introduce the unit to students by summarising what they will learn and how this builds on earlier work. Review the unit at the end, drawing out the main learning points, links to other work and ‘real life’ applications.

Previous learning To meet the expectations of this unit, students should already be familiar with the common chemical reactions of metals and with the reactivity order of metals. They should also be familiar with some of the common physical properties of metals, such as good conductivity of heat and electricity, and magnetism.

Expectations By the end of the unit, students know that the ease of extraction of a metal from its ore depends on its position in the reactivity series. They know that metals are malleable, ductile and good conductors of heat and electricity, and they link the uses we make of well-known metals to their particular chemical and physical properties. They contrast the physical properties of metallic and non-metallic elements.

Students who progress further explain a number of properties of metals and alloys in terms of the crystalline structure and the metallic bond. They explain why some alloys can be made into strong permanent magnets that retain their magnetism well. They cite the sequence of reactions in a furnace that uses carbon to reduce ores and understand the role of limestone in the process.

Resources The main resources needed for this unit are: • collection of objects showing uses of a variety of different metals • alnico magnet • class sets of DC power supplies • Internet access

Key vocabulary and technical terms Students should understand, use and spell correctly: • anode, cathode • metal, non-metal • names of common metals, such as: sodium, potassium, magnesium,

aluminium, zinc, iron, lead, copper, silver, gold • conductivity, malleability, ductility, flexibility • alloy • names of common alloys, such as: steel, brass, bronze, solder,

cupronickel, duralumin • occurrence, ore, flotation, smelting, electrolysis • oxide, basic, acidic

UNIT 8M.3 10 hours





8.13.1 Deduce a reactivity series for common metals based on their reactions with air, oxygen, water and dilute acids.

8.13.8 Know that the ease of extraction of a metal from its ore depends on its position in the reactivity series.

10A.18.7 Describe, with essential chemical reactions, the extraction of steel from iron ore and recycled scrap iron in the electric arc furnace.

8.13.9 Know that metals are ductile, malleable and good conductors of heat and electricity, and that these physical properties vary from metal to metal.

8.13.13 Explain the physical properties of metals by the particle theory.

8.13.10 Link the properties and uses of some well-known metals, such as gold, silver, copper, iron and aluminium.

8.13.11 Know that some metals, such as iron and nickel, can be magnetised.

4 hours

Properties and uses of metals

4 hours

Making metals

2 hours

Metals and non-metals

8.13.12 Contrast the physical properties of metallic and non-metallic elements.

Unit 8M.3


Activities


Exhibition of metals and their uses This topic covers what we use metals for, where we get them from and how we make them. To start the topic, make an exhibition that shows the large range of uses that we have for metals. Include as many uses as possible, from tools to electronics, from jewellery to the construction industry.

Ask the class to help you make the exhibition by bringing in interesting items from home and downloading pictures from the Internet to make a collage of metal uses.


Enquiry skill 8.1.6


Physical properties of metals Recall work on the heat conductivity of metals in Unit 8P.3. Ask the class which metals conduct heat best and which the worst. Ask a similar question about electrical conductivity. Put on the board two lists of metals showing the order of how well they conduct heat and electricity. Draw the attention of the class to the similarity between the lists.

Give out some samples of common metals in sheet form. Ask students to describe them. Ask how easily the metals bend and how soft or hard they are. Tell students to place the metals in order for each of these properties.

Show the class some samples of metal wires. Ask them how they think the wires are made. If possible, show some video clips of wire being made from a hot metal ingot.

Introduce and define on a posted word list for the unit some important words that describe some of the properties of metals, such as malleable, ductile, flexible, conductor.

Ask the class to summarise all the physical properties of metals in their books. Give help where appropriate.

4 hours

Properties and uses of metals Know that metals are ductile, malleable and good conductors of heat and electricity, and that these physical properties vary from metal to metal.

Link the properties and uses of some well-known metals, such as gold, silver, copper, iron and aluminium.

Uses of metals In this topic, relate the uses of metals to their properties and also how much it costs to produce them. Set students the task of finding out, from books or the Internet, the main uses of the metals aluminium, copper, gold, iron (steel), lead, silver, tin and zinc. Ask more advanced students to provide information on rarer metals, such as niobium (columbium), tantalum, tungsten and platinum.

Tell students, working in groups, to share information and make a table in their books that contains three columns: the metal’s name, the uses of the metal, and the reason for the use.

Ask groups to share what they have found out. Summarise the information on the board or OHP, adding information of your own when there are gaps. Tell students to complete their tables.

Give some time to a discussion of the uses of rarer metals, such as tungsten (incandescent light filaments), niobium and tantalum (electronic components in mobile phones and other instruments), and platinum (car exhaust catalytic converters).


Enquiry skill 8.1.6

Unit 8M.3



Explaining it all by particles Recall work on particles in Grade 7. Show diagrammatically on the board or OHP the structure of metals, in which the particles are arranged in rows and layers.

Ask what students think might happen to the rows of particles when a metal is stretched and when it is bent. It is likely that some will suggest that the particles move further apart. Tell them that the forces holding the particles together are very strong and will stop any gaps appearing between particles. Remind them that, if gaps appear, the metal will contain spaces and so its density (Grade 7) will decrease. This does not happen. Explain that the layers of particles move easily over each other and the particles can easily rearrange into fewer layers when the metal is bent or stretched.

Introduce more advanced students to the metallic bond (this is covered in Grade 9), which can show how the sea of electrons is likely to make movement of layers easier and will also facilitate the conduction of heat and electricity by moving electrons.

Alloys Explain to the class that steel is mainly iron but it also contains some carbon, and that the amount of carbon it contains affects the properties of steel. Show some different kinds of steel: sheet mild steel, knives, a toy car (cast iron). If possible, show the difference in the crystalline structure between the metals involved (pictures can be found on the Internet).

List on the board a few common ‘special steels’ and their uses, such as steels with vanadium or chromium added. Describe how the added metal changes the properties of the steel.

Summarise the discussions in the form of a table.

Ask more advanced students to find out how and why heat treatments affect the properties of steel – beating when it is molten makes it softer, quenching makes it harder.

Define the concept of an alloy, using steel as an example.

Ask students to find out more about the properties and use of alloys by setting them library tasks such as: • find out what modern aircraft are made of and why; • find out what coins are made of; • find out what is meant by ‘9 carat gold’; • find out what metal statues are made of and why; • find out what solder is made of.

Summarise their answers in a table on the board or OHP and discuss the importance of alloys. In particular, it is important to note that alloys very often have new and useful properties that the constituent metals do not have.

Encourage advanced students to study how the particle theory can explain why alloys are often much harder than the main metal they are made from.



Magnets Students should know that iron, cobalt and nickel can all be magnetised. Remind them of the particle model of a magnetised metal, in which the particles are ‘molecular magnets’. When these are aligned in the same direction, the object is a magnet; when they are aligned randomly, the object is not a magnet.

Show more advanced students how the particle model explains why some alloys, such as alnico, can be made into more powerful magnets that lose their magnetism less easily than pure metals. Show examples of alnico magnets.

Where do we find metals? Ask students to write down the names of the best-known metals in a table in order of their reactivity (work from Unit 8M2), with the most reactive at the top. Ask them what they know about where each of the metals is found. They will probably know that gold can sometimes be found uncombined with any other element in streams and riverbeds. They will probably be able to tell you that the metal sodium is found in salt and that there is a lot of that in the sea.

Provide a list of common metals for them to base this exercise on.

Help students complete the table showing that gold and silver at the bottom of the table are often found uncombined, those metals in the middle (e.g. iron, zinc, aluminium) are often found combined with oxygen or sulfur, while those at the top are often found combined with non-metals such as chlorine. Point out the pattern here: the most reactive metals are found combined with the most reactive non-metals.

4 hours

Making metals Know that the ease of extraction of a metal from its ore depends on its position in the reactivity series.

How do we extract the metals? Ask the groups to try to find out, from books or the Internet, something about the processes of making the three metals gold, iron and aluminium. Alternatively, explain in outline, using illustrative material from the Internet, the three different processes involved. Show that in all cases the initial processes involve extraction from mines or quarries followed by ore concentration.


Extracting and concentrating the ore Produce a flow chart on the board or OHP showing the steps in the process of extracting, concentrating and refining metal ores. Then address each stage of the flow chart in turn. Finally, tell students to make their own flow chart in their books or electronically, using presentation software and downloaded illustrations.

Show, with the aid of photographs, how large-scale mining involves considerable environmental damage. This offers an opportunity to discuss the problem of balancing environmental considerations with satisfying the needs of humans. This discussion should take account of: • the fact that rich deposits of ores are now largely depleted and we are now mining ores of

lower concentration, which often leads to greater environmental damage because of the larger amounts of ore used and the large amounts of waste produced;

• the movement to recycle metals, which is becoming of increasing importance as the price of metals rises.

ICT opportunity: Use of presentation software and the Internet.

The Friends of the Environment organisation in Doha has produced a videotape on ways of encouraging good environmental practices, such as recycling, in schools.



The second point could be reinforced by the school starting some recycling projects, such as collecting used batteries or recycling aluminium drink cans.

Describe, with photographs and diagrams, the froth flotation process that is used to concentrate ores. Give outline details on how it works.

The next step is the chemical extraction of the crude metal. Ensure that students understand that how this is done depends on where the metal is in the reactivity series. Download and show illustrations of extraction using carbon (such as iron electric arc furnace) and using electrolysis (refer to the plans to establish an aluminium smelter at Ras Laffan). Distinguish between extraction using electrolysis (metals high on the reactivity series) and purification using electrolysis.

The electric arc furnace has replaced the traditional blast furnace in most parts of the world.

Metals made from metal oxides – extraction using carbon This process can be simulated in the laboratory with copper oxide on a charcoal block and using a blowpipe to generate the heat. (Clearer results can be obtained using lead oxide because the lead melts into a ball, but lead vapour is toxic and, although it will be produced in small quantities, you may wish to be cautious.). Mix the oxide with a little powdered charcoal before heating on the block. This can be done in groups.

Explain the purpose of the calcium carbonate that is usually added to the ore when this process is used in furnaces to extract metals. Ask more advanced students to consider the whole sequence of reactions in a furnace, showing how the actual reducing agent is the gas carbon monoxide.

Safety: Fire hazard. Ensure that groups use a fireproof mat and that the charcoal blocks are fully extinguished with water at the end of the activity.

Metals made by electrolysis Descriptions of demonstrations of the safe extraction of elements such as calcium or sodium by electrolysis can be found on the Internet, but these should only be undertaken by confident and experienced chemists with due regard for fire precautions.

Students can, however, work in groups to simulate the purification of copper by electrolysis of copper sulfate solution between copper electrodes. Introduce the terms anode and cathode (and place them on the topic word list) and explain that the anode is made of impure copper and the cathode, pure copper. Point out that a large current will produce a layer of copper on the cathode that rubs off easily, whereas a smaller one produces a stable layer.

Encourage more advanced students who are familiar with ions to study the details of the electron transfers involved.

Use about 2 mol/dm3 copper sulfate. Work in a 100 cm3 beaker. Use a DC powerpack, not cells, as the current taken is quite high.



Looking at the elements Show examples of solid metallic and non-metallic elements, particularly common ones such as aluminium, iron, copper, phosphorus, sulfur and iodine. Ask for observations on their physical properties. Demonstrate that the non-metals do not conduct electricity by showing that molten sulfur does not conduct.

Show (and discuss in terms of molecular structure with more advanced students) that carbon is exceptional in that it is a non-metal but that one allotrope, graphite, conducts electricity. If a sufficiently large diamond is available, it can be shown that this form of carbon does not conduct electricity.

Displays of elements arranged in the form of the periodic table are commercially available

Safety: Phosphorus. Use the red allotrope; the white allotrope is a potential fire hazard, particularly in hot climates, as it takes fire spontaneously unless stored under water

Burning metallic and non-metallic elements This activity may be done in groups, but it is advisable that the burning of sulfur and phosphorus should be done either in a fume cupboard or as a demonstration in a well-ventilated laboratory.

Ask groups to set fire to a small amount of the elements magnesium, calcium, sulfur, phosphorus and carbon (charcoal). They should set fire to the element on a spatula and then lower it slowly into a boiling tube containing a little deionised water. The burning will cease. Tell them to shake the tube to mix the air in it with the water and then test the water with pH paper. Give an opportunity for the groups to share results and conclusions that metallic oxides are basic and non-metallic ones, acidic.

Explain the meaning of basic and the difference between basic and alkaline.

Safety. Use a fireproof mat under the equipment. Make sure students do not look directly at burning magnesium.

Enquiry skill 8.1.2

2 hours

Metals and non-metals Contrast the physical properties of metallic and non-metallic elements.

Consolidation Tabulate the differences in physical and chemical properties of metals and non-metals.


Assessment


The list below shows some uses for common metals. In each case explain why the metal is appropriate for this use.

a. Aluminium (in alloys): used to make aeroplanes, cooking pans, high voltage electricity cables, window frames, wrapping chocolate.

b. Copper (in alloys): used to make coins, household electrical wiring, domestic water pipes.

c. Iron (in steel): used to make car bodies, girders in bridges, and for reinforcing concrete in buildings.

d. Tin: used for coating mild steel food cans.

What method is most likely to be used to extract the following metals from their ores? Give reasons for your answers.

a. Zinc.

b. Potassium.

Explain why only those metals at the bottom of the reactivity series were known 2000 years ago.

The table shows the percentage by mass of the most abundant elements in the Earth’s crust.

a. What is the percentage by mass of all the other elements together?

b. Draw a bar chart illustrating the abundance of the metals in the table.

c. Sodium is found mainly as its compound sodium chloride. Explain why most of it is found in the sea.

d. Aluminium is the most abundant metal in the Earth’s crust but iron is the metal that we use most of. Give a possible reason for this.

e Calcium is a very common metal in the Earth’s crust but we have hardly any use for it. Explain why this is so.

Element Percentage Element Percentage

Oxygen 46.6 Sodium 2.8

Silicon 27.7 Potassium 2.6

Aluminium 8.1 Magnesium 2.1

Iron 5.0 Titanium 0.4

Calcium 3.6 Phosphorus 0.1


We often make metals more useful by giving them additional properties by mixing small quantities of other metals to form alloys.

a. What useful properties can be given to iron by adding:

i. 1% carbon;

ii. 4% carbon;

iii. vanadium;

iv. chromium?

b. What useful properties can be given to aluminium by adding magnesium?

c. What useful property can be given to tin by adding lead?

d. What useful properties can be given to copper by adding tin?

Unit 8M.3



Salts

About this unit This unit is the fourth of four units on materials for Grade 8.


The teaching and learning activities should help you to plan the content and pace of lessons. Adapt the ideas to meet your students’ needs. For extension and consolidation activities, look at the scheme of work for Grades 9 and 10A, and Grade 7.



Previous learning To meet the expectations of this unit, students should already be aware of key reactions of acids with metals, carbonates and alkalis. They should have experience in summarising chemical reactions in the form of word equations. Students should also understand that the rocks that make up the Earth’s crust contain pure substances called minerals that have been made by natural processes. A knowledge of the periodic classification of elements is required.

Expectations By the end of the unit, students know the reactions of acids with metals, carbonates and metal oxides. They name a number of common salts and state their uses.

Students who progress further express all neutralisation reactions in the form of word equations. They understand the difference between hard and soft water and know how hard water is formed. They recognise similarities between carbonates and silicates.

Resources The main resources needed for this unit are: • samples of crystalline minerals • samples of salts commonly used in the home • collection of salt crystals of different shapes and colours (e.g. sodium

thiosulfate, copper sulfate, potassium permanganate, lead iodide, potassium dichromate, potassium chromium sulfate), hand lens

• pictures of stalagmites and stalactites • sodium silicate in the form of water glass or dishwasher powder • Internet access

Key vocabulary and technical terms Students should understand, use and spell correctly: • acid, base, alkali, salt, neutralisation • mineral, crystal • limestone, carbonate, hard water, soft water, stalactite, stalagmite • silicate, sand • fertiliser

UNIT 8M.4 9 hours





7.14.7 Know that acids and alkalis react with each other and that the process is called neutralisation.

8.14.1 10A.21.4 Make salts from acids and bases by a variety of methods

7.14.9 Express chemical reactions in the form of word equations

9.13.7 Know that ionic compounds form crystals containing a giant lattice of ions whereas covalent compounds form discrete molecules.

7.14.8 Know that acids react with carbonates to liberate carbon dioxide, which can be identified by bubbling it through fresh limewater.

Know the different reactions by which salts can be made.

8.14.2 Explain why calcium carbonate does not react easily with sulfuric acid

4 hours

Making salts

3 hours

Naturally occurring salts

2 hours

Useful salts

8.14.3 Name a number of common salts and state their uses. 10A.18.4 Know what is meant by hardness in water and how it is produced naturally. Distinguish between temporary and permanent hardness.

Unit 8M.4


Activities


A salt collection Start an exhibition of a variety of different salts; include some from the chemical store showing their chemical names, and some common household salts in packets showing their common names. The purpose of this is to show (a) that salts are very common, (b) that we have many uses for them and (c) their solid crystalline nature. Draw all these points to the attention of the class and ask them, during the course of the topic, to help you increase the size of the exhibition and also to add pictures related to salts, their manufacture and use.

Spend some time clarifying the scientific meaning of the word salt and distinguishing it from ‘table salt’ or ‘common salt’, which is a specific salt – sodium chloride.

Examples of salts in the home are table salt, Epsom salts (magnesium sulfate), lavatory cleaner (often sodium hydrogen sulfate), cream of tartar (sodium hydrogen tartrate), soluble aspirin (sodium acetyl salicylate).


Neutralisation Recall work done in Grade 7 on acidity, in which students showed how an acid can be neutralised by an alkali. Recall that one of the products of this reaction was always a salt. Lead the discussion towards a definition of a salt as the product of neutralisation. Write some chemical names of salts on the board or OHP and show how they always have two halves, the first part coming from the alkali and containing the metal element, the second coming from the acid.

Ask students, in groups, to neutralise hydrochloric acid by stepwise additions of sodium hydroxide solution. Tell them to test after each addition by spotting onto litmus paper and when the paper has turned blue, to add acid dropwise until the litmus test shows a return to red. Then ask them to evaporate the solution to dryness (or to near dryness and then allow to crystallise naturally).

Discuss the product. Do not allow students to taste it but draw their attention to the fact that it has the cubic crystalline structure of common salt.

Help students summarise the reaction in the form of a word equation. Tell them that the second product of neutralisation is water.

Use approximately 2 mol/dm3 solutions.

Enquiry skill 8.3.4

Help students, where necessary, to summarise all reactions in this unit as word equations.

4 hours

Making salts Know the different reactions by which salts can be made.

Converting a metal into its salts Recall and selectively repeat work done in Unit 8M.2 on the reaction of acids with some metals. Repeat the action of sulfuric acid on zinc as an example. Give groups some sulfuric acid and some zinc and allow them to put the zinc in the acid in a boiling tube. Encourage them to test the gas coming off for hydrogen.

When the reaction has finished, there should be an excess of zinc, which should be filtered off and the filtrate concentrated and allowed to crystallise as the salt zinc sulfate.

Ask students to summarise the reaction as a word equation.

Granulated zinc may take quite a long time to react completely. The reaction can be catalysed by adding a tiny crystal of copper sulfate, or a few drops of copper sulfate solution (if a large amount is added it will contaminate the product).

Unit 8M.4



Carbonates, a common series of salts Show samples of limestone and marble. Question students about the origins of both (Unit 7E.1) so that they recall that they are the same compound: calcium carbonate. Confirm, by demonstration or group work, that they are both insoluble in water, even when heated, which is why they are widespread rock forms.

Give a small piece of both to students, in groups, and ask them to test the action of acid on them and to test the gas evolved for carbon dioxide. Ask groups to repeat the previous activity after the action has ceased and the limestone or marble is in excess. The salt isolated will be calcium chloride.

Spend some time discussing the acid part of this series of salts. Ask students to make some of the acid by blowing through water and testing the solution before and after. Explain that the acid is a weak one and is easily decomposed to carbon dioxide and water.

Show that calcium carbonate does not react with dilute sulfuric acid and explain the reason.

Use 2 mol/dm3 hydrochloric acid. Do not use sulfuric acid. Use freshly prepared limewater for the carbon dioxide test.

Looking at salt crystals Give each group a small collection of salt crystals of different shapes and colours and a hand lens to look at them. Ask them to draw conclusions about their physical nature (regular crystalline shapes, often coloured, often soluble). Encourage more advanced students to discuss the ionic nature of the compounds. Students should note that all specimens of the same substance have basically the same crystalline shape but that different salts may have different shapes.

Conclude that all salts are crystalline solids, many of which are water-soluble. Allow students to repeat earlier work on growing salt crystals if time allows. This is a highly motivating activity that could be started in class and then transferred to a science club for those more interested. More advanced students could try growing a chrome alum crystal and then growing it on in potassium alum to create a clear octahedral alum crystal with a black centre, clearly demonstrating the common crystalline structure of the alums.

Add a display of interesting crystalline salts, including crystals grown by class members, to the exhibition.

Good examples are sodium thiosulfate, copper sulfate, potassium permanganate, lead iodide, potassium dichromate, potassium chromium sulfate, as well as some of the more common ones

Some salts are available as cheap commercial grade crystals and can be bought in relatively large amounts for growing crystals. Copper sulfate, alum and chrome alum are good examples. Grown crystals should be painted with colourless nail varnish to prevent efflorescence

3 hours

Naturally occurring salts Name a number of common salts and state their uses

Know the different reactions by which salts can be made

Where can we find salts? Refer the class to the exhibition and recall work done on rocks and minerals in Grade 7. Ask the question ‘Where can we find salts?’ Conclude that some salts are synthetic while others, like minerals, occur naturally. A third category comprises those natural salts that have been purified for use, such as table salt. Show, discuss and place in the exhibition pictures from the Internet of salt purification lagoons, where table salt is made from seawater. Also add a variety of common minerals, or pictures of them, to the exhibition.

Make the point that not all minerals are necessarily salts as some, such as sand and quartz and hematite are oxides. Reinforce the distinction between an oxide and a salt made in Unit 8M.3.

Set students a homework task to find and bring to the classroom information on, and/or examples of, two more salts each. Incorporate these into the exhibition.



More about carbonates Show pictures of stalagmites and stalactites in caves. Explain that they are made of limestone (sometimes coloured by other minerals). Challenge the class for an explanation of how they got there and help them with a comment that they are sometimes quite wet to touch. Conclude that they are left when water drips from the ceiling and evaporates but refer the class to their conclusion that calcium carbonate is insoluble in water. Then set them a task to try to explain this mystery.

Give students, in groups, two water samples, one distilled (or deionised) and one temporarily hard, and ask them to shake both with a few drops of liquid soap (not detergent). Ask them to report the difference. They will note that the hard water makes a scum. Define the term hard water as water that forms a scum with soap.

Then ask them to evaporate some temporary hard water in an evaporating basin and test the residue with a small amount of acid. If they look carefully they will see bubbles. They may even be able to test the bubbles for carbon dioxide.

Explain that they have just done quickly what happens over millions of years to make stalactites. Explain how you made the hard water by bubbling carbon dioxide through a liquid that contained solid particles of calcium carbonate and that process caused some of the calcium carbonate to be dissolved. Explain that in very many parts of the world this process happens naturally and that drinking water is naturally hard. Discuss the formation of the soluble calcium hydrogen carbonate with more advanced students.

Ask students for suggestions as to how this process can happen naturally. Conclude that rainwater dissolves carbon dioxide and that the product can cause the limestone in the rock to dissolve. In the cave, when this solution evaporates, the reverse process happens very slowly, depositing limestone on the stalactite.

Show advanced students the two processes using a word equation.

Discuss the advantages of drinking hard water. Note that calcium salts are added to the Doha distilled water to improve its taste and its health value.

Temporary hard water can be made by bubbling carbon dioxide through a solution of calcium hydroxide and filtering.

What are silicates? Draw the attention of the class to the element silicon in the periodic table. Note that it is in the same column as carbon. Show a sample of silicon and also of silicon dioxide. Draw attention to the differences between the dioxides of carbon and silicon.

Question students to find out whether they can recall what happens when sodium carbonate is added to an acid. Consolidate by writing the word equation.

Make up a solution of sodium silicate (‘water glass’) in front of students and give each group some in a boiling tube. Ask them to add acid slowly and see what happens. The colloidal silicon dioxide formed can be heated to obtain sand, silicon dioxide, as an insoluble solid.

Ask students to write word equations for the reaction between sodium carbonate and hydrochloric acid and that between sodium silicate and hydrochloric acid, showing, in each case, the product left in solution.

Discuss the widespread abundance of silicates in rock and add some examples (or pictures of them) to the exhibition.

Dishwasher powder contains sodium silicate and could possibly be used if water glass is unavailable. Test the process beforehand.



Salts in the home Refer students back to the exhibition. Ask them to make a table in their books showing some details of salts commonly used in the home. They should tabulate: • the common name; • the chemical name; • what the salt looks like; • what the salt is used for.

Tell students to share their results and add to their table.

Discuss the naming of salts, showing the origins of the two halves of the name in the neutralisation process. Discuss also what the suffixes -ide, -ite and -ate tell us about the elements in the salt.

As a homework exercise, ask students to look at the contents of food packets and tins to find ingredients that seem to be salts. The following day, discuss what they have found and explain the purpose of these food additives, using the Internet as an information source if necessary

Enquiry skill 8.1.6

2 hours

Useful salts Name a number of common salts and state their uses

Fertilisers Obtain some bags of fertilisers and show the class the contents printed on the labels. List the salts mentioned.

Discuss the importance of the elements nitrogen, phosphorus and potassium to plant growth. Note which of these elements is present in each of the salts that make up the fertilisers.


Assessment


Noor made some copper sulfate crystals. She wrote a description of what she did.

‘I heated some dilute sulfuric acid in a beaker and added some copper oxide to it. I stirred the mixture until it became a clear blue colour. I added more copper oxide until no more would react and then filtered the mixture into a dish. A black solid was left on the filter paper. I left the solution in the dish for a week and saw that the liquid had gone and blue crystals were left.’

Use the information in Noor’s description to answer the questions below.

a. What colour is:

i. copper sulfate solution?

ii. copper oxide?

b. Write down a word equation for the reaction that took place in the beaker.

____________ + _____________ → ________________ water

c. Why did Noor have to filter the mixture?


Potassium nitrate is used as a garden fertiliser.

a. Name two elements that it contains that are required by plants to grow.

b. It is made from potassium hydroxide. Complete the following word equation for the reaction

potassium hydroxide + _______________ → potassium nitrate + ____________.

c. It can also be made starting from potassium carbonate. Write a similar equation showing the reaction.

d. This reaction produces a gas. Describe a test to identify the gas.

The flow chart shows how a sample of zinc sulfate could be made.

a. The zinc ore contains a mineral containing zinc mixed with many other impurities. Describe one of the processes used to purify it.

b. In the reaction zinc oxide → zinc an element is removed from zinc oxide to leave zinc. Give the name of the element.

c. Zinc sulfate can be made in a reaction between zinc and an acid. Give the name of the acid.

d. Write a word equation for this reaction.

e. A gas is given off during this reaction. Describe how you would identify it.

f. How would you ensure that the solution you have at the end of the reaction contains only zinc sulfate and does not contain any unchanged sulfuric acid?

g. How would you make some crystals of zinc sulfate from the product of this reaction?


Name three salts commonly found in the kitchen and state their uses.

Unit 8M.4

227 | Qatar science scheme of work | Grade 8 | Unit 8E.1 | Earth and space 1 © Education Institute 2005

GRADE 8: Earth and space 1

The Solar System

About this unit This is the only unit on Earth and Space in Grade 8. This unit builds on work done in Grade 6 and leads into work on the wider Universe in Grade 9.

The unit is designed to guide your planning and teaching of lessons on Earth and space. It provides a link between the standards for science and your lesson plans.




Previous learning To meet the expectations of this unit, students should already know how the relative movement of the Sun, Earth and Moon causes day and night, the seasons and the phases of the Moon. They should know that the Sun is a star and, like all stars, is a source of light, whereas we see the Moon in reflected light.

Expectations By the end of the unit, students explain night and day, eclipses, seasons and phases of the Moon in terms of the Sun–Earth–Moon system. They describe the relative positions of the planets and their conditions compared with conditions on Earth, and identify some planets in the night sky. They know that the Sun is a star and that it radiates light and heat but that we can see the Moon and the planets because they reflect light from the Sun. They recount a number of uses for artificial satellites. They assess evidence for our modern understanding of the Solar System and show how this understanding has evolved over time.

Students who progress further explain how the Moon causes tides and explain spring and neap tides. They explain how a geosynchronous satellite can appear stationary. They identify visible planets in the night sky and explain why Venus and Mercury are only visible either in the evening or in the morning. They know that our understanding of science often proceeds in major leaps and that these can be difficult for societies to accept. They explain the origins of the Solar System.

Resources The main resources needed for this unit are: • star maps and access to a telescope • data and photographs from the planets sent back by US planetary

exploration spacecraft • Internet access • display software and projection equipment

Key vocabulary and technical terms Students should understand, use and spell correctly: • spring tide, neap tide, gravity • seasons, lunar eclipse, solar eclipse • satellite, orbit, geostationary • planet, asteroid, rotational period, orbital period, moon • names of the planets • star, ecliptic, comet • astronomical unit

UNIT 8E.1 8 hours



8 hours SUPPORTING STANDARDS CORE STANDARDS Grade 8 standards

EXTENSION STANDARDS

6.13.1 Know that the Sun and stars are light sources and that the Sun is the source of our daylight.

8.15.1 Explain night and day, eclipses, seasons, tides, and phases of the Moon in terms of the movement and relative sizes of the Sun, Earth and Moon.

6.13.6 Know the causes of eclipses of the Sun and the Moon.

8.15.2 Describe the relative positions of the planets, and their conditions compared with conditions on Earth.

9.17.6 Describe how planets are formed when a star attracts the remains of an older exploded star into a disc around it by gravitational attraction.

6.13.7 Know that the Earth orbits the Sun once every year.

8.15.3 Be able to identify some planets in the night sky; know that we can see them and the Moon because they reflect light from the Sun.

6.13.2 Explain that we see the Moon at night because it is an illuminated object that reflects light from the Sun.

8.15.4 Know that the Sun is a star and that, like all stars, it radiates light and heat. 8.15.5 Know that the source of the Sun’s heat and light is a nuclear reaction in which matter is turned into energy.

8.15.6 Recount a number of uses for artificial satellites.

8.15.7 Assess evidence for our modern understanding of the Solar System and show how this understanding has evolved over time.

8.15.8 Understand the importance of the Sun–Earth–Moon system in telling the time. Know the reasons for the differences between the Islamic calendar and the Gregorian calendar.

3 hours

The movement of the Earth and Moon

5 hours

The Solar System


Unit 8E.1


Activities


If possible, work on this unit should involve some observations of the night sky. If there is no telescope or observatory that students can visit, much can be done using only binoculars. A star map should be obtained and displayed.

Star maps can be downloaded free from a number of websites such as http://www.skymaps.com and http://www.bbc.co.uk/science/space/myspace /nightsky/observingnotes.shtml.

Multimedia astronomy software is also available.


Recall work from Grade 6 on the movement of the Earth. Ask students to explain the cause of day and night and the seasons and eclipses. Use a model if one is available. Ensure that students understand that the Sun is a star and radiates light and heat. Correct any errors.

Tides Obtain tide tables for Doha harbour, preferably showing the days of the neap and spring tides each month as well as daily high and low tides. Note that high tides occur about every 12.5 hours: about two high tides per day. Ask students if they can recall the position of the Moon in the sky at the high tide point during the night (it is a good idea to do this around full Moon). Show on a model the position of the Moon at each high tide point during the day, noting that at high tide the Moon is either overhead or diametrically at the other side of the Earth. Ask for suggestions about what might cause the tides. Remind students that the Moon exerts a gravitational pull and that this can cause the water and air on Earth to bulge in the direction of the Moon. It is more difficult to explain the second bulge in the opposite direction (but you could talk about the Moon attracting the Earth away from the seawater).

More advanced students will probably be able to understand and explain, in terms of the movement of the Moon, why the tidal cycle is about 25 hours and not 24. They may also be able to offer an explanation for neap and spring tides if they are reminded that the Sun also exerts a gravitational attraction on the Earth (of about a fortieth the size of that of the Moon).

Java applets showing how the tides are affected by the positions of the Sun and the Moon can be found on the Internet.

3 hours

The movement of the Earth and Moon Know that the Sun is a star and that, like all stars, it radiates light and heat.

Explain night and day, eclipses, seasons, tides, and phases of the Moon in terms of the movement and relative sizes of the Sun, Earth and Moon.

Recount a number of uses for artificial satellites.

Understand the importance of the Sun–Earth–Moon system in telling the time. Know the reasons for the differences between the Islamic calendar and the Gregorian calendar.

Artificial satellites Obtain data on the orbit of a large artificial satellite such as the International Space Station (ISS) and ask students to look out for it when it is visible in the evening or early morning (i.e. when it is not in the Earth’s shadow) over Qatar. Ask them why it is possible to see such satellites? Some students may have noticed that the satellite they saw may have suddenly apparently disappeared; challenge them for an explanation.

Ask students to list all the uses of artificial satellites that they can think of. If possible, show them some in the classroom (e.g. satellite radio and TV, GPS (Global Positioning System) including photographs from satellites such as the Hubble Space Telescope and the ISS). This activity can be turned into a useful and interesting display.

Explain that all satellites must be moving in order to stay in orbit. Use a ball on a string (outside) to demonstrate that if a satellite slows it will no longer continue to orbit. Show also that the longer the string, the longer will be the period of orbit. Challenge them to explain how it is possible for a TV or radio satellite to remain always in the same place in the sky.

Sightings of the ISS for all major cities are listed on the NASA website at spaceflight1.nasa.gov/realdata/sightings/

Unit 8E.1



Calendars Some students may have done an exercise in Grade 6 to compare the Saudi Islamic and Gregorian calendars, such as that set out in Lesson plan 6.4. Re-examine this here, with a greater emphasis on how calendars have evolved to overcome the difficulty of using the lunar month as a unit in a calendar that, for agricultural reasons, must be based on seasons. Lesson plan 6.4 shows the Gregorian compromise made in the traditional length of the lunar month so that the calendar year has exactly twelve months.

Information on the World’s calendars can be found on http://webexhibits.org/calendars/index.html

Lesson plan 6.4

The planets Tell students to work in groups and ask each group to find out all they can about one planet. The Internet is an important source of information, and good photographs of all the planets exist. Tell groups that the main object of their work is to create a display and make a presentation to the others about their planet. This can be done using display software and projection equipment if it is available.

Create a large outline table to contain basic information about the planets and ask each group to complete the column for their planet. The information can include such details as size, distance from the Sun, rotational and orbital periods, surface temperature, number of moons and nature of the atmosphere.

Introduce students to the astronomical unit as a convenient unit of length for recording planetary orbit radii.

Ensure that students realise that we see the planets because they reflect light from the Sun, in the same way as the Moon.

ICT opportunities: Use of the Internet. See the NASA website for photographs from various planetary missions. Use of display software.

Enquiry skill 8.1.6

5 hours

The Solar System Describe the relative positions of the planets, and their conditions compared with conditions on Earth.

Be able to identify some planets in the night sky; know that we can see them and the Moon because they reflect light from the Sun.

Assess evidence for our modern understanding of the Solar System and show how this understanding has evolved over time.


Observing planets If possible, arrange opportunities for students to observe the ‘naked eye’ planets using a telescope. The positions of these planets in the night sky are published on many websites. Useful observations to make are of: • Venus, which is always visible only partially illuminated, like a new Moon. • Mars, noting its red colour. With a good telescope, its one moon can be seen. • Jupiter, whose four large moons are visible clearly in a telescope; plot their movement over

several hours (or days). A good telescope will show the ‘red spot’. • Saturn, whose rings are clearly visible, as is its largest moon, Titan.

Tell students to keep a diary of their observations, including sketches where appropriate.

Ensure that students can identify the visible planets in the night sky using a star map. Explain that they are all to be found on the ecliptic, the plane bounded by the apparent path in the sky followed by the Sun and the Moon, and have characteristic features such as brightness and colour. Challenge students in class to explain, using models if necessary, why the planets are only visible on the ecliptic and why Venus (and Mercury) is only visible in the evening and the morning.



Galileo and Copernicus Ask students to find out about the history of our understanding of the relative motion of the Earth and the Sun, especially the work of Copernicus and Galileo. Of particular interest is the difficulty experienced in the seventeenth century by Galileo in publishing his observations and conclusions that the Earth moved around the Sun when the conventional view (held as sacred by the powerful Catholic Church) at the time in southern Europe was the opposite. Copernicus, living in a different part of Europe, did not face this opposition when he published the same conclusions.

Encourage more advanced students to reflect on other major changes in scientific understanding that they have studied (e.g. Newton and gravity) and note that our scientific understanding often develops by major leaps that are sometimes controversial and not readily accepted by the societies in which the scientists live. Advise them that in Grade 9 they will meet more examples when they study the work of Mendel and Darwin in biology and Bohr’s atomic theory.

Pages on the work of these two scientists can be found on the Internet. Of particular interest to this unit is Galileo’s telescopic observations of Venus and of the moons of Jupiter, both of which were important evidence to suggest that Earth was a planet.

Enquiry skill 8.2.2

How the Solar System was formed Ask students to search on the Internet or in books for ideas on the origin of the Solar System. Two ideas may emerge: one is that matter was thrown out of the Sun and condensed and coalesced to form the planets; and the second – now universally accepted – is that the Sun attracted some debris from a long-exploded star or other source and that this formed a disc that gradually coalesced into planets. Ask students to assess the evidence for and against these ideas. You may have to provide some of the evidence if students do not.

The possible origins of the asteroid belt as an example of a planet in the process of gradually forming, or as an example of a planet that has in the past formed but then been disrupted by a major impact can be discussed. Discuss the asteroid belt. Ask students to consider whether it could be, for example: • an early stage in the formation of a new planet; • the result of the destruction of a planet by a major impact; • the material left over after the formation of the planets.

Ask advanced students to evaluate evidence for asteroid impacts on Earth in the past, in particular the theory that links such impacts with extinctions of major species, such as the dinosaurs.

Teach advanced students about the Kuiper belt, the origins and orbit of comets, and the cause of the comet ‘tail’.


Current estimates put the age of the Solar System at about 4.5 billion years.

Enquiry skill 8.1.6?


Assessment


Which of these diagrams best represents the movement of the Sun, Earth and Moon?

Draw a diagram to show the positions of the Sun, Earth and Moon at the time of a spring tide. Explain why this arrangement causes such a high tide.

Explain, using a diagram, why the planet Venus is never seen overhead in the night sky.

State two similarities between Earth and the planet Venus. State two differences between Earth and the planets Saturn and Jupiter.

Scientists are interested in knowing whether life exists on any of the other planets in the Solar System. Provide arguments for and against the possibility of life existing on the planets Venus, Mars and Jupiter.


The diagram below shows an eclipse.

a. State whether this is a solar or a lunar eclipse.

b. From the diagram, decide which of the following statements is true.

A. The eclipse can only occur when there is a new Moon.

B. The eclipse can only occur when there is no Moon visible in the sky.

C. The eclipse can only occur when there is a full Moon.

D. The eclipse can only occur during the winter.

Unit 8E.1

233 | Qatar science scheme of work | Grade 8 | Unit 8P.1 | Physical processes 1 © Education Institute 2005

GRADE 8: Physical processes 1

Energy

About this unit This unit is the first of four units on physical processes for Grade 8. It must be studied before Unit 8P.3 on heat

The unit is designed to guide your planning and teaching of lessons on physical processes. It provides a link between the standards for science and your lesson plans.

The teaching and learning activities should help you to plan the content and pace of lessons. Adapt the ideas to meet your students’ needs. For extension activities, look at the scheme of work for Grade 9.



Previous learning No previous knowledge of energy is required.

Expectations By the end of the unit, students classify common energy forms as kinetic or potential. They know that energy can be transformed from one form to another, and that the total energy remains constant during a transformation. They know heat is always produced during energy transformations and that getting rid of it is often an engineering problem. They assess the contributions of specific scientists.

Students who progress further carry out simple calculations on energy using joules. They understand that most energy that we use originally came from the Sun. They compare the amounts of energy used to make common objects. They know the contribution of Joule to our understanding of energy.

Resources The main resources needed for this unit are: • collection of potentially useful everyday materials

Key vocabulary and technical terms Students should understand, use and spell correctly: • energy transformations • forms of energy: light, heat, sound • kinetic energy, potential energy • joule

UNIT 8P.1 10 hours





8.16.1 Classify common forms of energy as either kinetic or potential energy.

8.16.2 Give examples of processes and devices that transform one form of energy into others.

9.16.6 Describe the different ways in which we can harness energy from the Sun, either directly or indirectly through wind energy and hydropower.

8.16.3 Know that during energy transformations energy is converted from one form to others but that the total energy remains the same.

8.16.4 Know that heat is produced in all energy transformations and that getting rid of waste heat energy is an engineering problem in many energy transformations.

8.17.3 Know that heat is transferred by conduction, convection and radiation and cite everyday examples of each.

8.16.5 Know that the petrochemical complexes in Qatar use seawater to remove waste heat and know why there are strict regulations that control the temperature of the seawater that is returned to the sea.

8.16.6 Know and use the joule as the unit of energy.

3 hours

What is energy?

5 hours

Changing energy from one form to another

2 hours

Measuring energy


Unit 8P.1


Activities


Energy concept map Show students how to draw a concept map around the word energy that illustrates what they understand the word to mean. Give them some time to do their individual maps and then collect data for a collective one on the OHP or board (or on a flip chart so that it can be saved). This exercise should reveal the variety of understandings that students have about energy. It will also tell you something about the misconceptions that you have to address and will determine how you plan the unit. The concept mapping exercise will be repeated at the end of the unit.


Twin pendulum challenge Set up two identical pendulums hanging from a piece of string or rope fixed horizontally between two suitable points. They should be about 25 cm apart. Make sure that both are still and then set one (only) moving at right angles to the horizontal string. Challenge students to explain what they see. If they do not explain the result in terms of transfer of energy from one pendulum to another, leave the question open and return to it later in the unit.

What things have energy? Ask students what kinds of things have energy. Some will probably suggest that food contains energy. Ask them to look, at home, on the labels of some foodstuffs for their ‘energy value’. Have some food labels in class to show as well.

Demonstrate that food contains energy by burning a sugar lump on a tin lid. Once ignited it will burn by itself. Let students try this in groups.

Give students data to plot a bar graph of the energy in a fixed mass of different foodstuffs as stated on the label. Include, for comparison, the energy in different fuels (e.g. Qatar gas, wood).

Ask if a book has energy. Some may reply that it must have because it is made out of paper and will burn. Then ask them if a book has any other kind of energy? Have ready a metre rule pivoted over a fulcrum such as a torch cell. The cell should be about 20 cm from one end. On the end place a rubber eraser or something similar. Drop the book on the raised end so the eraser flies into the air. Discuss whether the book had energy and why. Ensure they are familiar with the idea that the book has energy because of its position and that this is called gravitational potential energy (often just potential energy).

Ask students for other examples of objects that have energy. They will make many suggestions. List the sensible ones. An important one is themselves. Ask them if they can imagine life without energy.

The units of energy on many food labels will be archaic, particularly if the food is packed for the US market. Have conversion tables ready so that you can quickly translate any label into SI units. Note also that when US food labels refer to ‘calories’ they usually mean kilocalories.

3 hours

What is energy? Classify common forms of energy as either kinetic or potential energy.

Arriving at a definition of energy Ask students to try to provide a definition of what energy is. Avoid the ‘book’ definition at this stage and try to arrive at a phrase that incorporates as much as possible of their ideas but which is also scientifically acceptable. It may be something like ‘energy is something that is needed to do things or to make things happen’.

Return to the twin pendulum challenge and ask what is happening to the energy that you gave the first pendulum.

Unit 8P.1



Different forms of energy Refer back to the activities involving burning sugar and dropping the book. Ask students to describe the energy in the two objects before the experiment and what happened to it. Ask them to convert their answers into a flow chart. Refer again to the ideas of ‘energy of position’ being converted to ‘energy of movement’, and chemical energy being converted into heat energy; ask them to rewrite their flow charts to describe what happened to the energy in each case.

Introduce the key idea that energy is never made from nothing and is never destroyed; it is converted from one form to others. Write this clearly on the board or OHP. Set up a circus of activities such as those that follow and ask each group to go around the circus. They should, for each circus activity, follow the instructions and at the end, write a flow chart showing all the energy conversions they observed. Assist them with their observations as they go around the circus; ask, for example. whether they notice heat produced during any or all of the conversions.

After all groups have completed the circus, agree on an energy conversion flow chart for each one. Note particularly whether they think all the energy was accounted for or did some of it get ‘lost’.

Ideas for the energy conversions circus: • Switch on a radio. • Switch on a torch. • Stretch a rubber band and shoot a paper pellet. • Set up a small electric motor powered by a solar cell. • Ask students to use their muscles to perform some kind of activity, such as stepping up or

lifting some thing rapidly 10 times in succession. • Make a paper windmill and blow it. • Create a ‘come-back’ can using a mass and a rubber band inside. • Rub fingers on the desk. • Cut a spiral out of paper and hang it from its centre over a candle flame • Chimney windmill. Make a chimney out of three food cans with their ends removed, one on top

of the next. Paint the outsides black. Support the bottom one on two bricks so that air can get in the bottom. Hang a spiral over the end of the top one and put the whole chimney in the sun.

• Make a jet balloon by taping an inflated balloon to a straw. Hold the neck of the balloon so that the air does not escape. Thread the straw on a tight horizontal string so that the balloon will go along the string when you let go of its neck.

Enquiry skill 8.1.3 Safety: Make sure students do this safely.

5 hours

Changing energy from one form to another Classify common forms of energy as either kinetic or potential energy.

Give examples of processes and devices that transform one form of energy into others.

Know that during energy transformations energy is converted from one form to others but that the total energy remains the same.

Know that heat is produced in all energy transformations and that getting rid of waste heat energy is an engineering problem in many energy transformations.

Know that the petrochemical complexes in Qatar use seawater to remove waste heat and know why there are strict regulations that control the temperature of the seawater that is returned to the sea.

Where does energy go to? In some of the activities of the circus, and in the demonstration involving dropping the book, energy appeared to be ‘lost’; ask students what they think happened to it.

Give another demonstration. Hang a football or something heavy on the end of a long string from the classroom ceiling. Ask one student to pull the football to one side and sit so that it is just touching her nose. She must then let go of the football and must not move at all. The football will return to her face but will not quite touch her nose. What is happening to the energy of the ball?



A similar experiment can be done using a weight hanging on a long spring. Start the spring oscillating by holding the mass on the desk. It will not touch the desk on the second oscillation.

Link the discussion with Unit 7M.1 on particles and ask what will happen to the millions of air particles hit by the pendulum bob or the spring load. Some of the movement energy will be given to them. Advanced students may be able to link increased particle movement to temperature after completing Unit 7M.1. The lost energy of the pendulum appears as heat energy in the air but the temperature rise is undetectable.

In a number of the other examples in the circus, energy lost as heat will be evident (the torch and the radio for example). Quote more examples of energy transfers where waste heat is more evident (e.g. a car engine).

Ask how waste heat is managed in energy transfer systems such as: • a car engine (heat is transferred to circulating water and is in turn transferred to air blowing

through the radiator); • a computer (heat is transferred to air blown over the processor by a fan); • you (heat is transferred to water on the skin, which evaporates).

Refer, with pictures, to the disposal of waste heat in industry in Qatar. Waste heat at Ras Laffan is taken away to the sea using seawater. The outlet is never allowed to be more than 4 °C higher than the seawater inlet (discuss why). In Doha power station, the waste heat is used to distil seawater to make potable water.

Where does all our energy come from? Ask the class where we get our energy from. Ask them to think of all the different kinds of energy we use and where it all came from in the first place. This will link to work in biology in Grade 7 on food chains and in this grade on photosynthesis. It will also prepare the ground for work in Grade 9 on energy resources.

Interpret some of their ideas as flow charts. Lead to the conclusion that much of our energy came originally from the Sun. Show how the energy in the wind and in waterfalls comes originally from the Sun (water cycle Grade 5). Other primary sources of energy are fuels such as gas. Teach more advanced students about the origins of this energy in times past (to be covered in Grade 9).

As a consolidation exercise, get the class to draw complete flow charts showing the origins and fate of all the energy in a number of energy conversions (e.g. a radio, a bicycle, a camel, an apple).

Ask more advanced students to consider the energy used to manufacture particular objects (e.g. a pencil, a cell phone, a loaf of bread).

Students should be clear that, when we conventionally refer to ‘energy used’, we actually mean ‘energy converted’ (from a useful form to less useful forms).



2 hours

Measuring energy Know and use the joule as the unit of energy.


Ask students to use the Internet to find out what they can about James Prescott Joule and his key work on energy.

Explain Joule’s famous experiment in which he measured the mechanical input into a stirrer and noted and measured the temperature change in the water that was stirred in an insulated container. Note that, until then, mechanical energy was measured in units called ergs and heat was measured in another unit called calories and no one knew how many ergs were equivalent to one calorie. Create a small display of the work of Joule, with the help of information provided by students. Include the fact that the SI unit of energy that we now use is called after him.

Return to the list of different forms of energy used in the flow charts. Ask students to classify them according to whether or not they involve some kind of movement. Assist with more difficult energy forms, such as heat and sound, where the movement is not obvious. The other energy forms will all be energy that is stored. Introduce the words kinetic and potential to refer to these two categories.

Return to (or repeat) the falling book activity and note the examples of potential energy and kinetic energy. Define gravitational potential energy as energy of position and lead on to note that a weight of 1 N placed 1 m above a surface will have the SI unit of gravitational potential energy, which is the joule. Students can obtain an approximate idea of the size of a joule as the energy converted by a typical textbook (weight 5 N) dropping through 20 cm, or a typical apple dropping through about 1 m.

Encourage more advanced students to perform simple calculations of energy converted from gravitational potential energy into kinetic energy as objects of known mass fall under gravity.


Enquiry skill 8.2.2

Energy concept map revisited As a summary exercise, ask students to produce a new concept map based on the topic energy. As before, reproduce the most significant links on a flip chart Compare this with the original map and list the major changes. Address again any major misconceptions that still emerge.


Assessment


Draw flow charts showing all the energy transformations in the following:

a. a torch powered by a cell;

b. a jet engine running;

c. a bow shooting an arrow;

d. a clock driven by falling weights.

The statements below tell you what happens to the electrical energy used in some domestic appliances.

• When a kettle boils, 94% of the energy is used to heat the water.

• When a drill is used, 40% of the energy is wasted.

• When a radio is used, 40% of the energy is given out as sound.

a. What proportion of the energy going to the drill is converted to energy in the rotating drill bit? What kind of energy is this? What happened to the ‘waste’ energy?

b. Suggest what happened to the 6% of the energy supplied to the kettle that was not used to heat the water.

c. Which of the three appliances is the least efficient energy converter? Explain your answer.

A football has gravitational potential energy of 10 J. It is dropped and bounces to four-fifths of the height from which it was dropped. What is its gravitational potential energy when:

a. it hits the ground?

b. it reached the top of its bounce?


Complete the following sentence by selecting one of the options.

The source of energy for the Earth’s water cycle is the:

A. wind.

B. Sun’s radiation.

C. Earth’s radiation.

D. Sun’s gravity.

Adapted from TIMSS Grade 7–8, 1995

Unit 8P.1



Ibrahim carried out an experiment in which he measured the electrical energy taken by a kettle as it heated up water. He also calculated the heat energy given to the water. His results are in the table.

Electrical energy supplied (kJ)

Heat energy given to water (kJ)

5 4.5

10 6.0

15 13.5

20 18.0

25 20.0

30 23.5

a. Why is the amount of energy given to the water always less than the amount of electrical energy used?

b. Plot a graph of the energy supplied (x-axis) against the energy given to the water. Ibrahim made an error in one of his readings; which one was it?

c. Think of a reason why the shape of the graph changes as more energy is given to the water?

Enquiry skill 8.3.2

Design and make a machine, using everyday materials, that converts the energy from the Sun into another energy form.

Enquiry skill 8.1.3



Electromagnetism

About this unit This unit is the second of four units on physical processes for Grade 8.





Previous learning To meet the expectations of this unit, students should already understand that magnetism is a force that acts at a distance and that similar magnetic poles repel each other and opposite ones attract. Students should also be able to set up working DC circuits.

Expectations By the end of the unit, students name factors affecting the strength of an electromagnet and describe some applications of electromagnets in everyday life. They know how a current-carrying wire moves in a magnetic field and can apply this to make an electric motor. They make working models to illustrate scientific ideas and solve scientific problems.

Students who progress further know why iron, but not other metals, is used to make the core of practical electromagnets. They build simple relay-operated control circuits. They predict correctly the direction of the magnetic field around a wire and in a solenoid and also predict correctly the direction of rotation of a DC motor

Resources The main resources needed for this unit are: • sufficient mains operated laboratory power supplies for group work • investigation planning poster • electromagnetic equipment kit that includes all the small items and

materials needed to make and test electromagnets and motors • ceramic magnets with poles on the faces

Key vocabulary and technical terms Students should understand, use and spell correctly: • magnetism, magnetic field, compass • solenoid, electromagnet, core, laminated core • relay, trembler bell, solenoid tap, loudspeaker • motor, coil, commutator

UNIT 8P.2 8 hours





7.19.4 Distinguish between the north and south poles of a magnet and know that similar magnetic poles repel each other and opposite poles attract each other.

8.19.1 Know that a coil of wire carrying a current produces a magnetic field similar to a bar magnet; list the factors affecting the strength of an electromagnet.

8.19.2 Explain the function of the electromagnet in some everyday examples, such as in relays, electric bells and lifting devices.

8.19.3 Demonstrate that a wire carrying a current creates a magnetic field.

8.19.4 Demonstrate and explain how a wire and a coil carrying a current move in a magnetic field.

8.19.5 Know how the movement of a current-carrying wire in a magnetic field can be exploited to make an electric motor; know how and why an electric motor turns and understand the function of the commutator.

8.19.6 List and explain the main differences between a model electric motor, with a single coil and a permanent magnet, and commercial electric motors.

9.22.1 Distinguish alternating current (AC) from direct current (DC) and know why household electricity is AC and not DC.

4 hours

Electromagnets

4 hours

Electric motors

8.1.3 Make working models to illustrate scientific concepts and applications.

Unit 8P.2


Activities


Making an electromagnet Recall work on magnetism from Grade 7, particularly on the shape of the field due to a bar magnet and the rules of magnetic attraction and repulsion.

Ask students, in groups, to make an electromagnet using a large nail and plastic covered wire. Tell them to test the magnet by picking up paper clips or iron filings, and to find out what happens when the current is switched off. Ensure they understand the meaning of the word solenoid.

Challenge the groups to design an investigation on how the current taken by the magnet might affect its strength.

Ask them to use a compass needle to find, and identify, the poles of an electromagnet.

Electromagnets take a large current from cells. It is best to use laboratory power supplies set at a low voltage for this work. Use at least 1 m of wire to make the magnet.

Students could use a variable resistor in series with the magnet to vary the current. This will allow the power supply to be set at a fixed low voltage that will avoid overheating of the wire.

Enquiry skill 8.1.1


Plotting the field of an electromagnet Recall work from Grade 7 on plotting magnetic fields using iron filings and plotting compasses. Ask each group to repeat the work using their electromagnet.

Ask them to investigate the effect of reversing the current direction. Challenge them to devise a means of predicting the polarity knowing the current direction (or vice versa). Show them one or two of the methods that have been developed to do this.

Demonstrate, for more advanced students, the field down the centre of an electromagnet made from wire wound around a glass tube wide enough to put a plotting compass inside. Draw on the board or OHP the complete field due to a solenoid, including the direction of the lines of force.

4 hours

Electromagnets Know that a coil of wire carrying a current produces a magnetic field similar to a bar magnet; list the factors affecting the strength of an electromagnet.

Explain the function of the electromagnet in some everyday examples, such as in relays, electric bells and lifting devices.

What is the best material for the core of the magnet? Challenge the group to design an investigation that will find out what is the best material for making the core of an electromagnet.

Discuss the results of this investigation with the class. Draw from them, and list on the board or OHP for them to note as important conclusions, the following: • only a core that contains iron will enhance the strength of an electromagnet; • if a hard steel core is used, the core becomes permanently magnetised; • if a soft iron core is used, most of the magnetism is lost when the current is switched off.

Ask students about the advantages and disadvantages of the permanent magnetisation of the core. They should understand that for many uses, such as moving steel objects around in scrap yards, it is desirable that the magnetism should not be retained after the current is switched off.

Give out laminated C-cores to each group and invite them to make and test horseshoe magnets with them. These lose their magnetism almost completely when the current is switched off. The importance of laminated cores will be discussed in Grade 9 when alternating current is introduced.

More advanced students can be taught an explanation for the enhancement of the strength of the field by the iron core in terms of molecular magnets. This will explain why non-magnetic materials such as aluminium or copper are unsuitable for making the core of an electromagnet.

A variety of materials in a suitable form should be made available, including metals, such as aluminium and copper, and non-metals, such as wood and plastics. The examples should include both mild steel and a high carbon alloy steel.

The ‘soft iron’ often referred to in physics books as the ideal core is not commonly available. Mild steel (common nails) is a satisfactory alternative.

Unit 8P.2



Uses of electromagnets An important use of electromagnets that students will probably be familiar with is sorting scrap steel in scrap yards.

Give groups some applications of electromagnets, such as trembler bells, relays and electrically operated water taps, security locks and the coil in a loudspeaker. Ask them to look at these and explain how they work. Have OHT diagrams available showing what happens in each application when a current passes. Of particular importance is the relay, which provides a mechanism for a small current, as in an electronic circuit, to switch a large one, as in a commercial electric motor.

Challenge more advanced students to build (at home) circuits that will control a large electric motor (such as that from a washing machine) or a solenoid water tap, using a circuit powered by a1.5 volt cell. This can form the basis for understanding control circuitry (Grade 11).

Many working relays can be obtained from broken and discarded household appliances, such as washing machines, which will also probably contain working electromagnetically operated water taps.

Safety: Mains voltage should not be used; most mains motors and solenoid taps will also run on the output of a low-voltage power supply.

A simple electric motor Demonstrate a simple model motor that can be assembled, in front of the class, from everyday materials in a short time. Ask the class whether they can explain how it works. They will not understand it in detail, but careful questioning should bring out that the motor involves a coil with a current passing through it, which they know to have the properties of a magnet and is therefore capable of being repelled by a permanent magnet.

Ideas for model motors can be found on the Internet – see, for example, www.howtoons.org, which shows one made of a coil, two safety pins, a ceramic magnet and a 1.5 volt cell.

The magnetic effect of an electric current Perform the classic 1820 demonstration of Oersted. Place a wire over the top of a compass needle and pass a direct current through the wire from a power supply. Note the movement of the compass needle. Reverse the current direction to note that the compass deflection is reversed (if you prefer, you could do this demonstration at the beginning of the unit). Through discussion, draw out the conclusion that a conductor carrying a current must generate a magnetic field around it.

Discuss the shape of the field around the conductor, drawing diagrams on the board or OHP and mentioning the corkscrew rule to help students predict the field direction.

Set up the ‘kicking coil’ demonstration using a magnetic field created by two ceramic magnets on a former. Label the poles of the magnets clearly so that they can be seen by the class. Show that the coil moves out of the field when the current flows. Show the effects of reversing the current and then reversing the field direction.

This demonstration can effectively adapted for most overhead projectors. Orient the wire and needle with the Earth’s field before switching on the current.

A coil of about 10 turns some 30–40 cm in diameter is suitable

Draw diagrams on the board or OHP illustrating how the two magnetic fields interact creating a ‘catapult’ effect that explains the direction of movement of the coil.

Introduce Fleming’s left-hand rule at this stage to help students predict the direction of movement.

4 hours

Electric motors Demonstrate that a wire carrying a current creates a magnetic field.

Demonstrate and explain how a wire and a coil carrying a current move in a magnetic field.

Know how the movement of a current-carrying wire in a magnetic field can be exploited to make an electric motor; know how and why an electric motor turns and understand the function of the commutator.

List and explain the main differences between a model electric motor, with a single coil and a permanent magnet, and commercial electric motors.

Make working models to illustrate scientific concepts and applications.



Making a motor Support a small coil of about 6 turns between the poles of the magnet used in the last demonstration. Ask the class to predict what will happen when a current is passed through the coil. Discuss their predictions and arrive at a conclusion that the coil will turn until the north pole of the coil (refer back to the work on electromagnets) faces the south pole of the magnet and vice versa.

Ask the class what will happen if the current in the coil is then reversed. They will probably correctly predict that it will turn through 180 degrees, and this can then be demonstrated. Draw attention to the fact that the wires to the coil are becoming twisted.

Conclude with the class that this arrangement is the possible basis of an electric motor but that two technical problems require solutions: • a mechanism for reversing the current every 180 degrees must be developed; • a mechanism is required that ensures that the wires do not become twisted.

Give each group all the parts needed to make a working model electric motor that solves both these problems. Also give them a set of complete instructions, in diagrammatic form, for them to follow. Challenge them to produce a motor that will lift a mass attached to a cotton thread using no more than a 4.5 volt supply (three cells). Groups will need assistance, particularly with the construction of an effective commutator. Assist with advice only.

A small token prize could be awarded to the group building the motor that lifts the heaviest mass a given distance.

Using the motor as a generator The motor that students have made can be used as a generator. Tell them to wrap a piece of cotton once around the axle so that the axle can be turned by pulling on the cotton. Tell them to connect the leads from the motor to a microammeter. They will discover that turning the motor causes a deflection of the microammeter needle. Turning the motor the opposite way will cause the reverse deflection.

This observation will be taken further in Grade 9.

Practical electric motors Ask students to bring examples of electric motors to the classroom and/or to search the Internet for illustrations of motors of different kinds. This will offer an opportunity to study the very wide range of different kinds of electric motors in use. Ask students to find examples of very large and very small motors. Interesting topics that may arise are: • induction motors, particularly the linear induction motor; • very small motors – this could provide an opportunity for introducing the concept of

nanotechnology; • motors that run at precisely determined speeds, such as those in a digital watch or a CD

player; • stepper motors, which turn by an exactly predetermined amount – also found in CD players

and disk drives; • motors that drive very large pumps, such as those that pump cooling water at the Ras Laffan

industrial site.

A collection of different kinds and sizes of motors, built up over time, is a valuable visual aid for this and other units.


It is not intended that students should know how all these motors work as the detail of the mechanisms is beyond their knowledge. The intention is to alert students to the variety of sizes and uses of electric motors and to note that all work according to the same principle: the interaction of two magnetic fields.


Assessment

Possible assessment activities Notes School resources

The diagram shows a car park barrier. The weight of the barrier is balanced by an iron counterweight. When the switch is closed the barrier rises. Explain how the electromagnet can be used to raise the barrier.

QCA Key Stage 3, 2004, level 7 (part question)

A pupil wound a coil of copper wire around a glass tube and connected the wire to a battery. She placed a compass at each end of the tube and one compass beside the tube as shown.

Complete the diagram by drawing arrows in compasses X and Y to show the direction of the magnetic field.

Draw an arrow in the middle of the glass tube to show the direction of the magnetic field in the glass tube.

When the switch is opened, in which direction will the three compass needles point?

Give one way to reverse the magnetic field around the glass tube.

Two pieces of iron are placed, end to end, inside the glass tube as shown. When the switch is closed, the magnetic field is the same as in the first diagram. The pieces of iron become magnetised. Label the four poles on the pieces of iron.

When the switch was closed, the pieces of iron moved. Explain why they moved.


What is a solenoid?

Draw a diagram of a solenoid and show the lines of force of its magnetic field when a current passes through it.

Give three ways of increasing the strength of the magnetic field caused by a solenoid.

Give two uses of a solenoid. In each case explain what the solenoid does


Design a simple door lock that can be opened by passing a current through a coil but remains locked when no current passes. Draw a diagram of your design.

Unit 8P.2



Heat and temperature

About this unit This unit is the third of four units on physical processes for Grade 8.


The teaching and learning activities should help you to plan the content and pace of lessons. Adapt the ideas to meet your students’ needs. For consolidation activities, look at the scheme of work for Grade 4 and earlier units in Grade 8 and for extension activities look at Grades 9 and 11.



Previous learning To meet the expectations of this unit, students should be familiar with the concept of temperature and with simple means of measuring it. They should have a general understanding of heat as an energy form.

Expectations By the end of the unit, students distinguish between temperature and heat. They know that heat is transferred by conduction, convection and radiation, and that radiation can occur in a vacuum. They know that the heat conductivity of different materials varies. They know the cause of convection currents and how these affect the weather. They know how the nature of a surface affects how well it absorbs and radiates heat.

Students who progress further apply their knowledge to explain everyday applications of conduction, convection and radiation and understand how ocean currents are generated and how they influence weather patterns

Resources The main resources needed for this unit are: • a variety of different kinds of thermometer • datalogger and temperature sensor • equipment for determining fixed points, ice, uncalibrated thermometers • pair of parabolic reflectors, radiant heater • powdered charcoal, aluminium foil • metal beakers such as a calorimeter • conductivity rods, wax, drawing pins • Leslie’s cube • potassium permanganate crystals, straw

Key vocabulary and technical terms Students should understand, use and spell correctly: • thermometer, Celsius, datalogger • conduction, convection, radiation

UNIT 8P.3 12 hours





4.14.1 Estimate temperature using touch, and measure it accurately using a liquid-in-glass thermometer.

8.17.1 Know that temperature is a measure of how hot something is and the common unit of temperature is the degree Celsius.

11F.21.1 Define temperature and explain how a temperature scale is constructed. Know how different types of thermometer work and list their advantages and disadvantages.

8.17.2 Know that the amount of heat energy in an object depends on the mass of the object and what it is made of as well as how hot it is.

11F.21.6 Define, explain in terms of the kinetic particle model and use the concepts of specific heat capacity and specific latent heat. Offer explanations for the relative magnitudes of these quantities and for differences between materials.

8.17.3 Know that heat is transferred by conduction, convection and radiation, and cite everyday examples of each.

11F.21.2 Recognise that thermal energy is transferred from a region of higher temperature to a region of lower temperature and that regions of equal temperature are in thermal equilibrium.

3 hours

Heat and temperature

3 hours

Conduction

3 hours

Convection

3 hours

Radiation

4.14.3 Know that substances differ in their conducting and insulating properties.

8.17.4 Know that some materials are better conductors of heat than others; know the differences in the ability to conduct heat between solids, liquids and gases, and between metals and non-metals, and know some applications of these differences.

8.17.5 Explain the cause of convection currents in air and water.

8.17.6 Show how convection currents in air cause weather features

8.17.7 Know that the nature of a surface influences how well it absorbs and radiates heat.

8.17.8 Know that heat can be radiated through a vacuum and that this is how the heat from the Sun reaches the Earth.

9.20.6 Know that the electromagnetic spectrum can be considered as a spectrum of different forms of the same radiation, and that each part of the spectrum, of which visible light is one, has different properties and applications.

Unit 8P.3


Activities


Estimating and measuring temperature Recall earlier work from Grade 4. In particular, ask the class which sense they would use to estimate temperature. Recall that the back of the hand is particularly sensitive to temperature. Recall the unit of temperature – the degree Celsius – and show the class a number of different kinds of thermometer.

Organise students into groups and give each group a liquid-in-glass thermometer and show them how to use it. Challenge students to estimate (individually) and then check by measurement the temperature of different objects (e.g. the air around them, a windowsill in the sun, the outside temperature in and out of the sun, beakers of water at different temperatures. Ask individuals to write down their estimates in one column of a table and the actual checked temperature in another column.

Ask the class how a thermometer works. You may need to remind them of work done in Grade 7 on expansion and particle theory.

Different kinds of thermometer to show to students include: • a normal liquid-in-glass thermometer (not

mercury); • a clinical thermometer; • a datalogger with a temperature sensor; • a chromothermal patch used for measuring

body temperature.


Calibrating a thermometer Show the groups how to determine the lower and upper fixed points of the Celsius scale using condensing steam and melting ice. Give them the necessary equipment and ask each group to calibrate a thermometer.

Set, as a homework or library task, some research into the history of the Celsius scale of temperature. In the following lesson, ask students to summarise the main features of what they have found out about Anders Celsius and his temperature scale.

Safety: Care should be taken when generating steam to avoid steam burns.


3 hours

Heat and temperature Know that temperature is a measure of how hot something is and the common unit of temperature is the degree Celsius.

Know that the amount of heat energy in an object depends on the mass of the object and what it is made of as well as how hot it is.

Measuring temperature change – datalogging Demonstrate the use of a datalogger with a temperature sensor. Challenge the groups to produce ideas on solving a problem that involves the measurement of temperature. Ideas they may come up with include: • How fast does the inside of a car heat up if it is left in the sun? • How does that rate of heating compare with the rate of heating in the same car parked in the

shade? • What is the temperature difference between the outside and the inside of a window? • How does the temperature of an aquarium change during the day? • How fast does a cup of coffee cool down? Students will be able to suggest many of their own.

A particularly interesting one is the Mpemba effect (after the Tanzanian student who discovered it) in which the temperature of two identical (except for temperature) samples of water placed in a freezer are plotted. One sample is placed in when hot and the second when cold. The results are counterintuitive.


Unit 8P.4



The difference between temperature and heat This should be done as a demonstration after students have become familiar with the use of the datalogger. Heat up different quantities of water in two identical kettles; say 500 cm3 in one and 1000 cm3 in the second. Plot the heating curves using a temperature sensor in the same position in each kettle.

Ask students to explain why one heats up more slowly than the other and lead on to a clarification of the difference between temperature (hotness) and heat (energy).

Using a clinical thermometer Show students a clinical thermometer and ask them for any differences that they can see between it and a normal thermometer. They should note the limited range and also the constriction in the fluid column. Show an enlarged diagram of the constriction and explain its purpose and use.

The use of the clinical thermometer may be demonstrated but the temperature of the armpit should be taken, not the mouth, for safety reasons.

Introduction Perform an introductory activity such as asking two students to hold a rod in a Bunsen flame. One rod should be made of copper and the second should be made of glass. Ask them to take the rod out of the flame and put it down carefully when it is beginning to get too hot to hold. Ask the class for ideas why one rod heated up faster than the other

3 hours

Conduction Know that heat is transferred by conduction, convection and radiation, and cite everyday examples of each.

Know that some materials are better conductors of heat than others; know the differences in the ability to conduct heat between solids, liquids and gases, and between metals and non-metals, and know some applications of these differences.

Compare the conductivity of different solids Lead on to a discussion of how well different substances conduct heat and ask for ideas on how the heat conductivity of different rods may be compared. The class will be able to suggest a mechanism based on what they have just seen. Ask if anyone can think of a way of taking the temperature of the end of a rod a given distance away from a heat source. Some ideas may be forthcoming. A useful way is to stick a drawing pin onto the rod with wax; this will fall when the wax melts. The opposite end of the rod can be heated in a flame (or in water). Give out rods of different materials to each group and any other equipment needed.

Collect together the results and discuss them. It will be clear that: • metals conduct heat much better than non-metals; • some metals conduct heat better than others.

List the substances in order of conductivity.

Sets of conductivity rods made from different substances are commercially available. They should include copper: aluminium, glass, iron and brass. If the rods are heated with water, wood can also be used.



Conductors and insulators. Cooling curves Question the class to find out what they know about the use of thermal insulation – what is it used for and what is it made of? The discussion should include natural thermal insulation, such as the fur of animals, as well as clothes and the insulation of buildings and water pipes.

Collect together samples of materials that can be used to insulate. Show students examples of various materials that could be used for heat insulation (e.g. polystyrene, bubble wrap, felt, paper). Challenge them to devise a fair investigation to compare the insulating properties of different materials. If possible, allow each group to use a datalogger.


The cooling of water in a standard container surrounded by different insulating materials is the most common method for this investigation but, if groups devise alternatives, they should not be discouraged as long as the equipment is available. At the end of the investigation, ask each group to give a short presentation on what they did and found out and the steps they took to make the investigation fair (which should, in all cases, include an uninsulated control).

Summarise what students found out about the effectiveness of different insulating materials. Note that most effective insulators are effective because they trap air inside them and gases are effective insulators. Provide comparative figures for thermal conductivity of solids, liquids and gases and, through discussion with the class, draw general conclusions from them.

Introduction Ask each student to place the back of their hand about 5 cm from their neighbour’s body. Then ask them to place it the same distance above their neighbour’s head. They should notice a difference, though it is not very significant. Ask them to do the same with a filament light bulb or a candle and the difference will be much greater. Discuss possible reasons why most of the heat given off by a warm body rises up above it.

3 hours

Convection Know that heat is transferred by conduction, convection and radiation and cite everyday examples of each.

Explain the cause of convection currents in air and water.

Show how convection currents in air cause weather features

Convection currents in water and air Show the class how to set up two common investigations into convection. One investigates convection in a liquid and involves heating the bottom edge of glass beaker containing water and a tiny potassium permanganate crystal just above the flame in the water. The second involves a candle in a clear plastic trough with a lid containing a chimney at either end. The candle is placed below one chimney and a burning paper straw (not a plastic straw) or rope is placed near the other. In the first case, a circular convection current is set up in the water; the moving water is stained pink by the crystal. In the second case, the convection current due to the candle sucks smoke in at the cold chimney and out above the candle.

Tell some groups to set up one investigation and some, the other. Ask them to demonstrate their work to their neighbours.

Discuss what causes convection and why. Refer back to the movement of particles, thermal expansion and density, studied in Grade 7, and deduce that hot fluids will become less dense and rise. This movement sets up convection currents. Draw diagrams showing this for one, or both, of the examples.



Convection currents and weather patterns With the help of some pictures (from the Internet) explain how convection currents in the air cause weather patterns. Refer, where possible, to patterns that students are aware of, including the ‘sea breeze’ that blows off the sea during the day and off the land during the night. This is the same as the candle effect – during the day the land heats up more than the sea and during the night the sea is warmer than the land. Show the convection current pattern in the two cases.

Discuss the weather patterns in Oman and Yemen, where summer rains fall as moist wind is drawn off the sea towards the hot Saudi desert, resulting in rain on the high land when the air cools as it rises over the mountains.

Encourage more advanced students to discuss the origins of major ocean currents and their effect on the world’s weather patterns.

Introduction Carry out a short starter activity to raise interest. A simple one is to place two small metal sheets outside in the sun. They should be identical except that one is painted white and the other black. Ask the students to touch them. Another possible starter activity is to paint part of the back of the hand of each student with charcoal paint and on the other hand stick some thin aluminium foil. Then tell them to hold the backs to their hands towards a heater (or the sun).

Discuss the questions raised by the results with the class.

Safety: Make sure students are a safe distance from the heater – the blackened part of the hand can easily burn if held too close to a heater

Heating up water in different containers Ask students, in groups, to set up several metal containers of water, each identical except for the colour of the outside of the container. One container should be shiny, one should be painted white and a third should be painted matt black. Place them all in the sun with a thermometer (or a temperature sensor connected to a datalogger) in each. Tell students to record, in a table, the change of temperature of each over time and then plot graphs showing the changes, all on the same axes. Some assistance may be needed.

3 hours

Radiation Know that heat is transferred by conduction, convection and radiation and cite everyday examples of each.

Know that the nature of a surface influences how well it absorbs and radiates heat.

Know that heat can be radiated through a vacuum and that this is how the heat from the Sun reaches the Earth.

Leslie’s cube Give out a Leslie’s cube apparatus to each group. Ask them to fill it with hot water from a kettle and place identical thermometers the same short distance from each different side. Tell them to record the temperature of the thermometers after a short interval of time and then list the temperatures in order, noting the colour of the side of the cube next to them.

Good Leslie’s cube equipment can be made from soft drink cans



Consolidation Discuss the results of the investigations. Students will note that black painted bodies gain and lose heat faster than white bodies and shiny bodies lose and gain heat more slowly than either. Describe this kind of heat loss and gain as radiation.

Discuss some of the implications and applications of the observations, for example: • machinery designed to lose heat, such as a car radiator, is painted matt black; • the inside of a white car heats up more slowly in a hot climate than the inside of a dark car

(this could be tested); • how the structure of a vacuum flask relates to its function (this involves conduction too); • how colour, material and design are used in making clothes suitable for hot weather.

The energy from the Sun Discuss how the heat energy from the Sun gets to the Earth. Note that, because space is a vacuum, and conduction and convection both require a medium, the heat from the Sun arrives at the Earth in the form of radiation.

Extend this discussion with more advanced students to include the issue of global warming. Plastic bottles containing just air and air enriched with carbon dioxide can be sealed with a temperature sensor inside. When they are heated with radiant heat from a light bulb, more heat is absorbed by the air enriched with carbon dioxide, causing its temperature to rise slightly faster than the control bottle. This can be done as a demonstration or as group work if sufficient materials are available.

Demonstration using parabolic reflectors An impressive demonstration of radiant heat can be done with two parabolic reflectors. (Students will be aware of the use of these in instruments such as torches and satellite TV dishes.) Radiation can be focused to a point by them. If a radiant electric heater is placed at the focus of one parabolic reflector, the radiation can be projected in a beam across the room to another, where it can focused on a match head, which lights. The beam itself is invisible and only slightly warm.


Assessment


A metal spoon, a wooden spoon, and a plastic spoon are placed in hot water. After 15 seconds, which spoon will feel hottest?

A. The metal spoon.

B. The wooden spoon.

C. The plastic spoon.

D. The three spoons will feel the same.

TIMSS Grade 8, 1994

Explain the following observations:

a. Metal kettles and pans usually have plastic or wooden handles.

b. Windows in air-conditioned buildings often consist of two layers of glass with an air space in between them.

c. In some windows in modern buildings, the glass is coated with a very thin transparent layer of metal.

d. Car radiators are always painted matt black.

e. Hot water heaters are usually surrounded by a layer of polyurethane foam.


The two diagrams show air movement near a coastline during the day and night. Explain what causes these different wind patterns.

Unit 8P.3



a. The table shows the temperature of a pottery beaker of coffee left to cool down. Plot the curve on some graph paper.

Time (s) 0 10 20 30 40 50 60 70 80 90

Temperature (°C)

90 80 73 61 56 52 48 45 43 41

b. Some cold milk was added to the coffee at one point. When was the milk added?

c. Draw curves to illustrate the cooling curve that you would expect if the coffee was left to cool in:

i. a metal cup;

ii. an insulated plastic cup.

Explain the shape of your curves.

d. If the coffee was made in a vacuum flask it would remain hot for much longer. Give two reasons for this

Design, make and test a solar cooker that uses principles of focusing radiation and trapping heat.

Enquiry skill 8.1.3



Light

About this unit This unit is the fourth of four units on physical processes for Grade 8.





Previous learning To meet the expectations of this unit, students should know that light comes from the Sun and other illuminated objects, that we see things because light reflected from them reaches our eyes, and that white light can be split into light of different colours.

Expectations By the end of the unit, students know how shadows form, and represent a ray of light by a line. They know how light is reflected and refracted and describe applications and examples of reflection and refraction. They show how white light can be split into coloured light by refraction and give everyday examples of dispersion. They know that white light results from the superimposition of red, green and blue light and apply this to television and to colour vision.

Students who progress further understand how curved mirrors can focus light and can be used to create beams of light in car headlights and torches. They distinguish primary from secondary colours and predict the effect of combining any of them. They offer explanations for natural phenomena such a mirages and rainbows

Resources The main resources needed for this unit are: • overhead projector (OHP) • class sets of general optical equipment including ray boxes, mirrors,

prisms, glass and Perspex blocks • transparent plastic bottles • opaque beakers • laser pointer • Internet access

Key vocabulary and technical terms Students should understand, use and spell correctly: • reflection, mirror • incident ray, reflected ray • optical fibre, total internal reflection, critical angle • refraction, refracted ray, emergent ray • prism, colour, spectrum • mirage, rainbow

UNIT 8P.4 12 hours





8.18.1 Know that light travels in straight lines and that objects in the path of light cast shadows.

8.18.2 Know that the intensity of light can vary depending on the light source and its distance away; measure the intensity using a light sensor.

8.18.3 Represent a ray of light by a line in diagrams showing reflection, refraction and dispersion of light.

6.16.3 Know that we see light sources because light travels from them to our eyes and that we see objects that are not light sources because they are illuminated by light sources and light is reflected into our eyes.

8.18.4 Describe how light is reflected at a surface and understand the difference between reflection by rough and smooth surfaces. Know the characteristics of an image formed in a plane mirror. Describe everyday applications of reflection.

9.20.4 Explain the reflection of sound and light in terms of waves.

8.18.5 Describe how light is refracted at a plane surface and describe everyday applications of refraction.

9.20.5 Explain the refraction of light and water waves in terms of the change in velocity of waves.

6.16.5 Know that white light is composed of light of different colours.

8.18.6 Demonstrate how white light can be split into coloured light by refraction and explain examples of dispersion in everyday life (e.g. oil on water, rainbows).

9.20.6 Know that the electromagnetic spectrum can be considered as a spectrum of different forms of the same radiation, and that each part of the spectrum, of which visible light is one, has different properties and applications.

8.18.7 Know that objects appear coloured when viewed in white light because some colours are reflected by the object but others are absorbed.

8.18.8 Explain why objects appear one colour in white light but a different colour in coloured light.

8.18.9 Know the effect of superimposing red, green and blue colour filters.

2 hours

Properties of light

2 hours

Reflection

4 hours

Refraction

4 hours

Colour

8.18.10 Know that red, green and blue light, when superimposed, create white light and apply this knowledge to television screens and to colour vision.

8.18.11 Know that red–green colour-blindness is common among males.

Unit 8P.4


Activities


Introduction This unit offers an opportunity to revisit the main principles studied in earlier grades (particularly Grade 6) using a wide range of light equipment in a physics laboratory. To capture the interest of students, repeat one or two striking demonstrations involving light. For example: • Shine a laser beam around the laboratory (above head level for safety) and stick small

(plastic) mirrors on the wall at appropriate places to reflect the beam. It is surprising how often this can be done. Ask the class to note that the beam is invisible as it crosses the laboratory, but then make a small amount of smoke in the path of the beam at one point – immediately the beam can be seen.

• Create a bright spectrum on the ceiling of the laboratory by reflecting sunlight from outside into the laboratory through the door or window using a mirror placed at an angle in a trough of water to make a water prism which the light passes through twice.

In both cases discuss with the class what their observations tell us about the nature of light.


Light travels in straight lines Repeat the Grade 6 (Unit 6P.2) demonstration of the passage of a beam of light from a torch through three holes in three cards. Note that the beam can only emerge after passing through the holes when all three are lined up in a straight line. Remind students how shadows form.

Measure light intensity – datalogging Demonstrate the use of a datalogger with a light sensor. Challenge groups of students to produce ideas on solving a problem that involves the measurement of light. Ideas they may come up with include: • Does it get hotter outside as the light intensity increases? • Is there a difference between the light output from a fluorescent tube and that from a filament bulb? • What is the difference between light intensity outside a window and that on the inside of a

window? Students will be able to suggest many of their own.

This activity is deliberately very similar to one in the Grade 8 unit on heat. They are included here to provide practice in the routine use of a datalogger.


2 hours

Properties of light Know that light travels in straight lines and that objects in the path of light cast shadows.

Know that the intensity of light can vary depending on the light source and its distance away; measure the intensity using a light sensor.

Represent a ray of light by a line in diagrams showing reflection, refraction and dispersion of light.

Describe how light is reflected at a surface and understand the difference between reflection by rough and smooth surfaces. Know the characteristics of an image formed in a plane mirror. Describe everyday applications of reflection.

How do we see objects? Recall from earlier work that we use the sense of sight to see objects and that we see objects when light from them is reflected into our eye. Draw the attention of the class to the beam from the laser. When it hits the wall the spot can easily be seen, but when it hits a mirror the spot cannot be seen. Ask for reasons why. Explain that light hitting a smooth surface like a mirror is reflected only in one direction and we will not see it unless that one direction is into our eye. Light reflected from a rough surface is reflected in all directions and some of it enters our eye.

Draw diagrams on the board or OHP to show light being reflected from smooth and rough surfaces (greatly magnified) and show how we represent light rays using straight lines with arrows. Tell students to copy the diagram in their books as an example. Insist on the use of a sharpened pencil and a ruler for accurate drawing of light phenomena.

Safety: Take care not to allow the laser beam to be reflected into anyone’s eye.

Enquiry skill 8.3.1

Unit 8P.4



Reflection by a plane mirror

Show the class two methods for investigating reflection at a plane mirror: the parallax method using four optical pins and the simpler method using a ray box. Arrange students into groups and give each group both sets of equipment, together with instructions to remind them of the processes. Ask them to find the relationship between the angle of incidence and the angle of reflection using both methods (the groups can divide if necessary). Demonstrate the conventions for drawing a mirror in a ray diagram and also ensure that they are aware that the plane causing the reflection is the back of the mirror and not the front.

After carrying out the processes, each member of the group should have a table of results for different values of the angle of incidence, some determined by one method and some by the other. Ask them to draw some conclusions.

Then give instructions on how to find and compare the image and object distances for a plane mirror. Ask them to draw a conclusion from this activity also.

Finally, draw the attention of the class to the lateral inversion of the image in a plane mirror.

Summarise the three conclusions on the board or OHP and ensure that all have a record of them.


2 hours

Reflection Describe how light is reflected at a surface and understand the difference between reflection by rough and smooth surfaces. Know the characteristics of an image formed in a plane mirror. Describe everyday applications of reflection.

Uses of mirrors Ask the class, as a homework exercise, to make a list of some uses of mirrors. This list need not be confined to plane mirrors. Discuss their findings, perhaps listing them on the board of OHP. Add, if it has not already been noted, the use of curved mirrors in telescopes and refer to work in Unit 8E.1 showing photographs of planets and their moons.

Introduction, the appearing coin Give each group an opaque beaker. Ask them to put a coin in the bottom and then sit in such a way in relation to the beaker that they just cannot see the coin. Then ask them to pour water into the beaker and note what happens. Leave suggestions for explanations until after the main activity.

4 hours

Refraction Describe how light is refracted at a plane surface and describe everyday applications of refraction

Refraction of light by a glass block As with the previous activity on reflection, demonstrate the two methods for investigating the path of a ray of light through a glass block. Also give out instructions with the two sets of equipment to each group. Ask them to investigate the relationship between the angles of incidence and refraction both in and out of the block and the relationship between the incident and emergent rays.

They should, by the end of the session, have a table showing values for the two angles. At this stage they should be able to make some general qualitative conclusions, such as: • when light moves from one medium to another, its path bends; • the relative sizes of the angles of incidence and refraction depend on whether the light is

moving from air to glass or vice versa.

The concept of refractive index cannot be covered at this stage, as students will not meet the idea of a sine of an angle until Grade 9.

Make sure that all students note that the emergent ray is always parallel to the incident ray.



Real and apparent depth Ask for explanations of the ‘appearing coin’ at the start of the topic. Many will realise that it is linked to light bending during refraction but may not be able to explain it clearly. Put a diagram, on the board or OHP. Return to the beaker of water; this time put a pencil in the beaker so that half of it is in the water and ask students to note the apparent bend in it. Ask them whether they can draw a similar diagram to explain this. They will need assistance from the board or OHP.

Mirages and other natural phenomena caused by refraction of light Ask more advanced students to search the Internet to find out about natural phenomena caused by refraction and common in hot desert areas, such as mirages and ‘double sunsets’, in which the Sun appears misshapen or even split into two as it sets. Encourage them to show how these phenomena are caused by refraction of light passing through different atmospheric layers and to share their findings with the class. You or the students can make an interesting display of such phenomena using photographs from the Internet.


Total internal reflection Ask groups of students, using the ray box and the glass block, to investigate carefully what happens to the emergent ray as the angle of incidence is gradually increased. Ask for their comments. All will realise that at one point the light ceases to emerge from the block and is reflected back from the internal surface to emerge again at the front.

Ask them to measure the critical angle – the angle of incidence at the exact point when this transformation takes place. Give them blocks made of different materials (such as Perspex) and ask them to repeat the activity. They should note that the size of the critical angle is a characteristic of the material.

Introduce the term total internal reflection for this phenomenon.

Fibre optics (‘light pipes’) Carry out this demonstration in the dark using a bent glass rod. Shine a highly focused beam of light onto one end of the rod. Note the light emerging at the other end. This is very effective if a laser light is used. Ask for possible explanations drawing on the observations from the previous activity.

Show, using a diagram on the board or OHP, how light can travel down the inside of the rod by total internal reflection.

Discuss the applications of this phenomenon, particularly fibre-optic communications.

Challenge students to make, at home, a light pipe out of a stream of water emerging from the bottom of a plastic bottle. If the bottle is illuminated by a torch from the side opposite the hole, the light is internally reflected down the inside of the water stream, lighting it up. The most successful ones should be shown at school.

Enquiry skill 8.1.3



Introduction

Refer back to, or repeat, the demonstration of the spectrum made by the water prism at the beginning of this topic. Note and name the colours of the spectrum.

Provide groups with the necessary optical equipment to produce a spectrum using a glass prism. Ask them to trace on paper the paths through the prism of the rays of violet and red light at the ends of the spectrum.

In the subsequent discussion of the results, ensure that two important points emerge: • white light is made up of coloured light; • light at the blue end of the spectrum is refracted more than light at the red end.

Ask more advanced students to try to detect invisible radiation beyond the red end of the spectrum using a suitable infrared sensor. This could lead to the realisation, to be followed up in Grade 9, that the optical spectrum is part of a much bigger spectrum of radiation, the rest of which is invisible to us. Discuss equipment such as night vision binoculars.

Naturally produced spectra Show by diagrams how total internal reflection in raindrops can lead to the production of a rainbow. Show more advanced students how primary and secondary rainbows are produced.

Ask the class where else they may have seen spectra. Most will be able to refer to spectra produced by diffraction (e.g. by a CD or by a layer of oil on water). The mechanism of the production of spectra by diffraction opens a new area in the study of light which, except for the most advanced students, should be left to Grade 11.

4 hours

Colour Demonstrate how white light can be split into coloured light by refraction and explain examples of dispersion in everyday life (e.g. oil on water, rainbows).

Know that objects appear coloured when viewed in white light because some colours are reflected by the object but others are absorbed.

Know the effect of superimposing red, green and blue colour filters.

Know that red, green and blue light, when superimposed, create white light and apply this knowledge to television screens and to colour vision. Pigments – what colour is the book?

Show students a yellow book and ask them what colour it is. They will respond that it is yellow. Then show it to them in blue light and ask again. Some will say it is black. Some may say that it appears to be black. Others may say that it is still yellow but that we cannot see that it is yellow in blue light. Ask them all to justify the rightness of their assertions.

This kind of debate is important science as it illustrates how evidence can be interpreted in different ways to lead to apparently contradictory conclusions, all of which are, however, correct, based on the level of their interpretation of the evidence.

Discuss these contradictions with the class, showing how a deeper understanding of what is happening is required in order to reconcile the contradictions.

Ask what must be happening to the white light when it strikes the book if only yellow light reaches our eyes. This should lead to the deeper idea about how pigments work (i.e. pigments are chemicals that absorb light of particular colours, reflecting only the light that is the colour of the pigment). In this case, explain that while white light contains yellow light, blue light does not. Therefore the book will appear yellow in white light but black in blue light as no colour is reflected.

You can teach more advanced students about the primary and secondary colours, but this is probably unnecessarily complicated at this stage for most students.

Enquiry skill 8.1.2



Red, green and blue colour filters Reinforce the explanation of how pigments work by placing red, green and blue (primary colours) on an overhead projector. Bring any two of them together so that they overlap and note that no light gets through when they overlap. Conclude that the blue filter lets through only blue light and the green one, only green light. So where the two overlap, no light will get through. The same argument applies for the other two combinations.

More advanced students can do the same activity with the secondary colours, yellow, magenta and peacock blue, each of which lets through two of the primary colours. In this case, the three overlaps will be red, green and blue and the place where all three overlap will be black.

Combining red, green and blue light Ask students if they have come across the abbreviation ‘RGB’ in the context of ICT. Be ready to show them a reference to it (the ‘RGB’ colour sliders in the ‘Font color’ tab in Word, for example).

Demonstrate the effect of combining beams of red, green and blue light. This can be done using three torches with red, green and blue glasses. Ask students to explain why the area where all three beams overlap is white. More advanced students can be asked to explain the colours (yellow, magenta and peacock blue) where only two of the three beams overlap

Use the RGB colour sliders in ICT applications such as Microsoft Word to demonstrate the effect of combining two, and then all three, primary colours in varying intensities to create all other possible colours.

Explain, using a diagram, how the red, green and blue fluorescers in a colour television tube work to create all the colours. Also explain how colour vision works and the cause of red–green colour-blindness, a sex-linked inherited condition in about one in ten males.

At this point, you may wish to offer a colour-blindness test to the class using standard test cards. This should be treated sensitively, as it is likely that some of the boys may be red–green colour-blind without knowing it.

ICT opportunity: Creating colours by mixing red, green and blue font or background colours.

The blue sky and the red setting Sun This may be done by groups of students or as a demonstration (or as practical homework). Place a small amount of milk in a large plastic bottle of water so that it is slightly cloudy. In a darkened room, shine a torch beam through the bottle. Look at: • the colour of the cloudiness caused by the milk (a bluish colour); • the colour of the torch light coming out of the other end (a reddish colour).

Best results are obtained if the bottle is placed on its side (stoppered). Ask students what they think has happened to the light as it goes through the cloudy liquid. Ask, particularly, what has happened to the light at the blue end of the spectrum and what has happened to the light at the red end.

Explain that blue light is scattered by small particles like dust more readily than red light, so when the sunlight goes through the atmosphere the blue light is scattered making the sky look blue and the red light passes through. Ask them to explain why the Sun looks redder (a) when it is setting and (b) on days when there is a lot of dust in the air.


Assessment


The picture shows a pencil that is lying on a shelf in front of a mirror. Draw a picture of the pencil as you would see it in the mirror. Use the patterns of lines on the shelf to help you.

TIMMS Grade 8, 1996


The diagram shows the path of a ray of red light hitting a glass block.

a. Complete the diagram showing the path of the light passing through the block and out of the other side.

b. Draw another ray with the same angle of incidence showing the path of blue light through the block.

c. Draw a third ray showing total internal reflection. Show clearly in your diagram how the angle of incidence of this ray will differ from that of the first two.

Unit 8P.4



Explain the following observations:

a. The sky is blue.

b. Water can apparently be seen in the desert on a hot day.

c. A blue car often looks black in the light of street lamps.

d. A beam from a torch cannot easily be seen until it illuminates an object.

e. When you look in a mirror and move your right hand, the left hand of your image moves.

f. A stick placed so that half of it is in water appears bent.

g. We can see planets such as Jupiter and Venus in the night sky.

h. When we see a satellite passing overhead in the night sky, quite often it will suddenly disappear.

Design and make a periscope out of two mirrors and a cardboard milk carton.

Enquiry skill 8.1.3

science units grade 8 - csomathscience › 2011 › 10 › grade8.pdf · unit 8m.3: uses of metals...

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