K e y S t a g e 3 S c i e n c e

Transcription

1 Key Stage 3 Science

2 Series editors Consultant Authors Andy Cooke Jean Martin Sam Ellis Doug Wilford David Acaster Derek Baron Trevor Bavage Andy Cooke David Fagg Kevin Frobisher Jean Martin Mick Mulligan Doug Wilford PUBLISHED BY THE PRESS SYNDICATE OF THE UNIVERSITY OF CAMBRIDGE The Pitt Building, Trumpington Street, Cambridge, United Kingdom CAMBRIDGE UNIVERSITY PRESS The Edinburgh Building, Cambridge CB2 2RU, UK 40 West 20th Street, New York, NY , USA 477 Williamstown Road, Port Melbourne, VIC 3207, Australia Ruiz de Alarcón 13, Madrid, Spain Dock House, The Waterfront, Cape Town 8001, South Africa Cambridge University Press 2004 First published 2004 Printed in Dubai by Oriental Press Typeface Delima MT System QuarkXPress A catalogue record for this book is available from the British Library ISBN paperback Material in this book was previously published in Spectrum Year 7 Class Book (pp ), Spectrum Year 8 Class Book (pp ) and Spectrum Year 9 Class Book (pp ). Cover design by Blue Pig Design Co Page make-up and illustration by Hardlines Ltd, Charlbury, Oxford NOTICE TO TEACHERS It is illegal to reproduce any part of this work in material form (including photocopying and electronic storage) except under the following circumstances: (i) where you are abiding by a licence granted to your school or institution by the Copyright Licensing Agency; (ii) where no such licence exists, or where you wish to exceed the terms of a licence, and you have gained the written permission of Cambridge University Press; (iii) where you are allowed to reproduce without permission under the provisions of Chapter 3 of the Copyright, Designs and Patents Act 1988.

3 Contents Introduction Page vii Unit 7E Acids and alkalis 1 7E.1 What acids and alkalis are like 1 7E.2 Telling acids and alkalis apart 5 7E.3 Universal indicator and the ph scale 7 7E.4 Neutralisation and the rainbow experiment 9 7E.5 Where neutralisation is important 11 Unit 7F Simple chemical reactions 15 7F.1 Chemical reactions 15 7F.2 Reactions between acids and metals 16 7F.3 Reactions between acids and carbonates 17 7F.4 Reactions when substances burn 18 7F.5 Reactions when fuels burn 20 7F.6 Looking at a candle burning 22 Unit 7G Particle model: solids, liquids and gases 25 7G.1 Looking at and thinking about substances 25 7G.2 Thinking about theories 26 7G.3 A closer look at solids, liquids and gases 28 7G.4 Some evidence for the particle theory 29 7G.5 Using the particle model 32 7G.6 More uses of the particle model 36 Unit 7H Solutions 39 7H.1 Mixing solids and liquids 39 7H.2 Salt of the Earth 42 7H.3 The mystery of the disappearing solute! 43 7H.4 Separating solvents from solutes 45 7H.5 Chromatography 47 7H.6 Solubility 49 Unit 8E Atoms and elements 53 8E.1 Materials 53 8E.2 What the elements are like 55 8E.3 How we get all the other materials 60 8E.4 Representing the changes 62 Unit 8F Compounds and mixtures 65 8F.1 Elements and compounds 65 8F.2 Looking at compounds 67 8F.3 Compounds and some of their reactions 68 8F.4 What is a mixture? 69 v

4 Unit 8G Rocks and weathering 77 8G.1 Rocks vary 77 8G.2 Rock and rain 78 8G.3 Rocks and temperature changes 81 8G.4 Moving weathered pieces of rock 83 8G.5 Why sediments form layers 84 Unit 8H The rock cycle 89 8H.1 How sedimentary rocks form 89 8H.2 Limestones are not all the same 91 8H.3 Rocks are sometimes changed 92 8H.4 Rocks formed from molten magma 94 8H.5 Recycling rocks 97 Unit 9E Reactions of metals and metal compounds 99 9E.1 Why are metals useful? 99 9E.2 Reacting metals with acids 102 9E.3 Reacting metal carbonates with acids 104 9E.4 Reacting metal oxides with acids 105 9E.5 More about salts 106 Unit 9F Patterns of reactivity 111 9F.1 What happens to metals? 111 9F.2 Metals and water 112 9F.3 Reactivity of metals with acids 114 9F.4 Metals and oxygen 115 9F.5 Displacement reactions 116 9F.6 Sources and uses of metals 119 9F.7 Investigating metals and acids further 123 Unit 9G Environmental chemistry 126 9G.1 Are soils different from each other? 126 9G.2 Acid rain 128 9G.3 What causes acid rain 131 9G.4 Can we reduce the amount of acid in the rain? 132 9G.5 Is global warming really happening? 137 Unit 9H Using chemistry 141 9H.1 What chemical reactions take place when fuels burn? 141 9H.2 Chemical reactions as energy resources 146 9H.3 What new materials can chemical reactions make? 149 9H.4 Atoms and molecules in new materials 151 Scientific investigations 156 Glossary/Index 164 Acknowledgements 174 vi

5 7E Acids and alkalis In this unit we shall be finding out about acids and alkalis and how to recognise them. We shall also look at some uses of acids and alkalis and at neutralisation reactions. 7E.1 What acids and alkalis are like Acids are all around us It is amazing how many things around us contain acids. Some acids are in the food we eat. We use acids to make things work properly and to make all sorts of useful items. Some acids are harmless, but others are very dangerous. Fruit or drinks made from fruit often contain acids. They have a tangy, sharp taste. We say acids taste sour. 1 Look at the picture. Write down a list of substances that contain acids. 2 Write down: Limes and lemons taste sour because they contain citric acid. Lemons and limes prevent scurvy because they contain vitamin C. Vitamin C is also an acid, but it is a very weak acid. a one word that best describes the acid taste of lemon juice; b the name of the acid that gives lemon juice this taste. 3 a What is the name of the other acid in limes and lemons? b What disorder does this acid help to prevent? KEY WORDS acid sour hydrochloric acid hazard corrosive dilute harmful irritant risk alkali sodium hydroxide extract indicator full-range universal indicator ph scale neutral react neutralisation salt indigestion Unit 7E 1

6 Some acids are dangerous Not all acids are the same. Fruit juice is not dangerous but there are some acids that can be risky to use. Substances like hydrochloric acid have their own hazard warning sign. Hazard warning signs let people know that they need to be careful. People who use hazardous chemicals must protect themselves and others. The particular hazard of hydrochloric acid is that it is corrosive. This means that it will immediately attack your skin and start eating it away. The hazard warning sign shows this. 4 Look at the hazard warning sign for hydrochloric acid. What does the word corrosive mean? CORROSIVE Hydrochloric acid you need to be very careful. If you get hydrochloric acid on yourself, you should wash the area with lots of water. When you mix acid with water, we say that you dilute it. This makes the acid less dangerous. You also need to be careful with dilute hydrochloric acid. Dilute acids are harmful or irritant, so we use a black cross to warn people about their risks. 5 If you spill hydrochloric acid on your skin: a what can happen? b what do you need to do? Explain your answers. i This is the sign for an irritant. 6 Why must you always wear eye protection when you use hydrochloric acid? This is the sign for a harmful substance. 2 Unit 7E

7 About alkalis The group of chemicals shown in the picture are not acids but they do react with acids. These substances are alkalis. When acids and alkalis react, their properties are cancelled out. We make soap using alkali and oils. Your skin contains oils. When you get alkali on your skin, your skin oils react with the alkali and your skin feels soapy as it dissolves away. We call the wound a chemical burn. All these substances contain alkalis. 7 Make a list of household substances which contain alkalis. Some alkalis are safe to use. Others, such as sodium hydroxide, are just as dangerous as the strongest acids. Alkalis can be dangerous. These burns were caused by caustic soda. Caustic soda is also known as sodium hydroxide. 8 What is the hazard symbol on the bottle of bleach? 9 What do you need to do if bleach accidentally gets into your eyes? 10 Why do you need to show the label to the doctor if you accidentally swallow some bleach? THICK BLEACH CONTAINS SODIUM HYDROXIDE. Irritating to eyes and skin. Warning Do not use with other products. May release dangerous gases (chlorine). Store upright in a cool safe place away from babies, children and animals. Avoid contact with skin and eyes. In case of contact with eyes, rinse immediately with plenty of water and seek medical advice. After contact with skin wash immediately with plenty of clean water. IF SWALLOWED SEEK MEDICAL ADVICE IMMEDIATELY AND SHOW THIS CONTAINER LABEL. Unit 7E 3

8 Uses of acids and alkalis We find acids and alkalis in many natural substances. The chemical industry makes millions of tonnes of acids and alkalis every year. Car battery We use acids and alkalis to make many useful materials. 11 Name the acid or alkali used to make: a car batteries; b explosives; c soap; d fertilisers. 4 Unit 7E