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S 31701

ScienceStage 5

Chemicalcombinations

Number: 31701 Title: Chemical combinations

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This publication is copyright New South Wales Department of Education and Training (DET), however it may containmaterial from other sources which is not owned by DET. We would like to acknowledge the following people andorganisations whose material has been used:

Extracts from Science Syllabus Years 7-10 © Board of Studies, NSW 2002 Covers, Set 3 p 44

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Chemical combinations

I

Introduction

In this unit, you will be studying chemistry. But what is chemistryand why are you studying it?

You are surrounded by chemicals. A study of these things is a studyof chemistry. Chemists are interested in investigating matter –its composition, properties and reactions. In other words,chemists are interested in discovering what matter is made of,what it does, and what happens when it comes in contact with othertypes of matter.

Chemistry is important because knowing about matter allows us tochoose appropriate chemicals for different jobs. Knowing howchemicals react with each other gives us ideas for making newand useful chemicals.

In this unit, you will become more familiar with some reactionsof chemicals. You’ll begin to understand more of the chemicalreactions in your home, garden and everyday life.

This unit will be a useful introduction if you wish to go on toStage 6 Chemistry, but it will also be of interest to those studentswho would like to understand and explain how science affectsour everyday lives.

I hope you enjoy the unit and find it useful to broaden your grasp ofhow science, technology and society are interdependent.


II

Symbols used in this unit

You will find these symbols used in this unit.The key below shows you the meaning of each symbol.

This symbol appears beside exercises that should behanded in to your teacher.

You need to cut something to complete an activity.

If you have Internet access, you can obtainextra resources to use with this unit.

CAUTIONYou need to take particular care with an activity.Usually, you need to plan how to do something safelyand consider what to do if an accident occurs.

You must tell your supervisor that you are doingthis activity and explain to your supervisor how youwill do it safely. Your supervisor should be presentwhile you do the activity.

Wear your safety goggles during this activity.


III

Before you begin

What do you need to know before you begin this unit?

It would be helpful if you already can:

• describe some features of protons, electrons and neutrons

• describe the structure of an atom in words and diagrams

• identify an ion as an atom that has gained or lost electrons

• use symbols to represent elements and formulas to representcompounds

• identify that chemical bonds hold atoms together in compounds

• identify that a new compound is formed by rearranging atomsthat are present in other substances

• identify a variety of compounds using their common names andchemical formulas

• describe how indicators change colour to show differentstrengths of acids or base

• describe solutions using scientific terms

• describe what is meant by dependent, independent andcontrolled variables.

Here are some terms that you should understand for this unit.

Some of these terms have more than one meaning.The meanings given are the ones needed within this unit.

chemical change – a change in which a new substance is produced

classify – to put into groups using shared properties or features

common – usual

crystalline – make up of crystals

impure – not pure; not made of one element or compound only;a mixture

insoluble – unable to dissolve

logical – well reasoned; based on evidence

mixture – pieces of two or more substances close together

nucleus – the central core of an atom, containing protons and neutrons

objective – not affected by your feelings or ideas


IV

physical change – a change of shape or state; no new substancesare formed

pure – made from one element or from one compound only

radioactivity – release of particles and/or energy when the nuclei ofsome atoms break apart

soluble – able to dissolve

solute – the substance that dissolves in a solvent to make a solution

solvent – the larger part of a solution; usually a liquid that somethingelse is dissolved into

test – an experiment


V

Unit outline

Here are the names of the lessons in this unit.

Set 1 Working as a chemistLesson 1 A chemical investigationLesson 2 What happened?Lesson 3 Metal or not?Lesson 4 Copper, zinc and ?Lesson 5 Black and blue

Set 2 Describing some chemical reactionsLesson 6 Reactants and productsLesson 7 Taking a closer lookLesson 8 Another close lookLesson 9 Chemical equationsLesson 10 What is in it?

Set 3 Why do chemicals react?Lessons 11 and 12 Why do elements react?Lessons 13 and 14 How do compounds react?Lesson 15 Some important reactionsRevision lesson The last word


VI

What will you learn in this unit?

In this unit, you will solve a chemical puzzle.You will perform a chemical reaction then conduct teststo find out what has been made in the chemical reaction.As you do this, you will learn more about how scientists work.And like a scientist, you will have to think abouthow experiments are planned and performed safely.

You will also learn more about the science of chemistry.You will learn about:

• atoms

• elements and compounds, and patterns in their properties

• chemical reactions.

You will learn to:

• look for and use evidence when you make decisions in science

• write word equations for chemical reactions.

Assessment

Throughout the lessons in Chemical combinations, you will be able tosee how well you can do these things by completing activities andanswering questions, then checking your own answers.

You will show your teacher what you have achieved by completingthe exercises in the send-in pages.


VII

Outcomes and essential content

5.2 A student describes the processes that are applied to test and validatemodels, theories and laws.

Students learn about the nature and practice of science.Students learn to:

a) evaluate the role of creativity, curiosity, objectivity and logicalreasoning in describing phenomena, carrying out investigations andin the devising and testing of hypotheses

c) apply scientific processes to test the validity of ideas and theories

e) use examples which show that scientists isolate a set of observations,identify trends and patterns and construct hypotheses or models toexplain these

5.7 A student relates properties of elements, compounds and mixtures toscientific models, theories and laws.

5.7.1 Students learn about atomic theory. Students learn to:

a) describe features of and the location of protons, neutrons andelectrons in the atom

b) distinguish between elements, using information about the numbersof protons, neutrons and electrons

c) describe an appropriate model that has been developed to describeatomic structure

5.7.2 Students learn about elements. Students learn to:

a) identify the atom as the smallest unit of an element and distinguishbetween atoms and molecules

b) describe some relationships between elements using the PeriodicTable

5.7.3 Students learn about compounds and reactions. Students learn to:

a) identify that a new compound is formed by rearranging atoms ratherthan creating matter


VIII

c) construct word equations from observations and written descriptionsof a range of chemical reactions

d) identify a range of common compounds using their common namesand chemical formulae

e) qualitatively describe reactants and products in the followingchemical reactions:

combustion

corrosion

precipitation

acids on metals and acids on carbonates

neutralisation

decomposition

f) describe the role of indicators

5.13 A student identifies a problem and independently produces anappropriate investigation plan.

4/5.13 Students learn about planning first-hand investigations. Studentslearn to:

a) identify variables that need to be held constant if reliable first-handdata is to be collected

5.14 A student undertakes first-hand investigations independently withsafety and competence.

4/5.14 Students learn about performing first-hand investigations.Students learn to:

a) follow the planned procedure when performing an investigation

c) safely and effectively construct, assemble and manipulate identifiedequipment

f) demonstrate the use of safe and hygienic work practices includingthe correct use of safety equipment


IX

5.16 A student accesses information from a wide variety of secondarysources.

4/5.16 Students learn about gathering information from secondary sources.Student learn to:

a) use a range of sources, including databases, CD-ROMs and theinternet, to access information

c) extract information from column graphs, histograms, divided bar andsector graphs, line graphs, composite graphs, flow diagrams, othertexts and audio/visual resources

5.17 A student explains trends, patterns and relationships in data and/orinformation from a variety of sources.

4/5.17 Students learn about processing information. Students learn to:

f) identify trends, patterns, relationships and contradictions in data andinformation

5.18 A student selects and uses appropriate forms of communication topresent information to an audience.

4/5.18 Students learn about presenting information. Students learn to:

d) use symbols to express relationships, including mathematical ones,and appropriate units for physical quantities

5.19 A student uses critical thinking skills in evaluating information anddrawing conclusions.

4/5.19 Students learn about thinking critically. Students learn to:

b) identify data which supports or discounts an hypothesis, a questionbeing investigated or a proposed solution to a problem

c) predict outcomes and generate plausible explanations directly relatedto observations made

d) make generalisations in relation to a relevant set of observations orexperimental results

f) use models, including mathematical ones, to explain phenomena ormake predictions

g) use cause and effect relationships to explain ideas


X

5.22 A student plans, implements and evaluates the effectiveness of avariety of tasks independently and as a team member

4/5.22 Students learn about working individually. Students learn to:

a) independently plan and conduct investigations, communicateinformation and understanding and solve problems

b) set and work to realistic timelines and goals

c accept responsibility for maintenance of a safe working environmentfor themselves and others

d) evaluate the effectiveness of their performance in completing tasks

Extract from Science Years 7–10 syllabus © Board of Studies, NSW 2003, accessed

<http://www.boardofstudies.nsw.edu.au/syllabus_sc/index.html#science> 15 August 2005.


XI

What do you need for this unit?

The table below shows the materials and enclosures you needfor this unit, and when you will use them.

Set 1

• measuring cylinder

• filter funnel

• retort stand

• retort ring

• 3 beakers

• 1 piece of filter paper

• clock glass

• battery holder

• 3 leads with alligator clips

• light globe

• socket for light globe

• battery clip

• 4 pieces of zinc

• pieces of copper

• 1 teaspoon of copper sulfate

• 1 piece of blue litmus paper

• copper oxide

• plastic spoon

• marker pen or labels

• plastic wrap

• 2 ‘AA’ batteries

• ‘lead’ from HB pencil

• white vinegar

• plastic spoon

Set 2

• test tube

• cork to fit test tube

• beaker

• safety goggles

• 1 piece of zinc

• white vinegar

• hot water

• matches

• scissors

• glue or sticky tape

• coloured pencils – at least green, yellow and red


XII

Set 3

• beaker

• eye dropper

• safety goggles

• universal indicator paper

• 2 pieces of red litmus paper

• 2 pieces of blue litmus paper

• plastic spoon

• white vinegar

• a household cleaner,e.g. Windex, Ajax or Jiff

• clean teaspoon for food

• baking soda

• plain flour

• self-raising flour

Science Stage 5

Set 1: Lessons 1 to 5

ChemicalcombinationsSet 1: Working as a chemist

Chemical combinations Set 1

i



☞ Set 1 Working as a chemistLesson 1 A chemical investigationLesson 2 What happened?Lesson 3 Metal or not?Lesson 4 Copper, zinc and ?Lesson 5 Black and blue




ii

Set 1: Working as a chemist

Contents

What will you learn in Set 1? ................................................................... iii

What do you need for Set 1? .................................................................... iv

Lesson 1 A chemical investigation...................................... 1

Lesson 2 What happened? ................................................... 7

Lesson 3 Metal or not? ........................................................ 15

Lesson 4 Copper, zinc and ? .............................................. 19

Lesson 5 Black and blue ..................................................... 25

Suggested answers ................................................................................... 31

Send-in pages ............................................................................................ 35


iii

What will you learn in Set 1?

In Set 1, you will have opportunities to:

Lesson 1 • make observations and describe somechemical substances

• recall and use the definitions of element,compound, pure, impure, mixture, solution,solute and solvent

Lesson 2 • set up and use a filtration apparatus

• interpret results of an ammonia test forcopper in solution

• suggest what may have formed in the reactionso that you can plan more investigationsto test your ideas

Lesson 3 • compare the electrical conductivity ofdifferent samples

Lesson 4 • use litmus paper to test a solution to see if it is an acid

• plan a controlled experiment comparing different metalsin acid

• identify dependent, independent and controlled variables

• identify zinc and copper by testing samples andcomparing your results with their known properties

Lesson 5 • observe and compare the results of an experiment

• summarise reactions from several lessons

• interpret a flow chart


iv

What do you need for Set 1?

Lesson 1

• measuring cylinder

• 2 pieces of zinc

• 1 piece of copper

• 1 teaspoon of copper sulfate

• 2 beakers

• plastic spoon


• plastic wrap

Lesson 2

• filter funnel

• retort stand

• retort ring

• beaker


• clock glass

• 1 piece of zinc


• your set up experiment from Lesson 1

Lesson 3

• battery holder

• 3 leads with alligator clips

• light globe

• socket for light globe

• battery clip


• 1 piece of zinc


• ‘lead’ from HB pencil

• dried residue from Lesson 2

Lesson 4

• 1 piece of blue litmus paper

• 1 piece of zinc


• copper oxide

• white vinegar

• dried residue from Lesson 2

• 2 beakers

• plastic spoon


Lesson 5

• your set up experiment from Lesson 4


1

Lesson 1

A chemical investigation

A chemist can be a bit like a detective. First, the chemist watcheswhat happens when chemicals are combined. Does a chemical change,called a chemical reaction, occur? Or is it a physical change only?

Then the chemist studies any substances that are formed.What are they? How can they be tested? Why did they form?What could they be used for?

In this way, the chemist makes and organises observations,identifies and tests patterns in the observations and suggestsexplanations for what happens. The chemist must be very logical andorganised in the study of a reaction to solve the chemical puzzle.

In Set 1, you are going to conduct a chemical investigation.You’ll need to be objective as you make observations so thatyou see what really happens and not what you expect to see.You’ll need to be curious and creative to find out what was formedin the reactions. And, you’ll have to be very logical to pull togetherall the clues in the investigation to identify the chemicals thatare formed. You’ll also need to be organised.There are many experiments for you to do in this set!

Are you ready to begin?


2

Metal in solution

In this investigation, you will put zinc metal into a solution ofcopper sulfate. You will observe this experiment for two lessonsso it’s important that you find a place to leave the equipment set upso it won’t be disturbed.

What you will need:

Collect the equipment listed below.• 2 pieces of zinc• piece of copper• 1 teaspoon of copper sulfate• 2 beakers• plastic spoon• measuring cylinder• marker pen or labels• plastic wrap.

CAUTION Be careful!

Copper sulfate is a poisonous substance.Make sure your experiment is out of the reach of small children.Do not eat while you are carrying out this activity.

What to do:

Now that you have collected the things you need,follow the instructions below.

1. Make a copper sulfate solution by placing a teaspoon of coppersulfate into a beaker. Do not use all the copper sulfate supplied.Add 100 mL of water. Stir to dissolve.

2. Divide the solution into two by pouring half into another beaker.Label one beaker experiment and the other control.

3. In Question 1 and Question 2 on the next page, describe zinc metaland copper metal and then describe copper sulfate solution.

4. Place one piece of zinc into the beaker labelled experiment.Put the other piece of zinc and the piece of copper beside thebeakers.

5. Leave the beakers to stand overnight. (Remember to leave themin a place that small children can’t reach.)


3

Observations

Describe the appearance of the metals and solution at the beginning ofyour investigation. This will allow you to see if there are any changes tothe chemicals.

zinc copper sulfate solutioncopper

control

1. Write a description of the two metals.

copper:

zinc:

2. Describe the copper sulfate solution in the beaker labelled control.

Complete these descriptions after the experiment has been left overnight.

3. Look in the beaker labelled experiment. Describe any changes.

4. What do you think has happened?

Please check your descriptions in the answer pages.


4

You will be checking your explanation in the lessons that follow.Leave the experiment set up because you’ll come back to it inthe next lesson. You’ll use the solution in the beaker called controlin Lesson 2 and again in Optional Lesson 6. For now, cover itwith a lid or with plastic wrap so that nothing falls into it.Put the control somewhere safe and away from childrenuntil you need it again.

Before you continue, there are a number of terms that areused in chemistry that you may need to revise.

A review

Read the information below and try to answer as many questionsas you can to refresh your memory.

Pure substances

There are a large number of metals that we use in our lives.The metals you are observing in this activity are copper and zinc.These are both pure substances.

What are the two different kinds of pure substances?

The two kinds of pure substances are elements and compounds.

Are copper and zinc elements or compounds?

Copper and zinc are both elements.

Copper is made of copper atoms only. Zinc contains zinc atoms only.Now write a sentence explaining what elements are.

Elements are pure substances made up of one type of atom only.


5

Elements, such as copper and zinc, have chemical symbols.Can you remember the symbols for copper and zinc?Write them below.

The symbol for copper is Cu. The symbol for zinc is Zn.

The copper sulfate you dissolved in water is also a pure substance.Copper sulfate contains copper atoms, sulfur atoms and oxygen atoms.Is copper sulfate an element or a compound?

Copper sulfate is a compound (because it contains atoms of more than one elementthat have been chemically combined together).

Compounds such as copper sulfate have chemical formulas.Can you recall the formula for copper sulfate? Write it below.

The chemical formula for copper sulfate is CuSO4.

The formula for copper sulfate shows you the elements thatcopper sulfate contains. You might have expected a compoundcontaining copper, sulfur and oxygen to have a different name.However, a sulfur atom and four oxygen atoms form a special,stable unit that tends to stay together. Therefore this specialcombination of sulfur and oxygen is given its own name, sulfate.

Circle the sulfate part in the formula below.

CuSO4

Did you circle the part that is SO4? Remember, sulfate refers to one sulfur atomchemically combined with four oxygen atoms.

Compounds are different from elements. Can you describethis difference? Write a sentence about how they differ.

Compounds contain more than one type of atom whereas elements containone type of atom only.


6

Impure substances

There are a large range of solutions that you come into contactwith regularly. Things like sea water, household bleach, urine,lemonade, vinegar, battery acid and petrol are all examplesof solutions.

Are solutions pure or impure substances?

Solutions are impure substances.

Solutions are mixtures of various substances. In this activity,you made a solution of copper sulfate. How do you know thatyour copper sulfate solution is impure?

You made it by mixing together two compounds – water and copper sulfate –so the solution must be impure.

When copper sulfate dissolves in water:

(a) which substance is the solute? ___________________________________________________

(b) which substance is the solvent? _________________________________________________

A small amount of copper sulfate dissolves in water so copper sulfate is the solute.This means that water is the solvent.

What have you learned in this lesson?

Tick the box if you can:

❑ make observations and describe some chemical substances

❑ recall and use the definitions of element, compound, pure,impure, mixture, solution, solute and solvent.

Exercise 1

Now that you have refreshed your memory, turn to the send-in pagesand do Exercise 1. This will show your teacher that you understandeach of the terms you have used so far.


7

Lesson 2

What happened?

Your experiment has been standing overnight.What has happened to it?

In this lesson, you will observe and test chemical substancesto see if there have been any changes.

First impressions

Write down your first impressions.Compare the contents of the experiment beaker with the controlbeaker. What do you see? What do you think has happened?

This is a record of your thinking that you can look back towhen you have finished testing the substances.

Filtration

To get a good look at what has happened in the beaker labelledexperiment, you need to filter the mixture. To do this, you will need thefollowing pieces of equipment:

• filter funnel

• retort stand

• retort ring

• beaker


• clock glass.

You will also need a piece each of copper and zinc.


8

Folding filter paper

Begin by folding your filter paper.

Make a cone

Step 3

Fold filter paperin half again

Step 2

Fold filter paperin half

Step 1

Step 5 Moisten filter paper with water

Step 4

Place cone infilter funnel

Filtration apparatus

Then set up the filtration apparatus.

exp

erim

ent beaker labelledexperiment

filter paper

residue

beaker

filtrate

retort ring

filter funnel

retort stand

stirring rod


9

1. Once you have filtered the contents of the beaker markedexperiment, carefully examine the residue (the solid that remains)in the filter paper. Describe what you see.

2. Compare the solids left in the filter paper with a piece of copperand a piece of zinc. Are they similar in any way?

3. What do you think the solids from the beaker are?

Are you thinking like a chemist?You need to predict what substances have formed in the reaction so that you can decide how to test them.

You’ll be able to compare your answers with the answers of other studentsas you continue through Set 1.

Now follow these instructions

You need to pack up carefully so that you keep the substancesthat you need for other lessons.

• Put the filter paper with the residue on the clock glass andset it aside to dry. You will use it again in Lesson 3.

• Thoroughly wash the beaker labelled experimentthen wash your hands.

• DO NOT discard the copper sulfate solution in the beaker markedcontrol. You will need it again in this lesson.

• DO NOT discard the filtrate. (It is the colourless solutionin the beaker.) You will use it later in this lesson.


10

Now compare your description with the logbook entry that Year 10student, Max, wrote after doing this part of the experiment.

Metal in solution

The solution in the beaker is still clear but now it is colourless.

The things in the bottom of the beaker are hard to see so

we need to filter it.

After we filtered the mixture in the beaker, we ended up

with a clear, colourless solution and a mixture of solids in

the filter paper.

The clear, colourless solution looked different from the

clear, blue solution in the beaker labelled control. My

partner thinks that the blue had faded so we will test it

using ammonia solution later.

We had a closer look at what was left in the filter paper,

the residue. Anyway, there was a variety of solid bits that

were black, silvery and pinkish orange.

The black stuff looks like carbon. The silvery stuff looks

like some zinc left over from when we put it in the jar.

The pinkish orange stuff looks like copper.

We need to test the solids to see if they are carbon, zinc

and copper. Maybe we’ll think of how to test them by

tomorrow.

Max

Were your observations and thoughts similar to these?

What substances does Max think have been made in the reaction?Underline their names (or their descriptions if they are not named)in the report above.

There are answers in the answer pages.


11

Testing the solution

Compare the copper sulfate solution in the beaker labelled controlwith the filtrate. The filtrate is in the unlabelled beaker.

Describe the difference between the filtrate and the copper sulfatesolution in the jar labelled control.

The copper sulfate solution is blue but the filtrate is colourless.

Now you can empty and thoroughly wash the beaker of filtrate.Then wash your hands.

DO NOT discard the copper sulfate solution in the beaker markedcontrol. You will need it later in this lesson.

What has happened?

Max’s laboratory partner thinks that the blue solution fadedovernight. Max tried to explain that the solution in the control beakerdidn’t change so it couldn’t have faded but his partner remainsunconvinced. They have decided to test the solutions.

What test do you think Max and his partner used?

A test using ammonia solution.

Adding ammonia solution is a test for copper in a solution.Ammonia solution is colourless. When it is added to a solution thatcontains copper, the mixture turns dark blue.

What do you think would happen if the mixture does not containcopper in solution?

There is no colour change if the solution does not contain copper in solution.


12

Using the ammonia test

Max added ammonia solution to the control and to the filtrate.The results are shown below.

1. Before

controlfiltrate

clear, colourlesssolution pale blue solution

2. After ammonia solution is added

filtrate control

clear, colourlesssolution dark blue solution

What do you think? Do both these solutions contain copper?

You can see from the results that the solution in the control beakergoes darker when ammonia solution is added. The control beakercontains a solution of copper sulfate so there is copper in solution.

However, the colour of the filtrate doesn’t change colour withammonia solution. Therefore the filtrate doesn’t contain copper.Where did the copper that was in the solution in the experiment beakergo? What you think could have happened to it?

Look back at this answer that you’ve just written when Max and hispartner attempt to explain their observations in Lesson 3 and Lesson 4.


13

Testing the solids

Let’s now devise some tests that can be carried out on the solidsto see what they might be. To do this, you could follow the stepsset out below.

1. List the features or properties of each ‘suspect’ substance.

2. Test the properties of the substance(s) present.

3. Compare the results for these tests with the properties ofknown substances.

You’ll carry out Step 2 and Step 3 in the next two lessons.But you can do Step 1 now.

The first step

Can you remember any features, or properties, of the three elements,carbon, copper and zinc?

Complete the table below by listing some properties of these elements.

Properties of three ‘suspects’

‘Suspect’substance

Some properties

carbon

copper

zinc

How did you go? Please look at my answers in the answer pages.

In the next lesson, you will test each substance in the residueto determine some of its properties.


14



❑ set up and use a filtration apparatus

❑ interpret results of an ammonia test for copper in solution

❑ suggest what may have formed in the reaction so that you canplan more investigations to test your ideas.


15

Lesson 3

Metal or not?

In Lesson 2, you separated solids from a solution by filtering.There are a number of possible ‘suspects’ that these solids could be.You may have suggested that they are carbon, copper and zinc.In this lesson, you’ll begin testing the solids to determine their identity.

Testing conductivity

Metals like copper and zinc conduct electricity. Carbon is alsoan electrical conductor even though it is a non-metal. Let’s nowseparate out pieces of each ‘suspect’ substance and test them.If they conduct electricity then they are metals or carbon.

The carbon you will test is the ‘lead’ in an HB pencil.Pencils do not have the metal lead in them.The black, solid substance is graphite, the form of carbonthat conducts electricity.

What you will need:

Collect the following items:

• battery holder

• 3 leads with alligator clips on both ends

• a small light globe

• a socket to hold the light globe

• a battery clip


• a piece of copper

• a piece of zinc

• the ‘lead’ from a pencil

• dried residue from Lesson 2.


16

What to do:

First connect your electrical equipment. If you haven’t done thisfor a while or haven’t used this equipment before, you may need torefer to the diagram below.

Testing electrical conductivity

RE

AD

Y

NE

VE

RE

AD

Y battery holder

battery clip light globe

socket

lead

alligator clip

'AA' battery

place substanceto be tested here

NE

VE

RE

AD

Y

Test that your circuit works by tapping the free alligator clips together.Next, test each type of substance for electrical conductivity.The substance is a conductor if the light globe shines.Write your results into the table below.

Substance tested Electrical conductor?

black substance in residue

carbon in a pencil

silvery substance in residue

zinc

pinky-orange substance in residue

copper

Note: Keep all the substances listed in the table aboveas you will use them again, later in this set.


17

What do your results tell you about the electrical conductivity of each substance?Which substances do you think might match (be the same chemical)? Why?

Do you need to do some further testing?

Compare your results with the ones below that Max and his partner gotwhen they did the same experiment.

Does it conduct?

We tried the copper first then the pinkish orange solid.

They both conducted electricity because the light globe

worked when we put them into the electrical circuit.

Next we tried the zinc and the silver solid.

They both conducted electricity.

Lastly we tried the carbon and the black solid.

The carbon conducted electricity but the black solid

from our reaction didn’t.

From carrying out these tests, we think that there are

two metals in the residue: silvery-coloured zinc and

pinkish orange copper. We’re not sure about the

black substance but it is not carbon.

We’re going to look for extra information about

what the black substance could be in a textbook.

Max


18

In the next lesson, you will be further testing the three solids thatyou filtered from the reaction mixture. What tests can you think ofthat might help you to decide what they are?



❑ compare the electrical conductivity of different samples.


19

Lesson 4

Copper, zinc and ?

So far, you can probably say that the solids from the beaker markedexperiment were copper, zinc and a black substance that isn’t carbon.In this lesson, you will carry out one more test on the metals andinvestigate the identity of the black substance.

Metals in acid

Let’s have another look at the metals that you suspect are copper andzinc. You will put the metals into an acid. You can identify an acidbecause it changes the colour of litmus paper from blue to red.Litmus paper is an example of a chemical indicator because it can beused to show if a substance is an acid.

Some metals, magnesium for example, produce bubbles of gas whenthey are in acid. Other metals, such as gold, don’t produce anythingwhen they are in acid.

In this activity, you will compare what happens when copper andthe pinky-orange substance, and zinc and the silvery substance,are placed into acid.

What you will need:

For this experiment, you need the following items:

• 2 beakers

• piece of blue litmus paper

• piece of copper

• piece of zinc

• pinky-orange substance from your residue

• silvery substance from your residue

• white vinegar.


20

What to do:

Once you have collected your equipment, you need to check thatvinegar is an acid. How would you do this?

Pour some vinegar into a beaker. Dip a piece of blue litmus paper into thevinegar. If the litmus paper turns red then the solution is an acid.

Try this test. Is your vinegar an acid? ________________________________________________

Next, you are going to test the copper and the pinky-orange substancethat you suspect is copper with acid (vinegar). You need to plana controlled experiment so that you can compare them.What do you think you should do? Describe a suitable experiment.

What are you testing in your experiment?This is your independent variable because it is the thing you decideto change in the test.

What are you observing in your experiment?This is your dependent variable because the results depend onthe experiment you have planned.

What are some variables you will control (or make constant)in your experiment?

Turn to the answer pages and compare your answers with mine.Make any changes to your experiment plan above that are needed.


21

Now perform your experiment. Describe what happens.

Did the copper and the pinky-orange substancebehave in the same way as each other? _________________________________

Take the copper and the pinky-orange substance out of the beakersand rinse them in water. Tip the vinegar out of the beakers butDON’T rinse them.

Next, you are going to test the zinc and the silvery substance thatyou suspect to be zinc with acid (vinegar).

Exercise 4.1

Turn to the send-in pages and plan the test you will perform.Answer all the questions in send-in Exercise 4.1 before you continue.

Conduct your experiment. Describe what happens.

Did the zinc and the silvery substancebehave in the same way as each other? _________________________________

Do you think that the metals in the residue are copper and zinc?Why?


22

Compare your results and conclusion with Max and his partner’s.

Metals in acid

Results:

copper

pinkish orange substance

zinc silvery substance

MetalsBehaviour in acid

no bubbles

no bubbles

bubbles of gas

bubbles of gas

Conclusion:

The pinkish orange metal is the same colour as copper

and behaves the same way as copper in acid.

(It also conducts electricity like copper.)

We think it is copper.

The silvery metal is the same colour as zinc and

behaves the same way as zinc with acid.

(It also conducts electricity like zinc.)

We think it is zinc.

Do you agree with this conclusion?

Now that you have established the identity of the two metalsin the residue, it’s time to investigate the identity of thatthird substance.


23

Max and his partner have been busy looking up informationin a chemistry book. This is what they found.

Most metals that are left

exposed to air tarnish.

This means that oxygen

in air combines with the

metal to form a compound

called an oxide.

Tarnishing results in a dull

surface. Some metals are

coated in a white oxide layer

while others have a black

oxide coating.

Copper in air

Copper, when exposed to

the air, becomes black.

This is due to copper

combining with oxygen

to form copper oxide.

Copper oxide is a

black substance that

dissolves in acid.

The solution formed

is blue.

Metals in air

What do you think Max and his partner might do next?That’s right. Max and his partner are going totest the black substance in acid.


24

Is the black substance copper oxide?

Now it’s time to set up the experiment.

What you will need:

• 2 beakers

• black substance from the residue

• copper oxide from your minikit

• white vinegar

• plastic spoon

• marker pen or labels.

What to do:

1. Label one beaker A and the other beaker B.Pour the same amount of vinegar into each beaker.

2. Add half a teaspoon of copper oxide to the vinegar in beaker A.Stir the mixture.

3. Add some of the black substance from the residue to beaker B.Stir the mixture.

CAUTION4. Leave the two beaker to stand in a place where the experiment

won’t be disturbed (or accidentally thrown out or drunk!).

You will observe the results of this experiment in the next lesson.



❑ use litmus paper to test a solution to see if it is an acid

❑ plan a controlled experiment comparing different metals in acid

❑ identify dependent, independent and controlled variables

❑identify zinc and copper by testing samples andcomparing your results with their known properties.

Exercises 4.2 and 4.3

Now complete send-in Exercise 4.2 about indicators andExercise 4.3 about working scientifically.


25

Lesson 5

Black and blue

It’s time to observe and interpret the results of the experimentyou set up to identify the black substance.

What happened?

Look closely at the mixtures in the two beaker that you set upin Lesson 4.

1. Describe what has happened in beaker A.

2. Describe what has happened in beaker B.

3. What do you think the black substance from the residue was?Explain your answer.

Please check your answers.

Max and his partner thought that the black substance was copper oxidebecause both the black substance and black copper oxide producedblue solutions. What do you think these blue solutions may contain?

The solutions may contain dissolved copper.


26

Max and his partner tested two solutions for the presence of copperin Lesson 2. Do you remember what they did?

A blue solution containing copper goes dark blue when ammonia solutionis added to it.

Max and his partner tested for copper in both the solutionsmade by reacting copper oxide and vinegar.What do you predict the results to be?

The results of their tests are shown below.

Testing for copper in solution

add colourlessammonia solution

add colourlessammonia solution

copper oxide

Beaker A

pale blue solution

Beaker B

pale blue solution

black substancefrom residue

dark blue solution

dark blue solution

You can see that both solutions turned dark blueso both solutions contain copper.


27

Organising the results

Here is a list of the chemical combinations that you haveconsidered so far. Fill in the missing information in the listby looking back through Set 1.

Activity on Chemicals combined What formed?

page 2 solidcopper sulfate and water

page 2 copper sulfate solution and _ _ _ _ _ _ _ _ _ _

mixture ofthree solids and

colourlesssolution

page 12 copper sulfate solution and

_ _ _ _ _ _ _ _ _ _

solution dark blue solution

page 12 _ _ _ _ _ _ _ _ _ _ and ammonia solution no change

page 20 copper and acid

page 21 zinc and acid

page 25 copper oxide and acid

page 26 copper oxide and acid and

ammonia solution

There is a completed table in the answer pages.

Near the beginning of Set 1, you tried to predict what you madein the reaction between copper sulfate solution and zinc.You have been creatively and logically working through the evidenceto find an answer to the problem.

Do you think you have worked it out?

Max and his laboratory partner had the same puzzle.They thought it seemed like a huge task so they decidedto draw a flow chart to help them organise their results.

Their flow chart is on the next page.


28

Max’s flow chart

filter

stir

leave to stand

physical separation

conductor?

add acid add acidadd acid

conductor? conductor?

black silvery pinkish orange

pinkish orangemetal

copperzinc

blacknot a metal

copper oxide

water copper sulfate

clear, blue coppersulfate solution

zinc

clear, colourless solutionwith a mixture of solids

clear, colourless solution mixture of solids

silverymetal

This looks fairly complicated so let’s go through it.

Layout

1. The words in the boxes are names or descriptions of chemicals.

For example,

copper oxide is the black substance in the residue.

2. The words beside the arrows tell you what the experimenter didat each step of the experiment.

For example,

add acid means acid was added to the residue.


29

Steps

Max is having trouble explaining the flow chart to his partner.The diagram below shows Max going through the steps inthe investigation. Each step is labelled as A, B, C, D or E.As he explains, he points to the place on the flow chart thatshows each step.

D The three solids weretested for electricalconductivity to determineif they were metals.

C The mixture of solidswas separated from thecolourless solutionby filtration.

B Zinc was put into

the copper sulfate solution

and left to stand.

A The threesolids were testedwith acid.

E Copper sulfate was

dissolved in water to

make a blue solution.

??

??

?

1. Max is not explaining the steps (A to E) in the correct order.No wonder Max’s partner is having trouble understanding!Write the letter of each step where it is shown in the flow charton page 28.

2. Write the letters representing the steps of the experiment,in order, on the lines below. Add a brief description for each.

Step 1: ______________________________________________________________________________________

Step 2: ______________________________________________________________________________________

Step 3: ______________________________________________________________________________________

Step 4: ______________________________________________________________________________________

Step 5: ______________________________________________________________________________________


30

3. On Max's flow diagram, what words are used to identify:

the filtrate? _______________________________________

the residue? _______________________________________

Check all your answers in the answer pages.

Did you notice that the controls were not included in the flow chart?This is because the controls don’t actually change.They are used for comparison so that you can recognisewhen there is a chemical change in an experiment.

Another thing that was left out of the flow chart was the testto see if the filtrate had copper in solution. Remember,this was when Max and his partner added ammonia solutionto a copper sulfate solution and to the colourless filtrate.The filtrate didn’t contain copper so it isn’t shownbecause we are more interested in what the solution israther than what it’s not.



❑ observe and compare the results of an experiment

❑ summarise reactions from several lessons

❑ interpret a flow chart.

Exercises 5.1 and 5.2

Show your teacher what you have learned by completing thesesend-in exercises.


31

Suggested answers

Lesson 1 A chemical investigation

Page 3 Observations

1. copper: Copper is a pink or orange-coloured solid. It has a shiny surface and is hard but easily bent.

zinc: Zinc is a silvery solid. It is shiny and hard, but is easy to bend into shapes.

2. The copper sulfate solution in the control beaker is blue in colour.The solution is clear (you can see through it).

3. The zinc was covered with a black substance. If you look carefully,you can see some orange material on the surface of the zinc.

4. You will have your own ideas about what might have happened.You will test some ideas as you continue through the lessons in this set.

Lesson 2 What happened?

Page 10 Metal in solution

The substances that Max thinks were made in the reaction are:

• the clear, colourless solution

• a mixture of solids – black stuff that looks like carbon, silvery stuff thatlooks like zinc and pinkish orange stuff that looks like copper.

Page 13 The first step

‘Suspect’ substance Some properties

carbon (graphite) Carbon is a black solid which breaks easily.It is a conductor of electricity although it does notconduct as well as metals. Carbon is an insulatorto heat (it does not conduct heat very well).

copper Copper is a pinky-orange solid. It is shiny anda good conductor of heat and electricity.

zinc Zinc is a silvery, shiny solid. It is a goodconductor of heat and electricity.


32

Lesson 4 Copper, zinc and ?Metals in acid

Page 20 Here is a suitable experiment. Yours is probably similar.Put equal volumes (the same amount) of vinegar into each jar. Add the piece ofcopper to one jar and, at the same time, add the pinkish orange solid to the other.

The independent variable is the kind of substance. (You are testing twodifferent substances – copper and the pinkish orange solid.)The dependent variable is the way that the metal reacts with the acid.(You are observing to see if this is different.)Some variables you would control are the amount of vinegar, its temperatureand how long the substances are in the acid. It would be a better experimentif you could control the sizes of the pieces of each substance.Variables that you control are kept the same, or constant.

Lesson 5 Black and blueWhat happened?

Page 25 1. Some, or maybe all, of the black solid has disappeared.The solution has turned blue.

2. Some, or maybe all, of the black solid has disappeared from this jar.The solution has also turned blue.

3. The black substance was probably copper oxide since it behaves in thesame way as copper oxide.

Page 27 Organising the results

Activity on Chemicals combined What formed?

page 2 solidcopper sulfate and water copper sulfate solution

page 2 copper sulfate solution and zinc

mixture ofthree solids and

colourlesssolution

page 12 copper sulfate solution and

ammoniasolution dark blue solution

page 12 filtrate and ammonia solution no change

page 20 copper and acid no change

page 21 zinc and acid bubbles of gas(hydrogen) and

colourless solution

page 25 copper oxide and acid pale blue solution

page 26 copper oxide and acid and

ammonia solution dark blue solution


33

Lesson 5 continued

Steps

Page 29 1. Max’s statements are matched down the side of the flow chart.

filter

stir

leave to stand

physical separation

conductor?

add acid add acidadd acid

conductor? conductor?

black silvery pinkish orange

pinkish orangemetal

copperzinc

blacknot a metal

copper oxide

water copper sulfate

clear, blue coppersulfate solution

zinc

clear, colourless solutionwith a mixture of solids

clear, colourless solution mixture of solids

silverymetal

E

B

C

D

A

2. Here is a description of each step.

Step 1: E – make copper sulfate solution

Step 2: B – put zinc into copper sulfate solution

Step 3: C – filter experiment

Step 4: D – test electrical conductivity of residue

Step 5: A – test residue with acid

Page 30 3. On the flow diagram, the words used to identify:

the filtrate? are clear, colourless solution

the residue? are mixture of solids.


34


35

Send-in page Name ______________________________

Lesson 1: A chemical investigation

Exercise 1

Here is a description of some chemicals.

Cobalt is a silvery metal with the symbol Co.Cobalt chemically combines with chlorineto form cobalt chloride, CoCl2.

When cobalt chloride is dissolved in water,the mixture forms a pink solution.

In the far left column below, there is a list of terms that were definedin Lesson 1. In the middle column are the definitions of these termsbut the definitions are not in the correct order. In the third column,there are some examples that come from the description above.

Add lines to the diagram to match each term with its correct definitionthen each definition with the correct example. Notice that two examplescan be used twice.

Terms Definitions Examples

element a substance (usually solid) thatdissolves in another substance cobalt chloride

compound a pure substance made ofone type of atom only

mixture ofcobalt chlorideand water

solutiona substance (usually liquid)in which another substancecan be dissolved

cobalt

solute a pure substance containingmore than one type of atom pure water

solventan impure substanceoften consisting of a soliddissolved in a liquid


36


37

Send-in page Name ______________________________

Lesson 4: Copper, zinc and ?

Exercise 4.1

1. Describe a suitable experiment to compare the reaction with acidand zinc and the silvery substance that you suspect to be zinc.

2. What is the independent variable?

3. What is the dependent variable?

4. What are two variables that you will control in your experiment?

Exercise 4.2

1. Name the indicator that you used this lesson. _____________________________

2. What can you use this indicator to do?(What is the role, or job, of the indicator?)


38

Exercise 4.3

In this set, you have been investigating scientifically.You are being creative, curious, objective and logical as youtest and observe chemicals.

Read your 'first impression' about the chemicals on page 7.Then read another idea you had about the reaction at the bottomof page 12.

Explain how being creative, curious, objective and logicalhave helped you in this investigation.(If you can’t think of an example for each word, come back to this send-in exercise when you have finished Set 1. You may have thought of an example to use.)

creative _____________________________________________________________________________________

curious _____________________________________________________________________________________

objective _____________________________________________________________________________________

logical _____________________________________________________________________________________

Your teacher may organise a teleconference so that you can discussyour answers with other students.


39

Send-in page Name ______________________________

Lesson 5: Black and blue

Exercise 5.1

1. Here are the steps from the experiments you have performedin this set. However, they are still out of order.

Sequence the steps by writing 1 in the box beside the first stepand so on.

❒ Copper sulfate was dissolved in water to make a blue solution.

❒ The mixture of solids was separated from the colourless solutionby filtration.

❒ The three solids were tested with acid.

❒ The three solids were tested for electrical conductivityto determine if they were metals.

❒ Zinc was put into copper sulfate solution and left to stand.

2. Describe how you performed the step that you numbered 3.

3. On which page or pages did you follow the directions to performthe step that you numbered 4?


40

Exercise 5.2

In Set 1, you have worked scientifically to find out about the substancesin a chemical reaction between copper sulfate solution and zinc.

Use examples from this investigation to answer the questions below.

1. Scientists isolate sets of observations in investigations.(This means that they choose particular things that happen as important. They do not pay attention to everything.)

What is a set of observations that you isolated in your investigation?

2. Scientists identify trends and patterns in their resultsand observations.

What is a trend or pattern that you noticed during your investigation?

3. Scientists use these patterns to suggest hypotheses and models.(This means that they suggest an explanation of what happened. If they can, they try to explain why it happened.)

What is a suggestion that you made to explain part of yourinvestigation?

Science Stage 5


ChemicalcombinationsSet 2: Describing some chemical reactions


i




☞ Set 2 Describing some chemical reactionsLesson 6 Reactants and productsLesson 7 Taking a closer lookLesson 8 Another close lookLesson 9 Chemical equationsLesson 10 What is in it?



ii

Set 2: Describing somechemical reactions

Contents



Lesson 6 Reactants and products ........................................ 1

Lesson 7 Taking a closer look .............................................. 9

Lesson 8 Another close look .............................................. 13

Lesson 9 Chemical equations............................................. 17

Lesson 10 What is in it? ........................................................ 23


Send-in pages ............................................................................................ 39


iii



Lesson 6 • identify and describe reactants and productsin a corrosion reaction and in a reaction betweenan acid and a metal

• safely and efficiently perform a test for hydrogen

Lesson 7 • use and interpret models of molecules

• describe the reactants and products in thedecomposition of water

Lesson 8 • describe the changes that occur to atoms andmolecules when substances react

• identify and describe the reactants and productsin a combustion reaction

Lesson 9 • identify the reactants and productsin a chemical reaction

• write a word equation to describe a chemical reaction

Lesson 10 • classify a chemical substance as an element ora compound using a formula or a diagram

• use the periodic table to predict some propertiesof an element

• classify elements in the periodic table by state andby metallic/non-metallic properties

• decide if a compound has ionic or covalent bondsbased on the type of elements present


iv


Here is a reminder of the items you need for Set 2.

Lesson 6

• test tube

• cork to fit test tube

• beaker

• safety goggles

• 1 piece of zinc

• white vinegar

• hot water

• matches

Lesson 7

• scissors

• glue or sticky tape

Lesson 10

• coloured pencils – at least green, yellow and red


1

Lesson 6

Reactants and products

You observed several chemical changes, or reactions, in your investigationin Set 1. In this lesson, you will take a closer look at the chemicalsyou used and what was formed in these chemical reactions.

A summary of reactions

No doubt you can remember the chemical reactions you observedin Set 1. Sequence them below by putting 1 in the box beside thefirst chemical change you performed, and so on.

❒ Copper oxide reacted with the acid in vinegarmaking a blue solution containing copper.

❒ Copper chemically joined with oxygen that was dissolved inthe solution to form black copper oxide.

❒ Zinc reacted with ethanoic acid in vinegarto make bubbles of gas.

❒ Zinc was put into copper sulfate solution.Copper metal and a colourless solution were produced.

The order that you performed these chemical changes in Set 1 was 4, 2, 3, 1.

These are all examples of reactions because the chemicals that wereoriginally present have changed into new substances.

The chemicals that you combined—that were originally present—arecalled reactants. These were the substances that you mixed to causethe reaction.

The new substances formed in each reaction are called products.They are the chemicals that are formed, or produced, because thereaction has occurred.

Let’s look at the reactants and products in each of the fourchemical reactions that you observed in Set 1.


2

Metal in solution

In Lesson 1, you put a piece of shiny, silver-coloured zinc intoa pale blue solution of copper sulfate. After a short while,you saw the formation of pinky-orange solid on the zinc.The solution was left to stand overnight.

experiment experiment

leave overnight

It was easy to see the mixture of solids that formed in the jarsince the solution became colourless.

The different solids were tested in various ways to determinetheir identity. As a result of these tests, you could say thatsome zinc remained and some copper formed.

What has happened in the reaction? Copper sulfate, in solution,has produced copper metal. Remember, you decided that thesolution no longer contained copper sulfate since it didn’t turndark blue with the addition of ammonia solution as the control did.

Now answer some questions about this reaction.

1. What were the reactants?

2. Underline their descriptions in the paragraph at the top of this page.

3. What were the products?

Please read the comments in the answer pages before you continue.

Now let’s look at another change.


3

Copper in air

As well as copper and zinc, there was a black substance at the bottomof the beaker. You performed tests on this substance and decidedthat it could be copper oxide.

What happened to form the black substance? Copper metal andcolourless oxygen from the air chemically combined to producea compound called copper oxide. This is one example of a kind ofreaction called corrosion.

Corrosion means that a substance, usually a metal, is eaten away.Corrosion can occur because the metal reacts with water, with oxygenor with some other chemicals in the metal’s surroundings.

What are the reactants and products in this example of corrosion?Can you describe them?

Exercise 6.1

Turn to the send-in pages and complete Exercise 6.1 aboutthe reactants and products of this example of corrosion.

Other chemical changes that you observed in Set 1 includethe effect of acid on different substances.

Metals in acid

When zinc was placed in acid, bubbles of gas were produced.What was the gas?

Max thought that the gas was hydrogen. His laboratory partner wasconvinced that it was air. What do you think it was?

Since Max and his partner couldn’t agree on their prediction,they decided to test the gas that was produced when zinc was placedin acid. You can carry out a test to check your prediction too.


4

Supervisor needed

Tell your supervisor that you are carrying out this experiment.It involves a small explosion.

What you will need:

• a test tube

• a beaker

• safety goggles

• box of matches

• a cork to fit the test tube

• a piece of zinc

• hot water

• white vinegar.(Remember, vinegar is a solution containing a weak acid.)

Are you wearing your safety goggles?

What to do:

Now that you have collected everything you need,follow the instructions listed below.

1. Put the piece of zinc into the test tube.

2. Half fill the test tube with vinegar. Immediately put the corktightly on the test tube to prevent the gas formed from escaping.

3. Leave the experiment set up for a short while so that enough gascan build up to be tested. If you can’t see any bubbles,stand your corked test tube in a beaker of hot water.This should speed up the chemical change.Wait until the zinc and vinegar have nearly stopped bubbling.

4. What are the reactants in this reaction?

5. What products do you think are forming?


5

Read the information on the following page while you are waiting forthe reaction to finish.

Max and his partner had no idea how to test the gas. Do you know?They decided to look up the properties of hydrogen in a book so thatthey could determine a test. This is what they found.

Hydrogen is a colourless gas

at room temperature and

pressure. It is the lightest

and most abundant element

in the universe.

Hydrogen can be prepared

by the electrolysis of water.

This means that an electric

current is used to break apart

water molecules. (Oxygen is

also formed in this reaction.)

Hydrogen can be used

as a fuel. It is also used

in industry to produce

ammonia.

Care should be taken when

handling hydrogen as it

reacts explosively with

oxygen in the presence of

a spark or naked flame.

Hydrogen

After reading through this information, they worked out how theywere going to test for hydrogen. How would you carry out the test?

Max and his partner decided that they could put a naked flameinto the mouth of the test tube. If the test tube contained hydrogen,the hydrogen would react with oxygen and make a popping noise.There would be a small amount of hydrogen only so the testwouldn’t be dangerous. If there wasn’t a noise, then the gascould be air.


6

Where would oxygen needed for the test come from? ________________________

Oxygen from air could react with any hydrogen present in the test tube.

This test has to be done quickly so that hydrogen does not escape.Why would hydrogen escape?

Hydrogen is lighter than air so it would get away very quickly.

Now it’s time to test the gas in your test tube. Look at the diagram below.It will help you to do the test. Light a match, quickly take the cork outof the test tube and put the flame over the mouth of the test tube.

Testing for hydrogen

cork

test tube

zinc

acid

bubbles of gas

test tube

zinc

acid

bubbles of gas

build-up of gas

Perform the test yourself. What happened?Write your observations below.

Max and his partner wrote their observations.There is a copy of these in the answer pages.Compare your results with theirs.


7

Exercise 6.2

In Exercise 6.2, you’ll identify and describe the reactants and productsof this example of a reaction between an acid and a metal.Please complete this exercise now.

You observed another chemical reaction in this activity.It was in the test that you performed to detect the presence of hydrogen.Do you know what it was?

Complete the sentences below about the test for hydrogen.

When combines with oxygen, it does so explosively.A helps this to happen. The explosion makes a poppingsound when it happens in a .

Do you know any compounds that contain hydrogen and oxygen?There is one that you drink, wash in and swim in. Yes, that’s right. Water.Hydrogen and oxygen combine to form .This is an example of a chemical because reactantscombine to make a new product.

Check your answers.

Look around the mouth of the test tube you used in the hydrogen test.Can you see any small droplets of water? These are the product ofthe burning of hydrogen and oxygen in the explosion.

CAUTION Think about safety

The reaction to test for hydrogen is an example of combustion, or burning.You used a flame to make hydrogen begin to burn. The hydrogen inthe test tube burned so quickly that there was an explosion or pop.The hydrogen test is always done using a small amount of gas in a test tube.Using larger volumes of gas would be very dangerous.


8

What’s next?

In this lesson, you have considered the reactants and productsof four reactions that you observed in Set 1. (Remember, they areexamples of chemical reactions because new substances form whenthe reactants are combined. Some kinds of chemical reactions havespecial names, such as corrosion and combustion.)

In the next lesson, you will look more closely at some chemical reactions.But you won’t be able to see the changes that occur with your eyesbecause you’ll be thinking about what particles – atoms and molecules –do during a chemical reaction. You will need to use models to picturethese tiny, interacting particles.

But before you begin the next lesson, assess your progress for Lesson 7using the checklist below.



❑ identify and describe reactants and products in a corrosion reactionand in a reaction between an acid and a metal

❑ safely and efficiently perform a test for hydrogen.

Are you making good progress? Well done if you ticked all the boxes!


9

Lesson 7

Taking a closer look

Do you remember the difference between a chemical reaction anda physical change?

A quick review

Put simply, a chemical change makes a new substance buta physical change does not. So if a chemical change occurs,you expect to see a new product appear. Is this always easy?

How can you tell if a chemical change has taken place?Think back to the chemical changes that you have observed.Write down as many observations as you can rememberthat indicate a new substance has been formed.

Did you think of these observations?A solid is produced. There is a colour change. A gas is produced.A liquid is produced.

What about physical changes?What might you observe when there is a physical change?

A solid disappears. There is a colour change. A gas is produced.

Are there any similarities between the evidence for a chemical changeand a physical change? You can see that there are. For example, if a gas isproduced it is difficult to say if a liquid is evaporating (a physical change)or a new substance is being produced (a chemical change).

It can be very difficult to decide if the change you see is physical or chemical.


10

A closer look

How can you tell if the substances are the same ones that you started withor if they are different? Let’s compare the evaporation of water withthe combustion reaction from Lesson 6.

To see what is happening, you will need to use models to representthe chemicals involved. The table below shows ways to picturehydrogen, oxygen and water.

Substance Diagram (model) Composition

hydrogen 2 atoms* of hydrogenjoined together

oxygen 2 atoms of oxygenjoined together

water 1 atom of oxygen joined with2 atoms of hydrogen

Here is a diagram of anexample of a physical change –water evaporating.

The diagram shows watermolecules◊. You can see thatwater as a liquid has the samemolecules as water as a gas.Therefore, there are no newsubstances.

Water as a gas is the samesubstance as water as a liquid.

water as a gas

water as a liquid

* An atom is the smallest particle, or unit, of an element.

◊ A molecule is the smallest particle, or unit, of an element or compoundwith recognisable properties of the substance.


11

The chemical reaction between hydrogen and oxygencan be shown like this.

hydrogen and oxygen mixed together hydrogen and oxygen chemically combined

chemicalreaction

A new substance, water, is formed. The reactants have ‘disappeared’.

Use the table on page 10 and the diagram above to answer the following.

1. (a) How many atoms are in a molecule of hydrogen? _________________

(b) What kind of atoms are in a molecule of hydrogen?

(c) Is hydrogen an element or a compound? ______________________________

2. (a) How many atoms are in a molecule of oxygen? ____________________

(b) What kind of atoms are in a molecule of oxygen?

(c) Is oxygen an element or a compound? __________________________________

3. (a) How many atoms are in a molecule of water? _______________________

(b) What kind of atoms are in a molecule of water?

(c) Is water an element or a compound? ____________________________________

Please check your answers in the answer pages.


12

Chemists use the term chemical composition to describe the elementsthat make up a compound. Chemical composition refers to the typesof elements and the proportion of each element present. For example,the chemical composition of water is two hydrogen atoms andone oxygen atom in every molecule of water.

What is the chemical composition of copper sulfate?Remember, the formula for copper sulfate is CuSO4.

The smallest unit of copper sulfate will have a chemical composition ofone copper atom, one sulfur atom and four oxygen atoms.

Add the word chemical to the heading of the last column in the tableon page 10. Chemical composition is a better description of theinformation listed in this column.

The table and the diagrams on page 11 show that a chemical changeresults in a change in the chemical composition of substances.For example, hydrogen and oxygen have different chemical compositionsfrom water. After the chemical change, hydrogen and oxygen moleculesno longer exist. The atoms have been rearranged to form a new substance,water, so there are water molecules present only.

Exercise 7

Do you know what a decomposition reaction is?It is a reaction in which a compound is broken apart.

Turn to send-in Exercise 7 to represent an example of decompositionusing models and to identify and describe the reactants and products.



❑ use and interpret models of molecules

❑ describe the reactants and products in the decompositionof water.


13

Lesson 8

Another close look

A diagram of a molecule gives you a lot of information abouta chemical substance. It gives information about the number andtypes of atoms in the molecule. As well, it allows you to decideif a substance is an element or a compound.

In this lesson, you will use diagrams of atoms and moleculesto picture what happens when substances interact in reactions.

Burning carbon

You are probably familiar with the chemical substance calledcarbon dioxide. You might remember it as one of the colourless gasesthat you breathe out when you exhale.

There are many ways to produce carbon dioxide.One way is to burn carbon in air.The oxygen in air combines with carbon to form carbon dioxide.

What is another name for this kind of reaction?

Burning reactions are also called combustion.

What happens in this combustion reaction?

Exercise 8.1

Hopefully, you have become very confident about identifying anddescribing the reactants and products of reactions you observe.

Complete send-in Exercise 8.1 about a combustion reactioninvolving graphite (the carbon that is used as ‘lead’ in pencilsthat you examined in Lesson 3).


14

Looking at carbon and oxygen

Here are models for carbon and oxygen.

carbon oxygen

Use information in these models to complete the following tasks.

1. Describe the structure of carbon.

2. Is carbon an element or a compound? Explain your answer.

3. Describe a molecule of oxygen.

4. The symbol for the element oxygen is O.Write the chemical formula for an oxygen molecule. ___________________



15

You have noticed that the models for carbon and oxygen do not showisolated atoms. Atoms of chemical substances do not usually existon their own. They are generally in groups.

Atoms that join together into a ‘lump’, like carbon, are usually describedas a lattice. The atoms actually fit together in a neat, repeating pattern.

Other substances exist as tiny, separate molecules. For example, oxygenexists as a diatomic molecule. That is, each molecule of oxygen containstwo atoms. Di- is a prefix that means two. Oxygen is still an elementbecause every molecule contains oxygen atoms only.

There are other elements that form diatomic molecules. For example,chlorine (Cl2), nitrogen (N2) and fluorine (F2) exist as molecules,not as separate atoms. Unless you are specifically asked to write thesymbols for these elements, always show them as diatomic molecules.

Atoms are held together in lattices or in molecules by forces calledchemical bonds. You will investigate these forces in more detail in Set 3.

Looking at carbon dioxide

The combustion of carbon and oxygen produces carbon dioxide.

1. Describe a molecule of carbon dioxide.

2. Is carbon dioxide an element or a compound? Explain your answer.

3. Write the chemical formula for carbon dioxide. ___________________________


16

4. The atoms of carbon are joined together in layers in a lattice.Two atoms of oxygen are joined together in a molecule.After the combustion reaction, atoms are joined togetherin carbon dioxide molecules.

What do you think has happened during the chemical reaction?

Please check your answers for all the questions in the answer pages.

In this lesson, you have increased your understanding ofwhat happens during a chemical reaction. Atoms have to break awayfrom the reactants before they can chemically join together to makea new substance. Remember, atoms are held together by chemical bonds,making lattices and molecules. So chemical bonds within the reactantshave to be broken then new bonds can form, creating products.

During a chemical reaction:• substances are chemically changed• new substances are produced• bonds between atoms of the reactants are broken• bonds are formed between atoms to make products.

In the next lesson, you will be investigating a different way thatchemists show, or represent, chemical reactions.



❑ describe the changes that occur to atoms and moleculeswhen substances react

❑ identify and describe the reactants and productsin a combustion reaction

Exercise 8.2

Do you think that you can interpret diagrams of chemical changes?Complete send-in Exercise 8.2. (If you cannot do these questions,revise the lesson then try again.)


17

Lesson 9

Chemical equations

Do you have to write out long explanations when you describe everychemical change? How do chemists show, or represent, chemical reactions?In this lesson, you will write chemical equations to summarise somechemical reactions.

Reactants and products

The first thing you have to do is to identify the reactants and productsof a chemical reaction. You have been using these three termsthroughout Set 2. Write a definition for each one.

reactant: ___________________________________________________________________________________________

product: ____________________________________________________________________________________________

chemical reaction: _____________________________________________________________________________

A reactant is a substance that takes part in a chemical reaction.A product is a substance that is formed during a chemical reaction.A chemical reaction is a chemical change, or a change in thechemical composition of the substances present.

Notice that the definition for reactants has been improved sincethe one you used at the beginning of Lesson 6. Reactants are not justthe substances that are mixed together; they have to be involved inthe chemical change that occurs.

For example, think about the first reaction you did where you put zinc intocopper sulfate solution. You mixed water with the zinc and copper sulfatebut it was not part of the reaction. So water was not a reactant.


18

Now let’s practise picking which substance is the reactant andwhich is the product.

Reactant or product?

Highlight or circle the reactants in each description below.Underline the products.

If you think there are any other reactants or products that have notbeen described, write a comment about it.

1. Burning magnesium metal produces a grey substancecalled magnesium oxide.

2. Mercury can be formed by heating mercury chloride.

3. A red-brown gas called nitrogen dioxide evolves (is given offas a gas) when lead nitrate is heated.

4. Sodium reacts with water to make an alkaline solutioncontaining sodium hydroxide.

5. Hydrochloric acid produces carbon dioxide when poured ontocalcium carbonate.

Please check your answers and read the comments in the answer pages.


19

Now that you are becoming good at identifying and predicting reactantsand products, you are ready for the next step – writing word equations.

Word equations

Instead of having to write out a detailed description of a chemical reaction,chemists use equations. The first type of equation you will use isa word equation. This is the simplest type, where you write the namesof the chemicals involved in the reaction. An example is shown below.

carbon + oxygen → carbon dioxide

The reactants are shown on the left-hand side of the arrow andthe products are to the right.

reactants → products

The arrow tells you that a chemical reaction has taken place.Notice that where there is more than one reactant (or product),the names are joined with a + sign.

Write a word equation to show copper reacting with oxygento form copper oxide.

+ →

Is this the word equation you wrote?copper + oxygen → copper oxide

It is also correct if you wrote:oxygen + copper → copper oxide

Sometimes it is difficult to fit all of an equation on one line.For example, here is a word equation for the chemical reactionbetween zinc and copper sulfate that you performed in Set 1.

zinc + coppersulfate → copper +

zincsulfate

Notice that the two parts in the name of a compound can be writtenon separate lines but the whole equation runs across one line only.

Now name the reactants in the equation above.

Zinc and copper sulfate are the reactants. (Copper and zinc sulfate are the products.)


20

Writing word equations

Write a word equation for each of the following chemical reactions.

1. Hydrochloric acid reacts with zinc to produce a compoundcalled zinc chloride and hydrogen gas.

+ → +

2.

octane in petrol

carbon dioxideand waterare produced

oxygen from the air

+ → +

3.

copper (II)carbonate

copper (II)oxide

carbondioxide

→ +


21

4.

ammoniumchloride

ammonia hydrogenchloride

+ →

5. Objects made of iron become coated in iron oxide whenthey react with oxygen while in contact with water.This is an example of corrosion called rusting.

+ →

Please check your equations in the answer pages.

Now try these examples.Remember to put in the + signs and arrows for yourself.And watch out for reactants and products that are not named.

6. With sulfuric acid, cobalt carbonate forms bubbles of carbon dioxide,a salt called cobalt sulfate and water.

7. Ammonium phosphate was dissolved in water. Then lithiumchloride was mixed into water in another beaker. When the twosolutions were stirred together, a solid formed and settled to thebottom. It was called lithium phosphate. The mixture was filteredand the water evaporated away from the filtrate. Crystals ofanother salt appeared. It was called ammonium chloride.


22

8. Calcium hydroxide is a base that reacts with hydrochloric acid.This reaction is an example of neutralisation because it formsproducts that are not acids or bases. These products are water anda salt called calcium chloride.

9. The compound ethyl ethanoate. smells like tropical fruit It isproduced by heating ethanol and ethanoic acid in special glassware.The ethanol doesn't have any smell and the acid smells like vinegar.A drop of concentrated hydrochloric acid is added to make thereaction happen quickly. Ethyl ethanoate can be used as aflavouring in lollies and drinks. Some water that was made in thereaction is taken out before it can be used in food.

10. Ethanol is an example of a fuel because it releases energy whenit is burned. The wastes from the fuel are safe for living things –carbon dioxide and water.

Check your equations now.



❑ identify the reactants and products in a chemical reaction

❑ write a word equation to describe a chemical reaction.

Exercise 9

Now that you can write word equations to show chemical reactions,turn to the send-in pages and do Exercise 9.


23

Lesson 10

What is in it?

When you’re writing word equations, you need to name the substancesinvolved correctly. To name substances correctly, you need to knowif the substance is an element or a compound. If it is a compound,you usually need to know what elements it contains.How can you find out these things?

Ways of showing chemicals

Chemical substances can be represented by symbols, formulasor diagrams. Some examples are shown in the table below.

Chemical formula Diagram (model)

Na

Cl2

NaCl

Which substances in the table above are elements?

Na and Cl2 are the elements (because they contain one kind of atom only.Notice that Cl2 is diatomic whereas Na is a lattice).


24

Now, how do you name the substances on page 23? There are probablyat least 118 elements and many millions of compounds so theremust be a very clear, organised system for naming each substance.Let’s start with elements.

Elements

ReadDo you have to learn the names and symbols for all the elements?Of course not! There is an alphabetical list of 103 of the elements atthe back of this unit.

Or, you might prefer to look for the names and matching symbolsin the large chart at the very back of the unit. This chart is calleda periodic table of elements.

What element is that?

1. From memory, from the alphabetical list or from the periodic table,write the name of each element beside its symbol.

(a) C

(b) O

(c) F

(d) Zn

(e) Ca

2. Now write the symbols for each of these elements.

(a) iron

(b) copper

(c) nitrogen

(d) bromine

(e) magnesium

Please check your answers in the answer pages.

You usually also need to know some properties of elements to be ableto identify them in the reactants or products. How can you knowthe properties of elements?


25

Classifying elements

You probably recall that elements can be classified in different ways.For example, they can be grouped into solids, liquids and gasesat room temperature. This classification is based on state.

Most elements are solids at room temperature.

Only two, mercury (Hg) and bromine (Br), are liquids at room temperature.Use a green pencil to shade these two elements in the periodic table below.

The elements that are gases are towards the right-hand side of theperiodic table. Shade these elements yellow: hydrogen (H), helium (He),nitrogen (N), oxygen (O), fluorine (F), neon (Ne), chlorine (Cl), argon (Ar),krypton (Kr), xenon (Xe), radon (Rn) and probably ununoctium (Uuo).

Then complete the key below the periodic table.

1 H2 He

3 Li4 Be

5 B6 C

7 N8 O

9 F10

Ne

11Na

12Mg

13 Al14 Si

15 P16 S

17Cl

18Ar

19 K20

Ca21 Sc

22 Ti23

V24 Cr

25Mn

26 Fe27

Co28 Ni

29Cu

30 Zn31

Ga32

Ge33

As34

Se35

Br36

Kr

37Rb

38 Sr39 Y

40 Zr41

Nb42

Mo43 Tc

44Ru

45Rh

46 Pd47

Ag48

Cd49 In

50 Sn51 Sb

52 Te53 I

54Xe

55 Cs56

Ba57-71 72

Hf73 Ta

74 W75

Re76 Os

77 Ir78 Pt

79Au

80Hg

81 Tl82 Pb

83 Bi84 Po

85 At86

Rn

87

Fr88

Ra89-103 104

Rf105

Db106

Sg107

Bh108

Hs109

Mt110

Ds111

Rg112

Uub113 114

Uuq115 116

Uuh117 118

Uuo

57 La

58 Ce

59 Pr60

Nd61

Pm62

Sm63 Eu

64 Gd

65 Tb66

Dy67

Ho68 Er

69 Tm

70 Yb

71 Lu

89 Ac

90 Th

91 Pa92

U93

Np94

Pu95

Am96

Cm97 Bk

98 Cf

99 Es

100Fm

101Md

102 No

103 Lr

Key: State at room temperature

solid

liquid

gas

Ask someone to check that you have correctly located all of the elementsthat are liquids and gases.


26

Another very useful way to classify elements is as metals or non-metals.

Think back. What are some properties of metals that would help youto recognise them?

I hope you remembered that metals are usually shiny, malleable (able to be bent),ductile (able to be made into wires), conductors of heat and electricity andthat most metals are silver-coloured (except copper which is orangy-pink andgold which is yellow).

Shade the periodic table and key below to locate metals and non-metals.You could use a red pencil to show the metals.(Hint: The thick stepped line separates metals and non-metals in the table.)

1 H2 He

3 Li4 Be

5 B6 C

7 N8 O

9 F10

Ne

11Na

12Mg

13 Al14 Si

15 P16 S

17Cl

18Ar

19 K20

Ca21 Sc

22 Ti23

V24 Cr

25Mn

26 Fe27

Co28 Ni

29Cu

30 Zn31

Ga32

Ge33

As34

Se35

Br36

Kr

37Rb

38 Sr39 Y

40 Zr41

Nb42

Mo43 Tc

44Ru

45Rh

46 Pd47

Ag48

Cd49 In

50 Sn51 Sb

52 Te53 I

54Xe

55 Cs56

Ba57-71 72

Hf73 Ta

74 W75

Re76 Os

77 Ir78 Pt

79Au

80Hg

81 Tl82 Pb

83 Bi84 Po

85 At86

Rn

87

Fr88

Ra89-103 104

Rf105

Db106

Sg107

Bh108

Hs109

Mt110

Ds

111

Rg112

Uub113 114

Uuq115 116

Uuh117 118

Uuo

57 La

58 Ce

59 Pr60

Nd61

Pm62

Sm63 Eu

64 Gd

65 Tb66

Dy67

Ho68 Er

69 Tm

70 Yb

71 Lu

89 Ac

90 Th

91 Pa92

U93

Np94

Pu95

Am96

Cm97 Bk

98 Cf

99 Es

100Fm

101Md

102 No

103 Lr

Key: Metal or non-metal?

metal

non-metal

There is a shaded periodic table in the answer pages.


27

Now that you have checked your answers, transfer the information aboutstate and metallic/non-metallic properties to the large periodic tableat the back of this unit. You need to make a key on the table to showwhat each colour represents.

You can take the large page out of the unit, shade it and put it upon a wall where you can refer to it.

Why is it useful to classify elements?

One of the main advantages is that it helps you to predict theproperties of a element, even if you don't know much about it.

For example, find bohrium (Bh)—it is number 107—in the periodic table.From its position in the table, you would expect it to be a solid metal.This means that it should be shiny, silver, conduct electricity and heat,be malleable and ductile. All that information, and you have never seena sample of bohrium (and you probably won't ever see one either!).

Try these examples. Tick the properties that each element probably has.

cadmium

❒ solid ❒ conductor ❒ brittle

❒ liquid ❒ shiny ❒ dull

❒ gas ❒ malleable ❒ non-conductor

❒ silver ❒ ductile

neon

❒ solid ❒ shiny ❒ conductor

❒ liquid ❒ silver ❒ non-conductor

❒ gas


Exercise 10.1

In this send-in exercise, you will describe the patterns in theperiodic table for state and metallic/non-metallic properties.Please complete Exercise 10.1 now.


28

Compounds

Compounds can be classified by the type of bonding between atoms.Remember, a chemical bond is a force between atoms. This force holdsthe atoms of a compound together. There are two types of bondingbetween atoms in a compound—covalent and ionic.

Covalent compounds

Covalent compounds have covalent bonds that join atoms togetherinto molecules. How can you identify a covalent compound?The table below shows examples of covalently bonded compounds.

Some covalent compounds

Name Formula

hydrogen chloride HCl

carbon dioxide CO2

sulfur trioxide SO3

water H2O

phosphorus trichloride PCl3

Use information in the table to complete the following tasks.

1. List the elements in each of the covalent compounds in the table.

(a) HCl ____________________________________________________________________________________

(b) CO2 ____________________________________________________________________________________

(c) SO3 ____________________________________________________________________________________

(d) H2O ____________________________________________________________________________________

(e) PCl3 ____________________________________________________________________________________

2. Are any of the elements that you have named metals?How are the elements in covalent compounds classified?



29

Ionic compounds

The atoms in an ionic compound are held together by ionic bonds.The table below lists some examples of ionic compounds.

Some ionic compounds

Name Formula

sodium bromide NaBr

copper (II) carbonate CuCO3

calcium oxide CaO

magnesium sulfate MgSO4

iron (II) hydroxide Fe(OH)2

Use the information in the table to complete the following tasks.

1. List the elements in each of the ionic compounds in the table.

(a) NaBr _______________________________________________________________________________

(b) CuCO3 _______________________________________________________________________________

(c) CaO _______________________________________________________________________________

(d) MgSO4 _______________________________________________________________________________

(e) Fe(OH)2 _______________________________________________________________________________

2. Highlight or circle the symbols of the metals in the formulasin the table above.

3. Did you notice that each ionic compound contains a metal?Do ionic compounds contain non-metals too? ______________________________

4. What do all the ionic compounds in the table have in common?

Check your answers for all the questions.


30

Remember, covalent compounds consist of elements that are all non-metals.Ionic compounds contain non-metals and metals.

Exercise 10.2

Complete this send-in exercise about using patterns in the periodic tableto predict the kind of compound that will form between elements.



❑ classify a chemical substance as an element or a compoundusing a formula or a diagram

❑ use a periodic table to predict some propertiesof an element

❑ classify elements in a periodic table by state andby metallic/non-metallic properties

❑ decide if a compound has ionic or covalent bondsbased on the type of elements present.

What's next?

In Lesson 9, you found out that it is useful to write word equationsfor chemical reactions and you learned how to write them.But to write a word equation, you have to be able to identifythe chemicals as either elements or compounds.That's what you've learned about in this lesson.


31

Suggested answers

Lesson 6 Reactants and products

Page 2 Metal in solution

1. The reactants were zinc and copper sulfate.

2. Here is the first paragraph again from page 2 with the descriptions ofreactants underlined.

In Lesson 1, you put a piece of shiny, silver-coloured zinc intoa pale blue solution of copper sulfate. After a short while,you saw the formation of pinky-orange solid on the zinc.The solution was left to stand overnight.

3. The products were the colourless solution and the mixture of solids.

What were the solids? You identified them as leftover zinc, copperand copper oxide. The leftover zinc is not a product; it is unused reactant.So the solid products from this experiment were copper and copper oxide.

What was the colourless solution? What could be dissolved in it?Most of the zinc has ‘disappeared’ and there is still the sulfate part ofcopper sulfate that must be present in a product. You could guess thatthe solution contains dissolved zinc sulfate.

Hydrogen

Page 6 When the lighted match was brought near the mouth of the test tube,there was a ‘popping’ noise like a small explosion.

Page 7 Here are the completed sentences.

When hydrogen combines with oxygen, it does so explosively.A spark or flame helps this to happen. The explosion makes a poppingsound when it happens in a test tube.

Do you know any compounds that contain hydrogen and oxygen?There is one that you drink, wash in and swim in. Yes, that’s right. Water.Hydrogen and oxygen combine to form water.This is an example of a chemical reaction or change because reactantscombine to make a new product.


32

Lesson 7 Taking a closer look

A closer look

Page 11 1. (a) Each hydrogen molecule contains two atoms.

(b) Hydrogen contains hydrogen atoms only.

(c) Hydrogen is an element (because it contains one kind of atom only).

2. (a) Each oxygen molecule contains two atoms.

(b) Oxygen contains oxygen atoms only.

(c) Oxygen is an element (because it contains one kind of atom only).

3. (a) Each water molecule contains three atoms.

(b) Water contains an oxygen atom and two hydrogen atoms.

(c) Water is a compound (because it contains more than one kind of atomchemically combined together).


33

Lesson 8 Another close look

Looking at carbon and oxygen

Page 14 1. Carbon consists of a large number of carbon atoms joined together.(The atoms are joined into a lattice by chemical bonds.)

2. Carbon is an element because it is composed of carbon atoms only.

3. A molecule of oxygen consists of two oxygen atoms chemically bondedtogether.

4. The formula for an oxygen molecule is O2.

Looking at carbon dioxide

Page 15 1. A molecule of carbon dioxide consists of one carbon atom joined totwo oxygen atoms by chemical bonds.

2. Carbon dioxide is a compound because it contains two different kinds of atoms –it contains carbon atoms and oxygen atoms joined by chemical bonds.

3. The formula for carbon dioxide is CO2.

Page 16 4. During the chemical reaction, an atom of carbon breaks away from the latticeof carbon atoms. To do this, bonds must be broken. At the same time,bonds in a molecule of oxygen are broken so that its atoms separate.Then new bonds form as the oxygen atoms join with the carbon atom,forming a molecule of carbon dioxide.

Use the boxes below to complete send-in Exercise 7.

voltameterdevice fordecomposing water

electrical contactto provide electricalenergy for reaction

element compound


34

Lesson 9 Chemical equations

Page 18 Reactant or product?

1. Burning magnesium metal produces a grey substance called magnesium oxide.

Oxygen is also needed as a reactant when burning occurs.

2. Mercury can be formed by heating mercury chloride.

The chloride part of mercury chloride must be part of another productthat is formed. Chlorine atoms cannot just disappear in the reaction.

3. A red-brown gas called nitrogen dioxide evolves (is given off as a gas) when lead nitrate is heated.

The lead part of lead nitrate must be part of another product that is formed.(There are also some oxygen atoms left that are joined into a product.)

4. Sodium reacts with water to make an alkaline solution containing sodium hydroxide.

All the kinds of atoms in the reactants are also in the products sothese could be the only reactants and products. (But they are not;hydrogen gas is also a product.)

5. Hydrochloric acid produces carbon dioxide when poured onto calcium carbonate.

The calcium part of calcium carbonate must be part of another productthat is formed. The chloride part of hydrochloric acid also must be inanother product that has not been mentioned. The hydrogen part ofhydrochloric acid also must be present in a product. (There are someoxygen atoms left that are joined into a product too.)


35

Lesson 9 continued

Writing word equations

Page 20 1.hydrochloric acid + zinc → zinc

chloride + hydrogen

2. octane + oxygen → carbondioxide + water

3.copper (II)carbonate → copper (II)

oxide + carbondioxide

Page 21 4. ammonia + hydrogen chloride → ammonium chloride

5. iron + oxygen → iron oxide

6.sulfuric acid +

cobaltcarbonate → carbon

dioxide + cobaltsulfate + water

7.ammonium phosphate +

lithiumchloride → lithium

phosphate + ammonium chloride

Page 22 8. calciumhydroxide +

hydrochloric acid → water +

calciumchloride

9. ethanol + ethanoic acid → ethyl

ethanoate + water

10. ethanol + oxygen → carbondioxide + water

Did you include oxygen as a reactant? Well done! Burning needs oxygen.


36

Lesson 10 What is in it?

Page 24 What element is that?

1. (a) carbon

(b) oxygen

(c) fluorine (Check your spelling carefully!)

(d) zinc

(e) calcium

2. (a) Fe

(b) Cu

(c) N

(d) Br

(e) Mg

Page 26

Classifying elements

1 H2 He

3 Li4 Be

5 B6 C

7 N8 O

9 F10

Ne

11Na

12Mg

13 Al14 Si

15 P16 S

17Cl

18Ar

19 K20

Ca21 Sc

22 Ti23

V24 Cr

25Mn

26 Fe27

Co28 Ni

29Cu

30 Zn31

Ga32

Ge33

As34

Se35

Br36

Kr

37Rb

38 Sr39 Y

40 Zr41

Nb42

Mo43 Tc

44Ru

45Rh

46 Pd47

Ag48

Cd49 In

50 Sn51 Sb

52 Te53 I

54Xe

55 Cs56

Ba57-71 72

Hf73 Ta

74 W75

Re76 Os

77 Ir78 Pt

79Au

80Hg

81 Tl82 Pb

83 Bi84 Po

85 At86

Rn

87

Fr88

Ra89-103 104

Rf105

Db106

Sg107

Bh108

Hs109

Mt110

Ds111

Rg112,

Uub113 114

Uuq115 116

Uuh117 118

Uuo

57 La

58 Ce

59 Pr60

Nd61

Pm62

Sm63 Eu

64 Gd

65 Tb66

Dy67

Ho68 Er

69 Tm

70 Yb

71 Lu

89 Ac

90 Th

91 Pa92

U93

Np94

Pu95

Am96

Cm97 Bk

98 Cf

99 Es

100Fm

101Md

102 No

103 Lr

Key: Metal or non-metal?

metal

non-metal


37

Lesson 10 continued

Page 27 Why is it useful to classify elements?

From its position in the periodic table, cadmium is a metal. Therefore, it isprobably solid, silver-coloured, a conductor, shiny, malleable and ductile.

From its position in the periodic table, neon is a non-metal. It is at the veryright-hand side of the table so it is a gas. It is probably a non-conductor.

Page 28 Covalent compounds

1. (a) hydrogen and chlorine

(b) carbon and oxygen

(c) sulfur and oxygen

(d) hydrogen and oxygen

(e) phosphorus and chlorine

2. Covalent compounds contain non-metallic elements only.

Page 29 Ionic compounds

1. (a) sodium and bromine

(b) copper, carbon and oxygen

(c) calcium and oxygen

(d) magnesium, sulfur and oxygen

(e) iron, oxygen and hydrogen

2. The metals have been circled in the table below.

3. Ionic compounds contain both metals and non-metals.

4. All ionic compounds contain atoms of metallic elements andatoms of one or more non-metallic elements.


38


39

Send-in page Name ______________________________

Lesson 6: Reactants and products

Exercise 6.1 Describing a corrosion reaction

In your investigation, you observed that copper can corrode in air.Complete the tables below to identify and describe the reactants andproducts of this corrosion reaction.

Reactants Description of reactants

Product Description of product


40

Exercise 6.2 Describing a reaction of an acid and metal

You have just performed a reaction between an acid and a metal.Complete the tables below to identify and describe the reactants andproducts of this reaction.


Products Description of products

salt calledzinc ethanoate


41

Send-in page Name ______________________________

Lesson 7: Taking a closer look

Exercise 7 Describing a decomposition reaction

1. When water decomposes, it is broken into the elements it contains.Complete the tables below to identify and describe the reactantsand products of this reaction.

Reactant Description of reactant


2. Water is decomposed in a process called electrolysis.(You read about electrolysis in the 'textbook' on page 5.)

A diagram of the equipment to perform electrolysisis shown on the following page.

Cut out the labels and models of molecules fromthe bottom of page page 33. Use them to completethe diagram of electrolysis on the next page.

Be warned! You will not need all of the molecules on page 33to complete the diagram.


42

Complete the diagram below of electrolysis of water.

electriccurrent


43

Send-in page Name ______________________________

Lesson 8: Another close look

Exercise 8.1 Describing a combustion reaction

You have burned things before!What are the reactants and products when graphite (carbon) is burned?Complete the tables below.


Product Description of product


44

Exercise 8.2 Interpreting diagrams

For each question, write the formulas for all the substances anddecide if they are elements or compounds. Watch out for elementsthat form diatomic molecules! Then explain what you think happenedduring the chemical reaction.

1.chemicalreactionhydrogen chlorine hydrogen chloride

Substance Formula Element or compound?

hydrogen

chlorine

hydrogen chloride

Describe what happened in this chemical reaction.

2.chemicalreactionoxygen nitrogen nitrogen dioxide

Substance Formula Element or compound?

oxygen

nitrogen

nitrogen dioxide

Describe what happened in this chemical reaction.


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Send-in page Name ______________________________

Lesson 9: Chemical equations

Exercise 9

Write a word equation to describe each of the following changes.

1. Many years ago matches contain phosphorus. When the matchwas struck, phosphorus combined with oxygen in the air to givephosphorus pentoxide.

2. Natural gas is mainly methane gas. When methane burns,it forms carbon dioxide and water. Oxygen from the air isused up as methane burns.

3. When a car is badly tuned, the octane in the petrol combines withoxygen to give deadly carbon monoxide and water.

4. Hydrogen and zinc chloride form when zinc reacts withhydrochloric acid.

5. Copper oxide will corrode in sulfuric acid to give copper sulfateand water.


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47

Send-in page Name ______________________________

Lesson 10: What is in it?

Exercise 10.1

1. Most elements are metals. Describe how metallic elements arearranged in the periodic table to help you see that they are similar.(Hint: Describe how the metals [and non-metals] are arranged in the periodic table.)

2. The grouping of elements in the periodic table also gives youinformation about the states of elements.

Describe how elements that are solids and elements that are gasesare arranged in the periodic table to help you see that elementswithin these groups are related.

(Hint: Describe how elements that are solid and elements that are gaseousare arranged in the periodic table.)


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Exercise 10.2

For each compound, list all the elements in the compound.Then use your periodic table to decide if each element is a metal ora non-metal. Lastly, write down whether the compound has ionicor covalent bonding.

Compound Formula Elements Metal ornon-metal?

Ionic or covalentbonding?

arsenic hydride AsH3

nitrogen (IV) oxide NO3

copper (II) sulfate CuSO4

methane CH4

niobium (V) fluoride NbF5

Science Stage 5


ChemicalcombinationsSet 3: Why do chemicals react?


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☞ Set 3 Why do chemicals react?Lessons 11 and 12 Why do elements react?Lessons 13 and 14 How do compounds react?Lesson 15 Some important reactionsRevision lesson The last word


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Set 3: Why do chemicals react?

Contents



Lessons 11 and 12 Why do elements react? ....................................... 1

Lessons 13 and 14 How do compounds react? ................................ 15

Lesson 15 Some important reactions .................................. 23

Revision Lesson The last word ....................................................... 27


Send-in pages ............................................................................................ 37


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Lessons11 and 12

• use a periodic table to state the number of protonsand electrons in an atom

• use a name of an element to calculate the number ofneutrons in an atom

• compare the numbers of protons, electrons andneutrons in different atoms

• identify the properties of an element that aremost influenced by the number of protons, neutronsand electrons in its atoms

• identify the periods and groups of the periodic table

• identify patterns in the electronic configurations ofelements within periods and groups

• define the terms atomic number, mass number,isotope and electronic configuration

Lessons13 and 14

• safely perform a neutralisation reaction usinghousehold chemicals

• use indicators to distinguish between acids, basesand neutral substances

• identify and describe the reactants and productsof a neutralisation reaction

• perform a reaction between an acid and a carbonate

• identify and describe the reactants and productsof a reaction between an acid and a carbonate

• interpret a photograph and a report abouta precipitation reaction

• identify and describe the reactants and productsof a precipitation reaction

Lesson 15 • write general equations for some reactions

• match reactants with a general equation anduse the general equation to predict the products

RevisionLesson

• identify some words and terms from this unit withgiven meanings

• give the meaning of some words and termsused in this unit.


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Here is a reminder of the items you need for Set 3. To save time,it might be a good idea to get all these things ready before you start.

Lessons 13 and 14

• beakers

• eye dropper

• safety goggles


• 2 pieces of red litmus paper

• 2 pieces of blue litmus paper

• plastic spoon

• white vinegar

• a household cleaner, e.g. Windex, Ajax or Jiff


• baking soda

• plain flour

• self-raising flour


1

Lessons 11 and 12

Why do elements react?

Only a few of the elements are typically found as pure elements.Usually, elements are combined with each other to form compounds.Why do most elements tend to form compounds?To find an answer, you need to learn more about atoms.

What is an atom?

An atom is the smallest particle, or unit, in an element. There areabout 118 different kinds of atoms – one for each kind of element.

But the atom is not the smallest particle possible. Each atom is composedof smaller particles called fundamental particles.These fundamental particles are protons, neutrons and electrons.(And fundamental particles are probably made from even tinier particles. You can learn more about this in Stage 6 Physics.)

Here is a diagram of an atom of the element carbon.

electron

neutron

protonnucleus

electron shell

Use information from the diagram to describe the structure of an atom.

There is a sample answer in the answer pages.


2

How are atoms of different elements different?

Different elements contain different numbers of protons, electronsand neutrons. This is why each element has different properties.

How can you find out how many protons, neutrons and electrons arein an atom of an element? This is another place where the periodic tableis useful.

How many protons?

Did you wonder about the order of the elements in the periodic table?The elements are sequenced into the table using their number of protons.

1 H2 He

3 Li4 Be

5 B6 C

7 N8 O

9 F10

Ne

11Na

12Mg

13 Al14 Si

15 P16 S

17Cl

18Ar

19 K20

Ca21 Sc

22 Ti23

V24 Cr

25Mn

26 Fe27

Co28 Ni

29Cu

30 Zn31

Ga32

Ge33

As34

Se35

Br36

Kr

37Rb

38 Sr39 Y

40 Zr41

Nb42

Mo43 Tc

44Ru

45Rh

46 Pd47

Ag48

Cd49 In

50 Sn51 Sb

52 Te53 I

54Xe

55 Cs56

Ba57-71 72

Hf73 Ta

74 W75

Re76 Os

77 Ir78 Pt

79Au

80Hg

81 Tl82 Pb

83 Bi84 Po

85 At86

Rn

87

Fr88

Ra89-103 104

Rf105

Db106

Sg107

Bh108

Hs109

Mt110

Ds111

Rg112

Uub113 114

Uuq115 116

Uuh117 118

Uuo

57 La

58 Ce

59 Pr60

Nd61

Pm62

Sm63 Eu

64 Gd

65 Tb66

Dy67

Ho68 Er

69 Tm

70 Yb

71 Lu

89 Ac

90 Th

91 Pa92

U93

Np94

Pu95

Am96

Cm97 Bk

98 Cf

99 Es

100Fm

101Md

102 No

103 Lr

The numbers on the periodic table above show the number of protonsin one atom of each element. This number is called the atomic numberfor the element. In fact, the number of protons of each elementdefines the element and never varies.

For example, oxygen (O) has an atomic number of eight.Therefore, there are eight protons in each atom of oxygen.


3

Use the large periodic table from the back of this unitto complete the following tasks.

1. Name the element that has an atomic number of:

(a) 7

(b) 16

(c) 6

(d) 12

(e) 27.

2. How many protons are in each atom of:

(a) nickel?

(b) barium?

(c) zinc?

(d) silicon?

(e) chlorine?

Check your answers now.

How many electrons?

How are protons different from electrons and neutrons?Protons have a positive charge, electrons have a negative chargeand neutrons have no charge at all. Do atoms have a charge?No, they are neutral; that is, they have no overall charge. Therefore,the number of protons must equal the number of electrons in an atom.

Answer the following questions.

1. Chlorine has an atomic number of 17.How many protons are in a chlorine atom? __________________________________

How many electrons are in each atom? ________________________________________

2. The element copper has an atomic number of 29.How many protons and electrons are in a copper atom? ______________

3. The element arsenic has the symbol As.There are 33 electrons in an arsenic atom.What is the atomic number of arsenic? ________________________________________



4

How many neutrons?

Neutrons do not have a charge. But they do have mass.The mass of a neutron is very close to the mass of a proton.(Electrons are very tiny. They have almost no mass at all.)

Now compare these two atoms of hydrogen. They are called isotopesbecause they are different forms of atoms for the same element.

1. Explain why both of these atoms are hydrogen.

2. Would they still be atoms of hydrogen if they lost their electrons?

3. Let the mass of a proton equal 1. So the mass of a neutron is also 1.(In this comparison, the mass of an electron is 0.)Compare the masses of these two hydrogen atoms.

4. How does the number of neutrons in an atom affect its mass?

Please check your answers for all these questions now.


5

Mass number is the name given to the total number of protons andneutrons in the nucleus of an atom. If you know the mass numberfor an atom, you can calculate how many neutrons it contains.

Have you heard of carbon-12 and carbon-14? These names are usedin reports about carbon dating to find the age of prehistoric objects.Names like these tell you about the mass number of an atom of an element.

So how many neutrons are in an atom of carbon-12?Follow these steps to find the answer.

A Look up the atomic number for carbon. _______________________________________

The atomic number is in the periodic table. Carbon's atomic number is 6.

How many protons are in an atom? _____________________________________________

The number of protons is the same as the atomic number.So carbon has six protons.

B Write the mass number for an atom of carbon-12. ________________________

The mass number is the number in the name. It is 12.

C Subtract the number of protons from the mass number. _______________

This isn't very difficult, is it? 12 – 6 = 6

So an atom of carbon-12 contains six neutrons.(It also has six protons and six electrons.)

5. Find the number of neutrons in:

(a) carbon-14

(b) bromine-80

(c) uranium-235.

Compare your calculations with the ones in the answer pages.


6

Comparing atoms

Atoms of the same element must always have the same number of protons.But atoms of the same element may have different numbers of neutrons.Remember, atoms of the same element with different numbers of neutrons(that is, with different mass numbers) are called isotopes.

Do atoms of the same element always have the same number of electrons?Yes, if the atoms are uncharged. But recall that atoms can become chargedwhen they gain or lose electrons. Then the atoms are called ions.So atoms of the same element can have different numbers of electrons.

Consider the information in the table below about five different atoms.

Atom Atomicnumber

Massnumber

Number ofelectrons

A 7 14 7

B 7 15 8

C 8 15 8

D 8 15 7

E 9 16 9

Use information from the table to complete the following tasks.

1. Name the kind of atom (the element) for each atom.

A ________________ C _________________ E _________________

B ________________ D _________________

2. Which atoms are isotopes? Why?

3. Which atoms are ions? Why?

Check your answers now.


7

How do protons, neutrons and electrons affect an atom?

Complete these sentences to answer the question in the heading above.

The number of protons in an atom determines the kind of that it is. So the number of protons gives the atom

many of its .

The number of neutrons in an atom changes the of the atom. This can be important for some atoms because atomswith extra neutrons (extra mass) are more likely to break up andbe radioactive.

The number of electrons in an atom influences how the atomcombines with other atoms to form .

You need to check your answers carefully. They contain some new information.Read the sentences again before you continue.

These lessons are supposed to be about why elements react.(Look back at the lesson heading.) By studying atoms, you havefound that you need to look more closely at the electrons in atomsof different elements to understand why elements form compounds.

Electronic configurations

The diagram below is another way to represent an atom of carbon.(Compare it with the diagram on page 1 of this set.)

An atom of carbon

e = electron

n = neutron

p = proton

pp

pp

pp nn

nn

n n nucleus

e e

ee e

e

electronshell

The six protons that make this an atom of carbon are in the nucleus.The nucleus, which is the core or centre of the atom, is really much,much smaller than it is shown in this diagram.

The electrons are at different distances, or levels, from the nucleus.The way that the electrons are arranged is called the electronic configuration.


8

What is the electronic configurationfor the element carbon?

You can see from the diagramthat two electrons are in the shellclosest to the nucleus. The otherfour electrons are in the next shellfurther away from the nucleus.

tiny nucleus

e e

ee e

e

outermostelectron shell

inner electron shell

The arrangement of these electrons can be written 2.4.This shows that there are two electrons in the first shell, or level,and four electrons in the second level giving carbona total of six electrons.

2.4 is called carbon’s electronic configuration.

ReadNow turn to your large periodic table from the back of this unit.Look at the information that is included in the table for each element.

What information does this periodic table tell you about oxygen?

Your periodic table tells you that oxygen has an atomic number of 8,the chemical symbol O, (the name, oxygen) and an electronic configurationof 2.6. If you did not identify all this information, turn to the answer pagesand look at the key there.

Now let’s look more closely at the structure of the periodic table andthe patterns in the electronic configurations of elements in the table.Once you have identified the patterns, you can begin to think abouthow they help you understand why elements react.


9

Comparing electronic configurations in periods

ReadLook at the horizontal (acrosswards) lines of elements in the periodic table.There are seven of these rows. Each row is called a period.But the periods can be a bit confusing to see.

1. Write the number for the period to the left of each ofthe following elements on your large periodic table.

1 hydrogen2 lithium3 sodium

4 potassium5 rubidium

6 caesium7 francium

Remember, the elements are in sequence across each periodso that the atomic number increases.

2. Look at your periodic table again. Run your finger acrosseach period in turn. Make sure that the atomic number increasesby one as you move to the next element in the period.Watch out for the jump that you have to make in period 6 andperiod 7.

How did you go? Periods 1 to 5 were probably easy but after bariumin period 6 you had to jump down to the line under the table thatstarts with lanthanum. (Elements in this row are called lanthanides.)

The lanthanides are listed under the main table because the wholeperiodic table would be too wide to fit on a page if they were putinto the space where they belong in the order of atomic numbers.

The same thing happens in period 7 after radium.(The row of elements that has been moved out of the wayfrom period 7 are called the actinides.)

3. Test that you have found the periods in the table by completingthis task. How many elements are in each period?

1 _________________

2 _________________

3 _________________

4 _________________

5 _________________

6 __________________

7 __________________

Compare your answers with the ones in the answer pages.

Now, at last, you are ready to compare the electronic configurationsacross each period.


10

4. How does the electronic configuration change across period 1?(Hint: Move from left to right across the period.)

5. (a) How are electronic configurations of elements in period 2 alike?

(b) How are electronic configurations of elements in period 2different from each other?

6. Do you see the same kind of pattern in period 3? Explain.

Check your answers before you continue.

You have seen that elements in the same period have similarelectronic configurations. The only part of the electronicconfiguration that changes is the last number. The last numberincreases by one each time the atomic number increases by one.

Why do you think the electronic configuration changes each timethe atomic number changes? Yes, of course! The atom has thesame number of electrons as protons unless it is charged.

You have looked at the patterns in electronic configurations acrossthe first three periods only. There are patterns across the other periodsin the periodic table too. They get a bit more complex so you don’tneed to worry about them in this unit.


11

Comparing electronic configurations in groups

ReadNow look at the vertical (downwards) lines of elements in theperiodic table. Each column is called a group.

The middle groups are a bit complex—they are called transitionmetals—so you don’t need to worry about the patterns in theirelectronic configurations in this unit.

1. Ignore hydrogen*.Number across the top of the columns from 1 to 8 (Li, B, C, N, O,F, He) to give each group its number.

2. Check that you can find the groups (and periods) of the periodic tableby completing this task.

Name the element in:

(a) period 2 and group 4 ____________________________________________________________

(b) period 4 and group 2 ____________________________________________________________

(c) period 5 and group 8. ___________________________________________________________

Check your answers before you continue.

Now look down each group. (Leave out the transition metal groups.)What patterns can you see in the electronic configurations ofelements in the same group?

3. How are the electronic configurations different as you go downeach group?

4. How are the electronic configurations alike in each group?

Turn to the answer pages now.

* Hydrogen is put away from all the groups because sometimes it behaves likeelements in group 1 and at other times, it is more like a group 7 element.


12

You have observed that the elements in each group have the samelast number in their electron configuration. This means that atoms ofthese of elements have the same number of electrons in their outermostelectron shell. These are sometimes called the valence electrons.

The important thing about groups of elements is that they all sharesimilar properties. They react in very similar ways because they havethe same number of electrons in their outermost shells.

Electrons in the outermost shell

You will have realised by now that the outermost shell of an atomcan have up to eight electrons in it. All of the elements in group 8have eight electrons in their outermost shell; you can say that theiroutermost shell is full.

These group 8 elements are very, very unreactive. They seldom formcompounds. Scientists say they are very stable atoms.When atoms of other elements react, they do so to geta stable electronic configuration like a group 8 atom.

For example, all the elements in group 1 can become stable by gettingrid of one electron. Look at the electronic configurations for group 1in your periodic table to see that this is true.

1. How many electrons will elements ingroup 2 need to lose to become stable? ________________________________________

They all have two electrons in their outermost shell so if they can losetwo electrons, they will be stable with an outer shell of eight electrons.

All metal atoms give away, or lose, electrons so that they canbecome stable. (That is why metal atoms form positively charged ions.)What about non-metallic atoms?

2. Look at the electronic configurations of elements in group 7.How could they become stable?

Well done if you suggested that they need to gain one electron.

Atoms of non-metals gain extra electrons to become stable.(That is why non-metallic atoms form negatively charged ions.)


13

Why do ionic compounds form?

Metals readily react with non-metals because metallic atoms canlose electrons, non-metallic atoms can gain electrons and all the atomsbecome stable. When this happens, ionic compounds are formed.

Why do covalent compounds form?

Covalent compounds form when non-metallic elements react.Non-metals do not tend to lose electrons; atoms have to shareelectrons to get extra electrons from another non-metallic atom.By sharing electrons, each atom can have a stable outermost shellfor some of the time.

Take a deep breath!

Well done! You have had to do a lot of thinking and puzzlingto understand the explanation for why elements react.

Fill in the words in the sentences and puzzle below to summarisesome of the information you have considered.

1. An electronic configuration for an element shows how its electronsare arranged into .

2. Elements react so that their atoms become ,with eight electrons in their outermost shells.

3. Elements in the same group of the periodic havesimilar properties.

4. All atoms of the element have the same number of protons.

5. The number of protons in an atom is called its atomic .

6. Atoms of the same can have different massesif they have different numbers of neutrons.

7. of an element can have different radioactive properties.

1 2

3

4

5

6

7 Now check your answers.


14

What have you learned in these lessons?


❑ use a periodic table to state the number of protons and electronsin an atom

❑ use a name of an element to calculate the number of neutronsin an atom

❑ compare the numbers of protons, electrons and neutronsin different atoms

❑ identify the properties of an element that are most influenced bythe number of protons, neutrons and electrons in its atoms

❑ identify the periods and groups of the periodic table

❑ identify patterns in the electronic configurations of elementswithin periods and groups

❑ define the terms atomic number, mass number, isotope andelectronic configuration.

Exercise 11

Use your periodic table to answer the questions in Exercise 11in the send-in pages.


15

Lessons 13 and 14

How do compounds react?

It is not easy to explain why compounds react. You would expectcompounds to stay as they are if the atoms they contain are stable.The explanation for why they react has to do with energy;you can learn about it if you decide to study Stage 6 Chemistry.

So instead of looking at why compounds react, you will considerhow some compounds react in these lessons.

Patterns in reactions

You have already learned about some of the reactionsthat tend to happen to compounds.

For example, what is decomposition?

Decomposition is a reaction where a compound breaks apart.Sometimes it forms simpler compounds. Sometimes it is separated intothe elements that it is composed of.

There are many patterns in reactions of compounds.This is fortunate because it lets chemists predict what will happenwhen compounds are combined.

In these lessons, you will consider examples of three patterns.They are the reactions between:

• acids and bases

• acids and carbonates

• solutions that form a precipitate.


16

Neutralisation reactions

A neutralisation reaction occurs when an acid reacts with a base.So, to understand neutralisation, you need to learn more about acidsand bases.

Acids

There are many acids that you might use at home every day.Can you remember any examples? Vinegar contains ethanoic acid,fruit contains citric and tartaric acids, aspirin is made up of acetylsalicylic acid, and soda water is carbonic acid. In the laboratory,you could use a number of acids such as sulfuric, hydrochloric, nitricand phosphoric acid.

You will have noticed that these names for acids do not followthe rules that chemists use to name other compounds.You just have to learn the names and their matching formulasif you want to remember examples of acids!

Here are the names and formulas of some common acids.

Name Chemical formula

carbonic acid H2CO3

ethanoic acid CH3COOH

hydrochloric acid HCl

nitric acid HNO3

phosphoric acid H3PO4

sulfuric acid H2SO4

What are some properties of acids?

An acid that is commonly used in the laboratory (and in your stomach)is called hydrochloric acid. You may have tasted the acid fromyour stomach in a burb or if you have vomited. Acids taste sour.


17

But tasting acids is not a safe practice.Can you remember how you can test an acid safely?

An acid turns the indicator called litmus from blue to red.

Bases

Bases are a group of compounds that react with acids to form waterand a salt only. The most common examples of bases are hydroxides.

What are some properties of bases?

A base that is commonly used to make soap is called sodium hydroxide.Bases feel slippery but are also caustic. That is, they cause chemical burns.

How could you test a base safely? Once again, you can use an indicator.A base turns red litmus to blue.

Comparing an acid and a base

In some ways, acids and bases can be thought of as the opposites ofeach other. Acids make blue litmus red; bases make red litmus blue.When acids and bases are combined, they sort of cancel each other outand the reaction is called neutralisation.

Observing a reaction of an acid and a base

Perform the activity on the following page to observe neutralisation.But before you start, think about safety.

What special care do you think you should take with acids and bases?What could you do if an accident happened?

Both acids and bases can cause chemical burns. You must avoid gettingthese kinds of substances on your skin and always protect your eyes.Washing with lots of water is the way to clean away acids and bases.


18

Supervisor needed

Tell your supervisor that you are performing a reaction betweenan acid and a base. Explain the safety procedures you will be following.

What you will need:

Collect the items listed below:

• beakers

• eye dropper

• safety goggles

• plastic spoon


• 2 pieces of red litmus paper and 2 pieces of blue litmus paper

• white vinegar (you will need about 20 mL)

• a household cleaner (not a detergent)This could be a liquid cleaner such as Windex, ora cream or powder cleaner such as Ajax or Jiff.The cleaner should contain caustic soda or ammonia.Check that the cleaner is a base by testing it withdamp, red litmus paper. The paper should turn blue.

CAUTION Be careful!

You are using household products but they could still be dangerousif you do not use them safely. Read the safety instructions on thepackaging for the cleaning product. Follow the instructions.

Remember, cleaners which contain caustic soda can be dangerous.Take care not to get any on your skin and protect your eyesby putting on your safety goggles.

If you get any on your skin, wash it off straight away with lots of water.Your goggles should protect your eyes but if you think any of the cleanerhas entered your eyes, flush them immediately with plenty of water.Tell your supervisor because you may need medical attention.


19

Are you wearing your safety goggles?

What to do:

1. If you are using a liquid cleaner, pour about 20 mL into the beaker.If you are using a cream cleaner, mix about 10 mL of cleaner with10 mL of water. If you are using a powder cleaner, mix abouthalf a teaspoon with 20 mL of water.

2. If you haven’t already done so, test your cleaner with adamp piece of red litmus paper. The paper will turn to blue.(If it doesn’t, select another cleaner and begin again!)

3. Moisten the piece of universal indicator paper with water andstick it onto the inside of the beaker and just dipped into the cleaner.You must be able to see the indicator paper through the beakerthroughout the investigation.

Exercise 13.1

Read all of the instructions for this investigation before you begin.Record all your results in send-in Exercise 13.1.

4. Turn to Exercise 13.1 and record the colour of the indicator paperwith the base (with 0 squirts of vinegar) in the space provided.

5. Pour some white vinegar into the beaker.Half fill your eye dropper with vinegar. Call this one squirt.Use the dropper to add one squirt of vinegar to the cleanerin the beaker. Stir the mixture and look for any colour changeof the universal indicator paper.

If there is no change, add another squirt of vinegar.Count the number of squirts of vinegar you add until you seea change in the colour of the universal indicator paper.

6. Record your observations in the table in Exercise 13.1.Write the number of squirts of vinegar added and the new colourof the indicator paper.

7. Continue to add vinegar and record colour changesuntil the paper turns yellow-green.

8. Put a piece of red and a piece of blue litmus paper in the beaker.Notice and record any change in the colour.

9. Complete Exercise 13.1 by answering the questionsabout this investigation on page 40.

10. Wash all your equipment thoroughly so you're ready for the next task.


20

Reactions between acids and carbonates

Now for another reaction of acids. Have you ever tried droppingsome hydrochloric acid on an egg shell or on a sea shell or oversome marble? If you have, you would have seen some fizzingand a gas being given off. If you had enough acid and left thereactants together long enough, the shell or marble would 'disappear'.

Do you think this is a chemical change or a physical change?

The change is a chemical reaction because a new substance, the gas, is formed.

The substance that egg shell, sea shell and marble have in commonis called calcium carbonate. The gas produced is carbon dioxide.Water is also formed in the reaction.

What else do you think may be formed?

When you look at the names of the reactants, you should predict that there will bethe calcium part of calcium carbonate and the chloride part of hydrochloric acidavailable to form a compound. So the other substance formed is a salt calledcalcium chloride.

Observing a reaction of a carbonate with an acid

Perform this reaction between an acid and a carbonate.

What you will need:

Collect this equipment:

• 2 beakers

• eye dropper


• white vinegar

• baking soda

• plain flour

• self-raising flour.


21

Exercise 13.2

Read all of the instructions for this investigation before you begin.You will record your results in send-in Exercise 13.2.Turn to the send-in pages now so that you can complete the exerciseas you perform the experiment.

What to do:

1. Put half a teaspoon of baking soda in a beaker.Pour about 10 mL of vinegar another beaker.

Describe the reactants in send-in Exercise 13.2.

2. Use the eye dropper to add some drops of vinegar to the baking soda.Observe the reaction.

Describe the products in Exercise 13.2.

3. Use the same method to test a small amount of plain flour with vinegar.Does plain flour contain baking soda?

4. Now test a small amount of self-raising flour.Does it contain baking soda?

5. Complete Exercise 13.2 by answering Questions 3 and 4about this investigation on page 41.

A precipitation reaction

A precipitation reaction may occur when two solutions are mixed.A solution may be coloured or colourless, but it is always clear –you can see through it.

Sometimes when two solutions react, they form a solid that cloudsthe liquid so that you can no longer see through it. If you let thecombination sit, the solid will settle, or precipitate, to the bottom.The reaction in the photograph on the cover of this unit is an exampleof a precipitation reaction.

You may be able to perform a precipitation reaction in a laboratory,but for this exercise, you will need to use information from a reportby Max and his partner. (Remember them from Set 1?)

Exercise 13.3

Turn to the send-in pages and complete this exercise now.


22

What have you learned in these lessons?


❑ safely perform a neutralisation reaction using household chemicals

❑ use indicators to distinguish between acids, bases andneutral substances

❑ identify and describe the reactants and productsof a neutralisation reaction

❑ perform a reaction between an acid and a carbonate

❑ identify and describe the reactants and productsof a reaction between an acid and a carbonate

❑ interpret a photograph and a report about a precipitation reaction

❑ identify and describe the reactants and productsof a precipitation reaction.

In the next lesson, you will think again about the variety of reactionsthat you have investigated in this unit.


23

Lesson 15

Some important reactions

You have studied several different kinds of reactions in this unit.These examples help you to identify some patterns in the way thatcompounds react. These patterns are called general equations.

General equations

In this lesson, you'll review each of the different kinds of reactions.These reactions are:

• combustion (burning)

• corrosion

• decomposition

• acids on metals

• neutralisation

• acids on carbonates

• precipitation.

Combustion

Here is an example of the combustion of an element.

sulfur + oxygen → sulfur dioxide

This follows the general pattern for burning elements.The general equation is:

element + oxygen → oxide of element

Some compounds are also able to burn. For example, hydrocarbonsare a common group of fuels. Here is an equation for the burning ofa hydrocarbon called butane that makes up lighter fluid.

butane + oxygen → carbon dioxide + water

Write a general equation below for the burning of a hydrocarbon.

Turn to the answer pages to check your equation.


24

Corrosion

Corrosion refers to a group of reactions. They are reactions in whicha substance is eaten away. These reactions usually occur betweena metal and oxygen but may involve water or other chemicals in themetal's surroundings.

The simplest form of corrosion to describe is the reaction between ametal and oxygen.

sodium + oxygen → sodium oxide

Write a general equation below for this corrosion reaction.

Turn to the answer pages now.

Decomposition

What is decomposition?

Compare your definition with the one in the answer pages.

You cannot write a general equation for decomposition becausecompounds form different combinations of elements and compoundswhen they are broken apart.

Acids on metals

When magnesium is placed into hydrochloric acid, it forms a saltcalled magnesium chloride and bubbles of hydrogen gas.

Write a word equation for this reaction.

Now write a general equation for the reaction between an acid and a metal.

Look at the equations in the answer pages.


25

Neutralisation

Neutralisation is a reaction that occurs between an acid and a baseto produce a salt and water only.

Write a general equation for neutralisation.

Check your equation.

Have you wondered about the term salt?By definition, a salt is a compound (other than water) that is formedin a neutralisation reaction. A salt always contains a metallic ion anda non-metallic ion so it is an ionic compound.

There are many examples of salts; table salt, or sodium chloride,is just one example. Salts come in different colours but many salts arewhite crystalline solids. Some salts dissolve in water; others don't.

Acids on carbonates

Here is an example of a reaction between an acid and a carbonate.sulfuric acid +

calciumcarbonate → calcium

sulfate + carbondioxide + water

Write a general equation for this reaction.

Did you identify calcium sulfate as an example of a salt?Please compare your equation with the one in the answer pages.

Precipitation

Precipitation reactions occur between salts.They occur when some ions in a mixture form an insoluble salt.A general equation doesn't really tell you much!

soluble salt +

soluble salt → soluble

salt + insoluble salt


26

General equations for most reactions are very useful. They help you topredict what will happen when you combine elements and compounds.

You do not have to learn the general equations. But it would be a verygood idea to learn them if you plan to study chemistry in the future!

Using general equations

Try the problems below. You need to use the general equations topredict the products that will form. Then you can write a word equationfor the reaction.

Write a word equation for the reaction between:

1. potassium and oxygen

2. zinc hydroxide and nitric acid

3. calcium and hydrochloric acid

4. nitric acid and nickel carbonate.

Check your answers.



❑ write general equations for some reactions

❑ match reactants with a general equation anduse the general equation to predict the products.

In the next lesson, you will revise some of the definitions and termsyou have used in this unit.


27

Revision lesson

The last word

You can use this lesson to check that you understand all the termsfrom this unit.

Revision exercise 1

This optional exercise is a crossword puzzle using the words fromthis unit.

Start by solving the clues and then fill in the crossword grid.The grid is on your send-in page for this lesson.

You might find it easier to complete the puzzle if you remove thesend-in page from the back of the set and have it beside the clues.You might like to fill in the clues in pencil until you are sure ofthe answers.

The clues start on the next page.


28

Across clues

1 State of oxygen and hydrogenat room temperature and pressure

2 A type of change where no new substancesare produced

4 The name for the number of protonsin the nucleus of an atom

6 The state of sulfur and phosphorusat room temperature and pressure

10 The name of a substance which takes partin a chemical reaction

12 The particle in the nucleus of an atomwhich has a positive charge

14 The particle in an atom which hasa negative charge

15 A word which means burning

17 A type of compound made ofnon-metal atoms only

19 A pure substance containing one typeof atom only

21 The liquid which passes through thefilter paper in a filtration experiment

24 Another name for a row ofthe periodic table

25 A type of change in which a new substanceis produced

28 The liquid part of a solution

29 An experiment used for comparison

30 The state of mercury and bromineat room temperature and pressure


29

Down clues

1 Another name for a column in the periodic table

3 The name for a solid which dissolves in a liquidto make a solution

5 A type of compound which is made ofa metal and a non-metal bonded together

7 A word which means two atoms

8 The metal with the symbol Fe

9 The name for two or more atoms joined togetherinto a separate unit

11 A pure substance which contains more thanone type of atom

13 The particle in the nucleus of an atomwhich has no charge

16 The name for the solid caught by thefilter paper in a filtration experiment

18 Another name for the outershell electronsin an atom

20 The name for a substance formedin a chemical reaction

22 A short hand way of writing the nameof an element

23 A substance which feels slippery andturns moist red litmus blue

24 The types of substances which containone type of unit

26 The smallest part of an element

27 The force which joins atoms togetherin a compound

Make sure that you have written your answers into the puzzlein Revision exercise 1.


30



❑ identify some words and terms from this unit withgiven meanings

❑ give the meaning of some words and terms used in this unit.

Revision exercise 2

In this exercise, you will give the meanings of some of the wordsthat are not part of the crossword. Turn to the send-in pagesto complete this exercise.

Well done for completing Sets 1 to 3 of this unit!


31

Suggested answers

Lessons11 and 12 Why do elements react?

Page 1 What is an atom?

An atom has a nucleus in its centre that contains protons and neutrons.Electrons are arranged around the nucleus in electron shells.

How many protons?

Page 3 1. (a) nitrogen

(b) sulfur

(c) carbon

(d) magnesium

(e) cobalt

2. (a) 28

(b) 56

(c) 30

(d) 14

(e) 17

How many electrons?

1. 17 protons (because the number of protons is the same as the atomic number)and 17 electrons (because the number of electrons is the same as the numberof protons in a neutral atom).

2. 29 of each (because the number of protons and electrons are equal in aneutral atom; the number of protons is the same as the atomic number).

3. 33 (because a neutral atom has the same number of protons as electronsand the number of protons equals the atomic number).


32

Lessons 11 and 12 continued

How many neutrons?

Page 4 1. Both the atoms have a nucleus with one proton only. All atoms withone proton are atoms of hydrogen.

2. They would still be hydrogen atoms even if they lost their electron(because each atom would still contain one proton only).[If they lost their electrons, they would be hydrogen ions.]

3. The hydrogen atom on the left would have a mass of 1 butthe hydrogen atom on the right has a mass of 2.

4. Changing the number of neutrons in an atom alters its mass.More neutrons make an atom of an element heavier.

Page 5 5. (a) 8Why? Carbon's atomic number is 6 so it has 6 protons.The name, carbon-14, shows that this atom has a mass number of14.Therefore, number of neutrons = 14 – 6 = 8

(b) 45Why? Bromine's atomic number is 35 so it has 35 protons.The name, bromine-80, shows that this atom has a mass number of 80.Therefore, number of neutrons = 80 – 35 = 45

(c) 143Why? Uranium's atomic number is 92 so it has 92 protons.The name, uranium-235, shows that this atom has a mass number of 235.Therefore, number of neutrons = 235 – 92 = 143

Page 6 Comparing atoms

1. A nitrogen C oxygen E fluorine

B nitrogen D oxygen

2. A and B are isotopes because they are the same element (they havethe same atomic number) but they have different numbers of neutrons(they have different mass numbers). (C and D are not isotopes becausethey have the same numbers of protons and neutrons.)

3. B and D are ions because they have different numbers of protons(atomic number) from electrons.


33


Page 7 How do protons, neutrons and electrons affect an atom?

The number of protons in an atom determines the kind of elementthat it is. So the number of protons gives the atom many of its properties.

The number of neutrons in an atom changes the mass or mass numberof the atom. This can be important for some atoms because atomswith extra neutrons (extra mass) are more likely to break up andbe radioactive.

The number of electrons in an atom influences how the atomcombines with other atoms to form compounds.

Electronic configurations

Page 8 Here is a key to the information about oxygen in your periodic table.

8

Ooxygen

2.6

atomic number

chemical symbol

name of element

electronic configuration

Answers continue on the next page.


34


Comparing electronic configurations in periods

Page 9 1. Check that you have numbered the periods correctly.

11 H

2 He

23 Li

4 Be5 B

6 C7 N

8 O9 F

10Ne

311

Na12

Mg13 Al

14 Si15 P

16 S17

Cl18

Ar

419 K

20Ca

21 Sc22 Ti

23V

24 Cr25

Mn26 Fe

27Co

28 Ni29

Cu30 Zn

31Ga

32Ge

33As

34Se

35Br

36Kr

537

Rb38 Sr

39 Y40 Zr

41Nb

42Mo

43 Tc44

Ru45

Rh46 Pd

47Ag

48Cd

49 In50 Sn

51 Sb52 Te

53 I54

Xe

655 Cs

56Ba

57-71 72Hf

73 Ta74 W

75Re

76 Os77 Ir

78 Pt79

Au80

Hg81 Tl

82 Pb83 Bi

84 Po85 At

86Rn

7 87

Fr88

Ra89-103 104

Rf105

Db106

Sg107

Bh108

Hs109

Mt110

Ds111

Rg112

Uub113 114

Uuq115 116

Uuh117 118

Uuo

57 La

58 Ce

59 Pr60

Nd61

Pm62

Sm63 Eu

64 Gd

65 Tb66

Dy67

Ho68 Er

69 Tm

70 Yb

71 Lu

89 Ac

90 Th

91 Pa92

U93

Np94

Pu95

Am96

Cm97 Bk

98 Cf

99 Es

100Fm

101Md

102 No

103 Lr

3. 1 22 83 8

4 185 18

6 327 29 (or 32 if you expect the rest of

period 7 to be discovered!)

Page 10 4. One electron is added to the electronic configuration for each elementacross period 1.

5. (a) All elements in period 2 have two electrons in the electron shellthat is closest to the nucleus.

(b) The second number in the electronic configurations in period 2increases by one for each element across the period. (That is,each element across the period has one more electron in itsoutermost shell than the element before it.)

6. There is the same pattern in the way that the last number in theelectronic configuration changes. The last number in the electronicconfigurations increase by one for each element across period 3.(Each element across the period has one more electron in itsoutermost shell than the element before it.) Like the other periods,the other electron shells of elements in period 3 do not change.All the elements in period 3 have two electrons in their inner electron shelland eight electrons in their second shell.


35


Comparing electronic configurations in groups

Page 11 1. Check that you have numbered the groups correctly.18

1 21 H 13 14 15 16 17

2 He

3 Li4 Be

5 B6 C

7 N8 O

9 F10

Ne

11Na

12Mg 3 4 5 6 7 8 9 10 11 12

13 Al14 Si

15 P16 S

17Cl

18Ar

19 K20

Ca21 Sc

22 Ti23

V24 Cr

25Mn

26 Fe27

Co28 Ni

29Cu

30 Zn31

Ga32

Ge33

As34

Se35

Br36

Kr

37Rb

38 Sr39 Y

40 Zr41

Nb42

Mo43 Tc

44Ru

45Rh

46 Pd47

Ag48

Cd49 In

50 Sn51 Sb

52 Te53 I

54Xe

55 Cs56

Ba57-71 72

Hf73 Ta

74 W75

Re76 Os

77 Ir78 Pt

79Au

80Hg

81 Tl82 Pb

83 Bi84 Po

85 At86

Rn

87

Fr88

Ra89-103 104

Rf105

Db106

Sg107

Bh108

Hs109

Mt110

Ds111

Rg112

Uub113 114

Uuq115 116

Uuh117 118

Uuo

57 La

58 Ce

59 Pr60

Nd61

Pm62

Sm63 Eu

64 Gd

65 Tb66

Dy67

Ho68 Er

69 Tm

70 Yb

71 Lu

89 Ac

90 Th

91 Pa92

U93

Np94

Pu95

Am96

Cm97 Bk

98 Cf

99 Es

100Fm

101Md

102 No

103 Lr

2. (a) carbon

(b) calcium

(c) xenon

3. As you move down a group, the number of electron shells (numbers inthe electronic configuration) increases. So each element in a grouphas one more (full) electron shell that the element above it.

4. The electronic configurations for each element in a group have thesame last number. (All elements in the same group have thesame number of electrons in the outermost shell.)

Page 13 Take a deep breath!

1 S H E L L 2 S or levels

3 T A B L E

4 S A M E

5 N U M B E R

6 E L E M E N T

7 I S O T O P E S


36

Lesson 15 Some important reactions

Page 23 Combustion

hydrocarbon + oxygen → carbon dioxide + water

Page 24 Corrosion

metal + oxygen → metal oxide (or oxide of metal)

Decomposition

Decomposition is the breaking apart of a compound into simpler substances.

Acids on metals

magnesium + hydrochloric acid → magnesium

chloride + hydrogen

metal + acid → salt + hydrogen

Page 25 Neutralisation

acid + base → salt + water

Acids on carbonates

acid + carbonate → salt + carbondioxide + water

Page 26 Using general equations

1. potassium + oxygen → potassium oxide

(This is an example of combustion or corrosion.)

2. zinchydroxide +

nitric acid → zinc

nitrate + water

(This is an example of neutralisation. Zinc nitrate is a salt.)

3. calcium + hydrochloric acid → calcium

chloride + hydrogen

(This is an example of an acid on a metal. Calcium chloride is a salt.)

4.nitric acid +

nickelcarbonate → nickel

nitrate + carbondioxide + water

(This is an example of an acid on a carbonate. Nickel nitrate is a salt.)


37

Send-in page Name ______________________________

Lessons 11 and 12: Why do elements react?

Exercise 11

Use your periodic table to find the information you need for these questions.

1. Consider the information in the table below about five different atoms.

Atom Atomicnumber

Massnumber

Number ofelectrons

V 10 20 10

W 11 23 10

X 12 24 10

Y 12 25 11

Z 12 25 12

(a) Which atoms are of the same element? _________________________________

(b) Name the elements represented in the table.

(c) Which atoms are isotopes? Explain.

(d) Which atoms are ions? Explain.


38

2. Draw a line to connect the name of each fundamental particlewith a property of the element that it can help to explain.

Fundamental particle Property of element

proton some radioactive properties

neutron properties of how the elementreacts to form compounds

electron many properties that make oneelement different from all others

3. Describe the pattern of electronic configurations across a periodof the periodic table.

4. Describe the pattern of electronic configurations down a groupof the periodic table.


39

Send-in page Name ______________________________

Lessons 13 and 14: How do compounds react?

Exercise 13.1 Describing a neutralisation reaction

Record the results of your experiment in the table below.You may not need to use all the spaces.Remember, one squirt equals half a dropper of vinegar.

Squirtsof vinegar

Colour of theuniversal indicator paper

0

red litmus paper ____________________________________________________________________________

blue litmus paper ____________________________________________________________________________


40

Answer the following questions about your neutralisation experiment.

1. What colour change occurred with litmus paper and the baseat the beginning of this experiment? What did the change show?

2. What colour change occurred with litmus paper and theacid/base combination at the end of this experiment?What did the change show?

3. What do you think the colour changes of the universal indicatorpaper represent?

4. A reaction between an acid and a base always produces a substancecalled a salt and water only. You do not know the names of thechemicals you used but you can still write an equation usingthe general names for the chemicals. This kind of equation is calleda general equation.

Write a general equation for a neutralisation reaction.


41

Send-in page Name ______________________________

Lessons 13 and 14: How do compounds react? (continued)

Exercise 13.1 Describing a neutralisation reaction(continued)

5. Identify and describe the reactants of this neutralisation reaction.


6. Identify and describe the products of this neutralisation reaction.



42

Exercise 13.2 Describing a reaction betweenan acid and carbonate

1. Identify and describe the reactants of this reaction.


2. Identify and describe the products of this reaction.


3. Which flour contains baking soda? How could you tell?

4. Suppose you reacted cornflour with vinegar and observedbubbles of gas being formed. Is it possible that there isno baking soda in the cornflour? Explain your answer.


43

Send-in page Name ______________________________

Lessons 13 and 14: How do compounds react? (continued)

Exercise 13.3 Describing a precipitation reaction

Here is the logbook entry that Max wrote about the precipitationexperiment he completed with his partner.

A precipitation reaction

We dissolved a white solid called sodium carbonate in

some water. In another beaker, we dissolved white crystals

of magnesium chloride in water.

Then we mixed the two solutions together. There was an

immediate change. The solution went cloudly; it looked

like milk.

We let the chemical combination sit for the rest of

the lesson. A white precipitate settled to the bottom.

We predicted that the white solid formed was

magnesium carbonate. The colourless solution would

contain dissolved sodium chloride.

We filtered the mixture to remove the insoluble magnesium

salt. Then we evaporated the water from the filtrate and

found that it contained a white solid. My partner wanted

to taste it to see if it tasted like table salt but I said it was

silly to taste chemicals.

Max

1. Underline the names of the reactants in Max's report.

2. Circle the names of the products.


44

Exercise 13.3 (continued)

Here is a photograph ofanother student performingthe same experiment.

3. Use information from Max's reportand from the photographto complete the tables below.




45

Send-in page Name ______________________________

Revision lesson: The last word

Revision exercise 1

Use the clues on pages 28 and 29 to complete the puzzle below.

1 2 3

4 5

6 7 8

9 10 11

12 13

14

15

16 17 18

19

20

21 22

23

24 25

26

27 28

29

30


46

Revision exercise 2

Write a sentence to give the meaning of each term below.

1. neutralisation

2. formula

3. equation

4. acid

5. reaction

6. isotopes

Chemical combinations Elements and compounds booklet

102 of the known elementsNote: The small number before each element name is its atomic number.

EEEElllleeeemmmmeeeennnntttt SSSSyyyymmmmbbbboooollll EEEElllleeeemmmmeeeennnntttt SSSSyyyymmmmbbbboooollll EEEElllleeeemmmmeeeennnntttt SSSSyyyymmmmbbbboooollll

89 actinium Ac 79 gold Au 19 potassium K13 aluminium Al 72 hafnium Hf 59 praseodymium Pr95 americium Am 2 helium He 61 promethium Pm51 antimony Sb 67 holmium Ho 91 protactinium Pa18 argon Ar 1 hydrogen H 88 radium Ra33 arsenic As 49 indium In 86 radon Rn85 astatine At 53 iodine I 75 rhenium Re56 barium Ba 77 iridium Ir 45 rhodium Rh97 berkelium Bk 26 iron Fe 37 rubidium Rb4 beryllium Be 36 krypton Kr 44 ruthenium Ru83 bismuth Bi 57 lanthanum La 62 samarium Sm5 boron B 103 lawrencium Lw 21 scandium Sc35 bromine Br 82 lead Pb 34 selenium Se48 cadmium Cd 3 lithium Li 14 silicon Si55 caesium Cs 71 lutetium Lu 47 silver Ag20 calcium Ca 12 magnesium Mg 11 sodium Na98 californium Cf 25 manganese Mn 38 strontium Sr6 carbon C 101 mendelevium Md 16 sulfur S58 cerium Ce 80 mercury Hg 73 tantalum Ta17 chlorine Cl 42 molybdenum Mo 43 technetium Tc24 chromium Cr 60 neodymium Nd 52 tellurium Te27 cobalt Co 10 neon Ne 65 terbium Tb29 copper Cu 93 neptunium Np 81 thallium Tl96 curium Cm 28 nickel Ni 90 thorium Th66 dysprosium Dy 41 niobium No 69 thulium Tm99 einsteinium Es 7 nitrogen N 50 tin Sn68 erbium Er 102 nobelium No 22 titanium Ti63 europium Eu 76 osmium Os 74 tungsten W100 fermium Fm 8 oxygen O 92 uranium U9 fluorine F 46 palladium Pd 23 vanadium V87 francium Fr 15 phosphorus P 54 xenon Xe64 gadolinium Gd 78 platinum Pt 39 yttrium Y31 gallium Ga 94 plutonium Pu 30 zinc Zn32 germanium Ge 84 polonium Po 40 zirconium Zr

Chemical combinations Periodic table

A periodic table of elements

1

HHydrogen

1

2

HeHelium

2

3

LiLithium

2.1

4

BeBeryllium

2.2

5

BBoron

2.3

6

CCarbon

2.4

7

NNitrogen

2.5

8

OOxygen

2.6

9

FFluorine

2.7

10

NeNeon2.8

11

NaSodium

2.8.1

12

MgMagnesium

2.8.2

13

AlAluminium

2.8.3

14

SiSilicon2.8.4

15

PPhosphorus

2.8.5

16

SSulfur2.8.6

17

ClChlorine

2.8.7

18

ArArgon2.8.8

19

KPotassium

2.8.8.1

20

CaCalcium

2.8.8.2

21

ScScandium

2.8.9.2

22

TiTitanium2.8.10.2

23

VVanadium

2.8.11.2

24

CrChromium

2.8.13.1

25

MnManganese

2.8.13.2

26

FeIron

2.8.14.2

27

CoCobalt

2.8.15.2

28

NiNickel

2.8.16.2

29

CuCopper2.8.18.1

30

ZnZinc

2.8.18.2

31

GaGallium2.8.18.3

32

GeGermanium

2.8.18.4

33

AsArsenic2.8.18.5

34

SeSelenium2.8.18.6

35

BrBromine2.8.18.7

36

KrKrypton2.8.18.8

37

RbRubidium2.8.18.8.1

38

SrStrontium2.8.18.8.2

39

YYttrium

2.8.18.9.2

40

ZrZirconium2.8.18.10.2

41

NbNiobium

2.8.18.12.1

42

MoMolybdenum

2.8.18.13.1

43

TcTechnetium

2.8.18.13.2

44

RuRuthenium2.8.18.15.1

45

RhRhodium

2.8.18.16.1

46

PdPalladium2.8.18.18

47

AgSilver

2.8.18.18.1

48

CdCadmium2.8.18.18.2

49

InIndium

2.8.18.18.3

50

SnTin

2.8.18.18.4

51

SbAntimony2.8.18.18.5

52

TeTellurium2.8.18.18.6

53

IIodine

2.8.18.18.7

54

XeXenon

2.8.18.18.8

55

CsCaesium2.8.18.18.8.1

56

BaBarium

2.8.18.18.8.2

57–71 72

HfHafnium

2.8.18.32.10.2

73

TaTantalum

2.8.18.32.11.2

74

WTungsten

2.8.18.32.12.2

75

ReRhenium

2.8.18.32.13.2

76

OsOsmium

2.8.18.32.14.2

77

IrIridium

2.8.18.32.17

78

PtPlatinum

2.8.18.32.17.1

79

AuGold

2.8.18.32.18.1

80

HgMercury

2.8.18.32.18.2

81

TlThallium

2.8.18.32.18.3

82

PbLead

2.8.18.32.18.4

83

BiBismuth

2.8.18.32.18.5

84

PoPolonium

2.8.18.32.18.6

85

AtAstatine

2.8.18.32.18.7

86

RnRadon

2.8.18.32.18.8

87

FrFrancium

2.8.18.32.18.8.1

88

RaRadium

2.8.18.32.18.8.2

89–103 104

RfRutherfordium

2.8.18.32.32.10.2

105

DbDubnium

2.8.18.32.32.11.2

106

SgSeaborgium

2.8.18.32.32.12.2

107

BhBohrium

2.8.18.32.32.13.2

108

HsHassium

2.8.18.32.32.14.2

109

MtMeitnerium

2.8.18.32.32.15.2

110

DsDarmstadtium

2.8.18.32.32.17.1

111

RgRoentgenium

2.8.18.32.32.18.1

112

UubUnunbium

2.8.18.32.32.18.2

113 114

UuqUnunquadium

2.8.18.32.32.18.4

115 116

UuhUnunhexium

2.8.18.32.32.18.6

117 118

UuoUnunoctium2.8.18.32.32.18.8

LANTHANIDES 57

LaLanthanum2.8.18.18.9.2

58

CeCerium

2.8.18.20.8.2

59

PrPraseodymium2.8.18.20.8.2

60

NdNeodymium

2.8.18.22.8.2

61

PmPromethium

2.8.18.23.8.2

62

SmSamarium2.8.18.24.8.2

63

EuEuropium2.8.18.25.8.2

64

GdGadolinium2.8.18.25.9.2

65

TbTerbium

2.8.18.27.8.2

66

DyDysprosium

2.8.18.28.8.2

67

HoHolmium

2.8.18.29.8.2

68

ErErbium

2.8.18.30.8.2

69

TmThulium

2.8.18.31.8.2

70

YbYtterbium

2.8.18.32.8.2

71

LuLutetium

2.8.18.32.9.2

ACTINIDES 89

AcActinium

2.8.18.32.9.2

90

ThThorium

2.8.18.32.18.10.2

91

PaProtactinium2.8.18.32.20.9.2

92

UUranium

2.8.18.32.21.9.2

93

NpNeptunium2.8.18.32.22.9.2

94

PuPlutonium2.8.18.32.23.9.2

95

AmAmericium2.8.18.32.24.9.2

96

CmCurium

2.8.18.32.25.9.2

97

BkBerkelium

2.8.18.32.26.9.2

98

CfCalifornium2.8.18.32.27.9.2

99

EsEinsteinium

2.8.18.32.28.9.2

100

FmFermium

2.8.18.32.29.9.2

101

MdMendelevium2.8.18.32.30.9.2

102

NoNobelium

2.8.18.32.31.9.2

103

LrLawrencium

2.8.18.32.32.9.2

Chemical combinations Evaluation

We need your input! Can you please complete this shortevaluation to provide us with information about this unit. Thisinformation will help us to improve the design of these materialsfor future publications.

1. Did you find the information in the unit clear and easy tounderstand?

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2. What sort of learning activity did you enjoy the most? Why?

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3. Name any sections you feel need better explanation (if any).

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4. Were you able to complete each part in around 5 hours? If notwhich parts took you a longer or shorter time?

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5. Do you have access to the appropriate resources? This couldinclude a computer, graphics calculator, the Internet,equipment and people to provide information and assist withthe learning.

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Centre for Learning InnovationNSW Department of Education and Training

51 Wentworth RoadStrathfield NSW 2135

chemical combinations -...

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