As Chemistry Answer Book

Answers to Student Book text questions

Chapter 1.1 page 11 1 26 protons, 26 electrons, 30 neutrons. 2 a 11 protons, 11 electrons, 12 neutrons. b 53 protons, 53 electrons, 74 neutrons. c 36 protons, 36 electrons, 48 neutrons.

page 13 1 a 2Zn(s) + O2(g)  2ZnO(s) b 2K(s) + 2H2O(l)  H2(g) + 2KOH(aq) c CaCO3(s)  CaO(s) + CO2(g) 2 Molecular equation: KCl(aq) + AgNO3(aq)  AgCl(s) + KNO3(aq) Ionic equation: Cl–(aq) + Ag+(aq)  AgCl(s)

page 15 1

Atom

Number of protons

Number of neutrons

79Br

35

44

81Br

35

46

2 a 79.990 b 107.974 c 52.056

page 17 1 a 0.5 mol of oxygen-16 atoms. b 4 mol of carbon-12 atoms. c 0.25 mol of chlorine atoms. 2 a 18.06  1023 (or 1.806  1024) b 1.003  1023 c 24.08  1023 (or 2.408  1024) d 1.650  1023

page 21 1

Relative formula mass

The sum of the relative atomic masses of all the atoms in the chemical formula.

Relative molecular mass

The sum of the relative atomic masses of all the atoms in the chemical formula of a covalent compound.

Molar mass

The atomic or molecular mass in grams per mole.

Molar volume

The volume occupied by 1 mole of any gas under the standard conditions of 1 atm pressure and 298 K (25 °C).

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Answers to Student Book text questions

2 a Equal volumes of all gases contain equal numbers of molecules at the same temperature and pressure. This is useful because it enables you to measure the relative molecular masses of gases, and so calculate the formula. It also enables you to calculate the reacting volumes for gaseous substances from their molar ratios. b Avogadro’s ideas were based on relatively new and unaccepted ideas from Dalton. He had a reputation as a careless practical researcher, making people doubt such very theoretical ideas. He published in minor journals and, as a poor writer, his explanations were often not clear. His ideas conflicted with the models from the top scientists of the day. 3 a CH4(g) + 2O2(g)  CO2(g) + 2H2O(g) b 1 mol methane, 2 mol oxygen, 1 mol carbon dioxide, 2 mol water c 24 dm3 methane and carbon dioxide, 48 dm3 oxygen. d Need 21.3 dm3 of oxygen to produce 8 dm3 of carbon dioxide

page 23 1 a 198 g b 291 g c 164 g d 396 g 2 a 3 mol b 1 mol c 408 g d 12.75 g of Al2O3, 96 g of HI 3 a C 0.03211 mol, H 0.05178 mol, N 0.01605 mol, P 0.009616 mol, O 0.04170 mol b 10:16:5:3:13 c C10H16O13N5P3 d C10H16O13N5P3

page 27 1 a 60 cm3 2 a KCl(aq) + AgNO3(aq)  AgCl(s) + KNO3(aq) b 0.08 mol dm–3 c 0.597 g 3 Maximum K+ ions: 0.20 g and minimum K+ ions: 0.14 g 4 a People only report what they think researchers want to hear, and are unlikely to say things that put themselves in a bad light. Any other sensible points. b Studies would need to involve large numbers of people and would be carried out for several years with precise health measurements at the start and end of the research. A way to measure whether a participant reads and follows the label needs to be implemented.

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Answers to Student Book text questions

5 a 0.00006 g b Different pollutants may remain in the air for longer than others, or their concentrations may vary depending on a particular time of the day or time of the year. There is no indication as to what effect each pollutant has on the environment or on people. Any other sensible points.

page 29 1 a Depth of precipitate (mm)

20

15

10

5

0 0

0.5

1.0

1.5

2.0

2.5

3.0

4.0

Volume of 1.0M Pb(NO3)2 (cm3)

b 2.5  10–3 mol Pb(NO3) reacts with a known volume and concentration of KI; hence, you can calculate the moles reacting and their ratio and obtain a balanced equation. 2 OTC medicines are less powerful and safer/less toxic, with fewer side effects. Prescribed drugs are more powerful and, therefore, must be given in much smaller, accurate dosages to avoid dangerous overdosing.

page 31 1 92.6% (based on the amount of chlorine, which provides the smallest molar amount) 2 41%

page 33 1 Energy is released as bonds form. This increases the movement of the particles of reacting substances and, in turn, causes particles in the surroundings to vibrate more. So, the temperature is seen to increase as energy is transferred as heat to the surroundings. 2 An endothermic reaction needs energy from the surroundings to take place. The energy required to break the bonds in the reactants is greater than that released when new bonds are formed in the products, so the difference is absorbed from the surroundings. This is seen as a drop in temperature. An exothermic reaction releases energy to the surroundings. Energy released by bond formation is greater than the energy needed to break the bonds in the reactants, so energy is released to the surroundings. This is seen as a rise in temperature.

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Answers to Student Book text questions

Chapter 1.2 3 a Reaction A is endothermic, reaction B is exothermic. The final temperature is lower than the initial temperature for A and higher for B, so A takes in energy and B releases energy overall. b Endothermic (A): –20 °C. Exothermic (B): +30 °C.

page 35 1 Enthalpy is the total energy content of a system at constant pressure. Enthalpy change is the energy taken in or given out by a system during a chemical reaction at constant pressure. 2 An enthalpy level diagram represents the energy losses and gains as bonds are broken and formed during a reaction. It enables you to calculate whether a reaction is endoor exothermic. 3 Cool packs work by using endothermic reactions. When placed on injured tissues, the endothermic reaction in the cool pack takes heat from the injured tissue. This cools the tissue and often helps reduce swelling. 4

59%

60

55% 50

49% 45% 39%

Patients (%)

40

30

26% cooled patients uncooled patients

20

patients who survived but remained dependent 10

0

Dandenong

Bonn

The small studies have lasted a short period of time, which reduces reliability. Data collected by scientifically/medically trained staff and based on clearly observed medical outcomes, which increases reliability. Published in a reputable journal, so results are well regarded by other professionals. Some ethical issues – particularly for future experiments – if a process appears to give an advantage to heart attack patients, is it ethical to continue to deprive other patients of the cooling process? Any other sensible points.

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Answers to Student Book text questions

Chapter 1.3 2 Sensitive, so small samples can be used; sensitive, so very accurate results; differentiates between similar compounds; rapid, so allows analysis of many samples quickly; helps focus research on useful chemicals; identifies breakdown products, so scientists can check no harmful ones are produced; makes analysis of purity quick and easy.

page 55 1 Mass

Abundance (%)

54

5.84

56

91.68

57

2.17

58

0.31

The relative atomic mass of iron is 55.91 2 a 78Kr 0.094; 80Kr 1.6; 82Kr 9.83; 83Kr 9.95; 84Kr 47.83; 86Kr 14.60 b 83.9

page 59 1

40

3

Time since organism died (10 y)

30

20

10

0 0

10

20

30

40

50 Original

60

70

80

90

100

14

C (%)

NB this graph will affect answers 2 and 3 2 a 29 000 years b 7 000 years c 5 100 years 3 84 to 86% 14C; 79% 53

Answers to Student Book text questions

page 61 1 Mark for accuracy and clarity of timeline. 2

Rutherford: experimental data from the bombardment of thin metal foils with alpha particles led Rutherford to the idea of a small centre of positive charge (the nucleus) surrounded by large areas of negative charge (the positions of the electrons). This led to the solar system model of an atom. Bohr: experimental work with the emission spectrum of the hydrogen atom led Bohr to his ideas of the different energy levels or shells containing the electrons, which explained much of the observed behaviour of atoms.

page 63 1 The energy needed to remove an electron completely from an atom. Its value is that it shows the different energy levels of the electrons in the atom – the further they are from the nucleus, the easier it is to remove them. 2 1s 2s 3p 4s 3d

page 65 1 a 1s2 2s1 b 1s2 2s2 2p4 c 1s2 2s2 2p6 3s2 d 1s2 2s2 2p6 3s2 3s3 e 1s2 2s2 2p6 3s2 3s5 f

1s2 2s2 2p6 3s2 3s6 3d10 4s2 4p1

g 1s2 2s2 2p6 h 1s2 2s2 2p6 3s2 3s6 2 32

page 67 1 a [He] 2s2 b [He] 2s2 2p3 c [Ne] 3s2 3p4 d [Ar] 4s2 3d2 e [Ar] 4s2 3d10 4p2 f

[Kr]

2 The most likely place to find electrons is in the different subshells of the atoms. 3 The 5d subshell is full and 6s starts to fill before 5f as it is at a lower energy level.

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Answers to Student Book text questions

page 71 1 Because they have complete outer electron shells which are very stable, they are very unreactive – i.e. they are inert. 2 Vertical groups: all have the same number of electrons in the outer shell, but the number of shells increases. Horizontal periods: the number of electrons in the outer shell increases across the period. 3 a s

b

d

c s

d

p

e p

4 Human error: eg Chancourtois and the missing diagram, Newlands making ridiculous decisions in trying to make his ideas fit. Experimental inaccuracy: Dalton’s inaccuracies in working out masses which undermined his ideas. Creative thinking: Dalton’s imaginative ideas of each element consisting of a single type of atom, Dobereiner and his triads, Chancourtois and his arrangement based on similarities between every eighth element, Mendeleev with his imaginative leaving of gaps and predicting the properties, etc. Any other valid suggestions.

page 73 1 Transition metals have full outer s and p shells with inner d orbitals partially filled. The outer complete shells screen the incomplete d orbitals and make the elements less reactive. 2 The s block elements have unfilled or incomplete outer s orbitals. Noble gases have all their outer orbitals complete. This affects reactivity because in s-block elements the outer electrons are easily lost to form positive ions, which are left with a complete outer shell of electrons. The noble gases have no need to lose or gain electrons – they have a complete outer shell so they are very unreactive indeed.

page 77 1 The outer electrons are more strongly attracted to the positive charge on the nucleus as it gets larger across a period, and so it takes more energy to remove these electrons. 2 It becomes easier to lose an electron as the atomic radius increases down a group, so they are held less firmly as they are further away from the positive nucleus.

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Answers to Student Book text questions

3 Sulfur and phosphorus: sulfur has one more electron in its outer 3p subshell than phosphorus, which has a half-full outer p subshell (3 electrons). It takes more energy to remove an electron from a half-full subshell than from a subshell with fewer or more electrons in it, and this is why the first ionisation energy of phosphorus is higher than that of sulfur. Aluminium and magnesium: the first electron removed from aluminium is the one in the p subshell. Magnesium contains a full s subshell (2 electrons) and it is harder to remove an electron from a full subshell than from one which is still being filled. 4 The current model of the structure of atoms is of electrons found in electron shells which are at different energy levels. Within each shell are subshells of orbitals which contain different numbers of electrons at different energy levels. There is a set number of electrons in each full subshell, eg, s = 2, p = 6. A full orbital or a full shell is associated with stability and unreactivity. The trends observed in the periodic table confirm this model because they reflect the behaviour expected using the current atomic model. The arrangement of electrons affects the reactivity of the atoms and the way they bond together. This in turn is reflected in the physical and chemical properties of the elements, which can be observed experimentally – and the trends in these properties confirm that the patterns which are predicted by the current model of the atom are correct.

Chapter 1.4 page 79 1 The ion has the same number and arrangement of electrons as an atom of another element. Any suitable example, such as Co2+ is isoelectronic with Mn. 2 (a)

–

+

Cl

K

K

Cl

+

(c)

Na

Na

O (b)

2– +

Na

Na

Ca

Ca

O

–

Cl Cl

2+

Ca

Cl

Ca

–

Cl

(d)

2–

2+

O

O

page 81 1 The difference in the radii relates to the different numbers of protons in the nuclei. Positive ions will have a smaller radius because the remaining electrons are strongly attracted to the more positive nucleus. Negative ions with the same isoelectronic arrangement will have a larger radius because the total negative charge on the electrons exceeds the positive charge on the nucleus so the electrons are less firmly held by the nucleus.

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Answers to Student Book text questions

2 a The smaller the ionic radius the more tightly the electrons are held and so the less reactive the ion will be as more energy is needed to remove an electron. On the other hand if the ion needs to gain an electron, the smaller the ionic radius the more easily another electron will be attracted. Larger ionic radius – electrons lost more easily, gained less easily. b The ionic radii of the ions determine the coordination number. This ultimately affects the resulting crystal structure of the lattice.

page 83 1 Details of several different types of evidence, eg: physical properties of ionic compounds; conducting electricity when molten or in solution but not as solids (cf metals, covalent compounds); shattering when hit (cf metals, covalent compounds); electrolysis – separation of charged particles; electron density maps. 2 Sodium ions are A, chloride ions are B (Cl– 0.14 x 10–9 m, Na+ 0.9 x 10–10 m). Distance between ions in lattice 0.21 x 10–9 m.

page 87 1 The ionisation energy of an atom reflects the ease with which an atom will lose or gain an electron. A low ionisation energy suggests that an atom will lose an electron easily to form a positive ion. A very high ionisation energy either reflects a stable configuration, which means that the atom is unlikely to form an ionic bond, or that the electrons are held very tightly and therefore further electrons will be attracted to form a negative ion. 2 Lattice energy (enthalpy) is negative and relates to forming the bonds in a lattice. Bond enthalpy is positive and relates to breaking covelent bonds. 3 Ionic radius – the bigger the ionic radius, the less negative the lattice energy because the oppositely charged ions attract less strongly. Ion charge – the higher the charge, the more negative the lattice energy because the ions attract ions of opposite charge more strongly. 4 The theoretical lattice energy for silver halides is less negative than the lattice energy measured using Born–Haber cycles, and the difference becomes more marked passing down the group. The difference in the electronegativity of the ions in the lattice structures is much smaller in the silver halides than in the sodium halides. As a result, the bonds are less strongly ionic than might be expected by theoretical calculation because they have a degree of covalent character. This tendency increases as you move down the group and the halide ions get bigger – which is why the difference between the theoretical and the Born–Haber values gets bigger down the group. 5 a +121 kJ mol–1 b 643 kJ mol–1 c +4889 kJ mol–1

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Answers to Student Book text questions

page 91 1 a, b and d have covalent bonding. The combination of two non-metals involves sharing electrons. 2 In a normal covalent bond, both atoms contribute an electron to the shared pair. In dative covalent bonding both shared electrons come from the same atom. The bonds which result are otherwise identical. 3

C

O

O

C

O

C

O

O

C

O

4 By comparing the properties (melting temperatures etc) and the bond enthalpies of the covalently bonded atoms in the giant structures with the properties and the lattice energies of ionic crystals. 5 They show the position of the shared pairs of electrons as areas of great electron density. This reinforces the model of a covalent bond as shared electrons, which enables you to build up a picture of the shape of the molecule from the areas of electronegativity around the covalent bonds.

page 93 1 Metallic bond: consists of positive nuclei in a sea of negative electrons – so as a metal is hammered or stretched, nuclei and electrons move across and around each other, but still remain positive centres in the sea of negativity and so do not break. Ionic substance in an ionic lattice: if this relatively rigid arrangement moves, the positive and negative ions move close to other ions of like charge. They repel each other and so the material shatters easily. 2 Sodium has relatively large metal ions with a small charge (1+, 11 electrons not particularly tightly held) so it has a relatively low melting temperature and a not very high thermal conductivity. Magnesium has relatively small metal ions (2+, 12 electrons) and therefore a relatively low thermal conductivity. There is still a lot of metallic character in the bonds so its melting temperature is relatively high. Copper is very strongly metallic (small 2+ ions, 29 electrons). The ions are fairly small with a high charge density and a very positive nucleus. As a result the metallic bonds are strong and so it takes a great deal of energy to melt the metal – the melting temperature is high. There are also many electrons which move when heated, which explains the excellent thermal conductivity of the metal.

page 95 1 The distinction between inorganic and organic chemistry started off as ‘when heated, inorganic substances melt; organic substances (often from living organisms) burn’. For some time (until they were synthesised) it was believed that organic compounds could only be made by living organisms.

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Answers to Student Book text questions

Chapter 1.5 The distinction changed gradually as chemists learned more about the compounds, until now when it is: •

Organic chemistry: the study of carbon compounds, except the simplest ones such as the oxides and carbonates.

•

Inorganic chemistry: the study of all the 91 naturally occurring chemical elements and their compounds, including carbon and its oxides and carbonates.

2 a Inorganic chemists – involves nitrogen, hydrogen and oxygen. b Organic chemists – natural organic polymers are often involved. c Inorganic chemists – using metals and other inorganic chemicals.

page 99 1 Hazard: having the potential to do harm – toxicity, flammability, etc. Risk: the chance that a particular hazard will cause harm. 2 The level of potential hazard is high, so great care is taken to reduce the risk. Risk assessment is carried out regularly and all risks are considered and reduced to a minimum. 3 Any thoughtful suggestion such as: cost to users; potential harm to the environment; biodegradability; effectiveness as a pesticide; toxicity to users.

page 103 1 Carbon contains four electrons in its p shell so it needs an additional four electrons to attain a stable, full outer shell and to do this forms it four covalent bonds. Carbon can form very strong bonds with both other carbon atoms and other non-metals, and it can form double and triple bonds with other carbon atoms. This leads to an immense variety of possible molecules (and isomers). 2

Empirical C2 H 6 O Ethanol – a belongs to the alcohols

Propanoic acid – C3H6O2 b belongs to the caroxylic acids

Molecular

Structural

C2 H 6 O

C2H5OH or CH3CH2OH

C 3 H 6 O2

C2H5CO2H, C2H5COOH, CH3CH2CO2H or CH3CH2COOH

Displayed

H

H

Skeletal

H

H

C

C

H

H

H

H

C

C

H

H

OH

OH

O

O

C OH

OH

3 An atom or group of atoms which is typical of an organic family. They are important because: •

they enable us to sort and classify the huge range of organic molecules

•

they have a major effect on the properties of organic chemicals and so they set the trend for the properties of each homologous series.

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Answers to Student Book text questions

page 107 1 a 1-chlorobutane:

H

b 2,2,3-trimethylbutane:

H

H

H

H

C

C

C

C

H

H

H

H

H Cl

H

H H

C

C

C

H H H

H H

C

C

H H

C

C

H

H

H

H

H

2 Isomer: One of two or more compounds with the same molecular formula but with the atoms arranged differently. Isomeric forms are common because of the way the carbon atom makes multiple bonds with other carbon atoms to produce straight and branched chains and rings, and also because other atoms can be bonded in different ways to form structural isomers, such as methoxymethane/ethanol. 3 Pentane isomers are: n-pentane CH3CH2CH2CH2CH3; 2-methylbutane CH3CH2CH(CH3)CH3; 2,2-dimethylpropane (CH3)3CCH3 or CH3C(CH3)2CH3.

H

H

H

H

H

H

C

C

C

C

C

H

H

H

H

H

H

H

H

H

H

H

C

C

C

C

H

H

H H H

C

H

C

H

H

H

H H

H

H

C

C

C

H

H

H H

C

H

H

4 a Identical

b structural

c structural

d identical.

5 Structural formulae of the nine isomers: CH3CH2CH2CH2CH2CH2CH3, (CH3)2CHCH2CH2CH2CH3, (CH3)3CCH2CH2CH3, CH3CH2CH(CH2CH3) 2, CH3CH2CH(CH3)CH2CH2CH3, CH3CH2C(CH3)2CH2CH3, (CH3)2CHCH(CH3)CH2CH3, (CH3)2CHCH2CH(CH3) 2, (CH3)3CCH(CH3)2.

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Answers to Student Book text questions

Chapter 1.6 page 111 1 Member of the simplest homologous group of hydrocarbons with general formula CnH2n+2 2 C9H20 3 It takes millions of years for fossil fuels to form, and conditions are no longer suitable for the formation of oil. So the reserves of fossil fuels that we have are not being replenished and cannot be replaced. Once they are used up they will have gone for good. 4 Different alkanes with different length carbon chains have different boiling temperatures. These different sized molecules also have different uses. The idea of distillation is to separate different mixtures of compounds from crude oil. At each different temperature, a different combination of chemicals with different length carbon chains will boil and turn into gas, so they can be collected and used.

page 113 1 Catalytic cracking: heavier, long chain molecules from the refining of crude oil are heated in the presence of a catalyst to form lighter, short-chain molecules. Catalysts keep the temperature required as low as possible. Usually, crystalline aluminosilicates are used, which are also known as zeolites. Catalytic reforming: the catalyst. The chains are branched chains and so be used in the chemical

heavy straight-chain alkanes are heated with a platinum broken up and reformed into new isomers, which have prevent knocking in fuel, and into ring compounds which can industry.

2 The situation when the fuel/air mixture in the cylinder of a car engine explodes too soon, causing a knocking noise and lack of power. Particularly common when there is a large proportion of straight chain alkanes in the fuel because these ignite very easily. 3 Method 1: Adding tetraethyllead, which slows down the ignition of the fuel. Advantages: relatively cheap and easy to add. Disadvantages: lead pollution associated with health problems, such as possible brain damage in children. Method 2: Producing gasoline mixtures which are relatively high in branched chain alkanes in reforming process. Advantages: effective, works well, no extra pollution, uses heavy fractions from oil refinery. Disadvantages: uses heat and a catalyst and so is more expensive, relies on oil which is a finite resource. In most countries, including the UK, the latter is used for its reduced effect on pollution.

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Answers to Student Book text questions

page 115 1 Alkanes are unreactive because they have only single carbon–carbon or carbon– hydrogen bonds, which are very strong. The electrons are evenly shared in the bonds so there is very little polarity. 2 Homolytic: electrons are evenly shared between the atoms when a bond is broken – they both become free radicals with one unpaired electron. Occurs when there is little or no polarity in the bond. Heterolytic: unequal sharing of electrons when a bond between two atoms is broken – so one takes both of the shared pair of electrons and the other has none. Occurs when there is a degree of polarity in the bond. 3 Alkanes demonstrate the formation of free radicals during bond breaking. When this process happens in the human body (not necessarily in alkanes) the free radicals can cause considerable damage to the cells. Potentially they can set off the development of cancers by interfering with the normal growth-control mechanisms of the cells. Fruit and vegetables contain vitamins which react with and ‘mop up’ free radicals so they are deactivated and will no longer cause damage to the body cells.

page 117 1 a Undergo thermal decomposition or cracking to form smaller molecules. Equation example: CH4(g)  C(s) + 2H2(g) b They undergo complete or incomplete combustion depending on the levels of oxygen available. Complete: to make carbon dioxide and water; incomplete: to make carbon monoxide or carbon, and water. Equation example: 2C2H6(g) + 7O2(g)  4CO2(g) + 6H2O(l) 2C2H6(g) + 5O2(g)  4CO(g) + 6H2O(l) 2 Clear description of incomplete and complete combustion of alkanes. Include a suitable explanation of hazard and risk using vocabulary suited for a younger audience. Other suitable points.

page 119 1 With an input of light energy or ultraviolet light. 2 The equations should reflect the following: light is needed to provide the energy to initiate the split of the chlorine molecule. This forms free radicals which react with hexane to form hydrogen chloride and a hexyl free radical which reacts with another chlorine molecule to form chlorohexane in a chain reaction. Some comment on the production of polychlorohexanes needed – by reaction of early products with chlorine free radicals. 3 Any ideas that show awareness of the need for large studies, the difficulties of such trials on people, difficulties of self-reporting, need for longitudinal study over many years, etc.

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Answers to Student Book text questions

page 123 1 Production of greenhouse gases, particularly carbon monoxide and carbon dioxide. Production of oxides of sulfur and nitrogen which cause air pollution and acid rain. Use of a non-renewable resource: the environmental damage caused in extracting, refining and transporting the fuel with the use of more fossil fuels to provide the energy, etc. 2 Any one of a number of valid points: there must be evidence. No statement should be made that is not backed up by reference to a study, graph or similar. 3 For each case, data must be clearly displayed with appropriate axes, clear and correct labelling, keys, etc., depending on the method chosen. 4 a 76.9–79.3% b 21.8–25.3% c Variety of possible answers depending on the way of arguing. Most likely is that the effect of deforestation may not be as great as first thought as plants are only responsible for between a fifth and a quarter of the absorption of greenhouse gases. Also, this is a relatively small part of the total carbon reservoir. All arguments to be based on data. 5 Evidence of careful research and information backed by more than one source, not related to each other. Also display an understanding of the technology and its potential uses.

Chapter 1.7 page 125 1 a

H

H

H

C

C H

b

H C

C H

H

H

H

H

C C

C

H H

H

C

C C

H H

H

H 2 a C–C single bond: a sigma bond which has a symmetrical electron cloud so there is free rotation around the bond. The bond is relatively unreactive. C=C double bond: made up of a sigma bond and a pi bond. The pi bond has electron density concentrated in two regions opposite each other on the C–C axis. There is no rotation about the bond so there can be isomerism which leads to variations in the physical properties of the alkenes.

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Answers to Student Book text questions

b The double bond makes the alkenes more reactive than the alkanes as the electrondense region of the pi bond attracts electron-seeking groups. Melting and boiling temperatures are similar to those of the alkanes, but slightly lower. The double bond causes isomerism: different isomers have different melting and boiling points which makes it harder to give exact figures because there is usually a mixture of isomers present. 3 Any valid points, such as: Pros: fruit is available all year round; it provides a good source of income to people who grow, ship and store the fruit; it reduces wastage of food as the fruit can be ripened when needed. Cons: transporting and storing fruit is expensive and produces a lot of carbon dioxide; it is an unnatural process; it competes with and reduces use of locally grown fruit. a Ever increasing production of carbon dioxide would contribute to increased global warming with all environmental consequences. Labour in developing countries may be exploited to supply food for the developed world. Any other valid points such as there is a large carbon footprint associated with the practice - and global warming is of increasing concern. b There would be great hardship for people working in the fruit industry in developed countries as jobs would be lost in areas which are already under economic pressure; there would be job losses in storage and shipping companies; less consumer choice in developed countries would cause unrest; there may not be as much effect on global warming as expected – it would depend on what replaced the ethene process, such as growing bananas in heated greenhouses in the UK would have a similarly damaging effect on global warming.

page 128 1 Any relevant comments on the size of the trial, the length of the trial, control of diet before the trial, etc. Further studies: any relevant comments on setting up large-scale trials – idea of number in trial, timescale of trial, control of diet before trial, tomatoes in different types of diet, impact on lycopene levels over time, etc. 2 H3C

CH2 C

CH3

H3C

C

H C

H3C

C

CH3 C

H

H

Z -2-pentene

E -2-pentene

H

2

C

H

3

3-methyl-2-butene

CH3 H C H

CH2

H

CH C

C CH3

2-methyl-1-butene

64

CH3

H

CH3

CH2 CH2 CH 3

H C

C H

3-methyl-1-butene

H

C H

1-pentene

Answers to Student Book text questions

page 131 1 Alkenes contain a double bond and the energy required to break open the double bond is less than twice the energy needed to break the single bond (612 kJ mol–1 vs 347 kJ mol–1). 2 Alkanes: substitution with the input of light energy. Alkenes: addition reaction at room temperature. 3 C3H6(g) + H2(g)  C3H8(g) Heterolytic fission of the double bond takes place and the hydrogen atoms are added to form an alkane.

page 133 1 Movement of electrons – full arrow for a pair, half-arrow for a single electron. 2 An equation resembling fig. 1.7.19 in the Students’ book is appropriate. Overall reaction: C3H6(g) + Br2(l)  CH3CHBrCH2Br 3 It is an electrophilic addition reaction. The bromine molecule is partly polarised by the electron-rich pi bond in the propene. There is an electrophilic attack which produces a carbocation followed by an nucleophilic attack which results in the formation of 1,2-dibromopropane.

page 135 1 Alkenes molecules have a double bond which makes them reactive, so they join together to form long chains relatively easily. 2 Use of the tetrafluoroethene monomers to create a polymer chain like fig. 1.7.16 in the Students’ book.

page 141 1 The main problems are: •

carbon dioxide released into the atmosphere from burning fossil fuels to provide energy for production/transport and incineration;

•

atmospheric pollution from incineration where this is not done under the correct conditions;

•

landfill issues: most polymer products don’t biodegrade so have to be disposed of in landfill;

•

plastics pollution: polymers are found all over the world, in the atmosphere, on land and in rivers and the sea; these waste materials have an environmental impact on flora, fauna, etc.;

•

any other valid points.

2 Reusing means using the same object more than once – e.g. repeated use of carrier bags. Recycling means processing waste polymers from industry and domestic use to be reused in a different form as polymer products.

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3 They come from different sources: biopolymers have a renewable source (i.e. plant material) whereas conventional polymers are manufactured from chemicals produced from fossil fuels. Biopolymers are usually biodegradable (ie can be broken down by bacteria or other microbes) within 20–30 years; conventional polymers are usually not biodegradable and take very much longer to be degraded. Manufacture of biodegradable polymers is more expensive than that of conventional polymers. Any other valid points. 4 Appropriate graphs – clearly labelled axes, well drawn, etc. The hard form of PLA is better than PVC in most categories, although not as good as polystyrene. The soft form is best in all categories except tear strength, where it comes second. It therefore compares well, particularly when other benefits of production, biodegradability, etc. are taken into account. 5

Polymers usually contain a lot of energy. Energy recovery means recovery of some of the energy put into producing a polymer when it is eventually recycled or destroyed. The carbon footprint of the material can be reduced as the energy in the molecules is used to power the generation of electricity (which may be used to process new plastics) instead of using more fossil fuels or other non-renewable resources.

6 Using renewable energy in the manufacturing and processing stages reduces the carbon footprint by avoiding burning fossil fuels to make electricity. Reducing the use of polymers reduces the amount of electricity needed to make them and the amount of transport required to move them about, thus lowering the carbon footprint. Reusing polymers means that fewer polymer products need to be made so less electricity is used, so they have a lower carbon footprint. Recycling polymers takes less energy than processing the crude oil to make new ones so it uses much less electricity and leads to up to 2½ times less carbon dioxide being produced, which reduces the carbon footprint significantly. Using renewable resources to make bioploymers produces carbon dioxide in the harvesting, transport and manufacturing process but the plants have removed carbon dioxide from the atmosphere as they grew. This substantially reduces the carbon footprint of the polymer formed. Energy recovery makes effective use as a fuel of the energy trapped in the polymer, which means that new fossil fuels do not have to be burned. This reduces the carbon footprint of the polymer. 8 a A well-drawn bar chart with clear labels, and accurate readings. b They probably expected that iron would come out the best in terms of energy as well as other characteristics. In fact PVC scored well in many different categories – it had the least effect on global warming, the lowest energy content and it was the least toxic!

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Chapter 2.1 page 147 1 Tetrahedral. There are four pairs of bonding electrons. 2 Four pairs of electrons: two pairs are bonding electrons and two pairs are non-bonding pairs. The hydrogen sulfide molecule is a bent linear molecule similar in shape to water. 3 Three (double) bonds and no non-bonding electrons. 4 Bent molecule. Central oxygen atom has two pairs of bonding electrons and two pairs of non-bonding electrons. 5 Like XeF4 there are four bonds in one plane and two pairs of non-bonding electrons at right angles above and below the plane.

page 149 1

H

H C

C

H

C

H H

H H

H

2 It shows how the atoms are bonded together but it gives a false idea about bond angles. They look to be 90° but are in fact approximately tetrahedral. 3 Methanol, methanal and methanoic acid.

H

4

120°

109.5°

C

H

H

O

H The atoms are arranged tetrahedrally around the carbon atom (104°) and planar around the oxygen atom (120°).

page 153 1 In diamond, all the carbon atoms are bonded together by strong covalent bonds. The diamond is hard because it is difficult to split the structure. All of the electrons are fixed in bonds. In graphite, there is strong bonding within a 2-D layer but the forces between the layers are very weak so layers can slide over each other. There are free electrons within the structure that can move and conduct electricity. 2 Fullerenes are molecular but diamond and graphite are giant structures of atoms (macromolecular). 3 There has been insufficient long-term research of the penetration of the skin by nanoparticles.

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Chapter 2.2 page 155 1 Nitrogen, oxygen and chlorine. 2 Only a very slight increase. 3 There is only a small difference in electronegativity between carbon and hydrogen. Carbon is slightly more electronegative. This explains the almost regular tetrahedral shape of methane.

page 157 1 HF as there biggest difference in electronegativity.

O –

2 +

H

H+

3 Difference in electronegativity between lithium and iodine is 1.5 (2.5 – 1.0). From table 2.1.1, percentage ionic character = 43%. So possibly lower melting and boiling points, and soluble in an organic solvent.

page 159 1 a Non-polar. b Polar. c Non-polar. d Polar. 2 If dipoles act equally in opposite directions they cancel each other out, making the molecule non-polar. 3 In tetrachloromethane, the four dipoles acting tetrahedrally cancel each other out, but this is not possible in either chloromethane or dichloromethane.

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Chapter 2.3 page 163 1 a Dipole–dipole. b London forces. c Hydrogen bonds. 2 c, b, d, a. 3 A hydrogen atom must be attached to an electronegative atom - eg oxygen (in water), fluorine or nitrogen – for hydrogen bonding to take place.

page 167 1 A clear graph showing an increase in the boiling temperature as chain length increases because, although there are only weak intermolecular forces between the molecules, there are more places where they can operate. 2 a Boiling temperatures increase due to increasing size and mass of molecules. b Increasing boiling temperature from PH3 to SbH3 explained by increasing size and mass of molecules. NH3 is higher than expected as nitrogen has a higher electronegativity than the other elements in group 5 and hydrogen bonding is possible.

page 169 1 Since the enthalpy of hydration is greater than the lattice energy, the dissolving of calcium chloride in water will be exothermic and the temperature of the solution will rise. H

2 O

H

C

O H

H

C

C

H

H

H

H

O H H

H

O C

H

H

3 Sugar molecules are covalent but contain polar — O—H bonds. These polar groups can hydrogen bond to water molecules.

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Chapter 2.4 page 173 1 0 (zero) in both cases. 2 It is a way of tracking the movement of electrons which are not fully attached to a single atom. 3 a P: –3, H: +1 b Fe: +3, Cl: –1 c Na: +1, S: –4, O: –2 d Mn: +6, O: –2 4 Oxidation number of sodium changes from 0 to +1 so it is oxidised. Oxidation number of oxygen changes from +1 to 0 so it is reduced. Sodium is therefore the reducing agent and water the oxidising agent. 5 Cu(s) + 2AgNO3(aq)  2Ag(s) + Cu(NO3)2(aq) Cu(s)  Cu2+(aq) + 2e– Ag+(aq) + e–  Ag(s) Copper is oxidised and silver is reduced. 6 Zn(s) + H2SO4(aq)  ZnSO4(aq) + H2(g) Zn(s)  Zn2+(aq) + 2e– 2H+(aq) + 2e–  H2(g) Zinc is oxidised and hydrogen ions are reduced. 7 It does not represent a redox reaction because there are no changes in oxidation numbers.

page 175 1 MnO42– to MnO4– is an oxidation because the oxidation number goes from +6 to +7. As the reaction continues, MnO4– becomes reduced (oxidation number ends at +4). 2

Fe2(SO4)3

3 a I: –1 to –1. Neither oxidised nor reduced. b Zn: 0 to +2. Oxidised. c Hg: +2 to 0. Reduced. d Cu: +2 to +1. Reduced. e

Fe: +2 to +3. Oxidised.

page 177 1 2S2O32–(aq) + I2(g)  S4O62–(aq) + 2I –(s) 2 Br2(g) + 2Fe2+(aq)  2Br–(s) + 2Fe3+(aq) 3 Cu(s) + 2H2SO4(aq)  Cu2+(aq) + SO42–(aq) + 2H2O(l) + SO2(g)

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4 Ionic equation: 2MnO4–(aq) + 16H +(aq) + 10I –(aq)  2Mn 2+(aq) + 8H2O(l) + 5I2(aq) Molecular equation: 2KMnO4(aq) + 8H2SO4(aq) + 10KI(aq)  2MnSO4(aq) + 6K2SO4(aq) + 16H+(aq) + 5I2(aq)

Chapter 2.5 page 179 1 M2+(g) ➔ M3+(g) + e– 2 A magnesium atom loses two 3s electrons when it forms a 2+ ion. There are no electrons in the third shell and so the ion is smaller than the atom. 3 All group 2 elements have atoms with two electrons in the outer shell. In each case it is relatively easy to remove two electrons (shown by relatively low ionisation energies) but very difficult to remove three electrons which would involve breaking the stable lower energy shell. Removing two electrons becomes easier down the group.

page 181 1 The difference in energy between the promoted energy level and the normal energy level is within the visible spectrum for calcium but not for magnesium. 2 The wire should be cleaned with concentrated hydrochloric acid and repeated heating until no traces of metal ions remain and there is no colour to the flame. If this is not done it can lead to false observations. 3 The reactivity of group 2 metals increases down the group. Like the others, barium has two electrons in the outer shell. But these are further from the nucleus and therefore less tightly bound to the atom. There is also shielding of the nucleus by electrons in inner shells. 4 It forms the most stable compounds that need more energy to split up.

page 183 1 a Ba(s) + 2H O(l) ➔ Ba(OH) (aq) + H (g) 2 2 2 b BaO(s) + 2HCl(aq) ➔ BaCl2(aq) + H2O(l) 2

c Ba(OH)2(aq) + 2HNO3(aq) ➔ Ba(NO3)2(aq) + 2H2O(l)

Using moles/100 g is better because we are then comparing the same number of particles each time. 3 Barium sulfate is insoluble. When barium oxide reacts with sulfuric acid, an insoluble layer of barium sulfate is formed on the barium oxide. This prevents the barium oxide and sulfuric acid reacting further.

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page 185 1 a 4.0g dm–3 b 0.1 mol dm–3 2 0.0978 mol dm–3. About 1%. 3 Burette and pipette readings are to the nearest 0.05 cm3. Accuracy is often limited by the skill of the experimenter, eg detecting end points, swirling the liquid during mixing.

page 187 1 The ease of decomposition of nitrates and carbonates increases down the group. 2 2KNO3(s) ➔ 2KNO2(s) + O2(g) 2Ca(NO3)2(s) ➔ 2CaO(s) + 4NO2(g) + O2(g) SrCO3(s) ➔ SrO(s) + CO2(g)

page 191 1 Cu2+(aq) + 4I–(aq) ➔ 2CuI(s) + I2(s) Copper reduced from oxidation number +2 to +1 (reduction) and oxidation number of iodine increased from –1 to 0 (oxidation). 2 If the solution is not neutralised the acid reacts with sodium thiosulfate solution. 3 Zinc nitrate does not react with potassium iodide.

page 193 1 Using dilute hydrochloric acid is adding a chloride so the test will always give a positive result. 2 Sodium chloride gives steamy colourless fumes but sodium bromide will produce brown fumes of bromine.

page 195 1 The benefit of chlorine is obvious – prevention of bacterial contamination, giving us access to clean drinking water. Aside from the evidence of negative effects, the use of fluoride to improve dental health is arguably unnecessary as we can get fluoride from toothpaste, etc. Any other valid points. 2 Look for well referenced material, and logical arguments and conclusions which can be drawn from the evidence presented.

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Chapter 2.6 page 197 1 Keep all conditions the same apart from concentration when considering the effect of concentration, and the temperature the same when considering the effect of temperature. Carry out the experiment with different known concentrations of hydrochloric acid. Then choose one set of conditions and repeat this experiment at different temperatures. 2 In the much colder conditions in the refrigerator, the reactions which cause the food to decay are slowed down. 3 Flour dust mixed with air can explode because the air is in contact with a large surface area of flour.

page 199 1 a The syringe method. Bubbles will vary in volume and the surface of the water in the measuring cylinder will be disturbed. b Collecting the gas in a gas syringe as the gas would dissolve in water. 2 The density of hydrogen is very low. Therefore, the quantity collected would have a mass so small it might not be detected.

page 201 1 It suggests that the reaction will be slow as few of the colliding particles will have sufficient energy to react. 2 Their energy and the way they collide. 3 Distance apart, lack of means of communicating, language difficulties, not knowing what the other one had found out, etc.

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Chapter 2.7 page 205 1 a Because the mixture goes darker, it suggests the equilibrium has moved to the right to produce more nitrogen dioxide. b According to Le Chatelier’s principle, if the forward reaction is endothermic, raising temperature causes the equilibrium to shift to the right in an attempt to reduce the temperature. c The mixture will go paler as the equilibrium moves to the left. There are fewer molecules on the left-hand side so, according to Le Chatelier’s principle, if the pressure is increased the equilibrium moves to the left. 2 When chlorine is passed over iodine(I) chloride, the equilibrium moves to produce solid iodine(III) chloride. When the U-tube is tipped, chlorine is removed and the equilibrium moves to the left to reform more chlorine.

page 207 1 a Pressure will have no effect on the equilibrium as gases are not involved as reactants or products. The answer is not the same number of moles on each side – it is true but is not the explanation. b (i) Moves to the right. (iv) No effect.

(ii) Moves to the right.

(iii) Moves to the left.

Chapter 2.8 page 211 1 H

H

H

H

H

C

C

C

C

H

H

H

H

OH

H

H

H

H

H

C

C

C

C

H

H

OH

H

butan-1-ol primary

butan-2-ol secondary

H H

C

H H

H

H

H

C

C

C

H

OH H

2-methylpropan-2-ol tertiary

H

H

H

H

C

C

C

H H

H

OH

H C

H

H 2-methylpropan-1-ol primary

2 2CH3OH(l) + 3O2(g)  2CO2(g) + 4H2O(l) Carbon monoxide will form if there is insufficient oxygen.

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Answers to Student Book text questions

3 2P(s) + 3I2(s)  2PI3(l) 3CH3OH(l) + PI3(l)  CH3I + P(OH)3(l) 4 CH3CH2OH(l) + [O]  CH3CHO(l) + H2O(l) CH3CHO(l) + [O]  CH3COOH(l) The [O] is symbolic of the oxidation by acidified potassium dichromate(VI) 5 As it fumes with PCl5, this suggests it is an alcohol. It is not oxidised by acidified potassium dichromate(VI) so it is a tertiary alcohol.

page 213 1 H

H

H

C

C

Br

Br

H

Br

1,2-dibromoethane

2

H

C

C

Br

H

H

1,1-dibromoethane

Cl C 2 Cl 4

H

Cl C

C

Cl

Cl

page 217 1

Cl

H H

C

H

F

C

H

F

R12

R22

F

F

H

H

C

C

H

H

F

R152

2 Depletion of ozone layer, narcotic effects and at high temperatures they produce toxic fumes, etc. 3 The strength of C—Cl bond means that they are difficult to break down.

page 219 1 Reflux with aqueous sodium hydroxide – substitution reaction – to produce propan-1-ol

H

H

H

H

C

C

C

H

H

H

Cl

+

OH –

H

H

H

H

C

C

C

H

H

H

OH

+

Cl –

Reflux with alcoholic sodium hydroxide – elimination reaction – to produce propene

H

H

H

H

C

C

C

H

H

H

Cl

+

NaOH

H

H

H

C

C

H

+ C

NaCl

+

H 2O

H

H

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Answers to Student Book text questions

2 CH3I + NH3  CH3NH2 + HI methylamine CH3I + CH3NH2  (CH3)2NH + HI dimethylamine CH3I + (CH3)2NH  (CH3)3N + HI trimethylamine 3 There is only one carbon atom in iodomethane, and two carbon atoms are needed for elimination. 4 It is difficult to get a single product because of other reactions (see Q2). Carry out the reaction with an excess of ammonia.

page 221 1 Equal amounts of reactants, same temperature, same time. 2 Elimination.

Chapter 2.9 page 223 1 Substitution. 2 Hydrolysis.

page 225 1 High temperature and/or ultraviolet light. 2 Nucleophile. 3 Nucleophile.

page 227 1 B. Changing the concentration of hydroxide ion alters the rate of reaction. This change has no effect on A.

page 229 1 The ozone hole is smallest during the winter, then enlarges over spring and summer before shrinking again. This is linked to the mechanism which causes the depletion of the ozone in the atmosphere because the reaction which increases the breakdown of ozone is the homolytic fission of CFCs, producing an excess of free radicals which in turn cause the breakdown of the ozone. The fission of the CFCs is catalysed by sunlight – so during the Antarctic winter, when there is no sun, ozone builds up as

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Answers to Student Book text questions

it is made in the tropical areas and moves to the poles. Then in spring, the return of sunlight triggers the fission of the CFCs and the breakdown of the ozone, with resultant thinning of the layer. 2 Any valid points from the data, such as: The extent of the ozone hole changes through the year; the pattern of change is similar every year; the peak size is in September; the time of the peak size appears to have got earlier since the 1980s, from late Sept early October to mid September now; the maximum area has more than doubled since 1986; there is some suggestion that the maximum size may be reducing again; appears that both atmospheric CFC concentrations and ozone depletion may have reached a peak and be on the decline; some evidence that levels of skin cancer are increasing which could be a delayed effect of ozone depletion over time and hence greater UV exposure 3 The photos from pace and the data on ozone levels are both valid and reliable from reputable sources (eg NASA) and published in the public domain. The final set of data is partly measured and partly speculative and therefore considerably less reliable. 4 Any valid suggestions such as: Continued regular and reliable monitoring of the extent and timing of the ozone hole; continued monitoring of CFC levels and ozone depletion; continued monitoring of skin cancer rates in different areas of the world and the opportunity to test correlation and causation in the lab.

Chapter 2.10 page 231 1 a 73: presence of 13C. b 72. c 72: CH3CH2COCH3 + 57: CH3CH2CO+ 43: CH3CO+ 29: CH3CH2 + 15: CH3– 2 CH3CH2COCH3  CH3 CH2+ + –COCH3

page 235 1 P: CH3COOCH3 Q: CH3CH2COOH 2 C=O 3

O–H: 2500–3300 cm–1

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Chapter 2.11 page 237 1 Combustion – anthropogenic; volcano gases – natural. 2 It is present in larger amounts than other gases.

page 239 1 Carbon dioxide is produced during the building of the power station, in producing fuel rods and in transport, etc. 2 Rich people have the opportunity to choose alternatives, while poor people have a reduced choice and use the only materials available. 3 Global warming – due to greenhouse gases building up in the atmosphere. They trap some of the infrared radiation emitted from the Earth. This causes the Earth and its atmosphere to warm up. Depletion of ozone layer – ozone in the upper atmosphere has been depleted by free radicals in a chain reaction. This enables more ultraviolet radiation to pass through the atmosphere to the surface of the Earth.

page 241 1 Burning hydrogen in a power station will produce electricity and the only waste product is water. 2 Uncertainly about whether the process will work and the decline in the use of fossil fuels. 3 The removal of sulfur dioxide in flue gases is accompanied by additional carbon dioxide in the atmosphere.

page 243 1 Cost of fuels, development of alternatives. 2 Lyocell is biodegradable and can be recycled.

page 245 1 100%. There is only a single product. 2 a Removing wastes. Propanoic acid and high boiling temperature impurities are removed. b Catalysts and unreacted reactants are recycled. c No gases escape into atmosphere.

page 249 1 To remove the energy released in the exothermic reaction. This may be used, for example, to preheat reactants. 2 Rapid, can be used for small quantities. Any other valid points.

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