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1. Food i

THE ROYALSOCIETY OFCHEMISTRY

i

ContentsForeword .................................................................................. ii

History of the project ............................................................... iii

The book .................................................................................. iv

How to use ‘What’s your reaction?’ ........................................... v

Some classroom resources for delivering ‘What’s your reaction?’

vii

What is a chemist? ..................................................................... x

Acknowledgements .......................................................................... xi

Chapter1 Growing plants ................................................................. 1

2 Food ................................................................................ 14

3 Energy and fuels ............................................................... 25

4 Waste .............................................................................. 37

5 Water .............................................................................. 47

6 Rocks ............................................................................... 55

7 Solids, liquids, gases ......................................................... 64

8 Groups of materials .......................................................... 70

9 Properties of materials ........................................................... 78

10 Making new materials ....................................................... 85

11 How materials behave ..................................................... 93

Answers and notes to challenges ............................................ 101

Table of the elements and their symbols ................................. 111

The periodic table of the elements .......................................... 112

ii What’s your reaction?


ForewordIn recent years the amount of science taught in primary schools has increaseddramatically. The Royal Society of Chemistry has welcomed this development buthas been only too well aware that many primary teachers have only a limitedbackground in science. I am conscious that many primary teachers are working hardto increase their scientific awareness and I am delighted that the Society is able toprovide this resource to help them.

The level of commitment and enthusiasm shown by primary teachers is anexample to us all. The Royal Society of Chemistry is delighted to be able to supportthose who play such a vital role in producing the scientists of tomorrow.

Sir Rex Richards CChem FRSC FBA FRSPresident, The Royal Society of ChemistryDecember 1991

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iii

History of the projectNeville Reed, The Royal Society of Chemistry

The idea for producing this book originated in April 1989 at the Society’s Schools’Activities Committee. Ben Faust, a committee member, raised the concerns expressedto him by a group of primary teachers. They were being asked to teach science intheir schools although they themselves had only a limited science background.

In response, the Schools’ Activities Committee set up a small advisory group ofpeople with experience of primary science in schools. The group, David Archer, SueDale-Tunnicliffe, Audrey Randall, Kathleen Reed and John Slade, outlined thechallenges facing primary teachers and suggested possible ways in which the Societycould help.

The Schools’ Activities Committee agreed to recommend to the Society that abook for teachers which provided background information on science (with theemphasis on chemical science) should be produced. The Committee was delightedwhen Central TV agreed to support the initiative by allocating two programmes of its‘Programmes for Primary Teachers’ series to topics included in the book.

During 1990–91 the Society funded a one year School Teacher Fellowship post,awarded to David Archer, to write and compile the book based upon the Society’sChemistry Related In-Service Project (CRISP) work. The fruit of his endeavours is‘What’s your reaction?’.

The contents of the book are not linked to any curriculum or scheme but coverthe scientific background to topics taught in primary schools. In some cases the depthof treatment of some topics is beyond that which is required for understandingclassroom activities. This is deliberate because the Society believes that there is muchto be gained from a deeper understanding of scientific concepts where appropriate.

iv What’s your reaction?


The bookDavid Archer

The structure of the bookEach chapter of the book covers a different topic and is dealt with at three levels, A, Band C. Each level or section has a list of key ideas, text and diagrams, and challenges.At the end of this book there are answers and notes to the challenges together with alist and periodic table of the chemical elements.

Some ways of using the bookIt is envisaged that readers will wish to enter and leave a chapter at a point at whichthey feel comfortable. Teachers with little or no background in chemistry will wish toenter the chapter at level A and exit after completing the challenges and perhapsscanning the key ideas of the next level, B. It is hoped that in time the teacher willwish to read all of the book but it is not intended that it should be read through fromcover to cover.

A ‘fast track’ method could be employed by reading the ‘Key ideas’ and the‘challenges’, leaving the rest for later.

The challenges are provided in some cases to give practical examples to illustratea point, while others are there to encourage readers to ‘think on’. Answers and notesin this book might be used for group in-service work as well as at an individual level.

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v

How to use ‘What’ s your reaction?’Kathleen Reed, County Advisor for Science, Buckinghamshire LEA

The aim of this book is to improve and expand teachers’ knowledge of the underlyingchemistry concepts in the primary science curriculum. In England and Wales apartfrom the Attainment Target concerning materials there is a great deal of chemistry inthe other Attainment Targets, some of which may not be apparent to the non-specialist. The book is appropriate for use not only in England and Wales butthroughout the UK. Many teachers express a lack of confidence in their ownknowledge and fear that they may give children ‘the wrong idea’. This book willhelp teachers to examine their own ideas and resolve any misconceptions they mayhave.

Each of the 11 chapters can stand alone. Within each chapter there are threelevels of difficulty labelled A, B and C. Level A assumes no science knowledge at alland is concerned with the most basic principles. Level B may be most suited to thoseteachers who have some background in science and involves more complex ideas. Itis hoped that level C contains ideas to challenge all teachers. Listed at the beginningof the section (ie level A,B or C) is a list of ‘Key ideas’ that the section deals with.Following this is the ‘text’ which explains the underlying chemical concepts involvedin the Key ideas. Periodically within the text are ‘Challenges’ which pose a questionto be investigated. These may involve research in a library, a visit (eg to a gardencentre) to find information, or an activity. An important feature of the book is thereference throughout to the relevance of chemical ideas to every day life.

Since each chapter can be used independently the priority for tackling thechapters could be determined by the term’s topic. Growth may be best served byusing chapters 1 and 2. A topic on food could be backed up by parts of chapter 9which deals with acids and alkalis, chapter 3 which deals with food as a fuel, chapter4 which involves preservatives and chapter 2 which deals with classification of foods,digestion, and how we get energy from food.

Another prompt to use this book may come from those awkward questionschildren ask which sound so benign and yet have very complex answers or indeedno answer at all. The book may enable you to give a simplified explanation but itmay be inappropriate to try to explain because the concepts involved are tooadvanced. Teachers should however gain confidence themselves either in theknowledge they have gained or the knowledge that there is not a simple explanation.

There are various ways in which the book can be used for in-service training(INSET). It is possible for an individual to use the book on their own. Depending ontheir own knowledge they could start at level A and work their way through to levelC or they may find level A contains ideas with which they are already familiar andbegin with level B text. A teacher with a good grounding in science may want to useonly level C text to broaden their knowledge.

It is often more enjoyable and beneficial if teachers can discuss ideas with eachother, particularly if they lack confidence, and much could be gained by staffworking together. Ideally the science coordinator needs to be familiar with thecontents so that they have an idea of what levels A, B and C involve. Since thechapters are differentiated staff could divide into groups depending on which levelthey feel would be most appropriate for them. The science coordinator could helpthem in deciding by producing a simple questionnaire with true/false statementsconcerning some of the Key ideas which would help to indicate which level is anappropriate starting point for individual teachers. Teachers could then work throughthe text in groups of similar level tackling the challenges as they come to them. The

vi What’s your reaction?


coordinator needs to be aware of materials needed for the activities and make surethey are to hand. Some research (eg the visit to the garden centre) needs to beundertaken either after reading the text or perhaps prior to reading the text in orderthat the challenges can be tackled. Again this needs to be decided by the coordinatoror INSET provider. Since explaining ideas to others helps to consolidate what hasbeen learnt, a possible strategy may be for the level B group to present and teachtheir text to the level A group.

Another approach may be to begin with a challenge – eg 30 chapter 5C. If ice hada greater density than cold water, would any life on planet earth be possible even inhot countries? After discussion the science coordinator could use the supportingdiagrams in the text to explain what would happen if ice was more dense than coldwater and what the implications for life on our planet would be, and how a pondactually does freeze over. Teachers could then go on to read the text on water.

Similarly, challenge 27 chapter 5B. Is your local drinking water obtained fromsurface water such as a reservoir, or is it obtained from a borehole? Why do youthink water obtained from a borehole is considered purer and cleaner than thatobtained from a reservoir? A discussion could lead on to filtration as a means ofpurifying water (which may be familiar to many teachers) and a practicalinvestigation on filtering water through gravel of different sizes to see which is mosteffective.

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vii

Some classroom resources for delivering‘What’ s your reaction?’

John Stringer, Director, Early SATIS Project

There are many science schemes both commercially and non-commerciallyproduced, which are supported by ‘What’s your reaction?’ Below are examples ofhow four schemes relate to this publication; other schemes may be equallyappropriate.

Ginn ScienceGinn Science is a flexible, skills-based primary science programme that developsthrough five content strands, closely related to the strands of the new NationalCurriculum Proposals for Science (April, 1991). The Ginn Science strand ‘Materialsand their uses’ is one of five based on a hierarchical series of key ideas, starting withstatements like ‘certain materials have properties that are useful for building a house’(Ginn Science Level 1) and progressing to work on ‘plastics are artificial substanceswhich vary in their properties and uses, and which can be shaped into a variety offorms’ (Ginn Science Level 6).

Each module in Ginn Science – pupil activities, teacher notes and pupilinformation books – is complete and can be used thematically to introduce pupils topractical science. Ginn Science complements many (but not all) of the conceptspresented in this book. The appropriate modules are listed below.

All Year Round Science – Start Here!The two Central Television series, for pupils under eight years old (All Year Round)and for pupils eight and over (Science – Start Here!) include programmes thatdevelop ‘materials’ themes. The original fourteen are available on video; ten are stillbroadcast, together with four new programmes related to the SATIS 8 – 14 project.

SATIS 8–14 (Science and Technology in Society)SATIS is an initiative of the Association for Science Education. The low cost,photocopiable resources put science and technology in a social context through arange of activities. The SATIS 8 –14 project will be published throughout 1992; itsmaterial will include a BBC Radio series and four new programmes in CentralTelevision’s ‘Science – Start Here!’ series. Many of the SATIS units are directly relatedto the use of materials – eg ‘Wrapping chocolate’, ‘Natural bounce’ (rubber andsynthetics) and ‘Which wash?’ (soaps and detergents). The SATIS 8 – 14 project willbe available from The ASE Bookshop, College Lane, Hatfield, Hertfordshire, AL109AA.

‘Programmes for Primary Teachers’Two new programmes in this Central Television series will be broadcast duringSpring 1992. They are directly related to The Royal Society of Chemistry’s book andshow schools working on ‘Water’ and ‘Change’. The programmes can be recordedoff-air to complement ‘What’s your reaction?’ . Transmission details can be found inthe annual timetable, or in the booklet ‘Programmes for Primary Teachers’ availablefrom your local ITV company.The table shows how these resources relate to this book.

viii What’s your reaction?


What’s your reaction? –Reference to some published materials

What’s your reaction? Module from All Year Round Science – Start Programmes forChapter the Ginn Science programmes for Here! programmes Primary Teachers

Programme children for children Teacher support

1A Growing Plants L1 Plant growth a. New LifeL2 LeavesL4 TreesL5 Soils

1B L5 Soils

1C L5 SoilsL6 Food chains

2A Food L6 Food chains 2. Fire Plant Life*9. New Life

2B L5 Smell andBreathing

2C Energy andForces strand

3A Energy and Fuels Energy and 2. Fire 10. Full Circuit ChangeForces strand 7. Magnets andL4 Hot and cold Electricity

3B

3C Energy andForces strand

4A Waste L4 Caring for the 8. What rot! Survival*environmentL5 Tracks andtrails

4B L4 Caring for theenvironmentL5 Paper

4C L4 Caring for theenvironment

5A Water L2 Rain 6. Water 1. Rainy Days WaterL3 Weather

5B L5 Forecastingweather

5C L4 SolubilityL6 Water

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ix

What’s your reaction? Module from All Year Round Science – Start Programmes forChapter the Ginn Science programmes for Here! programmes Primary Teachers

Programme children for children Teacher support

6A Rocks L4 Rocks 1. EarthL5 SoilsL6 Rocks andcrystals

6B L6 Metals

6C

7A Solids, liquids, 1. Rainy Days Water, Changegases

7B L4 Hot and coldL6 Rocks andcrystals

7C

8A Groups of Materials and Paperchase*materials their uses strand

8B L6 Plastics

8C L4 FibresL5 PaperL6 Plastics

9A Properties ofmaterials

9B L6 Metals

9C

10A Making new L6 Plasticsmaterials

10B Energy andForces strand

10C L2 Magnetism 7. Magnets and 10. Full CircuitL6 Electricity Electricity

11A How materialsbehave

11B11C

Science – Start Here! programmes marked with a * are not currently broadcast and are only available on video.

x What’s your reaction?


What is a chemist?Tony Ashmore, The Royal Society of Chemistry

To many, a chemist is the person in the white coat who dispenses medicines from theback room of the corner shop or the raised platform at Boots. However, if you lookclosely at the nearby certificate on the wall you will find that person is in fact apharmacist working in a pharmacy and is a member of The Royal PharmaceuticalSociety of Great Britain.

But the medicines that you get from the pharmacy are produced by chemistsbecause it is the chemist who invents and manufactures the medicines that are sovital to our modern health service.

So what is chemistry? The answer is probably best summed up by the Chinesecharacter for chemistry which translates into English as ‘change study’. Chemistsstudy the way one substance can be changed into another – how it happens and whyit happens. So much of our modern world is dependent upon converting rawmaterials to useful products whether that product is the food in the supermarket,clothing, cars or medicines – all exist because chemists have learned how to changeless useful substances into more useful ones.

There is another important aspect of ‘change study’. Some of the world’s mostpressing environmental problems are caused by undesirable changes – depletion ofthe ozone layer and acid rain are two examples. These changes are complex and it ischemists who first have to research and understand the changes and proposesolutions to the problems. Whether these solutions are put into practice is a challengefor us all.

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xi

AcknowledgmentsThe Royal Society of Chemistry would like to thank the following for their helpfulcomments received about the text:

Eric Brick, the Head and staff, Manor Junior School Merseyside;J. Brown, High Conniscliffe Primary School, Darlington;Morag Campbell, Udney Green Primary School, Aberdeenshire;Patricia Diamond, School of Education, University of Belfast;Priscilla Gellatly, Nine Mile Ride Primary School, Berkshire;M. Grainger, Gurney Pease Primary School, Darlington;John McGarvey, Faculty of Education, University of Ulster;S. Millington, Blue Coat CE (Aided) Junior School, Durham;Robert Rumbelow, Dunchurch Boughton CE Middle School, Warwickshire;W. Woods, Lambourn CE School, Berkshire;Catherine Woodward, Department of Education, University College of Swansea.

Special thanks for their valuable comments are due to David Malvern, SeniorLecturer in Science Education, University of Reading; Paul Martin, Central TV plc;Kathleen Reed, County Advisor for Science, Buckinghamshire LEA; and John Stringer,Project Director, Early SATIS, University of Warwick.

The following individuals and organisations have also provided much appreciatedhelp and inspiration:

The Agricultural and Food Research Council (AFRC);The Biotechnology Directorate of the Science and Engineering Research Council(SERC);The Medical Research Council (MRC);The Natural Environment Research Council (NERC);Dr John Grainger and colleagues at The National Centre for Biotechnolgy Education(NCBE);The Meteorological Office;The Fertilizer Manufacturers Association Ltd;Welsh Water.

The author would especially like to thank Dr Neville Reed, Education Officer(Schools), The Royal Society of Chemistry for his guidance and help during theproject. Thanks are also due to the authors’ wife Margaret for her patience and histwo scientist daughters, Catherine the chemist and Martine the microbiologist forhelpful comments.

The Royal Society of Chemistry wishes to thank Berkshire Local Education Authorityand the governors of Nine Mile Ride school, Reading for seconding David Archer tothe Society, Mike Coles of the National Curriculum Council for his advice andCentral TV plc for supporting this initiative with two television programmes.

xii What’s your reaction?


1. Food xiii


xiii

What’s your reaction?

Compiled by David Archer

School T eacher Fellow

The Royal Society of Chemistry

1990–91

xiv What’s your reaction?


What’s your reaction?

Compiled by David ArcherEdited by John Johnston and Neville ReedDesigned by Imogen Bertin

Published by the Education Division, The Royal Society of Chemistry

Copyright The Royal Society of Chemistry 1991

The material included in this book may be reproduced without infringing copyright providingreproduction is for use within the purchasing institution only. The permission of the publisher must beobtained before reproducing the material for any other purpose.

For further information on other educational activities undertaken by The Royal Society of Chemistrywrite to:

The Education DepartmentThe Royal Society of ChemistryBurlington HousePiccadillyLondon W1V OBN

British Library Cataloguing in Publication Data

What’s your reaction?I. Royal Society of Chemistry372.35044

ISBN 1–870343–17–4

1. Food 111


111

Table of the elements and their symbolsName SymbolActinium AcAluminium AlAmericium AmAntimony SbArgon ArArsenic AsAstatine AtBarium BaBerkelium BkBeryllium BeBismuth BiBoron BBromine BrCadmium CdCaesium CsCalcium CaCalifornium CfCarbon CCerium CeChlorine ClChromium CrCobalt CoCopper CuCurium CmDysprosium DyEinsteinium EsErbium ErEuropium EuFermium FmFluorine FFrancium FrGadolinium GdGallium GaGermanium GeGold AuHafnium HfHelium HeHolmium HoHydrogen HIndium InIodine IIridium Ir

Name SymbolIron FeKrypton KrLanthanum LaLawrencium LrLead PbLithium LiLutetium LuMagnesium MgManganese MnMendelevium MdMercury HgMolybdenum MoNeodymium NdNeon NeNeptunium NpNickel NiNiobium NbNitrogen NNobelium NoOsmium OsOxygen OPalladium PdPhosphorus PPlatinum PtPlutonium PuPolonium PoPotassium KPraseodymium PrPromethium PmProtactinium PaRadium RaRadon RnRhenium ReRhodium RhRubidium RbRuthenium RuSamarium SmScandium ScSelenium SeSilicon SiSilver AgSodium Na

Name SymbolStrontium SrSulphur STantalum TaTechnetium TcTellurium TeTerbium TbThallium TlThorium ThThulium TmTin SnTitanium TiTungsten WUranium UVanadium VXenon XeYtterbium YbYttrium YZinc ZnZirconium Zr

6 of the known short livedmanmade chemical elementshave been omitted.

112W

hat’s your reaction?

THE R

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H

Li Be

Na Mg

K Ca

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Hydrogen

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CalciumPotassium

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Lanthanum Hafnium

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Iron

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Rhodium

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Nickel

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Platinum

Copper

Silver

Gold

Zinc

Cadmium

Mercury

Gallium

Indium

Thallium

Aluminium

Boron

Germanium

Tin

Lead

Silicon

Carbon

Arsenic

Antimony

Bismuth

Phosphorus

Nitrogen

Selenium

Tellurium

Polonium

Sulphur

Oxygen

Bromine

Iodine

Astatine

Chlorine

Fluorine

Krypton

Xenon

Radon

Argon

Neon

Helium

The Periodic Table of the Elements

1. Growing Plants 1


Key ideas

1A. Growing Plants☛ Plants require chemicals to live.

☛ When plants die the chemicals from which they were made will eventually berecycled.

☛ Recycling maintains the chemical balance. If plant material is removed fromwhere it grows an imbalance is created.

☛ Natural cycles have evolved to recycle certain chemical elements – eg carbon,nitrogen and phosphorus.

SoilNearly all plants make their own food through the process called photosynthesis (seechapter 2A). Carbon dioxide for the reaction comes from the air and water comesfrom the soil. In addition, many other chemical substances are required for naturalgrowth and these are usually available in the soil. Soil is a solid and is composed of amixture of particles of coarse and fine sand, silt and clay which is interspersed withliquids and gases. To a gardener a ‘good loam’ is soil where the sand or clay compo-nents are not present in excess and which contains some humus. Humus is decayingplant and animal remains which helps to retain moisture, creates air spaces in the soiland slowly breaks down to release chemical compounds including those of nitrogen,phosphorus and potassium. These chemical compounds are normally found in thesoil as chemicals dissolved in water – ie as solutions. In waterlogged soil most of theair spaces are filled with water; in compacted soil there are fewer air spaces.

Essential chemicalsAs soon as a seed starts to germinate and grow into a seedling it uses the chemicalsrequired for growth from the supply within the seed. Once this supply is exhaustedthe plant takes up the major chemicals required (ie those based on nitrogen, phos-phorus and potassium) from the soil. Leaf production requires a great deal of nitro-gen, root formation demands phosphorus while during the period of flowering andfruiting potassium is in demand. In addition, plants require the chemical elementsmagnesium, iron, manganese, sulphur, calcium, chlorine, boron, zinc and copper toincorporate into new compounds as a requirement for healthy growth.

So far the names of the elements have only been used when referring to theplant’s food requirements but while this is not strictly wrong it does not indicate whathappens in reality. Potassium metal for example will react with air and moisture andhas to be kept under oil. So potassium as the metal element is not the material to puton your indoor plants! Yellow phosphorus has to be kept under water to prevent itcatching fire when exposed to the air so, again, it is not exactly a friendly fertilizer!Nitrogen, the third main plant food is a gas and it is unreactive. So how are theseimportant elements made available to plants by the soil? The only way is for them tobe joined with other chemical elements to form chemical compounds.

For a compound to be used by the plant it must be soluble in water, non-toxic tothe plant and be acceptable to the metabolism of the plant. Nitric acid for example isa compound containing nitrogen but it is not very acceptable to plants except indilute solution such as that produced when rain dissolves ‘nitrogen oxide’ gasesformed during a thunder and lightning storm (see chapter 1B). Fortunately both soiland fertilizers contain compounds which plants can absorb eg nitrogen is usuallycombined with oxygen to form nitrates; phosphorus is usually combined with oxygento form phosphates; and potassium is usually combined with oxygen to form potash.

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2 What’s your reaction?


‘Potash fertilizer’ is an agricultural term and refers to a mixture of potassiumoxides and other compounds containing potassium. ‘Nitrate’ and ‘phosphate’ cannotexist on their own; they have to be attached to another element (such as a metal) orcontained in a compound. In fertilizers this is quite useful because it makes it possi-ble for other important chemical elements to be given to the plant. Calcium forexample can be given as calcium nitrate and chlorine can be given as potassiumchloride (see figure 1A.1). Some crops require particular chemical elements and mostof these are supplied as compounds - eg sodium chloride (table salt) which is arequirement of sugar beet.

A seed can be considered to be an embryo with its own supply of food, so eachseed has its own basic supply of nutrients which are essential for the early life of itsseedling. After these reserves have been used up nutrients have to be available in thesoil for continued growth.

Ancient woodland or forest probably provides the only remaining examples ofnatural recycling on land. Leaves, whole plants, branches and sometimes trees fall tothe ground. With the help of insects, fungi, bacteria, and their enzymes the materialsdecay to release their chemicals into the soil for use by the next generation of plants.

‘This load of cattle went to market,This load of grain went to the mill.......................................and as result, a whole lot of mineral saltswere removed from the farm.’

If any part of a plant is taken from the spot where it has been growing a ‘packet’ ofchemicals is in effect removed. The harvesting of one tonne of wheat grain effectivelyremoves about 18.1 kg of nitrogen, 3.6 kg of phosphorus and 4.0 kg of potassiumfrom the soil. The despatch to market of a tonne of fat cattle (on average, two cows) isequivalent to removing 24.5 kg of nitrogen, 6.8 kg of phosphorus, 1.4 kg of potas-sium and 11.8 kg of calcium from the land (see figure 4B.2).

FertilizersIn intensive agriculture (and even in a heavily cropped gardens) a deficit in chemicalfood can be created. An alternative scenario is that as a result of managementmethods (eg the burning of vegetation), high concentrations of mineral salts accumu-late in one area. After human intervention has taken place and the crops have beenharvested one of two things can be done to replace the nutrients. The grower caneither ‘move on’ and exploit another area, leaving nature to take its course as ancientman did, or the grower can put some chemicals back into the soil by applyingfertilizer.

The idea of applying fertilizers is not new. The first British settlers in NorthAmerica found that the Indians improved their crop yield by burying a small fish withevery maize seed they planted. Medieval farmers recognised the benefits of plantingclover and other legumes in rotation to increase the level of nitrogen in the soil.Legumes (eg peas and clover), increase ‘nitrogen’ in the soil through the action ofbacteria which are held in nodules on the roots of these plants (see figure 1B.2). Thebacteria are able to convert nitrogen gas in air into a form which plants can use. Thisprocess is part of the nitrogen cycle and a simplified version of this is shown in figure1A.2 (more details are given in chapter 1B). It is one of the recycling systems foundon earth, others include the carbon (see chapter 3) and phosphorus cycles.

1. Growing Plants 3


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Slightly alkaline conditions are best for maximum nutrient uptake



Figure 1A.2 Simplified nitrogen cycle

Challenge1

Visit a garden centre. Look at a packet of fertilizer for maturing tomato plants and notedown the NPK ratio shown on the packet. Find a fertilizer for grass and one forflowers. Again note the NPK ratio. What conclusions can you draw from these threeratios?

‘Organically grown - no chemicals used’Although we think we know what this phrase means, if taken literally it is misleading.What the producers should tell us is the form in which the chemicals are available.There are three types of fertilizer: ‘organic’, ‘natural’ and ‘chemical’. ALL three releaseessential chemicals into the soil for plants to use (see figure 1A.3).

Natural and chemical fertilizers do not provide humus. Although organic fertilizersgenerally contain some humus, the amounts are often low and additional humus isoften required. Most general fertilizers are marked with the plant food ratio of themajor components in the order N (nitrogen), P (phosphorus as phosphate) and K(potassium as potash). This is known as the NPK ratio or number.

Nitrogen in the atmosphere

Soil Some soilbacteria

Dead plantsand animals

and animal urine

Decay

Fertilizermanufacture

Legumes egclover, peas and

beans takenitrogen from the air

Rain during thunderstorms contains

useable nitrogen

Lightning

Plants

1. Growing Plants 5


Organic fertilizers Natural fertilizers Chemical fertilizers

Processed deadorganic matter

Naturally occurringminerals

Manufactured orprocessed chemicals

Driedblood

Kainite Saltpetre

Rockphosphate

Flowerfertilizer

Designer fertilizers oftencompounded for application

to a specific crop at aspecific time. Quick actingbecause chemicals do not

need breaking down

Potassiumchloride

fromCanada,Germany,

and “USSR”

SodiumnitratefromChile

Calciumphosphate

fromN Africaand US

Slow or quick actingdepending on howquickly they dissolvein the soil water. Separateminerals supply individualchemicals. This group isoften replaced withchemical fertilizers

Supplies nitrogen,phosphate and potassiumin a general mix. Usefulchemicals released slowlyas microorganisms breakdown organic matter.These fertilizers are moreoften used by gardenersthan farmers

Supergrass

fertilizer

NPK25/5/5

Hoof and

horn meal

Fish meal

Bone meal

Tomatofertilizer

Figure 1.A3 Fertilizers



1B. Growing plants☛ Chemical elements cannot normally be created or destroyed. They can exist

on their own (sometimes only for a short time), and they can be incorporatedinto different compounds.

☛ In the nitrogen cycle, elemental nitrogen is transformed into different com-pounds.

☛ Some of the nitrogen compounds included in the cycle can be used by livingthings; others cannot, and some can be toxic.

The nitrogen systemThe chemical element nitrogen is found in many organic compounds (although it isnot as common as carbon). However, it is essential for protein production in bothanimals and plants. Nitrogen is an unreactive gas, hence it is difficult to makenitrogen react with almost anything else.

Converting the inert to the essentialThe form in which nitrogen is most available is as a gas in the atmosphere where itmakes up about 80 per cent of the air we breathe. Most plants can only utilisenitrogen if it is available as ‘nitrate’ (see chapter 1A). Nitrogen can be ‘fixed’ orcombined with other elements by the power of lightning or the equally ‘striking force’of bacterial activity. Chemical reactions at high temperatures and pressures can alsomake nitrogen combine with other chemical elements. In essence there are four waysin which nitrogen gas can be converted to nitrate (see figure 1B.1).

By lightningThe electrical energy released when lightning flashes can cause nitrogen and oxygenin the atmosphere to combine and produce oxides of nitrogen. These acidic oxidesare soluble in water and will dissolve in rain to form dilute nitric acid.

nitrogen + oxygen → nitrogen monoxide → nitrogen dioxide

nitrogen dioxide + water + oxygen → nitric acid (rain)

On contact with the soil the nitric acid can react with (basic) compounds to producenitrates; eg

calcium carbonate + nitric acid → calcium nitrate + carbon dioxide + water

Fixation by this route removes about 7 million tonnes of nitrogen per year from theatmosphere and transfers it into the soil.

Industrial fixationDue to the importance of nitrate in increasing the amount of food produced, chemi-cal processes have been devised for converting atmospheric nitrogen to nitratefertilizer (see chapter 1C). In 1985 world production of one particular nitrate fertilizerwas 78 million tonnes!

Free-living nitrogen fixing bacteriaSome bacteria live an independent existence in the soil and can convert nitrogen gas

Key ideas



1. Grow

ing Plants

7

THE R

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AL

SOC

IETY O

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Nitrogen in the atmosphere

Animals(nitrogen as protein)

Excretion

and death

Eaten by

animals

Decay & deathPlants

Humus

Am

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Nitr

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ia &

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Ligh

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Nitrogen in the soil

Ammonia Nitrites NitratesNitrobacterNitrosomonas

Nitrification by nitrifying bacteria

NitrogenN2

Nitrous oxideN2O

Nitrite ionNO2

–

NO3–

Denitrifying bacteria, Pseudomonas, Bacillus

Fate of nitrogenous fertilizer when applied to cereal crops

55% taken up by crop

25% becomes

part oforganic

matter ofsoil

10%lostby

denit-rifica-tion

10%lostby

leach-ing to

ground-water

Figure 1B.1 The nitrogen cycle



to ammonia (eg the Azotobacter and Clostridium bacteria do this by using theenzyme nitrogenase). Clearly the amount of nitrogen fixed in this way will depend onthe number of bacteria present and estimates indicate that these bacteria convertabout 170–270 million tonnes of nitrogen gas a year to ammonia which is thenconverted to nitrate by different bacteria.

Nitrogen fixing bacteria in legumesLegumes are a group of plants that include clover, peas, beans, soya beans andlupins. Specialised bacteria (of the Rhizobium genera) resident in the soil colonise theroots of legumes and induce the formation of small lumps or nodules (see figure1B.2). In this relationship bacteria and plants coexist to their mutual benefit, thebacteria in the nodules convert atmospheric nitrogen to ammonia, and about 35million tonnes of nitrogen a year is converted in this way. This process can also takeplace in some non-leguminous plants and a great deal of research is being directed toengineer genetically this facility into other food plants. It is a farmer’s dream to haveall plants ‘fixing’ nitrogen from the air and this is certainly the biotechnologists goalbut it is probably the fertilizer manufacturers’ greatest nightmare!

Life depends on deathWhen waste material is produced by animals, and when plants and animals die, apotential source of nitrogen is made available. However, this nitrogen is ‘locked’ upin the form of large protein molecules in the waste material. Fortunately bacteria andfungi which occur naturally are able to break down dead and excreted matter toobtain the energy they require and, as a consequence, release nitrates into the soil. Inthe first stage proteins are broken down to the basic units (amino acids) via a processcalled microbial decomposition. The amino acids are then further broken down in aprocess called ammonification (because it produces ammonia).

protein from microbial microbialdead cells and → amino → ammoniawaste products decomposition acids ammonification

Although ammonia plays a key role in the nitrogen cycle, plants can absorb very littlenitrogen in this form so it is left to bacteria to change the ammonia into nitrate whichplants can absorb. The bacteria change the ammonia by oxidising it (essentiallyadding oxygen) to turn it first into nitrite and then into nitrate. This process is callednitrification.

Nitrosomonas Nitrobacterammonia → nitrite → nitrate

bacteria bacteria

The system isn’ t leak proofIt might appear that the recycling system for nitrogen is almost perfect. In the longterm it is, but there are three ‘leaks’ which give cause for concern in the short term.

i) Nitrates (especially nitrogenous fertilizer) are very soluble in water and caneasily be washed out of the ground by heavy rain or flooding. This process iscalled leaching and can account for nitrate finding its way into drinking water(see chapter 1C). It is estimated that approximately 10 per cent of fertilizerapplied to soil can be lost in this way.

1. Growing Plants 9


ii) Some ammonia gas can enter the atmosphere before and during theammonification process. This often comes from the slurry from animal rearingunits and not only is this a loss of nitrogen as ammonia, but it is difficult to‘recapture’ the ammonia back into the nitrogen cycle.

iii) The third ‘leak’ is very much part of the nitrogen cycle but from the point ofview of the farmer it is rather counter productive since nitrate can be con-verted back to nitrogen. This is brought about by denitrifying bacteria (egPseudomonas and Bacillus) in the soil gradually removing oxygen from thenitrate group to produce nitrogen as the end result.

nitrate → nitrite → nitrous oxide → nitrogen

Figure 1B.2 Root nodules

Challenge2

This experiment illustrates soil microorganism activity.Cut up about six 20 mm x 60 mm cotton material or paper strips and bury them in

the soil in a vertical position in a slot made by putting the blade of a spade in theground. Place them in six different spots throughout the garden. Pack the soil firmlyagainst each strip with the end of it just sticking out . Bury all six pieces on the sameday and after 4–6 weeks carefully retrieve the strips (they may be very fragile) andexamine them for signs of decomposition using a hand lens to help you.

Root nodulesNodules are found on the rootsof mainly leguminous plants.They contain bacteria whichconvert atmospheric nitrogengas into a form which is usefulto the plant



1C. Growing food☛ The manufacture of ammonia from nitrogen and hydrogen is one of the

world’s most important industrial chemical reactions.

☛ The ability to produce synthetic nitrogenous fertilizer has enabled food cropproduction to be greatly increased.

☛ An excess of nitrate and phosphate can cause problems in water courses.

☛ Nitrates and nitrites can help preserve food in addition to helping produce it.

Making ammoniaChemical compounds containing nitrogen are required by plants in a greater quantitythan those with either potassium or phosphorus. At the turn of the century an in-crease in the amount of food available to satisfy an increasing population requiredthe supply of nitrogenous fertilizer in much higher quantities, and over a shorterperiod of time, than the Chilean deposits (which were running out in 1900), and thenitrogen cycle could deliver. In addition nitrates were required for the manufacture ofexplosives for World War I. This supply problem was solved in about 1908 by thechemist Fritz Haber and the engineer Carl Bosch who invented a way of makingnitrogen and hydrogen combine to form ammonia. By doing this, Haber in effectfound an artificial way of ‘fixing’ nitrogen from the earth’s atmosphere. The ammoniaproduced in the reaction is a useful chemical in its own right and some farmers applyammonia (in solution) directly into the soil as a fertilizer.

In the Haber process nitrogen (N2 obtained from the atmosphere) and hydrogen(H2 obtained from natural gas and steam) are combined together to make ammonia(NH3). The reaction takes place at a high temperature (about 400 0C) and at a highpressure (about 200 times atmospheric pressure). The reaction is speeded up by theuse of a catalyst (see chapter 2C).

high temperature, highnitrogen + hydrogen → ammonia

pressure, catalyst

Since the reaction is reversible, ammonia is continually removed to prevent thereaction going into reverse.

From base to acidAmmonia from the Haber process is normally piped away to produce nitric acid(HNO3). Ammonia and excess air are passed over red hot layers of a platinum–rhodium alloy. Here the oxygen in the air combines with ammonia to form nitrogenmonoxide and steam.

ammonia + oxygen → nitrogen monoxide + water(steam)

On cooling nitrogen monoxide (NO) and oxygen from the air combine to producenitrogen dioxide (NO2).

nitrogen monoxide + oxygen → nitrogen dioxide

Key ideas



1. Growing Plants 11


The nitrogen dioxide can then combine with more oxygen from the air and dissolvein water to form nitric acid.

nitrogen dioxide + water + oxygen → nitric acid

Ammonia (NH3) is a base (see chapter 9C) and reacts with nitric acid to form ammo-nium nitrate, and with sulphuric acid to form ammonium sulphate, both of which areimportant fertilizers.

ammonia + nitric acid → ammonium nitrate NH3 HNO3 NH4NO3

ammonia + sulphuric acid → ammonium sulphate

Recent trendsThe new Leading Concept Ammonia (LCA) process developed by ICI in 1990, usesless energy and produces less waste than previous systems . In this process ammoniaand carbon dioxide are used to make a fertilizer called urea.

In 1985 world production of one particular nitrogenous fertilizer was 78,000,000tonnes but production in the Western world has now eased back. Even so we are stillseeing the effect of too much nitrate and phosphate entering water courses.

Richer in food?Eutrophication, or perhaps it should be called death by enforced gluttony, is a termwhich comes from the Greek word eutrophos, meaning ‘well fed’. Streams sufferingfrom eutrophication contain so much plant food (including nitrates and phosphates),that the algae reproduce rapidly. Growth of unicellular algae can cause the water tolook like pea soup and filamentous algae causes ‘blanket’ weed growth on or nearthe surface. Both types of growth are called ‘algal bloom’ and prevent light reachingsubmerged plants. In addition blanket weed also reduces water flow. Many farmstreams have become eutrophic and some larger areas in the English Lake Districtand East Anglian Broads have also suffered.

It is generally considered that fertilizer run off has contributed to the nitrogenlevels in waterways, and that human waste products – eg some washing powders –have mainly contributed to the excess of phosphate. (In both East Anglia and the LakeDistrict phosphate stripping equipment has been installed at some sewage works. Inthe stripping process iron (ferric) sulphate is added to the effluent and this producesinsoluble iron phosphate which drops out of the water leaving the liquid virtually freeof phosphate.)

When the algae die, bacteria which live off dead matter increase in number anddemand high levels of oxygen to live so there is a high biological oxygen demand(called BOD for short). As a result, most of the animals die because there is nooxygen left in the water, so in time the water becomes almost devoid of live animalsand plants with the bacteria having a great feast until they too die. However, ifenrichment stops the water will regain oxygen and life, given time (see figure 1C.1).



1. Healthy stream.Mineral salts inbalance. Wateroxygenated

Eutrophication is caused by excess nitrate and phosphate entering water courses

2. With excess nitrate andphosphate in water, algae growrapidly. Water can look likepea soup. Some algae can forma ‘blanket’ on the surface. Densealgal growth prevents some animal movement. Water flowreduced

Outfall fromsewage works

Surface runoff

Fertilizer leaching throughsoil and land drains

Seepage fromseptic tanksand livestockunits

3. Algae die. With extra deadorganic matter to feed on,bacteria reproduce in large numbers. Bacteria require oxygen to live and remove it from the water. Fish and other animals die due to lack of available oxygen. Fish sometimes float to the surface

Water healthcan be restoredby reducing inflowof nitrogen andphosphate andpossibly oxygenatingthe water

Figure 1C.1 Eutrophication

1. Growing Plants 13


Fertilizers, explosives, bacon and sausagesA strange grouping perhaps, but all of these products are associated with nitrogencontaining nitrates and nitrites.

NitratesThese are the salts of nitric acid. The nitrates of metals (eg potassium nitrate) are allsoluble in water, and the capacity of some nitrates to ‘draw’ water out of meat byosmosis makes them useful for curing bacon and ham joints (eg saltpetre – potassiumnitrate – was used extensively for ‘home curing’). Solubility in water is also importantwhen a nitrate salt is used as a fertilizer because in solution it is a readily used plantfood. Nitrates contain quite a lot of oxygen linked to nitrogen (and other elements).This available oxygen is used when potassium nitrate is used to make gunpowder(which is a mixture of carbon, sulphur and potassium nitrate). On ignition, largevolumes of gases are produced over a short period of time which, if confined, canlead to an explosion.

heatpotassium nitrate → potassium nitrite + oxygen

NitritesLook at the ingredients label on a packet of cooked meat or sausages and there is agood chance that sodium nitrite will be listed as an antioxidant. When used in redmeat, sodium nitrite prevents the meat turning grey or brown by forming a redcompound, nitrosomyoglobin, which keeps the meat looking attractive. It also hasthe effect of inhibiting the growth of some microorganisms and gives rise to theproduction of aromatic substances reminiscent of roast meat!

Challenge3

Try and find out how foods which are cured by ‘smoking’ are preserved.

Challenge4

Look at the labels on cooked meat and sausages and compile a list of those productswhich contain sodium nitrite. Make a note of whether the product is naturally red oris coloured.



Key ideas

2A. Food☛ Virtually all energy for human activity comes from the sun.

☛ Plants use light to provide the energy to form new chemical compounds byphotosynthesis.

☛ Living things produce carbohydrates, fats and proteins.

The sun as a source of energySun worshippers are probably more concerned about how to obtain a good tanwithout getting skin cancer than considering where the energy in their next mealcomes from. But in a sense all of us should be sun worshippers since whether we eatsteak and chips or a vegetarian salad, all the energy in the meal has its origins in lightfrom the sun, or at least in the energy obtained via light.

It has been calculated that in four days the sun can deliver energy to the earthequivalent to that locked up in all the known reserves of coal, oil and natural gas puttogether. The problem is that apart from a few solar cells on calculators and onsatellites, and solar panels for water heating there are few things capable of utilisinglight energy other than the process of photosynthesis (see figure 2A.1). The energy

Food(storedin root)

Carbon dioxidegas

Oxygen gas

Energy fromsunlight

Water

Photosynthesis takes placein the green leaves

The carrot we eat isthe plant’s own food storefor the following year when

it flowers and produces seed

Water

Mineral saltsfrom soil

Rain

Figure 2A.1 Photosynthesis




2. Food 15

required for photosynthesis is normally transferred as ‘white light’. White light ismade up of light of different wavelengths (which are perceived by humans as light ofdifferent colours). Light at one wavelength and having a particular colour transfers agreater or lesser amount of energy than light of a different wavelength. Light towardsthe violet end of the spectrum delivers more energy than light at the red end where ithas a longer wavelength. Visible light can range through the colours of the rainbowfrom violet to red and therefore covers a range of wavelengths. White light is amixture of all colours and different wavelengths, and comes in between theultraviolet and infrared parts of the spectrum. (Ultraviolet (UV) light is responsible forthe tanning effect on people and is also held responsible for an increasing number ofcases of skin cancer. Humans are normally protected from the worst effects of UVlight by the ozone layer.)

Water for photosynthesis normally comes from the soil and is taken up throughthe plant’s roots, while the carbon dioxide comes from the air surrounding the plant.Photosynthesis takes place in the leaves; carbon dioxide enters the plant throughsmall holes in the undersurface, while oxygen (produced as a by-product) alsoescapes through these holes. The sugars produced during photosynthesis remain inthe leaves or are transported to other parts of the plant. In fruits or other storageorgans, such as carrots and potatoes, the sugars can be turned into starch.Photosynthesis also requires the presence of the green coloured chemical chlorophyllwhich ‘traps’ light energy and enables it to be used.

chlorophyllwater + carbon dioxide → sugars + oxygen (energy taken in)

in plants

Some idea of the significance of photosynthesis can be gained from the fact that0.4 hectares (one acre) of corn can produce 10,000 kilograms (kg) of sugar per yearfrom 4,000 kg of carbon supplied as carbon dioxide.

The Bible says ‘Man cannot live by bread alone’, and while the meaning of thismay not be connected with diet, it might just be possible to live on wholemeal breadand water. Most foods contain carbohydrates, fats and proteins. Take a look at the‘Nutrition Information’ panel on a tin of garden peas. You will see that plants canmake other classes of foods. The label on one particular supermarket tin of gardenpeas (with no salt, sugar or additives) shows that each 100 gram (g) serving contains4.5 g of protein and 0.6 g of fat as well as the 8.1 g of carbohydrate. This shows thatplants are able to make fats and proteins in addition to carbohydrates. They can alsoproduce vitamins and accumulate mineral salts such as compounds of calcium andsodium. Some of the chemical elements obtained from the soil are essential for theproduction of particular chemical compounds - eg chlorophyll, in which magnesiumis part of a complex structure. All of the carbohydrates, fats and proteins required byhumans can be obtained from plants but in the case of protein there is a problem.

Challenge5

Plant two separate samples of the same type of small seed – eg cress – on kitchen rollor blotting paper. Grow one sample in the dark and the other in the light. Record thesowing date and see how long the sample in the dark lasts compared with the samplewhich is able to photosynthesise. (Don’t forget to keep the samples moist.)

ProteinsUnlike carbohydrates and fats, proteins contain the chemical element nitrogen aswell as carbon, hydrogen and oxygen. Some proteins also contain sulphur and



Figure 2A.2 Modelling digestion

phosphorus. Humans require protein for growth and repair of tissue but on someoccasions it can be used to provide energy. When protein is digested it is brokendown into the basic building blocks from which it was made, the amino acids (seefigure 2A.2). In all there are about twenty essential amino acids which are requiredby the human body. Eight of them (nine in infants) cannot be made within the bodyand have to be ‘imported’ into humans as part of the protein eaten. Generally all theamino acids required are available from proteins provided by meat. Plants provideproteins but only in smaller quantities. In a human diet, plants and animals willprovide different proteins and hence different combinations of amino acids.Consequently a planned balanced diet is required (whether a person is a vegetarianor not), to ensure that all the amino acids needed are included. Meat will provide allof the necessary amino acids, but plants need to be used in different combinations toyield the same result.

CarbohydratesThese are chemical compounds of the elements carbon, hydrogen and oxygen only.Included in the carbohydrate group are sucrose (cane sugar), starches and cellulose.All sugars are carbohydrates but not all carbohydrates are sugars. Sugars arecrystalline, soluble in water and sweet in taste. Other carbohydrates are non-crystalline, insoluble and tasteless – eg starch can be found in the kitchen as

Amino acid

Amino acid

Amino acid

Tray

Sleeve

Tray 1

Sleeve 1

Sleeve 2

Sleeve 3

Modelling the digestion of protein in humans

All proteins are made up of ‘building blocks’called amino acids. Three matchboxes joinedtogether represents part of a protein and it iscalled a tripeptide. Each matchbox representsan amino acid. The different shadings representdifferent amino acids

During digestion enzymesbreak down proteins into separateamino acids. In the model thematchboxes are slipped apart

Tray 2

Tray 3


2. Food 17

cornflour and is present in rice, potatoes and bread while a considerable amount ofcellulose is found in vegetables, nuts and pulses. Although cellulose is not brokendown in the human gut it plays an important role as dietary fibre, absorbing someunwanted and possibly toxic chemicals.

FatsFats, like carbohydrates, are composed of only carbon, hydrogen, and oxygen. Fromthe point of view of the human diet it is thought best to avoid foods containing hardfats like lard, suet and cocoa butter which contain saturated fatty acids. This isbecause research has shown that a link may exist between the intake of saturatedfatty acids, the production within the body of cholesterol, and the development ofcoronary heart disease.

Oils and fats containing unsaturated fatty acids such as olive oil and sunflower oilare thought to be healthier since they are not associated with the development ofheart disease. Oils containing pure unsaturated fatty acids tend to be more liquid atroom temperature (compared to saturated fats which tend to be solid), so it can befairly easy to tell which is better for you. In any event gram for gram, fats providemore energy than carbohydrates.

1 g dietary protein provides 4 kcal (17 kJ) of energy1 g dietary carbohydrate provides 3.75 kcal (16 kJ) of energy1 g dietary fat provides 9 kcal (37 kJ) of energy(kcal = kilocalorie, kJ = kilojoule)

Energy is usually measured in units called joules (J). To raise the temperature of 1 g ofwater by 1 degree Celsius (1 0C), 4.2 J of energy are required. A kilojoule (kJ) is 1000joules. The fact that burning a standard size match releases about 4 kJ of energymight help interpret these figures. On food labels and diet sheets the term calorie (cal)or kilocalorie (kcal) is often used. One calorie equals 4.2 J and 1 kcal equals 4.2 kJ.

Challenge6

Look at the Nutrition Information panel on the containers of the items you eat at aparticular meal and make a combined table for all the items. If the labelling givesfigures for a typical serving you could use these, but many products will only carry ananalysis for each 100 g of the food.

Analysis per 100 g of food item

Shreddies Brown bread Baked beans (Safeway) (Heinz)

Energy(kJ) 1520 941 306Protein(g) 10.5 10.1 5.0Total fat(g) 2.0 2.4 0.3Carbohydrate(g) 74.5 38.4 13.1Fibre(g) 8.1 6.3 7.3

average one slice average serving = 45 g = 36 g serving = 210 g

Look at your table or the one above and inspect it to see which food items providemost of your protein, fat and carbohydrate intake. How could you use a variation ofthis table to keep track of your diet?



2B. Food☛ The human digestive process is ‘chemistry in a 10 metre long tube’.

☛ Respiration releases energy from food.

Food for thoughtVery little of the food we eat can be absorbed directly into the blood transport systembecause most has to be broken down into smaller, simpler, units. These units have tobe transported, sorted and rebuilt into new compounds and some units are discarded.Breaking food down into smaller units is called digestion. In humans this is, assomeone once put it, a series of chemical reactions taking place in a 10 metre (m)long tube with an appetite at one end (see figure 2B.1). Many of the chemicalreactions that take place during digestion happen much more quickly due to theaction of enzymes (see below). If it were not for enzymes the reactions would take solong that an alimentary canal three or more times longer would be needed! (Figure2B.2 shows the main chemical aspects of digestion.) Most of the end products ofdigestion are transported via the blood to the liver which acts like a chemicalprocessing plant. Unwanted protein material is broken down and made soluble in theform of nitrogenous waste before being excreted through the kidneys as urine. Fromthe liver, the remaining material that is useful is passed back into the bloodstreamand used to form new tissue or respired to release energy.

Key ideas



Figure 2B.2 Some chemical aspects of digestion

MouthFood: starchSecretion: slightly alkaline salivaEnzyme: amylaseProduct: maltose (a sugar)

Trachea

Oesophagusor gullet

StomachFood: protein materialsSecretion: very acidic gastric juiceEnzyme: pepsinProduct: polypeptides (sections of protein)

Pancreas

Large intestine

Small intestineFood: sugars and sectionsof proteinSecretion: alkaline juiceEnzymes: maltase, sucrase,lactase and peptidasesProduct: Glucose, fructoseand amino acids

Rectum

Anus

Caecum and appendix

DuodenumFood: fatsSecretion: alkaline bile(from gall bladder)Enzymes: noneProduct: fat droplets

Also:Food: starch, proteins, fatsSecretion: alkaline pancreatic juice(from pancreas)Enzymes: amylase, trypsin, peptidases and lipaseProduct: maltose, polypeptides,amino acids, fatty acids and glycerol


2. Food 19

In parts of the digestive system conditions can be very acidic and it is worthconsidering how the tissue of the gut can withstand a concentration of acid whichwould damage the hand!

Food tube for thought

The alimentary canal of a humanis about 10m long. Most of it is‘coiled up’ in the abdomen. Ifit had to be a straight tube, thehuman abdomen would need tobe about 30 times taller.

During an average lifetime about51 tonnes of food and 47,712 litres(10,500 gallons) of liquid willhave entered the tube

Figure 2B.1 Food tube



→ →→ →→ →

CatalystsHave you ever tried to mow a lawn with a hand mower that has rusted over thewinter, clip a hedge with rusty shears or even ride a rusty bicycle? Hard work isn’t it?But it can be done. By putting a little oil in a few critical places the mowing, clippingor cycling becomes easier and quicker. The oil has not been used up but its presencehas enabled the job to be speeded up. In these cases the oil was acting as a surfacelubricant, reducing the friction between the rust (a form of iron oxide) particles.Catalysts work in a similar, but NOT identical way. The efficiency of catalysts in non-biological reactions seems to depend to a large extent on the available surface areawhere the reaction can take place.

For the reaction to take place the chemicals involved need brief but intimatecontact with the catalyst so it follows that the greater the surface area of the catalyst,the greater will be the amount of chemicals able to react. This may not matter toomuch in a laboratory, but in cars fitted with exhaust gas catalytic converters it mattersa great deal. The way catalysts work is not fully understood but it is thought that theyare able to lower what is termed the ‘energy of activation’. In simple terms this meansthat less energy is required to make the reaction happen (think back to the lawnmower analogy). Catalysts are used in adhesives – ie two component glues, and inthe industrial manufacture of ammonia, polythene and many other chemicals.

EnzymesEnzymes are catalysts found in living things and without them essential reactionswould be too slow for life as we know it to exist. Since all enzymes are proteins andwork best under conditions normally found in living cells they are destroyed by thefactors which affect proteins, such as high temperature, and too acidic (or alkaline)an environment. Enzymes are very specific. They will only assist a reaction whichthey are specifically designed to help. An example of this is provided by the label ona packet of detergent containing an enzyme. It states ‘enzyme biologically breaksdown stains containing proteins like blood, gravy and milk’, therefore these enzymeswill not remove fat or carbohydrate stains.

Summary of enzyme action

Food type Enzyme type Products

Carbohydrates Carbohydrases Sugars,particularly glucoseFats (lipids) Lipases Fatty acids and glycerolProtein Proteases Amino acids

VitaminsUntil the beginning of the 20th century it was thought that a good diet for humansconsisted of water, carbohydrates, fats and proteins. Provided the food was fresh andthere was a good balance of meat and vegetables, this was largely true. The effect ofpreserved food eaten on long sea voyages, and poor diets in certain groups of peopleled scientists to believe that very small quantities of certain ‘mineral elements’ andchemical compounds called vitamins were essential not only for life but also for goodgeneral health. Mineral elements such as iron, calcium and phosphorus are neededfor the development of bone and blood while others, including many of the vitamins,are closely associated with the working of enzymes.


2. Food 21

Pause for breathPhotosynthesis is a chemical way of collecting, transferring and storing energy and its‘opposite’– respiration – is a chemical way of releasing energy in all living things. Infact, respiration is so important that it is often listed as a characteristic of life. Inaerobic respiration (the main and most efficient type of respiration), oxygen is used tohelp release energy, with water and carbon dioxide produced as by-products.

The chemical process of respiration is complicated, but like photosynthesis theoverall reaction can be expressed simply and in many ways it can be considered as areversal of photosynthesis.

enzymesglucose + oxygen → water + carbon dioxide (energy given out)

Sports people sometimes become short of oxygen during a period of intense activityand certain parts of their body will respire anaerobically rather than aerobically.During this period lactic acid is produced instead of water and carbon dioxide; and itis this which causes stiffness of the joints.

enzymesglucose → lactic acid (energy given out)

Sports people know that further gentle exercise will cause lactic acid to be respiredaerobically and the stiffness will go.

It is generally considered that aerobic respiration is more efficient at releasingenergy than is the anaerobic system. The aerobic system releases energy slowly,whereas the anaerobic system is less efficient but releases energy very quickly.

Challenge7

There used to be a very strict ruling that flowers had to be removed from hospitalwards at night. Consider the chemistry of photosynthesis and respiration. Do youthink there were good reasons for this rule?

Hot versus cold food in relation to energy intakeThe amount of extra energy taken in by eating food hot is very low, almost negligible,compared with the energy provided through digestion and respiration. However, dueto the temperature of the food the energy is almost instantly available and does nothave to be released through the usual process of respiration. It is worth noting that250 ml of soup served at a temperature of 60 0C will only add about 25 kJ (6 kcal) tothe basic energy value of 595 kJ (140 kcal), but the psychological effect can bebeyond value! It should also be remembered that not all the energy mentioned on thefoodstuff label is released by digestion and respiration.



A piece of material cut into smallerpieces produces a greatly increased surface area

Figure 2C.1 Surface area

2C. Food☛ The rate at which a reaction takes place can be all important.

☛ Reactions can be slowed down or speeded up by using a variety of techniques.

Taking controlNo matter what we do, we always like to think that we are in control. It is the samewith the world around us. For instance if we are making a jelly we use hot water, tearthe jelly into cubes, and stir the cubes into the water. Have you ever thought why wedo this? Why not try a simple test? Boil a kettle and pour equal amounts of water intotwo jugs. Take an ordinary jelly and tear it in half. Take one of the halves and break itinto cubes. Place the cubes in one jug and the half jelly in the other and stir both.Which lot of jelly dissolves first? You should find that the cubes dissolve first. Butwhy? The reason is that the small cubes together have a larger surface area, so agreater area is in contact with the hot water it is dissolving in (see figure 2C.1). Thejelly dissolving in water illustrates a general rule, namely, when things react, thegreater the surface area (ie the smaller the size of the particle), the faster the rate ofreaction.

Key ideas



1 cm

1 cm

4 cm

Surface area = 2 (8 x 4 +4 x 1 + 8 x 1)= 88 cm2

Surface area of separate cubes = 32 x 6 cm2 = 192 cm2

8 cm


2. Food 23

The second part of the investigation also involves cubes of jelly. Boil a kettle ofwater. Place some hot water into one jug and an equal amount of cold water into asimilar jug. Add a cube of jelly of the same size to each jug and stir. Which dissolvesfirst? This illustrates another general rule. When things react, the higher thetemperature, the faster the rate of reaction. At room temperature, a rule of thumb isthat every 10 0C rise in temperature doubles the rate of reaction (ie the time for thereaction to be completed is halved).

Another way of controlling what is going on is to vary the concentration of thematerials used. Use the reaction between bicarbonate of soda (sodiumhydrogencarbonate) and vinegar (acetic acid)[see challenge 54] where a gas, carbondioxide is given off when these two are mixed. The rate at which the gas is given offcan be used to indicate how fast the reaction is taking place. Pour some vinegar intoa jug. Into another jug pour an equal amount of vinegar solution made by adding oneteaspoon of vinegar to 500 ml of water. Add one teaspoon of bicarbonate of sodacarefully to each jug. Which gives off the gas the fastest? You should find that the oneusing the undiluted vinegar does. The vinegar is more concentrated so it reacts withthe bicarbonate of soda faster. As a general rule, therefore, the more concentrated thereacting substances, the faster the reaction.

A fourth way of controlling reactions is to use a catalyst. Enzymes are catalystsused by biological systems and a common example of a biological catalyst is yeast.Obtain a sachet of brewers yeast. Dissolve a tablespoon of sugar in 1000 ml of water.Pour 500 ml of the solution into two jugs. Add the sachet of yeast to one of the jugs.Cover the jugs with a cloth and place both of them in a warm place (about 21 0C).After a couple of days look at the jugs. The one with the yeast should be frothing, andthe one without the yeast unchanged. This is an example of a reaction which hasbeen catalysed. Yeast contains enzymes (biological catalysts) which convert sugar toalcohol and water in a process called fermentation. The other product is the gascarbon dioxide. The reaction continues until all the sugar is used, or the level ofalcohol rises to a point where it kills the living yeast (see chapter 2B).

Whatever the reaction, catalysts are unchanged at the end of it. Catalysts enablereactions to take place at temperatures far lower than they normally would and ingeneral catalysts are very specific: they may only work well for one reaction, at onetemperature and one level of acidity!

Challenge8

Look at a recipe for making bread. You will see that it is important NOT to add waterthat is too hot after adding the yeast containing enzyme. Why do you think this is?Another part of the recipe tells you to put the bread mixture in a warm place to prove(ie to rise). What does this tell you about the rate of the reaction in which sugars arebeing assisted in their conversion to carbon dioxide and water by enzymes in theyeast?

Challenge9

Hydrogen peroxide (which can be bought at the pharmacists for bleaching hair), canbe decomposed by the enzyme catalase, present in liver and potato, to give twoproducts, water and oxygen. Obtain some liver and cut off two small pieces of equalsize. (If liver is not available use pieces of potato.) Keep the liver in a refrigerator overnight. Remove from the refrigerator one piece of liver. Allow it to warm up to roomtemperature. Place 200 ml of hydrogen peroxide in each of two glasses. Stand oneglass of hydrogen peroxide into a bowl of ice/water for 1 hour. Stand both glasses ona saucer or plate (to catch any overflow). Then, add the cold liver to the coldhydrogen peroxide, and the warm liver to the warm hydrogen peroxide. Observe.



What do you notice? From this what can you conclude about the enzyme in livercalled catalase? This enzyme is the second fastest enzyme known. It is calculated thatone molecule of catalase can decompose 40,000 molecules of hydrogen peroxideper second at 0 0C!

Challenge10

Read the label on a packet of detergent containing enzymes. If you use this productto remove protein stains, egg, blood etc what do you think is happening chemically?From this what can you say about the solubility in water of (1) proteins and (2) theproducts formed by the action of the protein splitting enzyme?

1. Food 25


3. Energy and fuels 25

3A. Energy and fuels☛ We all depend on energy and without it life as we know it would cease.

☛ Energy cannot be destroyed, it can only be changed from one form to another.

☛ For a fuel to burn, heat and oxygen are required. Fuel, heat and oxygen formthe fire triangle.

☛ Everything contains energy in some form. Substances that contain a high levelof releasable energy are classed as fuels.

The different forms of energyIf you ask someone what words they associate with the term energy a probable replywould include heat (gas or electricity) and even an athlete. This is because peopletend to link energy with the form in which they use it and what it can do for themrather than what energy is. In these examples gas and electricity help humans to cookfood and keep warm, while an athlete uses food to provide the energy to run.

The main forms of energy are electrical, chemical, heat (thermal energy), nuclear,kinetic (from movement), potential (stored up energy); and probably the most funda-mental of all, wave energy (eg sound energy and energy from the sun, solar energy).It is solar energy, through photosynthesis (see chapter 2) which has provided thefossil fuels: coal, oil and natural gas.

Energy can be transferred. Each time energy is transferred some energy will belost, generally as heat, to the surroundings. Transferring energy of this type is ineffi-cient because not all of the energy you are trying to transfer ends up in the final form.However, the energy is never destroyed.

(1) (2) (3) (4) (5)chemicals → plants → coal → steam turbine → generator → heat and light

(power station)

1=light energy (wave), 2=chemical energy, 3=heat energy, 4=kinetic energy,5=electrical energy

An example of an energy transfer chain

Fossil fuelsFossil fuels are examples of substances that can react with oxygen to produce energy,usually as heat and light. For a fuel to be useful it must be convenient to control anduse, as is the case with the burning of natural gas (methane).

sparkmethane + oxygen → carbon dioxide + water (energy released)

From the word equation for the burning of methane it can be seen that a spark isrequired to provide energy to start the reaction. When the reaction is underway someof the energy released by the reaction helps the burning to continue.

The chemicals which provide oxygen are called oxidising agents; air is the mostcommon of these. Sometimes undiluted oxygen is used, eg oxygen is mixed withacetylene (ethyne) in oxy-acetylene welding when a very fast and intense oxidisingreaction is required that generates a lot of heat.

Solid explosives contain chemicals such as sodium chlorate which have a lot of

Key ideas





combined oxygen in them (see chapter 1C). Nearly all fireworks also contain achemical that can supply a lot of oxygen over a very short period of time. This helpsto produce the bright intense burning effect.

The fire triangleFor fuel to burn two additional factors are required, heat and oxygen. The threetogether form the fire triangle (see figure 3A.1). Remove any one of these and the firewill be extinguished.

Figure 3A.1 The fire triangle

Fuel from the earth – the hydrocarbonsHydrocarbons are made of the chemical elements carbon and hydrogen only andalthough that sounds simplistic, the way in which various numbers of carbon andhydrogen atoms can be arranged is huge. The gases we burn for heating are hydro-carbons such as methane (natural gas), propane (gas lighter fuel) and butane (camp-ing gas). Other hydrocarbons such as acetylene (ethyne) are used for welding andcutting, and ethylene (ethene) can be converted, by polymerisation (see chapter 8),into the plastic material – polythene.

Food as fuel – the carbohydratesSome of the first products formed in photosynthesis are carbohydrates. These areamong the most abundant constituents of plants and animals. Carbohydrates are asource of energy and can be converted to proteins and fats in living things. Thecarbohydrate group of compounds contains many which taste sweet. All carbohy-drates contain only the chemical elements carbon, hydrogen and oxygen, with theamount of hydrogen present being twice the amount of oxygen. Glucose is anexample of a carbohydrate.

Energy reserves in animals – the fatsAnimals cannot store carbohydrates such as starch. Instead they are able to storeenergy as fats which will yield energy during respiration. The arrangement and ratioof the carbon, hydrogen and oxygen in fats is different to that in carbohydrates.

The carbon systemClearly the chemical element carbon is central to many activities, including life itself.Carbon is a very abundant element but like nitrogen (see chapter 1) it is importantthat it is recycled to become available to future generations. Nature normally takescare of this and carbon as carbon dioxide in the atmosphere is turned by plants intonew and more complex compounds. When a fuel is burnt, carbon dioxide is pro-

Oxy

gen

Heat

Fuel

1. Food 27



Gas terminal

Carbon dioxide in the atmosphere

Power station

Coal Limestone quarry

Lime kiln

Dead and

decayingplants and

animals

Burningof fossil

fuel (coal)

Only plants canuse carbon dioxide

to make food throughphotosynthesis

Respiration

Burning offossil fuel

(oil)

Raincontainingdissolvedcarbondioxide

Oil bearingrocks

Natural gas

over millions of years and other industries

Figure 3A.2 A simplified version of the carbon cycle

duced and this becomes available again for photosynthesis (see figure 3A.2). This isfine so long as the system is kept in some degree of balance.

The climatic events of the carboniferous age ensured that a lot of carbon materialwas removed from the system. Carbon was removed into ‘underground storage’ ascoal, and oil was formed from organisms containing carbon compounds so thecarbon was ‘locked up’. This remained a ‘locked up’ form of carbon until humansdiscovered that coal could be burnt to provide heat. It is now thought to be in thesituation where as a result of burning carbon based fuels, too much carbon dioxide isbeing produced and not enough is being removed by photosynthesis or other means.(See figure 3B.1.)

Challenge11

We all need energy but some of us need less energy than others.Using the information on the packet labels, compare the amount of energy

available from 100 g of different hard cheeses. Which one would provide you withthe least amount of energy? Compare this figure with that for 100 g of cottage cheese.



3B. Energy and fuels☛ The chemical element carbon is contained in most fuels and foods.

☛ Energy made by plants can be stored in carbon containing compounds calledcarbohydrates which contain only carbon, hydrogen and oxygen.

☛ The fossil fuels contain carbon in the form of compounds of carbon andhydrogen only and are called hydrocarbons.

☛ Nature recycles carbon through a system called the carbon cycle.

☛ Burning fossil fuels is thought to contribute to the ‘greenhouse effect’.

Carbon based fuelsAll the materials we normally use as fuel contain the chemical element carboncombined with other elements to form carbon compounds. This is because most ofour usable energy comes from the sun through the process of photosynthesis (seechapter 2A). This process is centred on the conversion of carbon dioxide to com-pounds with a high level of energy and which are therefore capable of releasing a lotof energy. Fossil fuels are derived originally from plant material (see figure 3B.1), so itis not surprising that coal, oil and natural gas contain compounds with a high propor-tion of the element carbon in them. Carbon as the element can exist in differentforms: graphite and diamond are two naturally occurring pure forms; anthracite gradecoal and coke from coal are very largely pure carbon. The study of chemical com-pounds can be divided into two branches of chemistry - inorganic and organic.Organic chemistry includes virtually all the compounds found in living things and allthe chemicals derived from them.

The greenhouse ef fectSurrounding the earth up to a height of approximately 15 km above the earth’ssurface is a blanket of ‘greenhouse gases’. The blanket is not new but it is the compo-sition of the gases that make up the layer and the effect they are having which isgiving cause for concern. In a manner of speaking it is a safety blanket, since if itwere not there, the earth’s surface would probably be subject to great extremes oftemperature. It is estimated that the blanket keeps our planet some 33 0C warmerthan it would otherwise be. The blanket is composed of about 30 different gaseswhich insulate the earth and help preserve conditions conducive to life. This isbecause the structure of the blanket is such that it allows most of the short wave-length radiation (the visible light) from the sun, to pass through to the surface of theearth and warm it up. A little of this short wavelength radiation is reflected back fromthe gas particles into space.

When the earth’s surface has been heated up by the action of the sun it emits longwavelength radiation (infrared radiation). The greenhouse gases absorb quite largeamounts of this radiation and re-radiate it back to earth. In the past these gases havebeen a balance of carbon dioxide, water vapour and a few other gases (eg methane,nitrogen oxides and ‘low level’ ozone). The structure and composition of the gasmixture has been such that it allowed a proportion of the infrared radiation to escapeinto space through what are called radiation windows. During more recent times theamount of carbon dioxide and methane produced on earth has increased greatly andthis has been added to by other gases which absorb infrared radiation. This has upsetthe balance between retaining heat and allowing a proportion of it to escape intospace through the radiation windows. The net effect is that the radiation windows are



Key ideas

1. Food

29

THE R

OY

AL

SOC

IETY O

FC

HEM

ISTRY

3. Energy and fuels

29

Figure 3B.1 The carbon cycle

‘Greenhouse gases’Main ones are

carbon dioxide andmethane

Atmosphericcarbon dioxide

Volcanic activity

Limekiln Chalk,

limestoneand coral

Animalshells

The sea

River

Bicarbonate solutions

of calcium andmagnesium

Rocks andsoil

Carbonic acid

DissolvesEscapes

Photosynthesis

Plants

Animals

Eaten asfood

‘Slash and burn’deforestation

and stubble burning

Combustion

Combustion

RespirationOil, gas,peat, coal

Slowdecay

Methane

Anaerobic decay

Bac

teria

turn

cabon dioxide and hydrogen to methane

Rain



being shut and the atmosphere within 15 km of the earth’s surface is warming up.How this will affect life on earth is still the subject of much discussion (see figure3B.2).

Surface of the earth0 km

15 km

Blanket of heat absorbing

‘greenhouse gases’

Incomingsolar

radiationHeat re-radiated

from surfaceto space

Some radiationabsorbed by gasesin ‘greenhouse gas’

blanket

Some re-radiatedby atmosphere

out to space

Reflectedback to space

Heat re-radiatedfrom atmosphereback to surface

Atmosphere

Why can’ t you set light to paraf fin when it is in liquid form?For fuel to burn it must have oxygen and some heat. Paraffin in liquid form (not to beconfused with ‘liquid paraffin’ for medicinal use) at ordinary temperatures does notvaporise easily and it is not surrounded by the oxygen in air. If the paraffin is vapor-ised by heating, as in a blowlamp, it is mixed with air. Paraffin can also be vaporisedby ‘spreading’ the liquid out over a large surface area such as a piece of paper, awick or cloth. As a result of this a small amount of liquid is surrounded by a largeamount of air, and even a small amount of heat, such as that from one match, willignite it. A match applied to the same volume of cold paraffin in a small tin wouldnot.

Materials like petrol and methylated spirits are readily combusted because theyvaporise easily (see figure 3B.3) and mix quickly with the air available.

For there to be an acceptable temperature on earth there must be a blanket ofgases covering the surface. The addition of heat absorbing gases to the blanket

causes more heat to be absorbed by them and re-radiated back to earth.

Figure 3B.2 The ‘greenhouse gas’ system

1. Food 31



Substances that vaporise and burn easily are said to have a low flash point. This isdefined as the lowest temperature at which there is enough vapour for the fuel to beignited. Flash points are very important when storing flammable (sometimes calledinflammable) products, so public safety has to be considered when choosing whereto store them.

Challenge12

Find out how heat is conserved in a greenhouse. Why is the so-called greenhouseeffect a misnomer from a purist point of view?

Challenge13

Chip pan fires are not uncommon. Imagine putting a little cold cooking oil in a tinand igniting it using a match. Then imagine putting some of the same oil on a pieceof kitchen paper towel and lighting it. How would you expect it to burn comparedwith (i) clean paper towel and (ii) the oil contained within the tin.

Substance Flash point (0C)

Butane (some bottled gases) -60Ether -43Petrol -17(approx)Benzene -11Ethanol (similar to methylated spirits) +11White spirit +32(approx)Paraffin +60(approx)Glycerol (glycerine) +176

(Petrol, white spirit and paraffin are mixtures and flash pointswill vary from one blend to another.)

Figure 3B.3 Flash points of some flammable chemicals

Chemical fuels with a low flash point (eg petrol) ignite easily and are dangerous tostore in large quantities because of the risk of fire. Those with a higher flash point (egparaffin) do not ignite easily and are fairly safe to store provided they are kept cooland cannot be vaporised. Chemicals such as glycerol are not considered flammable.



3C. Energy and fuels ☛ Making and breaking chemical bonds between chemical elements results in

energy changes. Breaking chemical bonds requires a net input of energy.Making new bonds gives out energy.

☛ Different chemical bonds need different amounts of energy to break them.

☛ Chemical reactions can bring about a movement of electrons which can be asource of electricity.

☛ All chemical reactions require energy to start them. Some reactions result inenergy being given out, while other reactions require an input of energy tokeep them going.

Chemical energyChemical reactions are always associated with the transfer of energy. Some reactionsresult in a net inflow of energy while others result in a net outflow of energy.

To make a reaction take place, energy is required (called the activation energy)and this starts the reaction. (This energy may be supplied by a heating appliance - ega Bunsen burner, or from the surrounding heat in the atmosphere.)

Do you remember when you last ate some sherbet how cold your mouth felt? Thisis due to a chemical reaction taking place in your mouth. When the sherbet mixedwith water in your saliva, two chemicals reacted together. The reaction started takingplace because the warmth of your mouth provided the small amount of activationenergy required. The net result was that your mouth cooled as energy was transferredfrom it to the chemical reaction. This type of reaction is called endothermic becauseit requires energy to be supplied to keep it going. In the case of sherbet, however,very little energy is required but it is enough to bring about cooling in the mouth.

energy from mouthcitric acid + sodium hydrogencarbonate → sodium citrate + carbon dioxide + water

Key ideas



Figure 3C.1 Energy diagram for endothermic reaction

Moreenergy

Less energy

Energy level of

reactants sodium hydrogencarbonate and citric acid at start

Activationenergy

Energy level ofproducts sodium citrate, carbon dioxide and water

Energy taken in byreaction ie endothermic

1. Food 33



Heat supplied by the mouth provides activation energy (see later) and, because itis an endothermic reaction, it also requires heat to keep the reaction going.

As you can see from figure 3C.1 the energy of the products is more than theenergy of the reactants so energy needs to be supplied to this endothermic reaction.

Another example of a chemical reaction where there is a net inflow of energy is inthe manufacture of lime (calcium oxide).

Up and down the country there are lime kilns in which limestone is heated toproduce quicklime.

heatcalcium carbonate → calcium oxide + carbon dioxide (energy taken in) (limestone) (quick lime )

This reaction requires an INPUT of energy to keep it going and is another example ofan ENDOTHERMIC reaction.

After the quicklime has cooled it is slaked by adding water.

calcium oxide + water → calcium hydroxide (energy given out) (quicklime) (slaked lime )

This reaction GIVES OUT energy as heat and is called an EXOTHERMIC reaction.Originally, the slaked lime was used for liming fields (to reduce the acidity of thesoil). It was also used for making lime mortar before grey cement powder becamewidely available.

When a chemical reaction takes place the chemical elements in the chemicalcompound involved are often rearranged. For this to happen some links, calledchemical bonds, between the atoms are broken and other links or bonds are formed.Consider natural gas, methane, which has the formula CH4, in which four atoms ofhydrogen are linked to one atom of carbon.

methane

If we wanted to break 16 g of this compound down to carbon and hydrogenatoms, we would have to use 1662 kJ of energy to do so because each carbon-hydrogen bond on average requires 415.5 kJ of energy to break it.

Bond energies for different chemical bonds have been worked out by experiment,so it is possible to work out how much energy is required to break old bonds andhow much energy will be given out when new bonds are formed. Calculations candetermine whether the reactions will be either exothermic or endothermic and howmuch energy will be required or given out. We can use the burning of methane inoxygen as an example. The basic reaction is:

methane + oxygen → carbon dioxide + water

For this reaction an energy level diagram can be drawn (see figure 3C.2). As you cansee the energy of the products is less than the energy of the reactants so the differencein the energy is given out in this exothermic reaction.

C

H

H

HH



Figure 3C.2 Energy diagram for exothermic reaction

Challenge14

Mix up some Plaster of Paris in an old yoghurt pot using cold water. What do younotice about the yoghurt pot? Does it feel colder or hotter to you? What type ofreaction is this?

Electricity from chemicalsBatteries (eg the button type used in watches and the larger ones used in torches) relyon chemical reactions to produce electricity. If a pair of different metals are placedclose to one another but separated by a solution containing ions (see chapter 11B)and the circuit completed an electric current is produced. The solution containingions is called an electrolyte. If, however, the same two metals are separated by a non-electrolyte, then NO current will be produced. Solutions of salts, dilute acids anddilute alkalis are electrolytes and allow electricity to flow. Oils, distilled water andmany organic chemicals are not electrolytes and do not allow electricity to flow.

Pairs of metals that are widely separated in the following list will produce thegreatest flow of electricity. The list is called the electrochemical series (figure 3C.3)and also indicates how reactive a metal can be.

Moreenergy

Less energy

Energy level of

reactants methaneand oxygenat start

Activationenergy

Energy level ofproducts carbon dioxide

and water

Energy given out by reaction ie exothermic

1. Food 35



Calcium More reactivePotassiumSodiumMagnesiumAluminiumManganeseZincIronLeadCopperMercurySilverGold Less reactive

Figure 3C.3 The electrochemical series

A cell containing calcium (top of the list) and gold (bottom of the list) would producethe greatest flow of current, but would be too dangerous and expensive to use!

Button cells such as those used in cameras use the metals zinc and mercury, andhave an alkaline solution as electrolyte.

Ordinary carbon batteries contain the metal pair manganese (as manganesedioxide) and zinc, and the electrolyte is ammonium chloride (see figure 3C.4).

Alkali batteries also contain manganese and zinc as the metal pair with potassiumhydroxide as the electrolyte. The outer case is made of steel, does not take part in thechemical reaction, and is protected from corrosion.

▲

Figure 3C.4 Diagram of a ‘dry cell’ battery

Metal tip –

Carbon rod

Manganesedioxideand carbon

Zinc outer casecathode – negative (-) terminal

Ammoniumchlorideelectrolytejelly(this allowselectricity toflow between the anode andcathode)

Anode

positive (+)terminal



Challenge15

Children who say their parents will keep them off school if they have a higher thannormal temperature claim they can artificially raise their ‘under-tongue temperature’by using sugar. If this is true, what type of reaction is taking place, exothermic orendothermic? Check out the validity of this claim by placing a little white granulatedsugar under your tongue a few seconds before putting the bulb of a clinical thermom-eter in the same place.

1. Food 37


4. Waste 37

4A. Waste☛ Humans have always had and always will have influence on the environment.

☛ Human activity requires chemicals. Water and food are examples of chemicalswhich are essential for life.

☛ Human activity produces waste. The human body produces chemicals asnatural waste products and the human lifestyle produces refuse.

☛ Recycling materials is good conservation practice, but it is not always costeffective in economic or other (energy) terms.

Homo sapiens, the chemical user and producerHow many chemicals have you in your kitchen? ‘There aren’t any chemicals in mykitchen!’ could well be the indignant reply. But take another look, in just one packetof instant soup there are many chemicals (see figure 4A.1). Add to this list the ordi-nary kitchen chemicals such as acetic acid (vinegar) and sodium bicarbonate, thecleaning chemicals such as soap, bleach, white spirit and methylated spirits, and youhave a well stocked laboratory, sorry, kitchen!

Key ideas



Figure 4A.1 ‘Laboratory in a packet’

Souppowder

Water

sucrosesodium citrate

sodium -5'-ribonucleotidecitric acid

caramel (burnt sugar)hydrogenated vegetable oil

sodium glutamatesodium polyphosphate

hydrolysed vegetable proteinsodium chloride

starchcellulosespices

flavourings

These chemicals arepresent in one packet of

dehydrated soup



In addition to this list should be added all the chemicals used in an indirect way,such as those used to make inks, paper, perfume and paints. Most chemicals are usedwithout people realising it, for instance a farmer who did not wish to spray ‘chemi-cals’ on his crop kept pests at bay by spraying the crops with a mixture of nettle juiceand soap. All he had done was to replace one set of chemicals by another, becausesoap is made from chemicals, and nettles contain a chemical amongst others, whichcan induce an allergic response in humans, as almost every child knows!

Animals eat a variety of materials in order to obtain all of the substances theyrequire for healthy growth and life, although some components of the food humanseat cannot be digested – eg cellulose.

The failure to manage waste in a coherent way can lead to pollution, in fact onedescription of pollution is too much of the ‘wrong thing in the wrong place at thewrong time’. Pollution can range from ‘acid rain’ to noise pollution or the disposal oftoxic materials. But pollution is not a new problem. In the 19th century drinkingwater polluted by sewage caused many deaths from cholera.

In many cases it is difficult to decide what is an ‘acceptable’ level of unwantedmaterial and what is an ‘unacceptable’ level. Until recently we have tended topollute first, and then try to deal with the problem later. In some cases, and only withthe advantage of hindsight and further knowledge, it has been realised that pollutionhad been caused. For example a common problem with rivers is that of too much‘food’ being provided for particular groups of organisms, generally bacteria andalgae. This is called eutrophication (see chapter 1). This does not cause death bydirect poisoning rather it starves other organisms such as fish of oxygen. A strikingillustration concerning eutrophic material is shown in figure 4A.2.

Figure 4A.2 Milk, a chemical cocktail

Cows milk is a perfect food for calves providing all the nutrients they require. Notsurprisingly it is also a perfect food for bacteria. From the point of view of itspotential for creating eutrophic conditions in a stream, one pint (568 ml) of semi-skimmed milk is equivalent to 800 gallons (3636.8 litres) of treated sewage!One pint (568 ml) of semi-skimmed milk has the same potential for creatingeutrophic conditions in a slow moving stream as:

800 gallons (3636.8 litres), of treated sewageOR 46 gallons (209.12 litres), ie one drum of raw domestic sewageOR 4 pints (2.28 litres), of farm yard slurryOR 2 pints (1.14 litres), of silage effluent

A pint of semi-skimmed milk contains: (average analysis in mg – one thousandth of a gram)

MilkM

ilk

lklk

1. Food 47


5. Water 47

Key ideas

5A. Water☛ Water is one of the most important substances on this planet.

☛ Water is the world’s most used chemical solvent.

☛ Water is recycled in a natural system.

☛ Fresh water can be obtained from underground springs, reservoirs and surfacewaters.

☛ In heavily populated areas in the Western world all water for human consump-tion is normally treated to ensure it is pleasant to taste and free from diseasecarrying organisms.

WaterWater is a fascinating substance. It can exist as a solid (ice), liquid (water) and as agas (water vapour). It is the most common liquid we come across in our daily lives.We use it for drinking and washing, in recreation and in our industries. The numberof uses to which water is put is almost endless. Water is the substance on which lifeon this planet is based and without it there would be no life as we know it. About 75per cent of the human body is water, so it will come as no surprise to learn thathumans can only last about 5-10 days without water. In chapter 7 there are moredetails about some of the properties of water.

In the UK, water for domestic use is usually delivered directly to your home viaunderground pipes. This water is purified and suitable for drinking. An alternative todrinking tap water is to buy bottled water. If you read the label on the bottle you willsee that the water contains many things dissolved in it. Tap water also has thingsdissolved in it. Depending on what is dissolved in your water it may be called ‘soft’or ‘hard’. In any event if the treatment works has done its job, nothing harmful tohumans will be left in the water; in fact it is vitally important that things are leftdissolved in drinking water.

Challenge24

Look at different bottled waters. Do they all contain the same things? If they don’twhy do you think that there is a difference?

Liquid or solution?In our everyday lives we tend to interchange the use of the terms liquid and solution.If we were to be accurate, we would use liquid only when we were talking about apure substance. So in the case of water, pure water with nothing in it is a liquid,however when the water has things dissolved in it the result is called a solution. Oneof the most important properties of water is its ability to dissolve things in itself.When water acts in this way it is called a solvent.

How, where and why?The water used in the home is delivered by pipes. So how are we sure it is fit todrink? No doubt we have all had or seen the effects of drinking contaminated waterwhich can lead to tummy upsets. Piped water is made potable or drinkable byfiltration and chlorination. You can sometimes smell the chlorine in the water when itcomes out of the tap. Water for drinking and cooking must not contain live harmfulmicroorganisms; also it must be free of chemicals which could be dangerous





– ideally it should look and smell clean.In the UK, drinking water comes from either surface water, water collected in

lakes, or underground supplies. The water is piped to a water treatment works whereit is cleaned, and chlorinated to disinfect it. This kills any microorganisms in thewater.

Sufficient chlorine is added to kill any microorganisms entering the supply systembefore the water is used. When the water arrives in the home, we drink it thenexcrete it. The waste water is taken away and will eventually find its way to a sewagetreatment works where it is cleaned again. It moves in a cycle – the water cycle.Other natural processes also play a role in the cycle, as we can see in figure 5A.1.

Figure 5A.1 A simple version of the water cycle

Puddle

Clouds

Washing machine

Tumble drierWashing line

Watervapour

Wet clothes

I forgotmy Mac!

Rain

Heat from the sunbrings aboutevaporation

1. Food 49


5. Water 49

So how much water do we use ? The table below gives you some idea.

Personal use of water in UK (average amounts per day and taking 1pint to be equivalent to 568 ml – 1 milk pint bottle)

Drinking 3 litres 5.28 pintsCooking 5 litres 8.80 pintsGardening/car washing 12 litres 21.12 pintsWashing up dishes 15 litres 26.40 pintsPersonal washing 50 litres 88.02 pintsToilet flushing 70 litres 123.24 pintsTotal per day 180 litres 272.84 pints

Imagine having 273 bottles delivered to you door each morning! Don’t forget thatmost water is used by industry. For example, to produce a litre of soft drink 10 litresof water are used in manufacturing and packing it (figure 5A.2) and the manufactureof one average size car requires 50,000 litres of water. Now that’s a lot of baths!

Figure 5A.2 It takes 10 litres of water to produce 1 litre of soft drink

Challenge25

Estimate how much water you use every day. How could you save 10 per cent ofthis? How much would your daily consumption of water cost if you had to buy it inbottles?

10 litres waste water to drain from processing, cleaningpacking

1 litre ofsoft drink

1litre

10 litres water

Input Output

Juice concentratessugar, flavours

Soft drink factory



5B. Water☛ Water is an important substance which supports life on this planet.

☛ Domestic supplies of water are treated to make the water suitable for humanconsumption.

☛ Domestic water is not just one substance, it is a solution of substances dis-solved in water.

☛ The main substances dissolved in water are chemical compounds called salts.

☛ The water cycle is an important ecological system.

The water cycle

Key ideas

Well

Borehole

Aquifers

Reservoirs,rivers and lakes

Ocean

Soil moisture

Snow and ice

SnowWinds

Transpiration

Winds

Solar energy

RainEvaporation

TranspirationEvaporation

Figure 5B.1 The water cycle – humans interrupt the natural cycle byremoving water for their own use and then returning it to the cycle later

Water vapour is carried across the earth’s surface by the winds. When the waterparticles (water molecules) contained in the air vapour condense ie change from agas to a liquid, clouds are produced. This normally occurs when the air experiences achange of temperature. On further cooling clouds condense to form droplets of waterwhich fall as rain, hail or snow. This is what the meteorologists call precipitation.Some of the rain will find its way to the sea and oceans, and hence it returns to thewater cycle.

When water vapour is formed by the sun heating the oceans or other expanses ofwater, dissolved materials and suspended matter are left behind. Newly formed watervapour is probably water in its most pure natural state.

At nearly every stage in the cycle water is carrying other substances dissolved init. These substances can range from gases dissolved in the rain to fine particles ofrock washed down by a mountain stream. Some of these substances are welcome



1. Food 51


5. Water 51

additions while others we might rather do without!As rain falls it absorbs carbon dioxide and other gases in the air. In coastal areas

sea spray will add salts, especially sodium chloride. Carbon dioxide dissolved inwater produces carbonic acid and this makes rain slightly acidic. This is a naturalprocess and so all rain is acidic to some degree.

When the acidic rain passes through soil and rocks, especially in some areas, itreacts chemically to produce substances that dissolve in the water. Some of thesedissolved substances create ‘hard water’. (HARD because it is hard to make a soapylather with it.) This same chemical reaction is also responsible for carving out manyof the caverns found in ‘limestone country’. Limestone is a chemical compoundcalled calcium carbonate. Calcium carbonate reacts with the acid in the rain to forma compound called calcium hydrogencarbonate, which dissolves in the water to forma solution. This compound belongs to a class of chemicals called salts, and thisparticular compound is one of those responsible for hard water.

Rain collects naturally to form lakes, rivers and oceans. From these surfaces andothers, water evaporates to form new clouds. Humans interrupt this process to collectthe water for their own use. Our water is obtained by:

(i) collecting rain and stream water in a reservoir. This water often comes from alarge area of land called a water catchment area;

(ii) pumping it up from lakes and rivers;

(iii) pumping it up from deep boreholes in the ground. Deep boreholes supplywater from rocks and soil which holds water underground. The latter arecalled aquifers; and

(iv) pumping from a shallow well. Shallow wells can supply water from the watertable and some people still retain their own wells. At one time groups ofhouses would have their local well. ‘Well off’ people had their own well!

For public consumption water is generally sent to a treatment works to purify andsterilise it before it is piped to homes and factories.

Challenge26

Find out where your water comes from – ie which part of the country. You may besurprised at how far it has travelled.

What about these salts?It is extremely important that the water we drink is not pure water, but water withcertain salts dissolved in it to make a solution. The reason is to do with ourmetabolism. Briefly, our bodies contain salts and if we drank pure water the salts inour bodies would pass out of our cells and be excreted and in the end this wouldcause us to die!

Another associated reason for water needing to contain salts dissolved in it is sothat we can take into our bodies chemicals which we need in order to live. Forexample what is referred to as ‘salt’ in everyday life is a compound called sodiumchloride. This is vital for life but there are numerous other chemicals we need as welland some of these are found in tap water.

Challenge27

Is your local drinking water obtained from surface waters such as a reservoir, or is itobtained from a borehole? Why do you think water obtained from a borehole isconsidered ‘pure’ and cleaner than that obtained from a reservoir?



5C. Water☛ The water cycle is an important biological system which humans harness for

their own needs.

☛ Water is vital for life to survive on this planet.

☛ Pure water is a chemical compound with many valuable properties.

Water, water , waterMost of the earth’s surface is covered by water, so why is it so special? Because thereis so much of it we use it to do work for us. We use it as a means of transport, powergeneration and it is used extensively in industry, especially as a solvent. But why?The reason lies in its chemical and physical properties. Water is a chemicalcompound made from two elements, oxygen (the gas we use in respiration) andhydrogen. Water particles (called molecules) are made up of two atoms (the smallestpart of an element) of hydrogen and one atom of oxygen and have the chemicalformula H2O.

You may find it useful to know that as a rule of thumb, 1 g of water has a volumeof 1 cm3 and this is equivalent to 1 millilitre (ml) or one thousandth of a litre. So 100cm3 of water can be considered to have a mass of 100 g.

Most importantly, liquid water has some unusual properties. It has a boiling pointof 100 0C at atmospheric pressure, a melting point of 0 0C, a high surface tension anda given volume of water expands on freezing. These are not the properties of anormal liquid! You can see the effects of water having a high surface tension bylooking at a river. The insects which rest or walk on the surface of the water are onlyable to do so because of the high surface tension. The high surface tension can bethought of as producing a ‘skin’ on the surface of the water.

Challenge28

Look up the boiling point and melting point of oxygen and compare the values withthose of water?

Challenge29

Float a paper clip in a bowl of water. Add washing up liquid to the bowl and thepaper clip should sink. Why?

Water and lifeWhen liquid water has energy removed from it, the water molecules become lessactive and the liquid cools down. The liquid has its greatest density at 4 0C (3.98 0C tobe precise). At this temperature the water is still liquid, but the molecules are closertogether than at any other temperature. When the water is cooled further the solidform of water – ice – is formed as crystals. The structure of these crystals is such thatalthough they are solid, ice has an expanded structure, hence there is a great deal ofspace around the molecules. This means that the molecules of water occupy a greatervolume when they are solid compared to when they are liquid.

Key ideas



1. Food 53


5. Water 53

Figure 5C.2 How a pond freezes over

Figure 5C.1 Test tubes of water at different temperatures

Water is thus an unusual compound amongst substances. (Compare it with theproperties described in chapter 7.) If water did not have these properties there wouldbe very little life on earth, at least as we know it!

100 °C 4 °C 1 °C -1 °C

Water

At 4 °C water becomesdense and sinks

Surface water cooled by cold airblowing over pond (ie energy removed)

Warm waterdisplaced upwardsand then cooledby cold blowingair

Cold airSurface water cooled to 0 °C

and sits on dense water at 4 °C

Dense water, still liquidat 4 °C stays on bottom

1

2

3

Cold air

Less dense ice at 0 °C or belowfloats and forms insulating skin whichgives some protection to water below

ICE ICE

Dense water at 4 °C – pondorganisms able to move unaffected

by formation of ice particles

Cold air



Surface temperature 0 °C– ice forms and sinks

Surface water cooled by cold airblowing over pond (energy removed)

Warm waterdisplaced upwardsand then cooledby cold blowingair

Further cooling – more ice formsand sinks

1

2

Cold air

Warm waterdisplaced upwardsby ice

Ice layer 1

Further cooling – more ice formsand sinks

3

Ice layer 1Ice layer 2

Summer temperatures would onlymelt a little water on pond surface

4Solid layers of ice

– organisms frozen

Figure 5C.3 “If ice sank” (which it doesn’t)

Challenge30

If ice had a greater density than cold water, would any life on planet earth bepossible even in hot countries?

1. Food 55


6. Rocks 55

Key ideas

6A. Rocks☛ All rocks are derived from material produced in the interior of the earth.

☛ Rocks exposed at the earth’s surface are worn away by weathering.

☛ Rocks provide building stone which is subject to weathering.

☛ The solid particles found in the soil come from fragments of weathered rock.

RocksMolten rock (or magma) from the interior of the earth is the starting point for most ofthe rocks found on the surface of the earth. Magma finds its way to the surface bybeing forced out under pressure as molten lava and hot ash from volcanoes. Materialfrom the interior of the earth also surfaces from underwater volcanoes and move-ments of the sea bed. In addition to expelled lava and ash, large volumes of gasincluding carbon dioxide and sulphur compounds are released. The fine ash whencarried up into the atmosphere can affect the climate; the sulphur containing gasescan give rise to acidic conditions in the environment; and the large amounts ofcarbon dioxide produced adds to the greenhouse gas effect.

As soon as the new rocks have surfaced they become worn away and changed bydifferent processes. Weathering accounts for the breaking up of rock (see figure6A.1). Agents of erosion such as wind and waves will also break rock down intosmaller particles.

There are three main types of rock: igneous, sedimentary and metamorphic.Igneous rocks generally result from the cooling of molten magma. If the magma coolsquickly small crystals are produced, whereas if the magma cools slowly then largecrystals are formed. Granite, basalt and quartz are examples of igneous rocks. Graniteis formed when magma cools underground, while if the magma cools as it runs downthe side of a mountain it forms basalt.

Sedimentary rocks are produced by the build up of layer upon layer of fragmentsfrom other rocks or the deposition of dead animals (or plants) as in the case of somechalk and limestone deposits. Some sedimentary rocks such as rock-salt are theremains of salt water lakes from which the water has evaporated.

Metamorphic rocks are those which have undergone major change as a result ofheat and pressure. Slate is the result of heat and pressure changing the soft sedimen-tary rock called shale into something much harder. Marble is a metamorphic rockderived from limestone.

Rocks are made up of minerals and those minerals which contain metals arecalled ores. Some minerals are released when rocks are weathered eg the hard rockgranite eventually breaks down to clay, sand and the oxides of aluminium and iron,while the white china clay found in Cornwall, and the white coloured waste tips ofsand seen in the area, are breakdown products of Cornish granite.

Rock used as building stone is also subject to weathering, therefore stone that isphysically hard and which is less vulnerable to chemical attack will survive best.Before smokeless zones and emission controls were introduced, many buildings wereblackened by the smoke and fumes from local industry. Buildings constructed fromlimestone were particularly badly eroded by the smoky acidic fumes.





1. Rain seepsinto crack in rock

2. Frost actioncauses water tofreeze and expand.Crack made larger

3. Sun causes moistureto expand. Rock expandsin heat, contracts in cold

4. Rock particles break off and fallinto valley

The sea

5. In valley rock particlescan build up as silt andgravel, or can be transportedto the river mouth

6. At river mouthparticles candrop out toform mudflatsand saltings

Figure 6A.1 Weathering and transportation of rock

1. Food 57


6. Rocks 57

Challenge31

Try and find pieces of igneous, sedimentary and metamorphic rock. Look at each oneusing a hand lens to help you. What is the main structural difference between thesedimentary rock and the other two?

Challenge32

Place a drop of water on each of the three specimens, watch what happens and thenrank the three samples in order of permeability to water. Consider the implications ofthis from the point of view of natural drainage and underground water storage.

Chips of f the old building blockUnder acidic conditions (including both dry and wet acid deposition), calciumcarbonate (limestone) is converted to calcium sulphate and carbonic acid. This is dueto the action of the sulphuric acid in the rain and moisture.

calcium carbonate + sulphuric acid → calcium sulphate + carbon dioxide and water(limestone) (acid deposition)

Calcium sulphate is insoluble in water, so from the chemical point of view itmight appear that the only ‘nuisance’ chemical is carbonic acid (carbon dioxide andwater) which will gradually attack the limestone. Unfortunately, there is a furtherproblem. Calcium sulphate takes up more space than the calcium carbonate it isderived from. What can happen, therefore, is that acid rain seeps into a hairline crackin the limestone and reacts to produce calcium sulphate but the crack has to open upto accommodate the new compound. After this has happened several times a chip orpiece of limestone crumbles away and chemical weathering has well and truly takenplace. Many of the buildings damaged as a result of chemical weathering have nowbeen cleaned with high pressure water jets and new pieces of stone spliced in wherenecessary to return the building to its original mellow colour.

Challenge33

Place a drop of vinegar on each of the three rocks. With the help of a hand lensobserve whether any reaction is taking place. What conclusions can you draw fromwhat you observe?

Challenge34

Obtain a jar with a leak proof cap. Half fill it with soil and add water until it is threequarters full. Shake vigorously including turning the jar upside down several times forabout three or four minutes. Place the jar where you can see it without touching it,and look at it each morning and evening over the course of three or four days. Howmany layers can you identify? Look at these layers using a magnifying glass.



6B. Rocks

☛ Rocks provide the chemicals for the cement, paper, glass and many otherindustries.

☛ The extraction of some chemicals from the earth is fairly straightforward.

☛ The extraction of metals can be long and complicated.

Chemicals from rocksRocks are composed of one or more minerals and it is from minerals that we obtainmany metals and chemicals (see figure 6B.1). However, some rocks are made of onlyone mineral, limestone for example is made of calcium carbonate which in itscrystalline form is called calcite. Rock-salt generally contains only one mineral,halite, which is sodium chloride. Rocks such as limestone and rock-salt are some-times extracted and used as chemicals without further purification. Others, especiallythose minerals from which a metal is to be obtained have to undergo processes suchas crushing, ore separation and possibly electrolysis. (See chapters 6C and 10C.)

Mineral Main chemical compound

Bauxite Aluminium oxideCalcite Calcium carbonateGypsum Calcium sulphateHaematite ‘Iron oxide’Halite Sodium chlorideMagnesite Magnesium carbonateQuartz Silicon dioxide

(many of the chemicals are present in an impure form)

Figure 6B.1 Minerals

Rock salt, halite, sodium chlorideThere are huge underground deposits of salt in Cheshire in the UK and the sodiumchloride from these deposits can be extracted in two ways. It can either be dug outusing mechanical excavators or it can be removed by pumping water down aborehole and then pumping out a solution of salt in water (brine). Salt is a veryimportant chemical. In the days before refrigeration, salt was used for preserving foodand it was used so universally that it attracted a tax, the salt tax. Rock-salt is used tothe extent of about two million tonnes per year by local authorities for de-icingpurposes on roads and pavements alone. Three important chemicals can be pro-duced from salt.

Key ideas



1. Food 59


6. Rocks 59

Sodium chlorideChlorine ← SALT → Sodium carbonate

Worldwide use – 33 (washing soda)million tonnes per year, Worldwide use – 26

– uses: PVC, plastics, dry million tonnes per yearcleaning solvents – uses: glass

water purifying making, dyes andcolours, oils, fats

and waxes, food and drink

Sodium hydroxide (caustic soda)

Worldwide use – 26 million tonnes per year, soap, detergents – uses:

synthetic fabrics, other chemicals

Limestone, calcite, calcium carbonateLimestone is a sedimentary rock made by the gradual deposition of material includ-ing millions of small dead organisms which had hard shells covering their bodies.Large fossils are sometimes found in limestone and the use of a hand lens will enablethe small shells to be seen if they are present. Limestone is used extensively in theform of small lumps for road making and as an aggregate in concrete. Most of thisgrade of limestone comes from the Mendip Hills in Somerset and Buxton in Derby-shire. Better grades of hard limestone for building are obtained from the Purbeck areaof Dorset and Portland near Weymouth. Most of the powdered limestone used by thechemical industry comes from Derbyshire.

Sand, silica, silicon dioxideSand or silica is one of the most abundant minerals on the earth’s surface. It is anoxide of silicon, and silicon compounds account for about 28 per cent of the compo-sition of the earth’s crust.

Sand is used extensively in the building trade and in the manufacture of glass. Themineral grains are hard and are used for abrasive purposes eg in sandpaper. One

v

Limestone rock(calcium carbonate)

Lump

Making steeland sodiumcarbonate

Powder

Glass making,agriculture

Strong heating

Quicklime (calcium oxide).Used for refining beet sugar,

making steel and cement

Add water

Hydrated lime(calcium hydroxide). Used

in the construction industries, agriculture

and horticulture



particular oxide of silicon is quartz which in coloured form gives rise to amethyst,rose quartz and cairngorm.

Sand in your watch?Many watches have been ruined as a result of small particles of seaside sand enteringthe movement. However, every modern watch that sports ‘quartz accuracy’ relies ona small crystal of a special type of quartz (silicon dioxide). After being subjected tomechanical pressure these crystals display what is called the piezoelectric effect. In aquartz watch the passage of electricity from a small battery causes the quartz crystalto vibrate in a known and constant manner. This vibration is the central and highlyaccurate timekeeping device in the watch. The vibrations are converted into a formwhich moves the hands of the watch or alters the digits.

Diamonds and graphiteWhat do a diamond ring and a lead pencil have in common? The answer is that theyboth contain carbon. Diamonds are a pure and very hard form of carbon. The maindiamond deposits are in South Africa and this country exports diamonds for makingjewellery and smaller stones for making diamond edged cutting equipment such asspecial saws.

Graphite is a softer and different form of pure carbon and occurs as slipperycrystals, as a result of this property graphite is used as a lubricant. Graphite mined inKeswick in the UK Lake District is used for making the graphite ‘lead’ used in pencils.Mexico and Austria provide the larger quantities of graphite used by industry.

Challenge35

Obtain sand from different seaside beaches (or from one beach and builder’s sandand sharp sand). Wash a small sample of each and look at a few grains through ahand lens. Note and record particle shape, size and colour.

Next, place a few drops of white vinegar on the sample. Look at the grainsthrough the hand lens. What do you observe?

1. Food 61


6. Rocks 61

6C. Rocks☛ Many of the metals we use are obtained from rocks.

☛ In some rocks natural chemical changes produce radioactivity.

☛ In some areas where granite is present, the radioactive gas radon seeps out ofthe rocks and may be responsible for an increase in human deaths fromcancer.

Copper from rocksCopper was probably first noticed as a metal by accident. Hot carbon in a fire maywell have reacted with the ore malachite (copper carbonate) in other rocks surround-ing the fire and the molten copper would have run out.

Most copper ores are of low grade quality which means that for any coppercompound present, there is a large amount of waste matter. The waste is removed bycrushing the rock and then churning it up with a mixture of oil and water. The coppercontaining mineral particles stick to the foam and the waste material sinks to thebottom. The ore particles are separated from the foam and roasted in air and thenheated several times with different chemicals in order to remove impurities. At onestage air is blown through the molten metal and this causes some impurities to beoxidised. This copper still contains 2-3 per cent of impurities but is suitable for somepurposes.

A large amount of the copper currently produced is made by recycling scrapcopper (see figure 6C.1). Pure copper is produced using an electrolytic process inwhich only pure copper is transferred to the negative electrode. Impurities in thecrude copper used as the positive electrode fall to the bottom of the cell. (Aluminiumis also extracted and purified by using electricity, for details see chapter 10C.)

Why the need for such pure copper?To obtain 99.99 per cent pure copper is a lengthy and expensive process but if thecopper is to be used for conducting electricity, eg as copper wire, it has to be purebecause electrical conductivity is reduced by traces of foreign matter. For example,0.02 per cent of phosphorus in copper will reduce its electrical conducting efficiencyby 30 per cent.

Using biotechnology to extract copperIn the US about 10 per cent of the copper obtained is now extracted from very lowgrade ores by using bacteria. Bacteria of the genus Thiobacillus are encouraged togrow on the copper ores by aeration and spraying them with acidified water.

Bacteria assist in the leaching operation which produces copper sulphate solution.This drains from the piles of ore and is used in the electrolytic process to producecopper metal.

Challenge36

Copper is often melted with one or more other metals to produce alloys. Eachparticular alloy mix has characteristics of its own and so mixes can be tailor-made forparticular uses. Try and discover what copper alloys you have in your house. Some ofthe alloys have names of their own. One alloy of copper may be nearer to you thanyou think!

Key ideas





Radioactivity from the rocksGeologists believe that the very high temperatures associated with the magma deepin the earth are probably due to radioactive materials releasing energy. One elementwhich gives out radioactive energy is uranium. This element is found as pitchblendewhich is impure uranium oxide. Uranium containing ores are mainly found inAustralia, Canada, Namibia, South Africa, the US and possibly the “USSR”. In areasof the UK the igneous rock granite also contains some uranium and this causes thenatural background radiation to be higher in some areas - eg Aberdeen in Scotlandand South West England. Radioactivity is produced because a particular type ofuranium atom called uranium-238 is unstable and gradually decays to form themetallic and stable element lead-206.

It is very difficult to say how long it would take a sample of uranium-238 to turninto lead, but it is estimated that 94% will undergo decay in 18,000 million years.During this time radioactivity occurs and the element gradually changes from oneradioactively unstable element to another including thorium, protactinium, radium,radon, bismuth (unstable isotopes only) and polonium until finally it becomes stablelead-206 (see figure 6C.2).

It is usual to express the rate of decay of a radioactive element in terms of its half-life. This is a measure of how long it takes for half of any sample of radioactive atomsto decay.

Negative electrodeconnected to DCpower supply

Pure copperbuilds up here

Copper sulphatesolution

+Positive electrodelinked to DC power supply

Crude copper– copper goesinto solution here

Copper ions

move across

Some impuritiesfall to bottom andare recovered

Pure (99%) copper formedinto new items

Bars of crude copperMolten copper

Copper tubing and wire

Scrap copper

–

Figure 6C.1 Manufacture of copper

1. Food 63


6. Rocks 63

RadonRadon is a radioactive gas which is given off during the natural formation of lead-206from uranium-238. Since it is a gas it escapes from rocks and can find its way intobuildings. It has been suggested that naturally occurring radon may have contributedto deaths from cancer.

Radioactivity and carbon datingGenerally carbon exists in the form we call carbon-12 (C-12). C-12 is called anisotope; different isotopes of an element have different atomic masses and nuclearproperties, but the same chemical properties. Carbon can also exist as anotherisotope called carbon-14 (C-14), which is radioactive (the amount of radioactivity isvery small and relatively harmless). Both forms are present in the atmosphere and canjoin with oxygen to form carbon dioxide. Through photosynthesis carbon dioxidecontaining C-12 and C-14 forms of carbon become incorporated and ‘trapped’ inwood etc and a constant ratio of C-12 to C-14 is established and maintained whilethe plant or animal is alive. When death occurs the C-14 that decays is not replaced.It is known that the radioactivity of C-14 decays at a certain rate so by finding theratio of radioactive C-14 to non-radioactive C-12 in a sample it is possible to find itsage (see challenge 76).

Other dating methods such as tree ring counting have been used to calibratecarbon dating techniques. Now that this has been done ‘carbon dating’ methods areproving very useful for dating objects into which atmospheric carbon was incorpo-rated.

Figure 6C.2 Radioactive decay of uranium-238

100

75

50

25

12.5

% radioactiveuranium 238atomsremaining

4,500 9,000 13,500 18,0000Millionsof years

Halflife

1/2 gone

3/4 gone

7/8 gone15/16 gone

(Represents 16 atomsuranium-238)

Newly-formedmineral

16

8

4

2

1

(Represents 1 atomuranium-238)

Increasing time



7A. Solids, liquids, gases☛ Substances can exist as solids, liquids or gases.

☛ Some substances can exist in one or more state at the same time (eg ice inwater).

☛ Solids, liquids and gases have very different properties.

☛ Solids hold their own shape.

☛ Liquids take the shape of any container they are placed into.

☛ Gases take the shape of any container they are placed into and completely fillit.

☛ By using energy (normally in the form of heat), it is possible to turn a solidsubstance into its liquid form and then to the gaseous state.

Solids, liquids, gasesAll materials which you see around you are either solids, liquids or gases. Solids canbe recognised because they are firm and keep their own shape. We can explain whatwe mean by this using the example of water. Ice is solid water. An ice cube keeps itsshape when you place it in a saucepan, so it is a solid. As the ice melts, it turns into aliquid. The liquid does not have a shape of its own but takes the shape of the con-tainer it is placed in. So this provides us with a guide of how to identify a liquid. If thewater in the saucepan is heated it will boil and water in the gaseous or vapour state isformed; we call this steam. The steam rises out of the saucepan and, if you let thewater boil for long enough, will spread throughout an unventilated room in which itis produced. We can recognise gases because they take the shape of the containersthey are placed in and completely fill them (in this case the room).

Challenge37

Place some ice cubes in a saucepan. Heat the saucepan on a cooker. Watch whathappens. Try to relate what you have read to what you see.

Challenge38

When you have a steamy kitchen, what happens to the windows and why?

Changing statesSolids, liquids and gases are the names of the three physical states. For any substanceit is usually possible to change the substance from one state to another and as wehave seen above with water it is usually quite an easy thing to do. To change fromsolid to liquid requires energy, and this is usually supplied in the form of heat. Theprocess of turning a solid into a liquid is called melting. Similarly, energy is alsorequired to turn a liquid into a gas, and this process is called evaporation.

If you can turn solids into liquids then into gases it must be possible to do thereverse. This is an easy process requiring the removal of energy, and is usuallyachieved by cooling the substance. So when you cool steam it turns into water, andthe process is called condensation. This is what is happening when you have asteamy kitchen. The steam condenses on the windows ie turns from gaseous water toliquid water. Further cooling of water would turn it into ice, the solid form of water.This process is called solidification (figure 7A.1)



Key ideas

1. Food 65


7. Solids, liquids, gases 65

Figure 7A.1 The three states of matter

Freezing pointThe freezing point of a solid is the temperature at which the liquid is seen to solidify,that is turn from a liquid to a solid. Pure substances turn solid at a particular tempera-ture for example, water freezes and changes into ice (solid water) at 0 °C. This is alsothe temperature at which ice turns into water ie melts, and is known as the meltingpoint.

Boiling pointThe boiling point of a substance is the temperature at which the liquid boils and turnsfrom a liquid into a gas. Water, for example boils and turns into steam (water in thegaseous state) at 100 °C at normal atmospheric pressure.

Challenge39

In the winter salt is put onto the roads to melt ice. What is happening? To help youunderstand try measuring the temperature of a mixture of ice in a little water, andthen add salt. What happens to the temperature?

Heating

Melting

– turning to liquid

Evaporation

– turning to vapour

Solideg Ice

Liquideg Water

Gaseg Water vapour

Solidification

– turning to solid

Condensation

– cooling to a liquid

Cooling(sometimes requires refrigeration)



7B. Solids, liquids, gases☛ Everything can exist as a solid, liquid or a gas.

☛ Energy needs to be added to turn a solid into a liquid, or a liquid into a gas.

☛ Energy needs to be removed to turn a gas into a liquid or a liquid into a solid.

☛ When energy is added to a substance, not only can it change its shape but itcan also change its volume.

☛ When a substance is given energy, the particles which make up the substancebegin to behave differently.

Change of volumeIn the solid state, substances occupy the minimum amount of space possible with thenotable exception of ice. The units which make up a substance can be called parti-cles. The particles in a solid substance are densely packed, ie are very close to eachother, and are not free to move around, hence a solid has its own particular shape.When a solid is turned into a liquid, the particles are able to move around but keepin close contact with each other, so a liquid takes the shape of the container it is heldin. By moving they take up more space than when they were held rigidly in a solid,hence the volume occupied by the substance increases. On turning from a liquid intoa gas the particles are free to move wherever they can, regardless of where the otherparticles are. Gases, therefore, occupy the whole of the space within which they arecontained (see figure 7B.1).

Increase in energy

Increase in movement of particles

Energy Energy

Solid

Particles canvibrate and rotate within a fixed positionie they can only move‘on the spot’

Liquid

Particles can vibrate,rotate and move aroundeach other. Each particleis more excited andrequires more space inwhich to move

Gas

Particles can vibrate,rotate, move around each other and move rapidly in a random and haphazard way in the space available

The example of paraf fin (candle) waxThe particles making up candle wax are large and derived from oil. A candle atnormal temperatures (in the UK) is solid. When candles are made, hot wax (theliquid) is poured into a mould to cool down. On cooling the liquid wax turns into asolid, and at the same time it contracts (ie occupies a smaller volume).

Figure 7B.1 Changes of state

Key ideas



1. Food 67



Challenge40

Carefully melt a candle in a small metal tin until it turns into a liquid. Allow the tin tocool. When you can pick the tin up with your hands, tap the bottom to knock thewax out. Why does the wax come out of the mould so easily?

The exception – waterWater is an unusual substance in which the pattern, of a liquid having a largervolume than a solid, fortunately does not quite fit. This point is covered in chapter7C.

Physical changeMost substances can have their physical state changed time and time again byheating and cooling. The substances themselves are not altered in any other wayapart from being either solid, liquid or gas. This type of change is called a physicalchange and is reversible.



7C. Solids, liquids, gases☛ All matter is made up of units which we call particles.

☛ How much particles move determines whether the substance is in the solid,liquid or gaseous state.

☛ Particles in a solid are held in a rigid structure and vibrate about a fixedposition.

☛ In a liquid the particles move around freely but remain in contact with eachother.

☛ In a gas the particles move around independently of each other.

☛ The more particles that are able to move around the more energy they have.

☛ At a given temperature lighter particles move faster than heavier ones.

Changing physical statesA change of state requires the addition or removal of energy. A change from a liquidto a gas is usually achieved by heating the liquid. As you heat the liquid its tempera-ture rises, but will it keep on rising for ever? The answer is no. Take the example ofwater. When you heat a kettle of water the temperature rises from room temperatureas you supply energy as heat. The temperature keeps on rising until it starts to boil.Under normal conditions (atmospheric pressure), water boils, ie turns from a liquidinto gas, at 100 0C. But if you keep on adding energy by leaving the heat on, thetemperature does not rise, so where does the energy go?

Remember how the particles move in a liquid and a gas. In a gas they movearound independently, whereas in a liquid they move around in contact with eachother. In a liquid the particles are attracted to each other, so are held close together.When we change a liquid into a gas, we have to overcome the attraction that theparticles have for each other. As more energy is given to a liquid by heating, theparticles move around more freely but are still in contact with each other. At theboiling point the energy supplied to the water is used to break the attraction of theparticles for each other, hence they leave the liquid – ie turn into steam. The energyused at the boiling point to carry out this process is called the latent heat and has aspecific value for that particular substance and change of state.

Challenge41

Place a drop of methylated spirit on the back of your hand. Why does your hand feelcool at that spot?

Challenge42

Why do you think it is that if you take ice cubes out of a refrigerator, put them in ajug, and then add a little cold water to them, the added water does not turn to ice?

WaterAlthough water is the most common liquid we come across in our daily lives, it hassome properties which are unusual when compared to other liquids. A substanceusually has a larger volume when it is a liquid compared with its solid form. How-ever, with water the opposite is true. A given amount of ice (solid water) occupies a

Key ideas



1. Food 69



greater volume than an identical amount of liquid water.You can see the results of this phenomenon in winter when some people are

unfortunate enough to suffer burst pipes. What happens is that in the cold the liquidwater freezes, occupies a greater volume (ie expands), and the water pipe bursts.When the temperature rises the ice turns back into liquid water and runs out of thehole in the pipe.

Challenge43

Why on cold mornings does the milk in milk bottles sometimes burst the foil on thetop of the bottle?

Sublimation – a state by-pass systemSome substances have the rather unusual property of being able to pass directly fromthe solid state to the gaseous state without becoming a liquid. Similarly some gasescan become solid without first turning to a liquid.Some examples are:

carbon dioxide solid (dry ice) → gas

sulphur vapour → solid (flowers of sulphur)

This process is called sublimation.



Key ideas

8A. Groups of materials☛ Humans have always been closely involved with materials and their proper-

ties.

☛ Every substance on the earth has a set of properties associated with it.

☛ Substances can be classified according to their properties. These properties canbe chemical or physical.

☛ The way substances are classified can also be based on whether they aresynthetic or natural, or on the way humans use them.

The ages of ‘man’Humans have always been closely involved with materials they could fashion anduse. So close has been this involvement that periods of the history of humandevelopment are named after materials – eg Stone Age and Iron Age. For a spearprimitive man required three materials each having different properties – a headwhich could be sharpened, a long, strong, shaft and thonging to join the two.Civilisation demands materials which will out perform natural materials.

Which group does it go in?If you have a quick look around any house you will notice that materials fall into twomain groups, namely natural materials and those made by humans. In many cases thedivision is clear but sometimes it is not. In this chapter items have been classifiedunder various headings but it is important to recognise that other groupings arepossible.

Natural materialsThis group includes wool, cotton, cork, wood, leather, stone, sand, gravel, salt, coal,gypsum, asbestos, talc, metals, and metals combined with other substances. Not allmaterials should be considered harmless to humans simply because they are natural;asbestos, for example can be harmful.

Materials made by humansThis group can be divided into two sub groups:(i) Converted raw materialsThese items are derived from natural materials but have been refined or altered byhumans – eg pottery, china, earthenware, metal objects, coke, charcoal andagricultural lime.(ii) SyntheticsThese are derived from substances which occur on the earth but chemists havechanged the natural products into new materials – eg plastics of all kinds; syntheticfabric materials; glass and the new ceramic materials; some medicines and drugs;and new materials called composites – ie reinforced plastics and carbon fibre.

Properties of materialsAnother way of classifying materials is to group them according to their properties.Humans love to touch and handle things because we are curious about ourenvironment, so we like to know via the use of our senses whether something is hard,soft or flexible; or solid, liquid or gas; or whether it can be dissolved in water. Inspeech we say ‘as hard as nails’ and ‘as wobbly as a jelly’. These are terms which




7. Solids, liquids, gases 718. Groups of materials 71

relate the use of materials and their properties. Once we know about the properties ofa material we are able to think of a possible use for it.

Challenge44

Make a list of the plastic equipment in a kitchen, and research what each item wasmade from in the late 1800s or early 1900s.

Challenge45

Cooks used to keep table salt in either a wooden box or an unglazed earthenwarecontainer. What properties of wood and unglazed earthenware made themparticularly appropriate for this use?

Material Properties Uses

Wool Warm, wearable, knittable, resilient, Warm clothing, especially knitwear,accepts dye colours, will burn insulation, carpeting

Cotton Cool, wearable, accepts dye Cool clothing, lightweight rainwear,colours, absorbent, dries fairly especially when treatedeasily, strong, will burn

Wood Fairly hard, strong, easy to cut, Construction and building trade,and shape. Can be slightly flexible. furniture making, paper makingWarm to touch. Burns. Can bepulped to separate fibres

Gravel Hard, cold to touch, often non- Roadways, drives, making concreteporous, does not rot or burn

Talc Extremely smooth, slippery Dry ‘lubricant’ on items like skin andsubstance, can be ground to powder rubber. Filler

Figure 8A.2 Properties and uses of some natural materials

Raw Use in Conversionmaterial natural state agent Use in changed state

Clay Lining canals Heat Clay bricks, drainpipes, domesticand ponds, making (in kiln) utensils and ornamentspottery

China (white) Making ‘china’ and Heat Fine china, cups, plates,clay ceramics. As a filler (in kiln) industrial ceramics

powder in ‘glossy’paper and plastics

Limestone Lump cement, iron Heat Refining beet sugar (as calciumand steel making. (in kiln) oxide), steel making andRoadstone and agricultureconcretePowder glass makingand agriculture

Figure 8A.1 Uses of raw materials in unconverted and converted state



Key ideas

8B. Groups of materials☛ There are many ways of classifying materials. One of the most useful is to put

materials having similar properties into a group or class.

☛ The properties of some materials change when the material is heated orcooled, therefore it is important to know the usual state of a material so thatcomparisons can be made.

Classification of materialsMaterials may be classified as metals, ceramics, glass, fibres, plastics and foods (seefigure 8B.1).

MetalsMost people think they would recognise a metal if they saw one. True, but there aresome metals such as sodium which react so quickly with air and water that they haveto be stored under oil. When these metals are cut the bright surface tarnishes quicklybecause it reacts with oxygen.

Very few metals are found in nature as the usable metal because most react withair and water. Most metals are found as ores in which the metal has combined withother chemical elements.

Properties and uses of metalsMetals are usually easily hammered into shape (malleable), are flexible, shiny whenfreshly cut, and often noisy when hit. They are good conductors of heat andelectricity, able to be pulled into long strands (ductile), and have high melting andboiling points. They can be made to change state from solid to liquid and back tosolid, or to soften as an aid to casting or fabrication. Some metals will reactchemically with almost anything, others such as gold and platinum hardly react at all.

Since metals are easily manipulated and fabricated they have found extensive usein the production of everything from brooches to bridges. Unfortunately most metalstend to be relatively heavy and corrode over a period.

GlassGlass is made by humans. The Egyptians made glass 4000 years ago so it has beenproduced for a long time. Ordinary glass is made by heating together sand, limestoneand sodium carbonate (which are cheap and readily available). Only the energy costsare high. Glass is 73 per cent silica (sand) by weight, the rest of the material mayinclude chemicals to produce specialised and coloured glass.

Glass ceramicsCeramic comes from the Greek word meaning pottery. Today the word is used todescribe the product of heating clay and its compounds, with glass, to a hightemperature. Glass ceramics are virtually unbreakable and hardly expand on heating.

PlasticsTo a chemist a plastic bucket is an example of a polymer in use. So what is apolymer? Look at figure 8B.2.





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Monomer Basic chemical unit

Straight chainpolymer

Thermoplastic –will soften onheating eghigh densitypolythene

Branched chainpolymer

Thermoplastic –will soften onheating eg lowdensitypolythene

Cross-linkedpolymer

Thermosetting –usually rigid –decomposes onheating egmelamine, epoxyglues, phenol andformaldehyde resins

To illustrate the formation of polymers we can use the paper clip model. Different

molecular arrangements produce different properties

Figure 8B.2 Polymer types and characteristics (using the paper clip analogy)

Using the paper clip analogy, a polymer is made up of individual chemicalscalled monomers linked together to form larger molecules. Although polymers andplastics are fairly new as synthetic materials, they are not new to biology. Therewould be very little of us left if someone took all our polymers, such as tendons andmuscles, away!

FibresFibres can be natural or synthetic. Natural fibres can be of plant origin eg cotton, oranimal origin eg wool. Textiles can be made from natural fibres, synthetic fibres or amixture of the two. In some fabrics, the fibres are not woven but bonded. Tissuepaper is an example of a bonded fabric.

Natural fibres including cotton, linen and cellulose from plants, are chieflycarbohydrates, while wool, silk and hair are animal proteins. Synthetic fibres includenylon, polypropylene, polyester (eg terylene) and acrylics.

Short fibres can be spun and twisted to make a long thread. Synthetic fibres areoften made into long lengths by melting and extruding. Weaving and knitting pro-duces further properties.

Uses of textilesWe associate textiles with clothes and furnishings, but industry also uses textiles. Cartyres and fan belts contain many textile threads and most modern ropes are madefrom synthetic fibres which do not rot.



Contact lensesare plastic

Spectacle framesprobably plastic

False teeth are polymers

Synthetic andnon-syntheticpolymers (nylon,terylene, wool),cotton used inclothing

PVC andpolyurethane polymersused in footwear

Tendons areproteins

Muscle blocksare proteins

Toe and fingernails are polymers

Long chainmolecules:

Collagen aroundbones is protein

Haemoglobin in blood

Glycogen in liver

FoodFood material is arguably the most important material of all (see chapter 3). All foodis composed essentially of three main groups of chemicals together with water andmicronutrients. These classes of compounds embrace all our food whether a fivecourse meal or a packet of sandwiches. The chemical groups are carbohydrates, fatsand proteins. Trace minerals and vitamins are normally found in sufficient quantitiesin Western food if a balanced diet is consumed. The carbohydrates supply energy;fats provide insulation and when broken down chemically, supply energy and water.Proteins together with mineral salts provide our hard and soft tissue.

Challenge46

Use a magnifying glass to look at a synthetic fabric – eg nylon and a natural fabric,wool. What do you think the observable differences are? How do you think what youhave seen will affect the moisture absorbing qualities of the fabric?

Figure 8B.3 Your personal polymers

Made by humansMade in humans



8C. Groups of materials☛ In order to produce new materials, substances can be combined so that the

best properties of each contributes to the new material.

☛ Chemists sort materials into groups according to their properties. They haveplaced the basic units from which all materials are made, the elements, intogroups. Each group contains elements which have similar properties andcharacteristics.

☛ When elements are joined together to form compounds, the compoundsdisplay a new set of properties. Chemists also find it useful to group thesecompounds together.

Materials with combined propertiesTake your mind back to the last time you saw an office block or factory being built.You may have seen concrete with steel bars sticking out of it, because two materialswere being used and their different properties combined. Concrete is capable ofcarrying heavy loads; it has good compression strength, but if you placed a load atthe end of a bar of ordinary concrete the concrete would probably snap. However, ifthe bar is reinforced with steel (which does not snap), you have the best of bothmaterials. (Building in concrete is also cheaper than steel and it requires lessmaintenance.)

Glass ceramicsGlass ceramics out perform glass in almost every respect except that they are opaque.Overheating glass containing silver chloride makes it opaque but virtuallyunbreakable while glass containing oxides of lithium and titanium hardly expands onheating. These glass ceramics find uses in ‘freezer to oven’ kitchenware and in themanufacture of nose cones for rockets.

Composite materialsA glass-fibre boat is an example of the use of a composite material. Flexible butstrong, glass-fibre is combined with plastic resin to produce a smooth, firm, strongmaterial. In other examples carbon fibre reinforcement of polymers produces alightweight material of great strength and can be used in the manufacture of tennisand squash rackets.

Polymer additivesNo, not the latest replacement for monosodium glutamate in food! These additivesare combined with basic polymers to modify them and give them different properties– eg pigments can be added to give colour. Adding plasticisers makes a polymermore flexible and soft. Some plastics contain only about 20 per cent of polymer, therest is filler, such as clay, which can change the property of a plastic. Fillers made ofstarch or sugar are claimed to make plastic biodegradable because bacteria utilise thecarbohydrate and in so doing cause the polymer to break down.

Challenge47

There is a movement which suggests that biodegradable plastics should be bannedbecause if they are mixed with recycled plastics they cause problems. Think throughthe pros and cons of this debate which presents an enigma ie now there arebiodegradable plastic they may not be such ‘a good thing’.

Key ideas





Groups of elementsEvery scientist looks for patterns in data collected from experiments and observations.If a pattern appears from the data, then there is a chance that a prediction can bemade about some perhaps unknown property, trend, or even undiscoveredsubstance.

In 1869 Mendeleyev, a Russian chemist, made a brilliant job of putting all knownchemical elements in one big table, grouping them according to various physical andchemical properties. He left gaps in the table where the elements were undiscovered,predicting that the ‘missing elements’ would be discovered one day. In the modernversion of Mendeleyev’s table (see figure 9C.1 and at the end of the book), chemicalelements which are similar are boxed together.

Classes of chemical compoundsWhen chemical elements combine together the compounds formed have differentchemical and physical properties which allows chemists to draw up new groups.Certain groups of compounds for example are derived from a parent acid eg nitratesare derived from nitric acid and many nitrates have similar properties. Below is a listof some common groups of chemicals together with the name of the parent chemical(see chapter 11).

Nitrates – nitric acid Sulphates – sulphuric acidChlorides – hydrochloric acid Acetates – acetic acidCarbonates – carbonic acid Phosphates – phosphoric acid

Because many of the chemicals associated with life contain the chemical elementcarbon, the study of more complex carbon compounds is called organic chemistry.Some of these compounds can be grouped as:

Carbohydrates:Members of this group all contain the elements carbon, hydrogen and oxygen only,joined together to form complex compounds eg glucose and fructose, sucrose,lactose, maltose and starch.

Hydrocarbons:Some members of the group are used as fuels and their chemical names havebecome household words - eg methane (marsh gas) and butane (gas in blue cylindersused by campers). Petrol is a mixture of hydrocarbons. All hydrocarbons containcarbon and hydrogen as the only chemical elements.

Proteins:This is a chemical and food group. All proteins are polymers made from units calledamino acids.

Challenge48

Taste small samples of glucose, castor sugar and starch (use cornflour as your starch).Which one gives the sweetest taste? They are all carbohydrates.



Key ideas

9A. Properties of materials☛ There are, at the moment, 109 known chemical elements.

☛ Some chemical elements occur in nature in the form of the element itself, butmost elements are found joined together in compounds.

☛ Chemical elements can join together to form chemical compounds.

☛ There are millions of chemical compounds which occur in nature, and it isalso possible to create new ones.

☛ Chemical elements and compounds are used by everyone in everyday life.

☛ Mixtures of substances can be separated to give useful pure substances.

Earth, fire, air and water ....The ancient Greeks believed that all substances were made up of earth, fire, air andwater combined together in different amounts. We now know that all substances aremade from chemical elements. You will know of some chemical elements since weuse them in our daily lives, aluminium foil for example is just aluminium metal,copper pipes are used for central heating and diamond is a form of pure carbon.

Air is a mixture of substances (see chapter 11A), and two of the majorcomponents nitrogen and oxygen, are chemical elements. One of the things chemistsdo is to obtain pure substances because we find uses for some of these, but we alsocombine the pure elements together to form compounds.

Challenge49

Look up in an encyclopedia some of the chemical elements and note the wayshumans use them. How many elements do you use in your everyday life?

Egg shell in the mixture?When we cook we often separate eggs from their shells. Sometimes we even separatethe egg yolk from the egg white. We can separate chemical substances from eachother, and do so to obtain pure substances because these are extremely useful.

Separating mixturesMixtures of solids and liquids are easy to separate. We just filter off the solid to leavea liquid in one container and the solid elsewhere, normally in a filter funnel. It is aprocess which we use in cooking. When you have boiled vegetables, say carrots, youcan pour the result through a sieve (the equivalent of the filter funnel). The carrots areleft in the sieve, the water in the container (possibly the sink)! We do this because wedon’t want the water, but we want the carrots. This is an example of separating asolid from a liquid.

Separating one solid from another is a little more difficult. In some countries tablesalt is obtained from salt water. Table salt (sodium chloride) is very soluble in water.The salt water often contains mud and other insoluble particles, and these areseparated from the solution by allowing the liquid to stand in a tank. After a period oftime the mud and other particles fall to the bottom of the tank. The solutioncontaining the salt can then be carefully run off into a separate tank and, in hotcountries, allowed to stand until the water has evaporated. The crystals of solid saltare then collected. In this example the solids are separated using the property thatone solid is soluble in water and the others (mud etc) are not.



1. Food 79


9. Properties of materials 79

Sometimes we need to separate two liquids. We do this by using the property ofboiling points. (Liquids have different boiling points ie temperatures at which theychange from a liquid into a gas). This process is called distillation and is used whenmaking distilled alcoholic drinks such as gin and whisky. In distillations the mixtureof liquids is heated in a container. The liquid with the lower boiling point turns to agas first and leaves the container. The vapour is directed out of the container andcooled; it condenses and changes back into a liquid. So the lower boiling liquid canbe separated from the higher boiling one. If heating is continued then the higherboiling liquid will distill and can be collected in another container.

Heat

Coolingwater out

Coolingwater in

Vapour condenses in thistube which is surrounded

by cold water

Liquid

Figure 9A.1 Distillation

If the two liquids are physically different, such as oil and water, they can beseparated by skimming or draining one layer off. This is done when cream isskimmed off milk and fat taken off gravy.

Challenge50

Air is a mixture of gases. How can we separate air into its parts? Will it help tochange the state of air – ie make air liquid?

ChangeIf none of the 109 chemical elements which are known were capable of joining upwith one another, no human life would exist! Substances are formed by joiningchemical elements together. This either occurs naturally or can be done by humans.In the natural environment for instance, rusting is iron reacting with oxygen andwater in the air, the red/brown substance which is formed is called hydrated ironoxide.

We bring about a chemical change when we light a candle. Candles are made upof compounds in which carbon and hydrogen are joined together, so when a candleburns these compounds burn using the oxygen in air to form two new products -carbon dioxide and the oxide of hydrogen, water. Changes of this nature are not easyto reverse: they are chemical changes in which the products of the reaction are oftenvery different in form and function from the ‘parent’ materials.



Key ideas

9B. Properties of materials☛ Chemical change is often difficult to reverse.

☛ Everything around us is made of chemical compounds.

☛ Chemical elements can be divided into two classes: metals and non-metals.

☛ Non-metals react with oxygen in the air to give oxides, most of which dissolvein water to give acids.

☛ Metals which react with oxygen in the air form oxides, most of which do notdissolve in water.

☛ An important class of chemical compounds are ‘salts’.

ReactionsNitrogen and oxygen in the air are sometimes joined together to form nitrogendioxide by the action of the electrical discharge from lightning. Nitrogen dioxidedissolves in water to form nitric acid. Therefore, under these conditions rain containsnitric acid. Fortunately, the amount of nitric acid in the rain is quite small, but it hasan important role to play in the nitrogen cycle (see figure 1B.1). Carbon dioxide is theoxide of the element carbon which also dissolves in water to give the acidic solutioncarbonic acid. ‘Natural’ rain is very often acidic with a pH of between 4.5 and 5.6(for explanation of pH see chapter 9C). The general rule is that most acids come fromoxides of elements which are non-metals. Another common non-metal oxide issulphur dioxide. We use sulphur dioxide as a sterilising solution and it is made whensodium metabisulphite and citric acid are mixed in water.

Challenge51

Buy some sodium metabisulphite and citric acid from a shop. Mix them together inwater. Carefully smell the gas. It has a sickly smell.

Challenge52

Put some ‘Andrews’ in water. The fizz is another gas – carbon dioxide. Does it have asmell? What do you notice about how soluble this gas and the one in Challenge 51are in water?

MetalsThe majority of the chemical elements are metals. Most metals will react with theoxygen in the air to form oxides but some metals will not do this or will only do so athigh temperatures. It is quite important that they behave in this way, for instance, ironreacts readily, but gold doesn’t! So this is one of the reasons why gold is used injewellery and iron is not!

The different reactivities of metals helps to explain how the elements occur innature. Metals which are reactive are normally found in compounds; metals likesodium, magnesium, iron, aluminium and calcium are found in compounds(commonly called ores), but unreactive metals like gold, silver and copper can occuras pure elements.



1. Food 81


9. Properties of materials 81

Upset tummy ?We all get upset stomachs from time to time. The pain we get is normally due to ourstomachs being too acidic. In our stomach there is an acid which is used to digestthe food we eat. The acid is hydrochloric acid, and the pain is caused by the acidworking on the stomach wall. The remedy for the pain is to take a medicine whichneutralises the acid and what we do is carry out a chemical reaction in our stomach!A common treatment taken by people is a medicine such as ‘Milk of Magnesia’.

Challenge53

Look at a bottle of Milk of Magnesia. What is the chemical that is used to react withthe acid? What metal does the compound come from?

The remedy.....Milk of Magnesia is a suspension of a chemical compound called magnesiumhydroxide in water. In your stomach the hydrochloric acid is neutralised by themagnesium hydroxide when they react together to form magnesium chloride andwater. The magnesium chloride belongs to a class of compounds called salts. Theproducts of the reaction are harmless, and eventually we feel better!

AcidsThere are a number of acids which we use in our everyday lives. Vinegar is asolution of an acid, acetic (ethanoic) acid in water, and lemon juice is mainly citricacid dissolved in water. Some other acids should also be familiar: sulphuric acid incar batteries, and hydrochloric acid in our stomachs. What they all have in commonis that in water all of these acids form hydrogen ions, H+ ions, and the number ofthese ions in water determines how strong the acid is. The opposite ion to the H+ ionis the OH– ion, called the hydroxide ion. When acids are neutralised the H+ ions areremoved. Also during neutralisation salts are formed: nitric acid forms nitrates;hydrochloric acid forms chlorides; and sulphuric acid forms sulphates.

Challenge54

Take some pickled beetroot juice and place it in a glass. Add bicarbonate of sodauntil no more gas is given off. What happens to the colour? If the beetroot is pickledin acid and the gas is demonstrating that the H+ ions are being removed, what ionsdo you think will be present when the solution goes blue?

Challenge55

Look at items around the home. Make a list of the chemicals that appear on thelabels. How many are salts? Which acids do they come from?



9C. Properties of materials☛ Properties of oxides are a way of identifying if a chemical element is a metal or

a non-metal.

☛ Acids can be neutralised by bases and alkalis.

☛ Whether a substance is acidic or alkaline is indicated on the pH scale.

Is that what it is ?You may be surprised at the number of oxides which are used in everyday life. Whitepaint can contain titanium dioxide to give it the white colour, sulphur dioxide is usedas an alternative to chlorine in bleaches, and ‘sand’ is silicon dioxide.

The characteristics and properties of the oxide of an element can be used toclassify it as a metal or non-metal. The 109 chemical elements are arranged into amap called the Periodic Table. Elements in a vertical line (called groups) have similarchemical properties (figure 9C.1). If we look at where the elements with acidic oxidescome you can see that they are in the right hand corner.

Elements in the cells containing a black triangle are generally considered to benon-metals. Some metals, however, have properties similar to the non-metals (see theback of the book for a key to the chemical symbols used in the table above).

Measuring acidityHow acidic a substance is can be measured by the number of the hydrogen ions in alitre of the substance. In 1909 the chemist Sorensen worked out a way to describethis ‘strength of the hydrogen’. In French this is ‘poissance d’Hydrogene’ and ‘pH’remains to this day a standard way of describing acidity.

Sorensen, ‘the father of pH’, suggested that since the most acidic situation couldbe described as having 1 g ion of hydrogen per litre and the most alkaline as havingonly 1 x 10-14 gram ions hydrogen per litre; then a scale using the indices 0–14 (fromthe negative log of the hydrogen ion concentration) could be used to communicatethe acidity of a substance. The pH scale thus runs from 0-14. Neutral substances havea pH of 7.0. This is illustrated in figures 9C.2 and 9C.3.

Key ideas



Figure 9C.2 The pH scale

pH0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

1 10-1 10-2 10-3 10-4 10-5 10-6 10-7 10-8 10-9 10-1010-11 10-12 10-1310-14

Strongly acidic Mildly acidic Neutral Mildly alkaline

Strongly alkaline

Concentration of H+ ions in grams per litre

The index without the minus sign becomes the pH value

1. Food

83

THE R

OY

AL

SOC

IETY O

FC

HEM

ISTRY

9. Properties of m

aterials83

H

Li Be

Na Mg

K Ca

Rb Sr

Cs Ba

Fr Ra

Sc

Y

La

Ac

Ti

Zr

Hf

V

Nb

Ta

Cr

Mo

W

Mn

Tc

Re

Fe

Ru

Os

Co

Rh

Ir

Ni

Pd

Pt

Cu

Ag

Au

Zn

Cd

Hg

Ga

In

Tl

Al

B

Ge

Sn

Pb

C

Si

As

Sb

Bi

N

P

Se

Te

Po

O

S

Br

I

At

F

Cl

Kr

Xe

Rn

Ne

Ar

He

Elements in the cells containing a black triangle are generallyconsidered to be non-metals. Some metals, however, haveproperties which are like those of the non-metals (see the backof the book for a key to the chemical symbols used in the table above).The lanthanide and actinide elements have not been included.

Figure 9C.1 The periodic table



Figure 9C.3 The pH of common substances

NeutralisationWe know that the acid that causes upset stomachs can be neutralised by taking Milkof Magnesia. (Compounds that neutralise acids are called bases. If a base dissolves inwater it is called an alkali.) This is an example of a reaction which has widespreadapplications because the neutralisation of acids enables us to make a useful class ofcompounds called salts.

Challenge56

We can carry out a neutralisation in the home using foods and cooking materials. Inorder to see what is going on we can use indicators. These are substances thatchange colour when the pH changes. Indicators are commonplace in nature.

Pour some pickled red cabbage juice into a container. Add a little water. Add tothe red solution small amounts of sodium carbonate (washing soda). Notice that a gasis given off. This is carbon dioxide. But also notice that as you add the solid, thecolour of the solution changes. When the addition of solid causes no more gas to beproduced, the solution should be green/blue. The indicator which gives red cabbageits colour is only red when the solution is acidic (ie pH is less than 7) so the indicatorchanges to a blue colour when it is alkaline.

Neutralise the acid in the red cabbage solution by adding small amounts ofsodium carbonate. Exact neutralisation is the point when the colour is light green/blue. Try the indicator on other substances like lemon juice.

So what’ s going on?Pickled red cabbage is made by putting cabbage in vinegar (acetic acid). Sodiumcarbonate reacts with the acid to give a salt (sodium acetate), water and carbondioxide. We can write what is going on in an equation:

sodium carbonate + acetic acid → sodium acetate + carbon dioxide + water

At neutralisation the acetic acid exactly balances the sodium carbonate.

pH0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Increasingly acidic Neutral Increasingly alkaline

Water

Humansaliva

and milk(6.9)

Humanblood(7.35)

Sodiumbicarbonate

Milkof

magnesia

Washingpowder

Sodiumhydroxide(causticsoda)

Bathcleaner

(onebrand)

Dishwasherpowder

Slightlyacidicsoil

Infantgastricjuice

Carbonicacid

Gastricjuice(1.77)

Vinegar

Lemonjuice

TCP

VitaminC

(powder)


10. Making new materials 8510. Making new materials 85

Key ideas

10A. Making new materials☛ Many useful substances occur in nature.

☛ Substances can be changed from one physical state to another ie from a solidto a liquid, which can make the substances more useful in our lives.

☛ Humans have made many substances by using chemical reactions.

☛ Chemical reactions are responsible for making the millions of new substanceswhich we use in our everyday lives.

Changes of stateWe are all used to making new chemical compounds. Many of the activities weroutinely undertake as we go about our daily lives require the making of onesubstance from another. Care is needed in interpreting some of these changes. Forexample the turning of water into ice, is not the making of a new substance butsimply changing a substance (water) from one physical state (liquid) to another(solid). It’s the same substance in both states (see chapter 5A). Turning one substanceinto another is something different.

If you drive a car the engine will probably run on petrol. Here the petrol (amixture of substances made from the chemical elements carbon and hydrogen) isburnt in the engine to form new compounds and at the same time energy in the formof heat is released. This process powers the car and the new compounds that areformed leave the car via the exhaust.

Challenge57

Look up in a book how a car petrol engine works. What are the names of the newsubstances formed when petrol is burnt?

CandlesIn many respects burning candles is like burning petrol in a motor car. Candles aremade from candle wax, which is made from two chemical elements (joined together):carbon and hydrogen. When you light a candle the wax, with the help of the wick,burns; that is it combines with the oxygen in air to form new substances: carbondioxide and water. At the same time heat and light are given off. If the candle burnstoo fast there may not be enough oxygen, so instead of all of the carbon in the waxending up as carbon dioxide, some may form carbon monoxide or just carbon.

Challenge58

Light a candle. Place an old metal spoon just above the flame for a few minutes. Takethe spoon out of the flame and allow it to cool; what do you think the black soot is?Place a tin of cold water about 3 cm above the top of the flame. Droplets of watershould form on the bottom of the tin. Where do you think they have come from?

When a candle burns, because of the heat that is generated, most of the productsare formed in the gaseous state. Water is formed as a gas and will turn to a liquid ona cool surface. The sooty candle flame you see is due to particles of carbon beingformed. The other major products – carbon dioxide and carbon monoxide – arecolourless and normally gases at room temperature, so we don’t expect to see them.





In a car we don’t want to produce carbon or carbon monoxide (a poison), so a carengine burns petrol with carefully controlled amounts of air. It’s rather like a gascooker: the roaring blue flame is the fuel (made from carbon and hydrogen), burningin an excess supply of air. If we didn’t do this and carbon monoxide was formed thenwe’d poison ourselves with carbon monoxide! (This is one of the reasons why gasappliances have to be serviced so regularly.)

Another example of a chemical reaction is rusting. Here iron is reacting with theoxygen and water in the air to form a new compound called hydrated iron oxide.This is a red/brown substance, rust. The oxide is crumbly and breaks off, exposingmore iron, so the process repeats itself again and again until no iron is left!

You may be thinking that all chemical changes involve the oxygen in the air.Many do, but the vast majority don’t, for instance, the chemical reactions that takeplace during baking.

Challenge59

What is the ingredient that is added to cakes or bread to make them rise?

FermentationThe fermentation of alcohol is an example of a chemical change. In fermentationsugar is converted into a substance commonly called alcohol (its real name is ethanolor ethyl alcohol). The sugar is a compound of the chemical elements carbon,hydrogen and oxygen. When you ferment the sugar, there are substances in the yeastcalled enzymes which turn the sugar into alcohol. Other substances are also formed.

diastase maltase starch → maltose → ethanol + carbon dioxide

(alcohol)

The enzymes diastase and maltase come from yeast cells

Summary of fermentation

Challenge60

Why not make some home made wine or beer. What do you think the gas is that isgiven off during fermentation? Cheers!



Key ideas

10B. Making new materials☛ In everyday living we use many chemical reactions.

☛ Chemicals are sometimes used to bring about physical changes.

☛ Nature uses microorganisms to carry out many of its chemical reactions.

☛ Chemical reactions always involve either the input or release of energy.

☛ One important type of chemical reaction is the changing of metal compoundsfound in ores to the pure metal.

Washing me, washing you?It is sometimes difficult for people to appreciate that chemical reactions play such afundamental part in our everyday lives. Somehow, the idea of a chemical reactionbrings to mind awful smells, newspaper headlines of pollution, tall chimneysbillowing out smoke and things we don’t understand. In fact many of the former areincorrect. The vast majority of chemical reactions are undertaken by us as we goabout our everyday lives without us even noticing them. And, in fact, as a society, weare accomplished chemists, although we don’t think in that manner.

In this section three examples illustrate different types of reaction. The action ofsoap shows how a chemical can bring about a change in physical conditions. Makingyoghurt shows how microorganisms can bring about chemical reactions and theproduction of iron illustrates the more traditional view of a chemical reaction.

When we wash ourselves or our clothes we are using a physical change not achemical reaction. In soap, their are two parts. One part makes the soap particledissolve in the water, the other part is responsible for dissolving the dirt (see figure10B.1).

However, when it comes to removing stains we might resort to a bleach.Common bleaches contain either a chemical called chlorine or sulphur dioxide astheir active ingredient. They work by reacting chemically with the offending stain, tochange it and remove it from the article. This is a chemical reaction not a physicalchange (see chapter 9A).



How soap works

(i) In a soap and water wash, each soap molecule has a water loving end, (W)and a grease loving end (G)

W ----------- G(ii) When soap molecules contact a grease spot, the grease loving end of the

molecule attaches itself to the spot with the water loving end sticking out.

Continued overleaf

FabricWater

WG

WG

WGW

G

WG

WG W

G



How soap works… continued

(iii)This happens all over the spot and so the grease is surrounded by a film ofsoap molecules with their water loving ends sticking out.

(iv)With agitation by hand or from a washing machine, the grease droplet,surrounded by a soap film, is released. Since oil is lighter than water thedroplet floats off the fabric. The soap solution must also keep the particlessuspended so that they do not drop back again on to the fabric.

FabricWater

WG

W G

WG

G W

G

W

G

W

Fabric

Water

WG

W G

WG

WG

G W

G

W

G

W

Figure 10B.1 Washing with soap

Food for thought?A very commonplace use of a chemical reaction which is utilised in nature is themaking of yoghurt.

Challenge61

Make some yoghurt. You will need: 500 ml UHT or one pint of ordinary fresh milk.Fresh, live ie not pasteurised, plain yoghurt. Dried milk powder like ‘Marvel’, a non-stick saucepan, tablespoon, thermometer, Thermos type flask. (Instead of the Thermosflask use a ‘yoghurt maker’ if you have one. A warm airing cupboard might do.)You must work with clean equipment in a clean area.

Procedure:(i) If you are using ordinary fresh milk, bring one pint to the boil and allow it to cool.Remove any skin which forms.(ii) Heat 500 ml of UHT milk, or the one pint of milk already boiled and cool, to 430C. (Do not heat beyond this temperature, if the temperature does rise allow to coolbefore starting stage iii.)(iii) [a] For firm yoghurt, mix in 50 g of dried skimmed milk powder eg ‘Marvel’.

[b] Mix in one level tablespoon of plain yoghurt.(iv)Pour the mixture into a pre-warmed heat retaining flask. Seal and leave for 7 hours.(v) Pour the yoghurt into a basin. Stand the basin in cold water and stir the yoghurt gently.



(vi)Cover the basin and place in refrigerator for 4 hours to cool and thicken further.Your yoghurt will keep in a refrigerator for 4-5 days. Adding a small amount of

marmalade creates a pleasant flavour but only add this just before you eat theyoghurt otherwise the marmalade tends to separate.

What makes milk ‘yog’?Basically it is the effect of chemicals produced by bacteria on the milk. In ordinaryyoghurt there are two types of harmless bacteria, Lactobacillus bulgaricus andStreptococcus thermophilus. With warm conditions and plenty of food the bacteriamultiply and release chemicals including acetaldehyde (ethanal). This gives yoghurtits characteristic flavour. Chemicals including lactic acid released by lactobacilliresult in the breakdown of milk protein and the release of peptides. This encouragesthe streptocci to produce formic acid and carbon dioxide and this helps create acidconditions (pH 4.4-4.6) which in turn causes milk protein to be coagulated. At theend of the incubation the two organisms are present in about equal proportions.Continued incubation encourages Lactobacillus bulgaricus to produce more lacticacid which imparts a more acidic taste to the yoghurt.

The coagulation of the protein and the acidic conditions created help preserve theyoghurt for a longer period of time than ordinary milk. If acidic conditions areprevented by adding sodium hydrogencarbonate (sodium bicarbonate) at stage (iii),the milk will not ‘yog’.

For the ‘yoghurt reaction’ to work the microorganisms must be alive and healthy.They must be warm enough to be active ie warm enough for chemical reactions totake place within them. They must also have plenty of food from which to obtainenergy, together with the chemicals needed for growth and reproduction.

Energy needed?It is nearly always necessary to supply energy to a chemical reaction to get it going.You may not even realise that you are doing it. In the case of a chemical reactionwhich occurs at room temperature the energy is coming from the room itself. Morecommonly you need to supply vast amounts of energy. This is particularly true whenthe chemical element iron is obtained from its ore.

Challenge62

Take three nails and put them into three jars with screw top lids. Half fill one jar withwater, fill a second jar to the same level with water and this time add a teaspoon ofsalt. In the third place the nail on its own. Put on the lids. Which one rusts thequickest? Does the result surprise you? It’s the reason why you should always washyour car if you’ve been near the seaside.

In air, iron will slowly react with the water and the oxygen to form a newcompound, hydrated iron oxide. It will come of no surprise to you to learn that thechemical element iron does not occur in nature in its pure form. Iron is foundcombined with other chemical elements in chemical compounds which we call ores.These ores are not much use to us, but iron is because we can use it to make steel, asubstance used in everyday life.

Iron, used to make steel, is extracted in a blast furnace. In fact iron was one of thefirst metals to be extracted by humans, hence the title ‘iron age’.

Operation iron – how a blast furnace worksThe blast furnace is used to convert iron ore into iron. Iron ore (haematite) contains‘iron oxide’ and this material together with coke (carbon) and limestone (calciumcarbonate) is loaded into the top of the furnace by conveyor belt or skip on a



continuous basis.Inside the furnace a chemical reaction takes place. Hot air (containing oxygen) is

blasted into the already hot furnace. The oxygen in the air reacts with the coke toproduce carbon monoxide.

coke + oxygen in air → carbon monoxide(reaction A)

This reaction gives out a lot of heat and the gas carbon monoxide reduces the ironoxide in the ore to metallic iron. Carbon monoxide does this by joining with theoxygen in the iron oxide to form carbon dioxide leaving molten iron (reaction B).

carbon monoxide + ‘iron oxide’ → carbon dioxide + iron (reaction B)

The molten iron is drained or tapped off from time to time and run into moulds.When the mould is full and slightly overflowing it resembles a mother pig with a rowof teats and became known as pig iron.

Limestone is used in the furnace to remove impurities by combining with them toform slag. When heated, calcium carbonate turns to calcium oxide and this combineswith the sand (an impurity in the ore) to form ‘slag’.

Figure 10B.2 The blast furnace

Challenge63

One interesting property of iron, or substances that contain a lot of iron (steel) is thatthey are attracted by a magnet. Make a list of the things in your home that aremagnetic. Of those things which are magnetic and are kept outside (ie bicycle), whyare they painted? What has happened to the parts where the paint has beenscratched?

Hopper

Bell300 °C

500 °C

Tap hole

Slag

1000 °C

Reaction A

Firebrick

Molten iron

Air blast

Slag hole

Reaction Bup to 1200 °C



10C. Making new materials☛ Most chemical reactions require the input of energy.

☛ Chemical reactions can be used to produce important metals which we use inour everyday lives.

☛ A large number of chemical reactions can be classed as oxidation or reductionreactions.

My metal ore won’ t react....A number of chemical reactions require heating to start them off. For example, theextraction of iron from iron ore in a blast furnace requires the use of large amounts ofcoke, not only to help change the iron oxide to iron (ie reduce it) but also to providethe heat to sustain the reaction. A number of metals can be obtained from their oresby using heat and carbon. Most of the ores used are the oxides of metals and theprocess whereby a metal oxide is changed into the metal is called reduction. Thereverse process, the reaction of a metal with oxygen to form the oxide is calledoxidation. Other metals which are extracted in a similar fashion to iron include zinc,and copper (see figure 6C.1).

For the ores of some metals, no matter how long you leave them in hot coke, nochange takes place. These are the reactive metals and to obtain these metals fromtheir ores we have to be a little more crafty. But why bother? Some of the morereactive metals are used quite extensively. The best example is probably aluminium;it is one of the world’s most abundant chemical elements. In the home we use thefoil, but it is also used to make drinks cans, power lines, metal alloys for aircraftframes and so on. Aluminium, like all the reactive metals, is found as an ore in itsnatural state. The common ore is called bauxite, which is another name foraluminium oxide. You cannot get aluminium from aluminium oxide by heating theoxide with coke. So how do you do it?

Challenge64

Take a HP2 (or equivalent) battery and two short pieces of copper wire. Place piecesof copper wire on each terminal of the battery and put the other ends into a glass ofwater in which you have dissolved three or four teaspoons of sodium chloride (tablesalt). Look very closely at each piece of wire. Why do you think that bubbles of gasare forming?

Electricity as a source of energyIf you pass an electric current through a solution of a salt in water the solution willconduct the electricity. Not only that, but at the points (the electrodes) where theelectricity is put into the solution, a chemical reaction takes place. One of thechemicals to be given off will be chlorine (did you smell it in your reaction above?),the other will be hydrogen. Another example of the use of electrical energy inchemistry is in the extraction of aluminium.

Using electricity to extract and purify aluminiumAluminium is made from bauxite. Sodium hydroxide is used to remove silica andoxides of iron from the bauxite to leave aluminium oxide (alumina). Aluminiumoxide does not dissolve in water and its melting point is very high. It will dissolve inmolten cryolite (sodium aluminium fluoride and aluminium fluoride) and so

Key ideas





aluminium oxide in molten cryolite is used for the electrolytic production ofaluminium. Heat to keep the cryolite molten is provided by the passage of the currentused for the electrolysis.

When the current is passed aluminium ions in the electrolyte are attracted to thecarbon cathode where they collect electrons and become aluminium metal. Themolten aluminium sinks to the bottom of the cell and is removed from time to timeby siphoning it off.

Crust of solidelectrolyte

– Electricity supply(cathode)

Carbon cathodelining of cell

Insulation

Electrolyte of aluminium oxidedissolvedin cryolite – kept molten by passageof electricity

Carbon anode

Moltenaluminium

+ Electricity supply(anode)

Figure 10C.1 Electrolytic cell for making aluminium

The cost of extracting and purifying aluminium keeps its price fairly high. Theproduction of 1 kg of aluminium requires about 144 kWh (kilowatt hour) of electricalenergy. Despite this cost aluminium is a desirable metal for beverage cans because itis light to transport. The latest aluminium beverage can has a mass of about 16.9 gwhile a steel can with an aluminium top is about 37.5 g and a glass bottle of similarcapacity is about 185 g. Recycling of aluminium is important because it is cheaperthan extracting the metal from its ore.

Oxidation – reduction?Two commonly used terms in chemistry are oxidation and reduction. In its simplestform oxidation can be taken to mean the addition of oxygen in a reaction, andreduction the removal of oxygen.

Challenge65

Look up in the index of a chemistry text book the terms oxidation and reduction. Isiron ore oxidised or reduced in the blast furnace?

Challenge66

In the extraction of aluminium, at which electrode does the oxidation take place andwhich the reduction?

1. Food 93


11. How materials behave 93

Key ideas



11A. How materials behave☛ Everything is made up of tiny units called atoms.

☛ When atoms are collected together they make up substances.

☛ Chemical elements are substances which contain the same kind of atom.

☛ At present there are only 109 known chemical elements.

☛ Most chemical elements occur naturally, but some of the 109 have beenproduced by scientists.

I know it’ s there but I can’ t see it...Funny stuff this air which is all around us. We can’t live without it, we can’t smell itand we can’t feel it, but everyone knows it is there! We accept it is there even thoughwe cannot see it because we can see the effects air has. For instance, wind is themovement of air. No one can see the air moving, but everyone can see flags thatflutter in the wind, or yachts being blown along with the wind in their sails. Similarlyno one has ever seen the smallest unit which makes up substances. These units arecalled atoms.

Atoms are so small that we can only tell they are there when they do something,eg when atoms join together.

Challenge67

Convince yourself that although you can’t see something, there is something there.Try breathing out in a room at normal temperature. You should see nothing. Nowrepeat the exercise by breathing out in the top of an open chest type freezer or on acold morning. Notice that now you can see your breath, but it was there in the roomonly you couldn’t see it. What do you think you see?

AirThis invisible air that is all around us is made up of a number of substances as listedin the table below.

Per cent by volumeNitrogen 77.32Oxygen 20.80Carbon dioxide 0.03Water vapour 0.92Argon 0.93Other gases trace about 0.002

Air is a mixture of substances. Most of the air is nitrogen, but the particularlyimportant part of air for life on the planet is the oxygen. We breath in the oxygenwhen we respire and exhale carbon dioxide. In doing so our bodies use the oxygento ‘burn’ our food to provide energy (see chapter 2B). When we breath out we alsoexhale water (that is what you see on cold mornings), nitrogen, argon, other gasesand some unused oxygen. Some people don’t realise that we exhale some oxygen,but if we didn’t, we couldn’t give people the so-called ‘kiss of life’.

Nitrogen, oxygen and argon have one thing in common. They are all chemicalelements. This means that the particles of oxygen all have the same type of atom. The



atoms in nitrogen are all similar but are different to those in oxygen.Everything you can see around you is either a chemical element or a substance

made up of many of them. It is likely that most things you see will be made up ofmany elements as there are only 109 different ones available. Life would be prettylimited if there were only 109 substances! Each of the 109 chemical elements has asymbol – a shorthand way of representing the element.

Challenge68

Look up the names and chemical symbols for the chemical elements in anencyclopaedia or a chemistry reference book. How many do you recognise?

Joining chemical elementsIf you join two or more chemical elements together you form a chemical compound.Water is an example of a chemical compound formed from the elements hydrogenand oxygen (both gases at room temperature). The gas carbon dioxide is formed fromthe elements carbon and oxygen. There are millions and millions of chemicalcompounds. We humans have millions of chemical compounds in our bodies, andour bodies are made up of different types of chemical compounds. There is no gettingaway from chemicals!

Challenge69

Sometimes chemical elements are not what they seem. Take an ordinary pencil, andsharpen it so it has a long point. Look at the black point quite closely, it is asubstance called graphite (not lead!) and is a form of the chemical element calledcarbon. The graphite is soft so when you press the point on paper it leaves a mark.What you are doing is leaving a small amount of graphite on the paper. What do youthink numbers such as 2B and 3B refer to?

1. Food 95



Key ideas

11B. How materials behave☛ Everything is made from chemical elements.

☛ Combining chemical elements together enables chemical compounds to beformed.

☛ The atoms which make up chemical elements are made up of a number ofsmaller particles called protons, neutrons and electrons.

☛ Protons have a positive charge and electrons a negative charge.

☛ Atoms are neutral which means they have the same number of protons andelectrons.

☛ Neutrons have no charge at all.

AtomsThe particles called atoms are made up of smaller particles called protons, neutronsand electrons. This is how the atoms are different. All of the atoms of a chemicalelement have the same number of protons and electrons. So in carbon, for instance,all of the atoms have six protons and, therefore, six electrons. It does not matterwhere you get the carbon atoms from they always contain this number of protons andelectrons.

The protons have one positive charge on them and electrons one negative charge.So if there are the same number of each in an atom then the atoms must be neutral. Itis quite important that atoms are electrically neutral or else strange things couldhappen. Take the example of carbon, in the form of diamond. If the atoms in it werenot electrically neutral then diamond rings would repel each other!

In an atom, the protons and neutrons are found in the middle and electronsaround the outside. The middle of an atom is called the nucleus.

Ion not ironConfusion often exists between the words ion and iron. It is quite easy to distinguishbetween the two. Iron (chemical symbol Fe) is the name given to one of the 109chemical elements, it is also the name of the household appliance used to pressclothes. There is a simple connection as to why they both have the same name.Before electricity, lumps of iron were heated and used to press clothes hence thename ‘iron’ which we still use today. The element iron is a metal that is used ineveryday life. What we usually call a lump of iron is usually the element iron withother things added to it. If we add carbon, and some other metals in small amountswe get steel.

Challenge70

Given where the various parts of an atom are found, which do you think are easiestto remove?

Challenge71

Iron is magnetic, that is a lump of iron or mixture which contains large amounts ofiron will be attracted to a magnet. Aluminium is not magnetic. Both aluminium(symbol Al) and steel are used to make cans for foods. How could you identify what acan is made from so that it can be placed in the correct skip for recycling?





So what about ion? This is the term which refers to charged atoms (or groups ofatoms). Ions are readily formed.

Challenge72

Turn on a water tap and allow the water to dribble out. Take a plastic ruler and rub iton a woollen jumper, then hold the ruler near the water. Given that water is polar –that is, attracted by things with a charge, how do you explain your observations.

The electrons which are on the outside of atoms can be removed and when this isdone ions are formed. If electrons are lost positive ions are formed (remember thatelectrons are negative). You can do the opposite and make atoms gain electrons,whereupon negative ions are formed.

A lot of chemical compounds are made up of ions. The table salt which you useon food is a compound called sodium chloride. It is made up of two chemicalelements sodium (symbol Na) and chlorine (symbol Cl) which have combinedtogether to give sodium chloride. The element sodium is changed into sodium ions –positive ions, and the chlorine is changed into chloride ions – negative ions. The twoions have opposite charges and attract each other to form sodium chloride (NaCl).

When SODIUM and CHLORINE combine:

Sodium atom (Na)no charge Chlorine atom (Cl)

no charge

Na Cl

Na+ Cl–

one electron

attract each other

Sodium becomes charged becauseit LOOSES ONE of its negativelycharged electrons and therefore hasa positive charge of ONE. When anatom has a positive charge it is a function of the electrons only. Inshorthand it is Na+ and called thesodium ion.

Chlorine becomes charged becauseit has RECEIVED ONE negativelycharged electron and therefore hasa negative charge of ONE. When anatom has a negative charge it is a function of the electrons only. In shorthand it is Cl– and called thechloride ion.

By moving round as a pair in the compound sodium chloride, both ionsare mutually satisfied; in fact lots of ions join together to form a crystal.

Why then did they link together in the first place? That is like asking whya particular man and woman form a friendship, it is all to do with chemistry!

Chlorine ion– charge

Sodium ion+ charge

Figure 11B.1 Making ions

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So there is a large group of compounds that is made up of ions with oppositecharges. These are called ionic compounds. Covalent compounds form anothergroup in which atoms do not give up or gain electrons but share electrons with eachother.

What about these neutrons....We seem to have forgotten about the neutron. The neutrons are found in the middleof the atom, with the protons. They have no charge but have the same mass as theprotons. Both have a mass of one unit. (Electrons have a mass of 1/1835 unit.)

Atoms of carbon always contain six protons and six electrons. Most carbon atomscontain six neutrons but a small number have eight. The different numbers ofneutrons make no difference to how carbon atoms behave chemically. We call atomswith the same number of protons but different numbers of neutrons – isotopes. Notall isotopes are stable; some isotopes are unstable and the atoms break up. When thishappens radioactivity is given off. This is happening all the time and gives rise tonatural, or background, radiation.



11C. How materials behave☛ Atoms are the smallest unit in a chemical element.

☛ Atoms can be turned into ions with either a positive or a negative charge.

☛ Ions of opposite charge attract each other and form ionic compounds.

☛ Atoms can join together by sharing each others electrons to form covalentcompounds.

☛ There are three types of radiation: alpha, beta and gamma.

☛ The half-life of a radioactive element is the time for half the number of atomsto break up.

ModelsThere are a number of different models for atoms because no one has ever seen anatom. We use models to help us explain the way atoms behave. For our purposes wecan consider atoms to be rather like a peach. The nucleus can be considered to bethe stone, with the electrons being found in the flesh of the peach. But it must beremembered that most of an atom is empty space so the flesh only represents wherethe electrons may be found.

Figure 11C.1 Peach/atom analogy

We can represent the atom in a pictorial form. In the case of hydrogen (symbol H),the most abundant atom has one proton and one electron, we can represent it as:

Flesh/electronsStone/nucleus(protons and neutrons)

Figure 11C.2 The hydrogen atom

Key ideas



Nucleus

one electron

Structure: one proton having a positive (+) charge one electron having a negative (-) charge

1 proton

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If we remove the electron we form an ion which contains one proton, hence it has apositive charge and can be written as H+. It is this ion which is present in acids.

We can also join hydrogen atoms together by sharing electrons, and this is calleda covalent bond:

Figure 11C.3 Hydrogen molecule

Challenge73

Look at a bottle of mineral water. On the label you will see names such as nitrate,sulphate, bicarbonate, and chloride. These are all negative ions and are based on thenon-metallic elements nitrogen, sulphur, carbon and chlorine respectively. Inaddition, on the label you will see sodium, calcium, magnesium and potassium theseare NOT the elements but the positive ions of the metallic elements. Look at otherlabels. How many other ions can you find? Look up the names in a reference book.

All in water ....Both tap water and bottled water have chemical compounds in them. Most of thesecompounds belong to a class called salts, but you cannot see them because the saltsare dissolved in the water. To dissolve in the water the compounds must form ionsand that’s why on the side of bottled water there is a list of ions. The shorthand forsome common ions in water are:

nitrate NO3– sulphate SO4

2– bicarbonate HCO3– chloride Cl–

The nitrate ion is a collection of four atoms, one nitrogen and three oxygen,joined together and has a charge of one minus

sodium Na+ potassium K+ calcium Ca2+ magnesium Mg2+

Challenge74

In the kitchen we sometimes use a compound called bicarbonate of soda whenbaking. The chemical name for this substance is sodium bicarbonate (sodiumhydrogencarbonate). What do you think the chemical shorthand for this compoundis?

electrons

Two hydrogen atoms sharing two electrons

This is a hydrogen molecule (H2) and is how hydrogen occurs in nature

protonproton



Challenge75

You may be lucky enough to own a diamond or two. Take a look at a diamond, itsparkles but you know you can’t write on paper with it because diamonds are veryhard. Graphite and diamond are names given to a chemical element – carbon. Theyare the same chemical element but have a different physical form, hence differentproperties. What’s worrying is that diamond is less stable than graphite, so alldiamonds should end up as graphite, possibly in pencil leads! Why don’t they? (Thisis a tough one!) It would make for some expensive pencil leads!

Simple as one, two, three?To work out the chemical formulae of simple compounds all that you have toremember is that compounds have no overall charge, so the electrical charges on theions must be the same in number and opposite. Let’s try an example between sodiumand chloride ions. Sodium is one positive, chloride one negative; so the number ofcharges is equal and the charges are opposite. Therefore, the formula is NaCl, thename sodium chloride, and it is electrically neutral.

Calcium and sulphate both have two equal and opposite charges so the formula isCaSO4 – calcium sulphate. You will have come across this substance if you havebroken a limb because it is also used in Plaster of Paris. What about sodium andsulphate ions? Sodium has one positive ion, sulphate two negative. So if thecompound has to be electrically neutral overall, two sodium ions are needed for eachsulphate ion so the formula is Na2SO4 – sodium sulphate. Easy isn’t it?

When atoms fall apart......When the nucleus of an atom breaks down radiation is given off. This is a naturalprocess which is going on around us all the time (see chapter 6C). It is important toremember that the type of radiation which is produced by humans is no differentfrom that known as natural radiation. When atoms break up there are three forms ofradiation which can be given off: alpha, beta and gamma.

Alpha radiation is a charged particle made up of two protons and two neutrons,so has a two positive charge. These particles travel only a small distance in air.

Beta radiation consists of fast travelling electrons; they travel further than alphaparticles in air.

Lastly, and possibly, the potentially most dangerous form of radiation is gammaradiation. These are packets of high energy which are very difficult to stop.

Many of the atoms take many years to break up. Carbon-14 atoms (those with 8neutrons) for example have a half-life of 5568 years. This means that if you have 100atoms of this particular isotope, then after 5568 years you will have 50 leftunchanged.

Challenge76

Look up in a reference book how carbon dating works. Try to see if you can discoverthe results of the Turin shroud experiment. Do you think it is authentic?

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Answers and notes to challenges 101

Answers and notes to challenges1 Garden Centre

Typical N:P:K ratios on fertilizer packs:

N P K

Tomato (Phostrogen) 12.5 5.0 24.5Grass (Fisons Lawn Feed) 14.0 2.0 4.0Flowers (Fisons Flowerite) 4.0 3.0 6.0

Conclusions: fruit production requires a large input of potash. Production of leafmaterial requires a large input of nitrogen. Production of flowers requires a moreevenly balanced fertilizer but with potassium present in the greatest amount.

2 Degradation by microorganismsResults will be variable. This experiment is a modification of a standard experimentdesigned to determine the microbial activity of soil against time. The faster the rate ofdecomposition, the greater the microbial activity of the soil.

3 Preservation of smoked foodsThese are often preserved by adding salt and/or dehydrating the product. The smokealso deposits some antibacterial chemicals on the food.

4 Looking at labelsMeat products containing sodium nitrite often have a deep red colour as opposed tothe usual ‘pink’ of uncooked meat.

5 Growing cressTime taken will vary with conditions such as temperature, but samples grown in thedark will become tall, yellow and fall over. Plants grown in the light should be deepgreen in colour and should not fall over.

6 Keeping track of your dietConvert energy figures to the measurements used on diet sheet. (1000 calories = 1kcal.)

7 Flowers in hospital wards at nightThere are no good reasons unless you have so many flowers that the carbon dioxideproduced by them during respiration reaches levels that could cause narcosis. It isworth stating that carbon dioxide is heavier then air and so the gas would build upfrom the floor upwards. This is why it is used in fire fighting. Due to its narcoticeffect, carbon dioxide can be used to ‘put down’ animals in a painless way byincreasing the amount of carbon dioxide breathed in.

8 Bread makingHeat above a certain temperature can kill yeast which is a microorganism. The heataffects enzymes in the protein of yeast. Rate of reaction: warmth will increase the rateof reaction up to a certain limit. In unit time the greater the production of carbondioxide, the more effectively will the dough rise. (Bakers like a lot of small bubbles tocreate an even texture. Few people like large bubbles or ‘holes’ in their bread.)



9 Catalase enzyme in liverWhen the liver and hydrogen peroxide are warm the reaction takes place morequickly. (The rate of reaction is increased). With potato the reaction is not nearly sovigorous but it does work.

10 Detergents containing enzymesAt a biochemical level proteins are being split up to amino acids. Proteins areinsoluble in water. Amino acids are soluble in water. If protein stained clothing is putin very hot water, the protein becomes heavily denatured and hard to remove.

11 Energy in cheeseThe following table will save you label hunting.

kcal kJ

Blue Stilton 411 1701Caerphilly 375 1554Cheddar (English) 379 1571Derbyshire 402 1667Double gloucester 405 1678Lancashire 373 1545Leicester 401 1662Wensleydale 377 1563Cottage cheese (plain, low fat) 98 413

12 Heat in a greenhouseIn a greenhouse, heat from the sun or from heaters is physically trapped by the glassor polythene. In the greenhouse effect so-called greenhouse gases do not form aphysical barrier. The gases allow some solar radiation to pass though to the earth’ssurface. On radiation from the surface the wavelength has changed and is nowabsorbed by the gases which in turn re-radiate it back to the surface of the earth. Theearth in turn radiates the heat it absorbs to the greenhouse gases. In practice some ofthe heat is lost to outer space and heat from the sun is absorbed by the earth’ssurface.

13 Burning rateAssuming the oil is cold the order will be as follows:

oil soaked towel > clean paper towel > oil in tin.

14 Plaster of ParisThe pot should feel warmer especially if the appropriate amount of water was addedin one go.

15 Sugar under tongueExothermic, however, no observable difference was found in several subjects tested.This does not mean it could never happen. Heat is certainly produced when somesolutions are made up in the laboratory.

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16 Chemical preservatives in foodThe following list gives some advantages and disadvantages.

Advantages Disadvantages

No added preservative present so When the product is openedthere is no question of whether microorganisms (bacteria,preservatives are safe or not yeasts, viruses), can enter theeither now or in retrospect. product and start growingPeople who are allergic to if conditions are right.certain preservatives can eat Unless refrigeration iswith little or no concern. kept at the appropriate (low)

temperature organisms can live onfood. Food once exposed tomicroorganisms and then leftunrefrigerated can spoilquickly. Some foods may containpreservative or, as in the case ofyoghurt, bacteria which producepreservative chemicals.

17 Household refuseLandfill sites are now often lined before tipping starts. The gas produced is methanewhich can be used as fuel. Methane production in older unmanaged tips nearhousing has caused explosions and property has been damaged.

18 Extractive industry walkThe answer depends on whether top soil has been saved and reinstated. In olderquarries and pits this is unlikely to have happened. In time certain plants will growunless the mining spoil is toxic eg contains lead and copper wastes.

19 Waste products from animalsNo specific answer – just a thought to ponder over.

20 Bottle banksA variable answer depending on the distance to your bottle bank. Obviously it isbetter to walk or take your empties when you ‘do a big shop’.

21 Talk about ‘Preventing Acid Rain’The quarrying and removal of limestone would be a major problem (loss of rockycountryside and amenity value, production of dust by extractive process, heavylorries on roads, safety).

A lot of gypsum is now mined so this could be replaced by the power stationproduced material. In time there could be an appreciable problem.

Plaster of Paris hills. Perish the thought, but we do have climbing walls made ofconcrete and brick!

22 Warmer climate in the UKGlobal warming will cause the sea level to rise. Flooding would occur along the Eastand SE coast of the UK. Diseases associated with a warm climate – eg malaria –would spread further north and south of the equator.



23 Spray cansButane (the gas used in some cigarette lighters and as a camping gas supply) is beingused by some companies as a propellant gas. Other replacement gases are underdevelopment. For the normal, healthy person there are few situations in which apump spray container cannot replace the spray can. The pump spray also has anadvantage in that the spray droplet size can be altered. For people with conditionssuch as arthritis, operating a pump spray presents problems especially if using a hairspray.

24 Bottled waterBottled waters from a variety of sources contain various amounts of different salts.Whether a particular spring or mineral water contains salts depends largely on thenature of the rocks through which it has percolated. Some bottled waters are high innitrate and/or sodium. One bottled water for example contains 42 mg/litre of nitrate.The permitted maximum nitrate level in tap water is 50 mg/litre but only rarely is thisfigure reached. There is no legal limit for nitrate in bottled water.

25 Using water and saving waterThe answer will depend largely on personal habits. Check your own intake againstfigures in the table.

Ways of saving water: if you use electricity for cooking, use a jug kettle in whichless water can be boiled than in a conventional kettle. Replace washers on drippingtaps. Place some large pebbles in WC cisterns to lower amount of water used at eachflush. Install a water heater by the kitchen sink so that you have instant hot water anddo not have to wait for the water to run hot. (Clearly although this may save somewater it may not be a very sound financial investment.)

The price of bottled water will vary. Some bottled water is more expensive thanpetrol!

26 Where does your water come from?The west side of the UK receives the highest rainfall and is a useful water collectingarea for many towns and cities. As you move east a greater amount of water is takenfor water supply from rivers and deep boreholes.

27 Borehole versus reservoir waterIt is generally considered that water which has filtered through the ground has hadcontaminating material removed from it. While this is still true with regard toinsoluble material which can be filtered off, many soluble compounds can remain.Some of these (eg nitrate) are a cause for concern. Water collected in reservoirs isseen to be exposed and vulnerable to pollution, but to a lesser extent than rivers.Water from the latter sources is subject to a greater degree of purification than waterfrom boreholes.

28 Boiling points and melting points (at atmospheric pressure)Boiling point of oxygen is -183.0 0CMelting point of oxygen is -218.4 0CBoiling point of water is 100.0 0CMelting point of water is 0.0 0C

29 Floating a paper clipThe surface tension (or ‘skin’) supports the paper clip. Detergent lowers the surfacetension of water and the paper clip will no longer be supported.

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30 Life and iceOrganisms ‘higher’ than microorganisms would probably not live because thechances of large masses of water melting after they had been frozen would probablybe very low (see text). In addition any aquatic life would be trapped and frozenbeneath the ice so removing a source of food and oxygen. Life in countries borderingthe equator would extend further in time but eventually would probably be overtakenby a water shortage.

31 The structure of three types of rockA layering effect can often be detected in sedimentary rocks. Examples are shale,slate and some sandstone and limestone.

32 Permeability of rocksSedimentary rock is the most permeable. Igneous rock is the least permeable.Sedimentary rocks are best for water storage.

33 Testing rocks with acidRocks containing calcium carbonate will produce bubbles of carbon dioxide whenvinegar (acetic acid) is applied. These rocks will often be made of chalk or limestone.

34 Shaking soil and waterThe number of layers will depend on the soil sample. There is nearly always a layerof humus floating on the top.

35 Looking at sandSome particles will be angular, some round and the colour of individual grains willnot always be the apparent colour of the total mass of sand.

Testing with acid. Some sand will react with acid and bubbles of carbon dioxidewill be given off. Some sand contains a high proportion of broken up animal shell iecalcium carbonate.

36 Copper alloysOver the years more than 500 alloys containing copper have been developed forvarious uses. List of some alloys: Brass – copper ca 65 per cent and 18-35 per centzinc; Bronze – copper ca 80 per cent and 5-20 per cent tin and possibly a little zincand/or lead; Nickel silver – copper ca 60 per cent, zinc 20 per cent and nickel 20 percent; Monel metal – copper 32 per cent and nickel 65 per cent; German silver –copper 55 per cent, nickel 25 per cent and zinc 20 per cent (used for ornaments);9 carat gold – copper 66.5 per cent and gold 33.5 per cent (pure gold is 24 carats);Phosphor bronze – copper 94 per cent, tin 5.7 per cent and phosphorus 0.3 per cent(used for clock springs); Gun metal – copper 88 per cent, tin 10 per cent and zinc2 per cent.

37 Melting iceThe cubes initially have the shape of the container in which they were frozen. As thecubes melt and their volume diminishes the water spreads over the bottom of thepan. The water takes on the shape of that container, the liquid finding its own level.Continued heating produces water vapour which fills the saucepan completely. It canbe allowed to spread throughout the room or trapped in the pan by putting a lid on.



38 Steamy windowsIf the windows of a kitchen are fairly cold water vapour coming into contact withthem will condense on the glass and form droplets. Some of the droplets may thenjoin together and form a trickle of liquid water. When a cold lid is put over asteaming saucepan a similar effect can be observed.

39 Ice and salt.If salt (sodium chloride) is added to ice a ‘cooling mixture’ is obtained which canproduce a temperature as low as -21 0C.

The salt dissolves in any film of water on the ice producing a system containingsolid salt, ice and salt solution. Salt has the appearance of causing ice to ‘melt’.

40 Wax in a mouldWax will fall out of a mould fairly easily because as the liquid wax cools the volumeof the wax contracts.

41 Cooling ef fect of methylated spiritsMethylated spirit vaporises easily but to do so it requires heat. If ‘spirit’ is put on theback of the hand heat will be drawn from the area of skin around the spot, hence a‘cooling’ effect on the hand will be felt.

42 Ice cubes in waterThe water does not turn to ice provided it is not put back into the refrigerator becausea balance is reached between ‘room heat’ melting the ice (and preventing the coldwater getting colder) and the ice staying frozen (and turning incoming water to ice).

43 Frozen milkWhen the water component of milk freezes it occupies a larger volume than theoriginal liquid. This larger volume cannot be contained in an otherwise full bottleand so the foil cap is forced off.

44 Kitchen equipmentColander – aluminium or enamelled steel. Washing up bowl – enamelled steel.Pastry cutters – tinned steel. Measuring jug – glass or pottery. Cutting board – wood.Cruet – pottery or wood.

45 Storing saltSalt ‘attracts’ moisture which can cause it to form into a hard mass and prevent itfrom flowing freely. Damp salt is also highly corrosive so metal containers are of nouse. Wood and unglazed pottery are used because these materials can removemoisture by acting like blotting paper, a process known as capillary action.

46 Looking at synthetic and natural fibresSynthetic fibres have smooth surfaces; natural fibres are much rougher. Smooth fibreswill not absorb as much moisture as natural fibres, so synthetic fibres dry morequickly.

47 Biodegradable plasticsBiodegradable plastics cannot be recycled because they break down before or duringreformation into another item. So valuable oil or gas and energy used in theirproduction is lost. If biodegradable plastic becomes mixed with undegradable plasticthe items formed will be of a poorer quality and hence unsuitable for recycling.

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48 Glucose and starchOf these three carbohydrates castor sugar is usually considered by humans to be thesweetest tasting compound.

49 Chemical elementsThe table of elements at the back of this book will help. Many modern materials aremade of chemical compounds. All compounds are made from chemical elements.

50 How to separate the gases in airTo do this you have to use the process of distillation (see text). In practice the air isfiltered to remove suspended particles such as those of soot and pollen. It is thencompressed and cooled to turn it into liquid air. Using distillation different gases areboiled off at different temperatures. Clearly the amount of heat applied has to be verycarefully controlled.

51 A gas producing reactionThis reaction produces sulphur dioxide gas. NEVER smell any gas by deep inhalation.Waft some of the gas towards you by moving your open hand.

52 Fizz from ‘Andrews’Very few people would say that carbon dioxide had a smell. Sometimes it ‘takes on’the smell of the container it is in. If you smell ‘Andrews’ when the bubbles of carbondioxide are escaping quickly, you may think it smells or feels ‘tingly’ but this is theeffect of the small droplets or aerosol on the lining of the nose. Sulphur dioxide ismore soluble in water than carbon dioxide.

53 Metal in ‘magnesia’Acid in the stomach reacts with the magnesium hydroxide. This compound containsthe metallic chemical element magnesium which as far as we know is harmless tohumans.

54 Beetroot juice no longer beetroot colourThe colour changes from red to blue. Hydroxide (OH–) ions are present.

55 Chemical items around the homeA useful place to look is on food packets. Reference to chapter 8C will help indicatewhich salts come from which acids.

56 Red cabbageUse of pickled red cabbage juice as a pH indicator. By and large indicators tendtowards red colour when a solution is acidic in character. (The pH will lie between0.0 – 6.9.) Lemon juice will cause a reddish colour to be produced.

57 Chemicals produced by a petrol engineAn electric spark ignites the petrol vapour which causes a mini-explosion in eachcylinder. The chemicals produced include carbon monoxide, oxides of nitrogen,water and carbon dioxide. The carbon monoxide and oxides of nitrogen can bechanged to different gases by the use of catalytic converters. The most common ofthese are those containing a mixture of platinum, palladium and rhodium spread overa honeycomb shaped ceramic core. The platinum and palladium convert carbonmonoxide and hydrocarbons to carbon dioxide and water. Rhodium convertsnitrogen oxide to nitrogen and water. The converters work most efficiently with an airto fuel ratio of 15 : 1.



58 Making the spoon blackThe black soot is almost pure carbon. The amount of soot produced depends on thecandle wax formulation. Some candles produce a lot of smoke and therefore a lot ofsoot. A good candle produces very little. The water comes from the water vapourproduced by burning the candle. The material ‘lampblack’ which is used, in makingcar tyres and black printing ink is made by burning ‘smoke producing oil’ andcollecting the smoke and vapours.

59 Rising cakesWhen cakes rise the raising agent, sodium hydrogencarbonate (bicarbonate of soda),is heated by the oven. New substances are formed: sodium carbonate, water andmost importantly carbon dioxide. The carbon dioxide is a gas and as it is produced itmakes the cakes rise caused by the gas bubbles rising in the mixture. The othersubstances don’t harm the taste – thank goodness! (Sometimes baking powder isused, this contains cream of tartar (potassium hydrogentartrate) in addition to sodiumhydrogencarbonate.)

60 Fermentation gasesCarbon dioxide is produced by fermentation and this is the gas which gives drinks thecarbonated or ‘bubbly’ effect. Fermented drinks produce the carbon dioxidethemselves. Non-fermented carbonated drinks have the gas added. Some fermenteddrinks have extra gas added.

61 Making yoghurtAll information is in the text.

62 Cars by the seasideSalt (sodium chloride), does speed up corrosion. Sea salt contains more salts than justsodium chloride, so quite a cocktail of chemicals can attack the cars owned bypeople who live near the coast.

63 Magnetic attractionThe list might include the steel parts of cutlery, stainless steel dishes and saucepansand parts of most tools. Paint is a way of preventing corrosion. Aluminium corrodesbut the oxide that forms retards further corrosion. ‘Iron oxide’ (rust) does not preventfurther attack.

64 Gases formed during electrolysisThis is a very common occurrence. The ions present in a solution of sodium chlorideyield, on electrolysis, hydrogen and chlorine. Salt and water can both split into ionsand the products will include two gases, chlorine at the positive (+) electrode andhydrogen at the negative (-) electrode. These will bubble up and escape.

65 Oxidation and reductionA book written for GCSE level (or equivalent) will provide the information. In theblast furnace the iron oxide in the iron ore is REDUCED to metallic iron.

66 Oxidation and reduction and aluminium extraction.Reduction takes place at the negative electrode where aluminium is formed andoxidation at positive one where oxygen is given off.

67 Your breath – now you see it, now you don’ tWhen you breathe out you expel water vapour. When you breathe out over the top

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of a freezer the water vapour is condensed and forms droplets of water. Visible steamis a collection of water droplets.

68 Names and symbols of the chemical elements.There is a list of these at the back of this publication. There are many more there thanmost people will recognise. Some of the very rare elements have only existed for ashort time and under special conditions. What is important is that they did exist andthat they performed as predicted.

69 Looking at graphite.When you look at your pencil check to see how the amount of blackness or graphiteis quantified. A 3B pencil is ‘blacker’ than a 2B pencil. Graphite rods are similar topencil leads but many times larger, and are used in the control of nuclear reactors inpower stations.

70 Taking apart an atom.The electrons are found on the outside of the atom so are the ‘easiest’ to remove andsome of them are removed during chemical reactions.

71 Steel can.Steel cans contain iron which is magnetic therefore cans containing iron will beattracted to a magnet; others will not. Some cans have steel cylinders and aluminiumends, so beware!

72 Water, ruler and jumper .Rubbing the ruler gives it an electrical charge. The water is attracted by the charge sothe water trickle bends towards the ruler.

73 Bottled mineral water .The number of ions will vary from one source to another. A GCSE level chemistrybook (or equivalent) would be a suitable text.

74 The chemical formula of sodium hydrogencarbonate.If you compare these words with the information in the table of elements andsymbols at the end of the book you will see that sodium is Na and hydrogen is H.Carbonate is a bit more difficult but to associate it with carbon, C would not be toofar out. The actual formula is NaHCO3.

75 Diamonds are forever ..but they could be turned to graphite.Both diamonds and graphite are forms of carbon. Diamond exists at a higher energylevel (see chapter 3C) and graphite at a lower level, so diamonds could be turned tographite. Fortunately the activation energy is so high that only someone who was nota ‘girls’ best friend’ would take the trouble to supply so much energy.

76 Carbon-14 dating.This method of dating material was developed by Libby in the late 1940s. Carbon-14is a radioactive isotope of carbon (carbon-12 is the more usual non-radioactive form)and the method depends on the rate of decay of this isotope for its usefulness.Carbon-14 is formed in the atmosphere by cosmic rays and like ordinary carbon-12combines with oxygen to produce carbon dioxide. During photosynthesis plants willtake in carbon dioxide, some of which will contain the carbon-14 isotope. Itemsmade from vegetation will therefore have carbon-14 ‘trapped’ in them. Similarly,animals eating vegetation either directly or indirectly will absorb carbon-14. There is,



therefore, an interchange of carbon-12 and carbon-14 with the environment and aconstant ratio is established. When plants and animals die the ratio begins to changebecause all the time carbon-14 is losing its radioactivity through the process calledradioactive decay. Scientists know the rate of decay and the ratio of carbon-14 tocarbon-12. From this they can date, by calculation, the approximate age of certainobjects. Libby himself agrees the system has limitations and proposed dates needchecking, but the method has been very useful.

and the T urin shroud...Most scientists now consider that the Turin shroud is not as old as has been claimed;some disagree. Others say it doesn’t matter anyway if believers like to think of it asbeing very old. What do you think?

the royal society of chemistry contents · 2015-11-25 · 1. food iii the royal society of...

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