2.1 Answers
Remembering
1 a true
b true
2 dense, malleable, ductile, conduct heat, conduct electricity
3 a gold: jewellery; silver: jewellery; copper: wires; mercury: thermometers.
b brass: doorknobs; bronze: ornaments; cupronickel: ‘silver’ coins; solder: electrical joins in circuitry
4 24
5 mild steel, tool steel, cast iron
Understanding
6 a the main component of an alloy
b a mixture where the main component is a metal
7 Alloys can have different properties from the base metals, which may be more useful. For example, iron corrodes easily but when alloyed with chromium it makes stainless steel, which resists corrosion.
8 On a scale of 0 to 24, it measures the proportion of gold in a gold alloy.
9 Coins are alloys; e.g. ‘silver’ coins are an alloy of copper and nickel. To make actual gold and silver coins from pure metals would cost more than the coin itself.
10 Poor conductors, as metals need free electrons to conduct electricity.
Applying
11 ductile, good electrical conductors
12 The charred, grill marks on the fish indicate that the metal is hotter than the air.
13 a copper (but aluminium content is also high in some gold coins)
b mercury
c iron
d copper
e chromium
Analysing
14 a , 50%
b , 37.5%
c , 91.7%
Evaluating
15 Mercury is a liquid over a large range of temperatures, expands and contracts a large amount with small changes in temperature, and is a good conductor of heat.
16 iron
17 Aluminium is very light so can be made into thick wires to carry a lot of electrical current.
Creating
18
a i 32 × 106 N/m2
ii 12 × 106 N/m2
iii 5 × 106 N/m2
iv 33 × 106 N/m2
v 19 × 106 N/m2
b 52–72%
c 1–45%
d 60% copper
e 48%, 78% and 94%
2.1 Practical activities
Prac 1: Metallic crystals
Common mistakes
Soiled or coated copper wire may inhibit crystal growth. If soiled or coated, clean with a piece of sandpaper or steel wool.
Possible results
Silver crystals will grow on the copper wire while the copper is being dissolved. The colourless solution becomes blue.
Suggested answers
1 Chemical change. Copper wire dissolves and silver is deposited. Clear silver nitrate becomes a blue solution.
2 From the silver nitrate solution: copper(s) + silver nitrate(aq) → silver(s) + copper nitrate(aq)
3 The copper wire left in the silver nitrate solution is thinner than the original wire, as it reacted with silver nitrate to produce copper nitrate solution.
4 The solution turned blue. Copper had replaced the silver in the solution to produce copper nitrate.
Prac 2: How much is it worth?
Common mistakes
Answers will vary depending on the accuracy in weighing.
Possible results
Mass of $1 coin = 8.978g
Mass of copper in coin=92% of 8.978 = 8.259 76g
Mass of aluminium in coin=6% of 8.978 = 0.538 68g
Mass of nickel in coin=2% of 8.978 = 0.179 56g
Mass of $2 coin= 6.631g
Answers will vary depending on current metal prices.
Mass of copper in coin= 92% of 6.631 = 6.100 52g
Mass of aluminium in coin= 6% of 6.631 = 0.397 86g
Mass of nickel in coin= 2% of 6.631 = 0.132 62g
Exchange rates vary and the rest of the answers will vary.
Suggested answers
1 No. All coins cost less to produce than their face value.
2 Silver has become too expensive, making the coins worth more than their face value.
3 Answers will vary depending on current metal prices.
2.2 Answers
Remembering
1 silicon dioxide
2 oxygen, silicon, aluminium, iron, calcium, sodium, magnesium, potassium
3 bauxite: aluminium; galena: lead; haematite: iron
4 a copper
b gold, silver
c potassium, sodium, calcium
d iron, zinc, nickel, tin
5 water penetration, collapse, venting poisonous gases, explosive gases, provision of fresh air
6 i C(s) + O2(g) → CO2(g)
ii CaCO3 → CaO(s) + CO2(g)
iii CO2(g) + C(s) → 2CO(g)
iv Fe2O3 + 3CO(g) → 2Fe + 3CO2(g)
v CaO(s) + SiO2(s) → CaSiO3(l)
7 Advantage: helps conserve limited metal resources.
Disadvantage: is too expensive for some metals.
8 a false
b false
c true
9 a aluminium
b iron
Understanding
10 a There is not enough metal in the ore, the ore is not easily accessible, the overall cost to the environment is too high, the overall cost to local communities is too high.
b There is a large quantity of ore, the ore can be accessed easily, there is a high percentage of metal in the ore.
11 a Smelting is a technique for extracting metals from ore that involves using heat with chemical processes.
b A non-renewable resource is a useful material of which there is limited supply in the Earth and which cannot be replenished.
12 very expensive and requires a lot of energy
Applying
13
Students to list any three of each of the following sites. Many other sites are possible.
Ore / SitesBauxite / Tomago, Gladstone, Pinjarra, Able, Nabalco
Chalcopyrite / Scuddles, Telfer, Gecko, Balcooma, Kurri Kurri
Galena / Paraburdoo, Whyalla, Century, Goongewa, Plenty River
Haematite / Mt Tom Price, Jimblebar, Newcastle, Yarrie, Port Kembla
Pitchblende / Angela, Beverly, Radium Hill, Manyingee, Jabiluka
Sphalerite / Blendevale, Plenty River, Elura, Scuddles, Balcooma
14 a
b
c
15 Mined material is crushed by rollers or steel balls within a ball mill. Impurities known as gangue are separated by froth flotation. The remaining ore is now ready for extraction.
16 a sodium chloride
b Sodium ion: negative electrode.
Chloride ion: positive electrode.
c 2NaCl(l) → 2Na(s) + Cl2(g)
d chlorine gas
17
Analysing
18 Investigation task.
19 a Minerals are rocks containing large amounts of a particular metal. If there is sufficient metal to make it worth mining, it is called an ore.
b A shaft is the main vertical hole bored down in an underground mine. Drive shafts come off horizontally from the shaft leading to the stope, which is an area where the ore has been excavated.
c Slag is the waste from a blast furnace, whereas gangue is the waste produced by froth flotation.
d Overburden is the dirt that has no value, which is removed from an open-cut mine in order to reach the ore, which has a high metal content.
Evaluating
20 Answers will vary depending on personal opinion.
21 At the bottom, with gold and silver.
Creating
22 Creative task.
23
24 Creative investigation task.
25
2.2 Practical activities
Prac 1: Chocolate chip mining
Common mistakes
Ensure that the cookie crumbs are contained and easily retrievable for reweighing. Trays will assist in containing the cookie crumbs.
Possible results
Students compare the amount of ‘valuable’ material mined with the waste produced. As a general rule, the desired element is a small fraction of the material mined.
Suggested answers
1 Results will differ across groups.
2 The composition of each biscuit should be roughly the same, although there will be variations.
3 Chocolate chip biscuits usually only have a few choc-chips in each biscuit and so the amount of ‘waste’ (biscuit crumbs) would be close to the amount of material in the biscuit itself.
4 The waste material after ‘extraction’ would not completely fill the ‘hole’ dug.
5 a The ore is the chocolate chip biscuit.
b The mineral is the chocolate chips (extremely valuable).
c The gangue is the leftover waste (biscuit crumbs).
Prac 2: Froth flotation
Common mistakes
Larger iron filings will be too heavy to float. Finely crushed iron filings will assist this activity.
Possible results
The kerosene coats the iron filings. The part of the detergent molecule that is hydrophobic attaches itself to the kerosene. The detergent then carries the iron filings to the surface.
Suggested answers
1 The detergent creates the froth.
2 The metal ore (basically rock) has to float on top of the water (in the froth), so the particles need to be as small and light as possible.
Prac 3: Extracting copper by electrolysis
Common mistakes
Ensure the voltage selected is suitable for the globe tolerance.
Possible results
Copper is formed at the negative electrode. The blue colouration of the solution will become less strong as the copper ions are converted into pure, metallic copper.
Suggested answers
1 Copper was formed at the negative electrode.
2 The blue colouration of the solution will become less strong as the copper ions are converted into pure, metallic copper.
3 Copper is formed at the negative electrode and the blue colouration becomes weaker.
4 Cu2+(aq) + 2e– → Cu(s)
5 Copper is sometimes found as a native metal. Otherwise, it is extracted from its ore by simply roasting it. These methods are far easier and cheaper than electrolysis.
Prac 4: Extracting copper by roasting
Common mistakes
Students may confuse the copper oxide with the ground charcoal. Ensure that each substance is labelled clearly to avoid any confusion.
Possible results
Pieces of copper metal will appear in the mixture.
Suggested answers
1 Copper metal will be produced.
copper oxide(s) + carbon(s) → copper metal(s) + carbon dioxide(g)
2 Students’ own answers required.
3 Students’ own answers required.
2.3 Answers
Remembering
1 a IV
b 4
c diamond, graphite
d carbon dioxide, methane
2 fossil fuels, drugs, plastics
3 a polythene, acrylic, nylon, polystyrene, melamine
b cellulose, resin, pitch
c asbestos
4 extrusion moulding, blow moulding, injection moulding
5 toys, bottle caps, outdoor furniture
6 blow moulding
7 hard, brittle, rigid
Understanding
8 Desirable: cheap, versatile, recyclable.
Undesirable: non-biodegradable, burn to form noxious gases, become brittle over time.
9 Thermoplastics are held together by long chains, but the chains are not cross-linked, so they can move and flow around each other when in liquid form. Because the chains are not cross-linked, these plastics will reset when cooled.
10 Cross-linking forms strong bonds across the polymer chains. Therefore, the chains are physically stuck to each other and cannot flow to form a liquid when heated.
Applying
11 a 6
b 2
c 4
12 A small molecule capable of joining together in a long chain is called a monomer. When small molecules join together they form a polymer. Small molecules join together in a process known as polymerisation and result in the production of plastics.
13 one carriage
14
Analysing
15 Monomers are the individual building blocks that make up polymers.
16 Both are plastics that are shaped by heating. Thermosetting plastics cannot be remoulded; they are hard, brittle, rigid and cross-linked. Thermoplastics can be remoulded, tend to be soft, flexible and are not cross-linked.
17 Investigation task.
Evaluating
18 No, because a thermosetting powder could not be remoulded into useful objects.
19 Plastics provide a very useful, cheap and versatile material for our society. However, plastics are not good for the environment because they do not biodegrade. They also pose a risk to animals that may be caught in plastics or have plastics caught in their digestive systems after swallowing them.
20 They could perhaps be used as a form of insulation, made into new weatherproof materials etc.
21 We will have to start taking our own shopping bags to the supermarket (which we should be doing already) or pay a small fee for biodegradable bags.
22 If they are made of synthetic polymers, then the polymer chains might contract under heat and cause the clothes to shrink.
Creating
23 Practical task.
24 Investigation task.
25 Design task.
26 Design task.
2.3 Practical activities
Prac 1: Identifying plastics
Common mistakes
Encourage students to use very small samples of plastic to expose to a flame in order to reduce the fire hazard.
Possible results
Results will vary depending on the plastic samples used. All of the plastics used should be thermoplastic. Perspex and nylon will be heavier than water. Polythene will keep burning once removed from the flame.
Suggested answers
1 Answers will vary depending on the plastic samples used.
2 Answers will vary depending on the plastic samples used.
3 Many plastics produce toxic fumes when burnt, so burning or heating them must be done in a fume hood. PVC produces hydrochloric acid fumes when it burns.
4 Dioxin, which is highly toxic.
5 None of these plastics sink in water or react with it.
6 Polythene will keep burning once removed from a flame.
Prac 2: Making casein plastic
Common mistakes
Do not heat the milk over 50°C, as the protein casein will denature and will lose its potential to form a polymer.
Possible results
Students make a polymer called casein from milk. When milk is acidified with the vinegar, it is transformed into a solid component, called curd, and a liquid component, called whey. The curd contains the protein casein.
Suggested answers
1 Casein plastic is thermoplastic (unless it is cross-linked using formaldehyde, which was not done in this experiment).
2 Casein was used as wood glue. The final test showed how the glue was made and how it worked.
3 As casein takes a long time to manufacture, it is not used much now. It was once used for things such as combs and handles.
4 Casein is hardened industrially using formaldehyde.
5 Junket (curds and whey) used to be a common dessert, but students will have a variety of reactions to junket. (Maybe, make some junket for them!)
2.4 Answers
Remembering
1 a false
b false
c false
2 a cotton, silk, linen
b nylon, Kevlar, spandex
c viscose, acetate, rayon
d rhizomes, bark, leaves
e bullet-proof vests, sails, fuel tanks
3 spinneret
Understanding
4 The fibres have rough surfaces that trap and hold on to the water.
5 They are a monofilament, so breaking fishing line requires breaking many strong, chemical bonds between the polymer chains.
6 A monofilament is a long strand made up of a single fibre.