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CHAPTER 13 – ATOMS AND CHEMISTRYCONCEPT MAP - ATOMS

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ATOM

ELECTRONSnegative charge

NUCLEUSpositive charge

has massive central

PROTONSpositive charge

NEUTRONSno charge

has very light orbiting

ATOMIC NUMBERof element

has parts has parts

ATOMIC MASSof element

ISOTOPESof element

combined number gives number gives

RADIOACTIVITY NUCLEAR FISSION NUCLEAR FUSION

slow breakdown gives

fast breakdown gives combining gives

NUCLEAR POWERATOMIC BOMB

ALPHA-RAYSBETA-RAYS

GAMMA-RAYS

STARS

gives out used insource of energy in

CHEMICAL REACTIONS

NON-METAL ELEMENTSMETAL ELEMENTS

POSITIVE IONS NEGATIVE IONS COVALENT BONDS

responsible for

lost by gained or shared by

lose electrons to form

gain electrons to form

share electrons to form

varying number causes

of of

IONIC COMPOUNDS

form VALENCY combining power

FORMULAECHEMICAL EQUATIONS

number lost, gained or shared determines

determines

used to write

MOLECULES

form

represented by

INTRODUCTORY NOTES

Chapters 13 to 18 are aimed at students in the third or final year of junior secondary or middle school. For some students, this will be the last year in which they will study science. With this in mind, I have tried to cover those aspects of science and technology that I believe all citizens in a scientifically and technologically literate society ought to know and understand, or at least be aware of. For other students, this year will be a preparation for higher level studies in science and I have tried to keep their needs in mind too. Teachers should be aware that students who are not going to be future scientists may find some aspects of some topics to be difficult. For these students it will often be sufficient to aim for awareness of the ideas and phenomena concerned, rather than mastery of them, and to adopt a qualitative rather than a quantitative approach.

Chapter 13 will be the last chapter in this book to deal mainly with chemistry. For some students it will not be an easy chapter and Chapter 9 should be regarded as a pre-requisite. The first seven modules relate to atoms and are somewhat theoretical. It may not be practicable for most teachers to provide hands-on activities for their students, however the use of clear drawings (on a board or on home-made wall charts) and simple models (for example with plasticine or small fruits joined with toothpicks) can help to make ideas easier to understand. Teachers should try to relate the work to students’ existing knowledge, experience and interests whenever possible. For example, students may have been X-rayed or may be aware of controversies regarding nuclear contamination and so on. Plenty of ongoing oral interaction with your students, and between students working together in small groups, will help to clarify difficult ideas and make them more accessible. By contrast, the next three modules concerning acids and bases represent the sort of practical school chemistry familiar in traditional chemistry courses. All the suggested practical activities should either be carried out by the students themselves or demonstrated by the teacher. Finally, the last eight modules are intended to make students aware of the vital role that the chemistry of carbon plays in living things and of how the chemical industry uses substances obtained from the Earth’s crust to manufacture the many useful materials that we take for granted in the modern world including fuels, plastics, metals, ceramics and concrete. A supplementary module (13.17) is not part of the program; it has been added as additional reading for students who may be interested in chemistry.

13.1 ATOMIC STRUCTURE – PROTONS, NEUTRONS AND ELECTRONS

Aims: To review relevant prior knowledge from Chapter 9 concerning elements and atoms. To inform students about the basic structure of atoms and the nature of protons, neutrons and electrons. To give students an overview of the coming chapter.

Activities: Review previous work on elements and atoms, especially Modules 9.4/5 and Appendix B. Stress the

small size of the atom and the fact that interactions between atoms are at the core of all the chemical reactions. Emphasise that all life processes and all technological process depend on these reactions.

Introduce the basic ideas of atomic structure. Use any suitable models and charts that may be available but do not overelaborate on the simple model given in the textbook. Make sure that students understand that like charges repel one another and unlike charges attract one another. Stress that (i) almost all the mass of an atom resides in the nucleus (a proton or a neutron has a mass almost 2000 times greater than that of an electron), (ii) every element has its own fixed number of protons in the nucleus, (iii) for every proton in the nucleus there is an orbiting electron, and (iv) electrons control the chemistry of elements.

Give students a very general overview of the work they will cover in the remainder of this chapter. Encourage students to try the questions at the end of the module. Follow up by discussing their

attempts. Make sure they are aware of, and understand, the correct answers.

Answers: Q1. (i) The nucleus of an atom is the central part of the atom. It consists of protons and neutrons and

accounts for almost the whole of the mass of the atom. (ii) A proton is a tiny, heavy, sub-atomic particle with a positive electric charge; it is found in the nucleus of an atom. (iii) A neutron is a tiny, heavy, sub-atomic particle with no electric charge; it is found the nucleus of most atoms. (iv) An electron is a tiny, light, sub-atomic particle with a negative electric charge; it orbits around the nucleus of an atom. (v) A

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proton or a neutron is almost 2000 times heavier than an electron. (More exactly, a proton has the mass of about 1836 electrons, and a neutron has the mass of about 1839 electrons!).

Q2. (i) The nucleus (which contains 7 heavy particles) is mainly responsible for the mass of the lithium atom. (ii) The electrons orbiting the nucleus are mainly responsible for the way the lithium atom interacts with other atoms (that is, for the chemical reactions of lithium).

13. 2 THE NUCLEUS 1 – ATOMIC NUMBER, ATOMIC MASS AND ISOTOPES

Aim: To help students understand the meanings of atomic number (represented by Z), atomic mass

(represented by A), and isotope.

Activities: Discuss thoroughly the material presented in the textbook, section by section, adding additional

examples that you think will interest your students. Use simple drawings/charts/models as available. Encourage students to try the questions at the end of the module. Questions 4 and 5 are important and

would be particularly suitable for discussion by students in small groups. Follow up by discussing their attempts. Make sure they are aware of, and understand, the correct answers.

Answers: Q1. (i) The atomic number of an element is the number of protons in the nucleus of one atom of the

element. (ii) The atomic mass of an element is the mass of one atom of the element compared to the mass of one atom of hydrogen. (Alternatively, it is the mass of one atom of the element on a scale such that the atomic mass of the common isotope of carbon is exactly 12). (iii) Isotopes are atoms of the same element with different atomic masses (owing to different numbers of neutrons).

Q2. Hydrogen is the element with the fewest neutrons in its atoms; 99.9% of hydrogen atoms have no neutrons at all!

Q3. Atomic number Z=1 for hydrogen; Z=6 for carbon; Z=8 for oxygen; Z=14 for silicon and Z=79 for gold (this information can be obtained from Appendix B).

Q4. If you subtract the atomic number Z, from the atomic mass A, you will get he number of neutrons in the nucleus. (Z is the number of protons in the nucleus and A corresponds to the total number of protons and neutrons in the nucleus).

Q5. If you subtract the atomic number of zinc (30) from its atomic mass (65.4) the answer ( 35.4) should be the number of neutrons. However you can’t have .4 of a neutron! Therefore zinc must have more than one common isotope and 65.4 must be the average atomic mass. [Students may be interested to know that zinc is unusual in having as many as five significant isotopes. They have atomic masses of 64 (48.6% of atoms), 66 (27.9%), 67 (4.1%), 68 (18.8%) and 70 (0.6%) which average out to 65.4].

13.3 THE NUCLEUS 2 – RADIOACTIVITY

Aims: To help students to know and understand the basic facts about radioactivity and ionising radiation. To inform students about radio-isotopes and the ways in which they are used.


examples that you think will interest your students. Some aspects of the work (for example ionising radiation, radioactive decay, and the uses of radio-isotopes) could be allocated to small groups of students to discuss, follow up and report back to the class on.

Encourage students to try the questions at the end of the module. Follow up by discussing their attempts. Make sure they are aware of, and understand, the correct answers.

Answers: Q1. (i) Alpha rays are fast moving alpha particles consisting of two protons and two neutrons bound

together. Beta rays are fast moving electrons. Gamma rays are very energetic electromagnetic rays. (ii) Ions are electrically charged atoms or groups of atoms. (iii) A Geiger counter is a device that detects ionising radiation by making clicks when radiation enters a window at the end of a tube. (iv)

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Background radiation is the natural ionising radiation that we are exposed to from the world around us. (v) Radioactive decay is the breakdown of the nucleus of a radioactive isotope, usually by emitting an alpha or a beta particle. (vi) Radioactive tracers are isotopes used to follow the movement of atoms in an organism or other system.

Q2. Ionising radiation is very dangerous because the energy it carries and the ions it creates damage or destroy living cells. People can be protected by (i) keeping sources of ionising radiation in lead containers, (ii) using ionising radiation behind lead screens, (iii) wearing protective clothing, and (iv) wearing monitoring devices such as film badges or scintillation detectors that can warn them if they are in a danger from radiation.

Q3. 7/8 of the 234Pa will have decayed after 3 days. (After one day, half will decay; after 2 days, half of the remaining half will decay making ¾ in total; and after 3 days, half of the remaining quarter will decay making 7/8 in total).

Q4. Animal remains can be dated using radio-carbon dating. While the animal is alive, it constantly replaces the natural proportion of radioactive 14C atoms in its body through the food chain when it eats plants (or other animals that have eaten plants). When it dies, the 14C atoms are no longer replaced and they decay with a half-life of 5730 years. By measuring how much of the 14C has decayed, scientists can estimate how long ago the animal died.

13.4 THE NUCLEUS 3 – NUCLEAR FISSION AND NUCLEAR FUSION

Aims: To help students to know and understand some basic information about nuclear fission (including the

example of 235U), the idea of a chain reaction, and the use of nuclear fission in the atomic bomb and in nuclear power stations.

To make students aware of basic idea of nuclear fusion as the process that generates energy in stars.


examples that you think will interest your students. As regards nuclear fission, stress the concept of the chain reaction; an analogy with human interactions may be helpful (where ‘positive feedback’ means that one thing leads to another and another and another so a small event blows up out of all proportion!).

As regards nuclear fusion, stress the potential value of controlled fusion as a cheap source of energy. Encourage students to try the questions at the end of the module. Follow up by discussing their

attempts. Make sure they are aware of, and understand, the correct answers.

Answers: Q1. Similarities as between nuclear fission and fusion: both are reactions of nuclei; both reactions

produce large amounts of energy in the form of heat, light and gamma rays; both reactions result in the production of isotopes of new elements. Differences as between nuclear fission and fusion: fission involves breaking down the nucleus producing isotopes of lighter elements but fusion involves the joining of nuclei producing isotopes of heavier elements; fusion produces more energy than fusion; (we can control fission reactions in nuclear power stations, but we cannot yet control fusion reactions).

Q2. A chain reaction is a reaction whose products initiate further reactions of the same kind (it is an example of positive feedback). An atom bomb uses enriched uranium with an increased proportion of 235U; when this isotope captures a neutron, fission occurs producing more neutrons which lead to an uncontrolled chain reaction. In a power station, the chain reaction is controlled by using (i) uranium that contains a lower proportion of 235U (so there are less nuclei to capture neutrons) and (ii) control rods to absorb some of the neutrons (so there are less neutrons to be captured).

13.5 THE ROLE OF ELECTRONS – IONIC AND COVALENT BONDING

Aims: To help students understand how the chemical behaviour of atoms is controlled by electrons (at a

qualitative level and without details of electronic configurations), referring to (i) the metallic lattice and electrical conduction, (ii) the contrasting behaviour of metal and non-metal elements, and (iii) ionic and covalent bonding in simple compounds.

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To reinforce the distinction between mixtures of variable composition as exemplified by alloys, and compounds of fixed composition that can be represented by definite formulae.

Activities: Start by reminding students of the basic ideas previously studied in Modules 9.4 – 9.7. Make sure

they are familiar with the idea of elements, with the symbols for the most common ones, and with the distinction between metal and non-metal elements. Get them to name the non-metal elements from their symbols in the box at the top right of the page. Go on to emphasise the idea that the electrons on the outside of atoms determine how they interact with one another - chemistry is controlled by electrons.

As regards metals, demonstrate electrical conduction (use the suggestions given in Module 4.3) and stress the idea that an electric current is a flow of electrons, that they carry a negative charge, and that the actual direction of flow is from negative to positive. Show them examples of common alloys such as brass and stainless steel and discuss the properties and uses of each. You could also discuss how the malleability (and ductility) of metals is explained by the fact that the positive ions tend to repel one another. They are only held together by the ‘cloud’ of negative electrons surrounding them and are relatively easy to displace and rearrange by hammering (or stretching). Balls of plasticine could be used to model lattices.

Important points to stress are the nature of ionic and covalent compounds, including their definite composition (and formulae) which should be contrasted with that of mixtures such as alloys. Show students examples of salt crystals and encourage them to make models of the NaCl lattice and of a few covalent molecules from balls of coloured plasticine, or small fruits with toothpicks for bonds.


Answers: Q1. (i) A lattice is a regular arrangement of particles (such as atoms, ions or molecules) in a solid.

(ii) An alloy is a mixture of two or more metals in varying proportions; a solid solution of one or more metals in another. (iii) An ionic compound is a compound of fixed composition composed of positive metal ions and negative non-metal ions. (iv) A molecule is a small group of atoms held together by covalent bonds. (v) A covalent bond is one in which two atoms share a pair of electrons.

Q2. An electric current is a flow of negatively charged electrons. The electrons flow from a negative terminal to a positive terminal.

Q3. Metal atoms can only form compounds by giving away electrons, creating positive metal ions and negative non-metal ions. Non-metal atoms can gain electrons from metals creating positive metal ions and negative non-metal ions, or they can share a pair of electrons with another non-metal atom creating a covalent bond.

13.6 THE NAMES, FORMULAE AND COMPOSITION OF SIMPLE COMPOUNDS

Aims: To introduce students to the naming of simple compounds, to a simple concept of valency as

combining power related to the exchange or sharing of electrons, and to show them how to use valency to work out the formulae of simple chemical compounds.

To introduce a simple concept of chemical radicals and to a few common examples of these. To show students how to calculate the percentage composition by mass of simple chemical

compounds using chemical formulae and tables of atomic masses.

Activities: Review Modules 9.6/7 and introduce students to the naming of simple, inorganic compounds

including the four radicals named in the textbook. Show students examples of as many compounds as possible. Stress that radicals do not exist alone, only as parts of compounds. Give students a list of formulae and ask them to name the compounds.

Introduce the concept of valency as combining power and relate this to the behaviour of electrons. Show them how to use valency to work out formulae and make sure that they understand the significance of the numerical subscripts in formulae. Help them to practice writing formulae from

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the names of simple compounds. Stress that compounds always have a fixed composition. The simple jigsaw game below may help students to understand how valency works.

Sow students how to calculate the percentage composition of a compound by mass, using the

example given in the text book. Give them additional examples to try, for example the percentage of iron in rust as Fe2O3 (70%), or the percentage of calcium in limestone (40%).


Answers: Q1. HCl, MgO, KNO3, AlCl3, Na2CO3, Cu(NO3)2, SO2, SF6, Al2O3

Q2. Ca 40%, C 12%, O 48% (see the calculation in table below)

13.7 CHEMICAL EQUATIONS

Aims: To help students learn to write balanced chemical equations for simple familiar chemical reactions. To show students how to calculate quantitative data concerning reacting quantities and yields from

chemical equations and tables of atomic masses.

Activities:

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Formula: CaCO3

Atomic masses: 40+12+(16x3)Formula mass: 100

% calcium: (40/100)x100 = 40%% carbon: (12/100)x100 = 12%% oxygen: (48/100)x100 = 48%

Na

Na

Cl

Cl

Ca O

To use this simple valency model, cut out shapes like these in stiff card. Colour and label them with symbols on both sides. Each ‘hump’ represents an electron being given away, and each ‘hollow’ represents a electron being gained or shared. It will soon be obvious that an Na needs one Cl, but a Ca needs two Cl. Similarly that an O needs one Ca, but two Na.

Review introductory work on equations in Module 9.8 and establish the basic form of the equations by writing word equations on the board. Use reactions that students are already familiar with.

Now substitute formulae in place of the names of chemicals. Go through the example given in the text book to establish the importance of balancing. Add examples of your own on the blackboard.

Finally, introduce the idea that balanced chemical equations provide quantitative information. Go through the example in the text book then work through examples of your own on the board.


Answers: Q1. (i) Not balanced (too many O atoms on the right). The balanced equation is:

2KNO3 2KNO2 + O2

(Note: Students often try to balance this equation by changing KNO2 to KNO. This is an opportunity to emphasise that formulae are fixed and unchangeable; KNO2 is the product formed when KNO3 is heated; it is called potassium nitrite; no substance exists with a formula KNO. When balancing equations, it is permissible only to add numbers in front of formulae. We can change the numbers of molecules or ions interacting, but not the formulae of substances).

(ii) Not balanced (too many O atoms on the right, and not enough H atoms). The balanced equation is:CH4 + 2O2 2H2O + CO2

(iii) Balanced. (Note: Ask students if they recognise this reaction! It is lime water – which is Ca(OH)2

in solution - going milky when CO2 is passed through it. The milkiness is caused by the CaCO3 which is insoluble).

Q2. 1 kg of iron makes 1.43 kg of rust.

The calculation is shown in the table on the right.

CONCEPT MAP – ACIDS AND BASES

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Equation: 4Fe + 3O2 2Fe2O3

Atomic masses: 4x(56) 2x[(2x56)+(3x16)]

Formula masses: 224 320

Mass rusting: 1 320/224

Answer: 1 kg 1.43 kg

ACIDS BASES

INDICATORS

SALT +

WATER (H2O)

METALOXIDES/HYDROXIDES

UNIVERSAL INDICATOR

H+ IONS OH- IONS

pH

change the colour of

mixture makes

neutralise each other forming

neutralise each other forming

changes colour of

measured by

solutioncontains

solutioncontains

are

13.8 INDICATORS AND THE pH SCALE

Aims: To inform students about acid/base indicators and introduce them to litmus and home made

indicators. To introduce students to the pH scale as a measure of relative acidity and show them how to use a

universal indicator and interpret the results.

Activities: Ask students what they know about acids and make a list any examples they know. Tell them about

the effect of acids on litmus (blue to red) and demonstrate this if possible. Include hydrochloric acid (available from hardware stores) as an example of a commercial acid. [Instructions for diluting hydrochloric acid are included at the end of Section 2 of the BS&T Equipment Lists].

Now show students that some substances have the opposite effect on litmus (red to blue) and tell them that these are called bases. Discuss and make a list of any examples they are familiar with, and demonstrate the reaction of some of these with litmus if possible. Include sodium hydroxide (available from hardware stores) as an example of a commercial base. [Instructions for making dilute sodium hydroxide are included at the end of Section 2 of the BS&T Equipment Lists].

Get students to collect coloured petals from one or two flowers and carry out the activity described under Making indicators in the students’ module; this could be a class activity or a demonstration. (Note that household ammonia or dilute sodium hydroxide solution give the better results as bases than sodium bicarbonate solution).

Describe the pH scale and demonstrate the use of universal indicator. (Do not try to explain the pH scale – that belongs in a much more advanced chemistry course). Stress that low values correspond to the strongest acids, that 7 corresponds to pure water (you can introduce the word neutral if you wish, but the idea of neutralisation is not introduced in the textbook until Module 13.10) and that higher values correspond to increasingly strong bases. If possible, conclude the lesson with a class activity or a demonstration using universal indicator (solution or paper) to test the pH of as many familiar solutions as possible.


Answers: Q1. (i) In indicator is a substance that changes colour with an acid or a base. (ii) A base is the

opposite of an acid; it changes the colour of indicators in the opposite way to acids (for example with litmus the change is red to blue for bases instead of blue to red for acids). (iii) Universal indicator paper is paper stained with a mixture of indicator solutions called universal indicator; when a drop of an acid or base is placed on the paper, the paper changes colour and the colour indicates the strength of the acid or base on the pH scale which goes from 0 for strong acids, to 7 for pure water, to 14 for strong bases.

Q2. (i) pH 13 is a strong base; (ii) pH 6 is a very weak acid (human saliva has a pH of about 6); (iii) pH 7 is pure water (or neutral); (iv) pH 2 is a fairly strong acid (but weaker than the acid in your stomach!); (v) pH 8 is a very weak base (sea water has a pH of about 8).

13.9 ACIDS AND BASES

Aims: To inform students about the characteristics of acids and bases and to introduce them to a few

examples of each, together with their uses. To make students aware (at a qualitative level only) of the role of water in relation to acids and

bases and the pH scale, and that solutions of acids are associated with hydrogen ions while solutions of bases are associated with hydroxide ions.

Activities: Discuss what students already know about acids and bases and establish the characteristics of each

as listed in the textbook. Show them samples of any acids and bases that are available and stress the

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dangers of strong acids and bases. Test any new solutions with litmus or pH paper. Make sure students are familiar with the names, formulae and uses of the acids and bases referred to in the text.

Discuss the role of water and of hydrogen and hydroxide ions as given in the textbook. Some students may find these ideas difficult. It is only necessary for most of them to grasp at the level of awareness that water plays a role, that hydrogen ions are associated with acids, and hydroxide ions are associated with bases.


Answers: Q1. Four characteristics of acids are: sour taste, corrosive, change the colour of indicators (in the

opposite way to bases), and produce hydrogen ions in solution. Four characteristics of bases are: soapy feel, caustic, change the colour of indicators (in the opposite way to acids), and produce hydroxide ions in solution.

Q2. When it dissolves in water, a base raises the pH by reacting with the water to remove hydrogen ions; at the same time the concentration of hydroxide ions rises.

Q3. (i) The pH is 1. [In the text we are told that water has an H+ ion concentration of 10-7 moles per litre and a pH of 7; and that strong bases have an H+ ion concentration of 10-14 moles per litre and a pH of 14. By analogy, if the H+ ion concentration is 10-1 moles per litre, the pH must be 1]. (ii) The concentration of H+ ions in sea water is 10-8 moles per litre. [In the text, the pH of sea water is given as 8, so the concentration of H+ ions must be 10-8 moles per litre – by analogy from the examples in part (i). Also in the text, we are told that sea water has ten times less H+ ions than pure water; pure water has 10-7 moles of H+ ions per litre, and a tenth of 10-7 is 10-8].

13.10 NEUTRALISATION AND SALT FORMATION

Aims: To introduce students to the idea of an acid being neutralised by a base and vice versa. To introduce students the idea of salts as the product, apart from water, produced during this reaction. To introduce students to the neutralisation of acids by carbonates. To make students familiar with simple practical methods for making salts from strong acids with both

soluble and insoluble bases and carbonates.

Activities: Demonstrate (or describe) the simple example of neutralisation given at the start of this module. Go

through the equation for this particular reaction and go on to establish the general equation. Discuss additional examples, including examples they can relate to.

Carry out the salt preparations described in the textbook, either as demonstrations or as class activities. [Hydrochloric and sulphuric acids, and sodium hydroxide can often be obtained from hardware stores; brief notes on the safe preparation of suitable dilute solutions – about 1 molar – are given at the end of Section 2 of the BS&T Equipment Lists]. Stress that the first method can be used with soluble bases and the second with insoluble bases. In the first method, the acid should be added a few drops at a time near the neutral point so as to avoid a significant excess of acid in the solution to be evaporated (this is less important with hydrochloric acid which also evaporates). In both methods, it is often best to allow the solution to evaporate slowly in a warm dry place. This often produces interesting crystals and avoids the decomposition that may occur when many salts are heated too strongly.

Generalise the idea of neutralisation to include the neutralisation of acids by carbonates, but stress that carbonates are not bases (the products are not a salt and water only).


Answers: Q1. (i) nitric acid, acid (ii) sodium sulphate, salt (iii) calcium hydroxide, base (iv) magnesium oxide,

base (v) calcium chloride, base (vi) lead carbonate, salt (note that carbonates are salts of a weak acid called carbonic acid, H2CO3 – they are not bases) (vii) aluminium oxide, base.

Q2. CaCO3 + 2HNO3 Ca(NO3)2 + H2O MgO + 2HCl MgCl2 + H2O

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Q3. Lead oxide is insoluble so the copper sulphate method applies. Add PbO to a little HNO3 in a beaker until no more dissolves. Decant or filter to remove the excess PbO, then evaporate the solution slowly by leaving it in a warm dry place.

PbO + 2HNO3 Pb(NO3)2 + H2O

13.11 CARBON – THE ELEMENT OF LIFE

Aims: To introduce students to the idea that carbon, originally obtained from the air by plants during

photosynthesis, is the basis of living organisms, and to make them aware of the nature, importance and uses of carbohydrates, lipids and proteins.

Activities: This is an advanced topic and at middle school or junior secondary level the intention should only be to

promote an awareness of, and interest in, the chemistry of life. The most suitable approach will depend your own and your students level of interest. Discuss with students the materials in the textbook and, as far as possible, link these up with relevant local knowledge and examples. Emphasise that all the carbon in living things was sequestered, in the first instance, by plants from carbon dioxide in the atmosphere through photosynthesis. Students should not be expected to remember details of formulae and molecular structures. However it would be appropriate to show them relevant samples such as starch (flour), table sugar (sucrose), cellulose fibres (for example look at the torn edge of a piece of paper with a hand lens or under the low power of a microscope), cellophane, cellulose acetate spectacle frames, domestic oils and fats, soap, cosmetics based on lipids, lean red meat as muscle protein, and so on.


Answers: Q1. Our bodies need … (i) … glucose as a source of energy through respiration. (ii) … cellulose for

fibre to provide bulk for our faeces. (iii) … lipids for storing energy and for constructing cell membranes. (iv) … proteins for growth of tissues and the repair of damaged tissues.

Q2. (i) Cellulose is used for making paper, fibreboard and plastics such as cellophane and cellulose acetate. (ii) Lipids are used in preparing foods, and in making soap, candles, perfumes and cosmetics.

Q3. (i) A polymer is a compound with molecules that consist of long chains of repeating units. (ii) A lipid is an oil or fat found in, or obtained from, a living organism.. (iii) A double bond is a covalent bond in which two pairs of electrons are shared between two atoms. (iv) Saturated fats are fats whose molecules do not contain double bonds between carbon atoms. (v) An amino acid is a compound with the following formula/structure (in which R represents a radical based on a chain of carbon atoms). C2H4O2NR – often partly expanded as NH2CHRCOOH, or more fully as illustrated:

Q4. Starch and cellulose have the same formulae, but they behave differently because they have different structures. In starch the glucose units are linked in a variety of different ways and the links are easily broken down. In cellulose the glucose units are firmly linked into long straight chains that are very hard to break down.

Note: The remainder of this chapter relates to aspects of the industrial chemistry including fuels, plastics, metals and ceramics. If any of these industries are carried out in your neighbourhood, and if it is practicable to do so, it would be very desirable to arrange to visit them with your students. This should be done as soon as possible after studying the topic.

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CONCEPT MAP – EARTH, CHEMISTRY AND INDUSTRY

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CALCIUM CARBONATE

METAL ORES

FOSSIL FUELS

COALOIL

EARTH’S CRUST

EARTH’S ATMOSPHERE

CARBON DIOXIDE

SUNLIGHT

CARBON COMPOUNDS IN PLANTS

(carbohydrates, lipids, proteins)

CARBON COMPOUNDS IN ANIMALS

(carbohydrates, lipids, proteins)

PLASTICSMETALSCONCRETE GLASS AND POTTERY

SILICA & SILICATES

HEAT AND ENERGY

INDUSTRY, TRANSPORT, ETC

photosynthesis

contains

food chains

make

used in

contains fossilised into

make make

fossilisedinto

make make

fossilised into

OLD STARS

90 ELEMENTS

nuclear fusion

planet formation

13.12 FOSSIL FUELS – COAL

Aims: To inform students about the formation and nature of coal, its mining and its importance as an industrial

fuel. To make students aware of the environmental and sustainability issues associated with the use of coal.

Activities: You could start by asking students where the electrical energy comes from that people and their

industries use every day all over the world. If possible show students samples of coal. Emphasise that this is the energy source that generates most of the world’s electricity; also that this energy ultimately comes from the sun and was stored by plants by photosynthesis hundreds of millions of years ago.

Run through the processes of coal formation and mining as outlined in the textbook, showing students samples of peat, lignite, coal and anthracite as available.

Stress the vast consumption of coal world wide and discuss the environmental and sustainability issues that this raises. Look out for magazine articles about these issues and discuss them with your class if possible. This is a good area in which to encourage students to research more detailed information.


Answers: Q1. (i) Coal is called a fossil fuel because it is the fossilised remains of prehistoric forests. (ii) Coal is

called a sedimentary rock because it was formed by the compression and consolidation of sediments in prehistoric wetlands and seas. Lignite is a soft, crumbly, brownish sedimentary rock containing 25 – 35% of carbon; coal is a hard black sedimentary rock containing more than 70% of carbon, and anthracite is a very hard, black metamorphic rock containing more than 90% of carbon.

Q2. Burning coal causes problems because (i) the product of combustion, CO2, is a greenhouse gas that causes the temperature of the Earth to rise; and (ii) impurities in the coal lead to the formation of acid rain that damages buildings and kills plants. To mitigate the CO2 effect there are plans for carbon capture and storage (CCS) whereby the gas is absorbed and stored instead of being released into the atmosphere. The technology for doing this is still at an early stage. To mitigate the acid rain, the smoke from power stations is processed to remove most of the sulphur and nitrogen oxides before it is released into the air. (To mitigate something means to try to minimise its effect).

13.13 FOSSIL FUELS 2 – OIL AND NATURAL GAS

Aims: To inform students about the formation, composition and mining of crude oil and natural gas. To inform students about the refining of crude oil by fractional distillation and about the nature and uses

of the main fractions. To make students aware of environmental and sustainability issues in relation to oil and natural gas.

Activities: Discuss the formation, mining and composition of crude oil as outlined in the textbook. If possible show

them a sample of crude oil (a sample of sump oil from the local garage, mixed with a little petrol, looks similar and would be an acceptable alternative). As regards the alkanes, draw their attention to the relationship between the number of carbon atoms and the boiling (and melting) point.

Discuss the refining of crude oil by fractional distillation as outlined in the textbook. Establish that the temperature in the fractionating column varies from about 400◦C at the bottom to the natural air temperature at the top, so that different components of the oil condense at different levels. Explain how the bubble caps help to mix the ascending gases and the condensing liquids. (A simple wall chart showing the refining of crude oil would be helpful – one with too much detail could be a distraction!).

Stress the vast consumption of oil world wide and discuss the environmental and sustainability issues that this raises. Look out for magazine articles about these issues and discuss them with your class if possible. This is a good area in which to encourage students to research more detailed information.


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Answers: Q1. (i) kerosene, (ii) diesel oil, (iii) natural gas or methane, (iv) petrol, (v) fuel oil. Q2. (i) CH4 + 2O2 2H2O + CO2

(ii) 2C2H6 + 3O2 6H2O + 4CO2 (Not so easy !)

13.14 PLASTICS

Aims: To inform students about the nature and properties of plastics and about the difference between

thermoplastics and thermosetting plastics (thermosets). To inform students about the chemical structure and uses of a few named thermoplastics, and about the

use of epoxy resin as an example of a thermoset. To make students aware of the advantages and disadvantages of plastics in relation to cost, properties

and sustainability and environmental issues.

Activities: Find out what students already know about plastics and start from there. Go through the first paragraph

in the textbook and have a good range of plastic objects ready to show them and discuss. Discuss the thermoplastics mentioned in the textbook. Supplement the discussion by showing students

samples of actual plastics. Models of molecules of plastics would also be useful. Discuss epoxy resins as examples of thermosetting plastics. If possible, demonstrate the use of a two-

part epoxy resin glue such as araldite rapid. Show them also how a fibrous material can be embedded in the glue before it sets. (Better still, if you have a fibreglass kit, you could demonstrate with that).

Finally discuss the pros and cons of plastics and make sure that students are aware of the sustainability and environmental issues involved. To show the serious nature of the pollution problem, you could get students to go around and see how many discarded plastic items (and how many different kinds of items) they can find. Emphasise that these objects (and many, many more) will still be there in 100 years because they do not decay!

Encourage students to try the questions at the end of the module. Follow up by discussing their attempts. Make sure they are aware of, and understand, the correct answers. Question 4 could be the basis for a class debate on the issues involved.

Answers: Q1. (i) A polymer is a substance whose molecules consist of long chains of repeating units. (ii) An

alkene is a member of a hydrocarbon series with the general formula CnH2n. (iii) An unsaturated organic compound is one whose molecules contain at least one double bond between carbon atoms. (iv) An initiator is a substance used to start a chemical reaction, particularly a polymerisation reaction. (v) A polymerisation reaction is a chemical reaction that results in the formation of a polymer. (vi) A thermoplastic is a plastic that softens on heating and can then be remoulded. (vii) Curing is the chemical process that occurs while a freshly made thermosetting plastic is hardening; chemical bonds are formed linking together the long chain molecules. (viii) Recycling means reusing an object or the material from which it is made (in order to avoid wasting resources). (ix) PVC stands for polyvinyl chloride.

Q2. The structure of polystyrene can be represented by the structural formula below (C6H5 represents the phenyl radical which consists of a ring of 6 carbon atoms).

… – CH2 – CH(C6H5) – CH2 – CH(C6H5) – CH2 – CH(C6H5) – CH2 – CH(C6H5) – …

Q3. Thermosets can not be remoulded because the long chain molecules are linked together by covalent bonds. (Chemical bonds are not easily broken by heating; if they are broken, then the substance is chemically changed into a different substance or substances).

Q4. Advantages of plastics: low cost, tough, light in weight, easy to make, colour and mould, resist corrosion and chemicals. Disadvantages of plastics: present industry unsustainable as it replies on non-renewable crude oil, rising cost as demand for crude oil overtakes supply, permanently litters and pollutes the environment and does not decay (even when buried in the ground!).

13.15 METALS FROM THE EARTH’S CRUST

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Aims: To inform students about the relative abundance of common elements in the Earth’s crust. To inform students about the occurrence of metals in the Earth’s crust and about two important

ways in metals are obtained from their ores as exemplified by iron and aluminium. To make students aware of the different uses to which iron and aluminium are put and of the

sustainability and environmental issues associated with them..

Activities: Discuss the relative abundance of common elements in the Earth’s crust and revise ideas from Chapter

9 about metal and non-metal elements. Find out what students already know about metals. Show them samples of as many different metals as

possible and discuss each of them. Discuss the information provided in the textbook leading to the idea of smelting by heating strongly in the presence of charcoal. (If you can get a lead compound such as red lead (Pb3O4) or white lead (PbCO3) from a builder of plumber, it is easy to demonstrate the smelting of lead. Put the ‘lead ore’ on a tin lid or saucer and put it into a hot wood fire. When the fire starts to die down, use tongs to find one or two pieces of hot charcoal in the fire, put them in contact with the lead ore, then build up the fire again. When it dies down you should find molten lead in the tin lid or saucer).

Go on to discuss the smelting of iron ore in a blast furnace as an example of how the majority of familiar metals are obtained. Similarly the smelting of aluminium by electrolysis. Discuss the uses of these two metals and the sustainability and environmental issues associated with making them.


Answers: Q1. (i) A radical is a group of atoms that occur together in compounds and that participate in chemical

reactions, but that do not exist alone. (ii) Reduction is the removal of oxygen from a metal oxide. (iii) A flux is a substance added to a solid to make it melt or dissolve. (iv) Slag is the top layer of the two liquid layers formed during the refining of many metals; the slag layer contains all the impurities. (v) An ore is a mineral from which a metal is extracted. (vi) Electrolysis is the process of splitting up of an ionic compound by passing electricity through it in a liquid state. (vii) Cryolite is a mineral form of sodium aluminium fluoride, Na3AlF6 . (viii) A native metal is a metal that occurs in an uncombined state.

Q2. Magnesium is the 6th most abundant metal in the Earth’s crust (remember that oxygen and silicon are non-metal elements so you cannot count them!).

Q3. To make 1 tonne of iron you need 1.4286 tonnes (1428.5 kg) of haematite and 0.1607 tonnes (160.7 kg) of carbon. (For the calculation, see the table below; start with the equation, look up the atomic masses in Appendix B, add up the formula masses, then calculate the answer).

13.16 CERAMICS, GLASS AND CONCRETE

Aims: To inform students about the materials and processes involved in the production of ceramics, glass,

cement and concrete. To make students aware of the uses of these products and of sustainability and environmental issues in

relation to the manufacture and use of cement and concrete.

Activities:

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Equation: 2Fe2O3 + 3C 4Fe + 3CO2

Atomic masses: 2x[(2x56)+(3x16)] 3 x 12 4 x 56

Formula masses: 320 36 224

Masses reacting: 320/224 36/224 1

Answer: 1.4286 tonne 0.1607 tonne 1 tonne

Encourage students - in advance - to bring suitable clays and ceramic objects to the class. Find out what they already know about ceramics. Discuss the information provided in the textbook, illustrating and extending this with reference to samples of local clays and of locally familiar ceramic products.

Repeat the same process for glass. Illustrate the discussion with samples of silica sand if available and with a range of glass objects including coloured glass if possible.

Repeat the same process for cement and concrete. Have a bag of cement or ready-mix to show them and if possible encourage them to try mixing a little concrete, preferably for a useful project! (Add the water a little at a time with thorough mixing until a workable mixture is obtained).

Discuss the advantages and disadvantages of replacing traditional building materials with concrete and make sure that students are aware of the environmental issues involved.

Answers: Q1. (i) A tea cup is usually made of a white clay called kaolin that has been ‘fired’ to a high temperature

in a kiln. (ii) Green glass is made of calcium and sodium silicates with silica a little copper silicate. (It is made by heating silica sand with sodium and calcium carbonates and a little copper oxide). (iii) Cement is made of limestone, sand and clay that have been heated together at 1400ºC and then ground into a fine powder. (iv) A concrete block is made of cement (1 part), sand (2 parts), gravel (3 parts) and water that have been mixed together and then allowed to set.

Q2. Some advantages of concrete: relatively cheap, easy to use, very versatile (can be used in many different ways), very strong (especially if reinforced with steel rods), weather-proof, long lasting, Some disadvantages of concrete: manufacture uses a lot of energy and creates pollution (greenhouse gases and acid rain), some people find the appearance ugly, concrete buildings are hot in tropical climates, needs good foundations or it will crack when the soil moves.

13.17 SOME OTHER ELEMENTS

This is an extra module intended to provide supplementary reading about a range of additional elements for those who may be interested. It is not included in the BS&T syllabus.

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