2-1 Uses Of Common Metals

I. Uses of common metals

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Topic

I.

Uses of common metals

Reference Reading

Integrated Chemistry Today, L.H.M Chung, Book 1 pg. 164 – 172, 177 – 183

Objectives

2.1 – give examples of the use of the following metals: iron, copper, aluminium, titanium and gold – relate the use of metals to their particular properties from given information, e.g. availability, price, corrosion resistance, density, lustre and malleability of the metals – be aware that the uses of metals are related to their corrosion resistance – recognise that metals are giant lattices of positive ions surrounded by electrons which are free to move throughout the lattice, i.e. 'sea of electrons' model (metallic bonding) – explain the electrical and thermal conductivity, and malleability of metals in terms of metallic bonding – recognise that few metals occur in the elemental form in nature – recognise that metal resources are limited and there is a need for conservation and recycling

Notes

I.

Uses of common metals

A. Uses of common metals Use of some common metal – iron, copper, aluminium, titanium and gold Metal

Year of discovery

m.p. / ºC 1540

Thermal conductivity fair

Electrical conductivity fair

Fe

***

Cu

***

1083

very good

very good

Al

1826

660

very good

very good

Ti

1825

1 933

fair

fair

Au

***

1063

very good

very good

Uses

Reasons for Use / price

making gratings, drain covers, cylindrical blocks for car engines, structural sheets and magnets making electricity cables, coins and radiators, for domestic plumbing and roofing making kitchen foil, aluminium can, window frames, overhead power cables, aircraft making aircraft

easy to produce, moderately corrosion resistant, ferromagnetic, hard, cheap very good conductor of heat and electricity, strong, very ductile and malleable

making jewelry, electronic components

Metals that have been known for thousands of years are marked with "***".

very malleable, light but strong, very good conductor and resist corrosion very corrosion resistant, light but very strong, expensive very precious, shiny and inert, soft when pure, dense, most malleable and ductile, extremely corrosion resistance, very expensive

I. Uses of common metals

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The use a metal mainly depends on 2 factors : 1. Economic reason – availability and price 2. Physical properties – e.g. Corrosion resistance, density, lustre, malleability etc. 1.

Economic reasons

a) Availability Availability of a metal depends mainly on two factors 1. Natural abundance and 2. easy of mining and extraction. Aluminium is the most abundant metal in the nature and has many desirable properties but it is not used as widely as iron. Aluminium is much reactive than iron. It can only be extracted by an expensive process – electrolysis of molten aluminium oxide. While iron can be extracted by heating the ore with charcoal strongly, which is less expensive. b) Price Besides the availability, price is mainly depending on the demand for the metal. Moreover, demand of a particular metal depends on its physical properties, whether it is suitable for a particular use.

2.

Physical properties of metal

a) Strength Iron is used in making many major structures e.g. bridge and building because it is cheap and very strong. b) Resistance to corrosion The extremely high corrosion resistance of gold makes it particularly suitable for making jewelry and electrical component. The jewelry made by gold will remain shiny almost forever. The electrical contact coated with gold with not be affected by the formation of oxide layer which account for the poor contact in electrical appliance. It is estimated that 40% of the steel produced is used to replace the damage due to rusting (corrosion of iron). Although resistant to corrosion to is a very desirable, metals resistant to corrosion are either too expensive or not as strong as iron. c) Density The high strength and low density of titanium make it suitable for building aeroplane in which the dead load have to be minimized. d) Lustre The shiny appearance of metal is called the lustre of metal. The lustre of silver and gold make them suitable for making jewelry. The lustre of aluminium make it suitable for making reflective surface and compact disc. e) Malleability and ductility The high malleability and ductility of copper enable it to be drawn into wire in making electrical wire.

I. Uses of common metals

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Use of other metals Metal

Year of discovery

m.p. / ºC 327

Thermal conductivity fair

Electrical conductivity fair

Pb

***

Ni

1751

1 453

fair

fair

Ag

***

961

very good

very good

Sn

***

232

fair

fair

Zn

***

420

good

good

Uses

Reasons for Use / price

making batteries, sheets for roofing, pipes, additives in petrol making stainless steel, plating metals, making coins, catalysts, ceramic chemical vessels, rechargeable Ni-Cd batteries making coins, jewelry and silverware, electrical and electronic components, medical instruments and as dental amalgam coating other metals making alloys

soft, has little strength, very dense and heavy

making galvanised steel, brass and other zinc alloys, making sheets for roofing and gutters

ductile, malleable and tough, moderate strength and hardness

precious, lustrous, inert, moderately soft, has some anti-microbial properties

malleable, can enhance solderability, offers a clean adherent surface for paints and lacquers corrosion resistant, very malleable, moderately hard

B. Giant metallic structure 1.

Structure of metal ('sea of electrons' model)

Metal has many properties different from ionic compound and covalent compound. These properties cannot be explained by any structures which have been discussed before. Therefore, scientist believes that there must be another structure unique to metal. a) Relationship between structure and properties of metal 1. 2. 2.

3.

4. 5.

High electrical conductivity ⇒ presence of free charge carrier ⇒ delocalized (free) electrons High thermal conductivity ⇒ presence of freely moving particle ⇒ delocalized (free) electrons High malleability and ductility ⇒ the bonding must be non-directional and be able to form again if the position of the atoms are changed ⇒ delocalized (free) electrons Hard ⇒ strong metallic bond ⇒ electrostatic in nature (comparatively electrostatic attraction is much stronger than gravitational attraction) High melting point and boiling point ⇒ strong metallic bond Shiny appearance (lustre) ⇒ presence of delocalized (free) electrons (it is observed that all substances possessing delocalized electrons have a shiny appearance e.g. graphite)

In order to explain the properties listed above, scientist has proposed a structure for metal, called giant metallic structure. All metals have either 1, 2 or 3 outermost shell electrons. When metal atoms come together, they donate their outermost shell electrons to form a sea of electrons. The ions left behind are arranged regularly to form a giant lattice of positive ions. The giant metallic structure can be considered as a lattice of positive ions immersing in a sea of delocalized electron.

Sea of electron model

I. Uses of common metals

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The attraction arises from the electrostatic attraction between the positive ion–delcoalized electron–positive ion. The attraction is known as metallic bond. Metallic bond is very similar to covalent bond but the bonding electron in covalent bond is localized and directional.

Origin of metallic bond

Metallic bond is non-directional (independent of direction) and capable to reform again at different position because of the mobility of the delocalized electrons. When a force is applied to a piece of metal, the positions of the atoms will be changed. At the same time, the delocalized electrons will also move together with the atoms and form a new bond at the new position. Therefore, the shape of metal can be changed without shattering. (high malleability).

C. Reactive nature of metal Most of metals exists in combined form in natural. For example, sodium in sodium chloride, aluminium in aluminium oxide. Only very few metals exists in uncombined (elemental) form in nature. Two of them are gold and mercury. And this is also why they are two of the earliest discovered metals.

D. Conservation of metal 1.

Consumption of metal

Like other natural resources, the reserve of metal resources is also limited. The following example show you how fast aluminium is consumed in Hong Kong. Weight of 1 aluminium can = 3 g/can Population of Hong Kong = 6,000,000 heads No. of days in a year = 365 days If everybody in Hong Kong consume 1 can of soft drink every day, the annual consumption of aluminium in making aluminium can will be 3 g/can × 6,000,000 heads × 1 can/head/day × 365 days = 6570000000 g = 6579 tones. This is enough to make 438 buses (each bus weighs about 15 tones.) Or in United States, the amount of aluminium used in making aluminium can each year is enough to rebuild the whole aerospace industry.

In order to conserve the resource of aluminium used every year, there are several alternatives 1. 2. 3. 4.

Use less aluminium to make each can or use other material to make the container (< 3 g) Have less population in Hong Kong (< 6,000,000,000 heads) Consume less soft drink (< 1 can/day) Have less number of days in each year (< 365 days)

So, which is the easiest way ? Is there any other alternatives ?

I. Uses of common metals 2.

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Damage to natural habitat in exploitation of metal

Besides the limited resource of metal, mining and extraction of metal ore also cause many environmental problems. The natural habitat around the mining site will be affected by the mining activities. Meanwhile, extraction of metal from the metal ore also produces many toxic wastes.

3.

Conservation of metal resources

Metal resources can be conserved according to 3R s (Recycle, Reuse and Replace) a) Recycle The metal scrap(waste) can be collected, sorted and purified again. Although the recycling process may not be economical at this stage, it help to reduce the use of new metal resource. b) Reuse Different part of an old car may be reconditioned and use as the spare parts of other cars. c)

Replace It may be possible to use other resource (e.g. plastic) to replace the metal in certain use. However, use of plastic will cause another kind of pollution.

Glossary

conductivity lustre giant lattice of positive ions reuse replace

Past Paper Questions

91 I 1 a ii 92 I 1 b i iii 93 I 2 b ii 94 I 7 b ii 95 I 6 b i ii iv 98 I 8 b ii iv

mining extraction sea of electron model

delocalized electrons giant metallic structure non-directional conservation recycle

91 I 1 a ii 1a The following is a part of the Periodic Table: Group

ii C

I II III IV V VI VII 0 Second Period a b Third Period c d e f g Referring to the letters indicated in the above table, answer the following questions Element d has a higher melting point than element c. Explain. because the metallic bond in element d is stronger. 1 mark Most candidates could not relate the higher melting point of element d to the fact that the metallic bond in it is stronger than the metallic bond in element c.

92 I 1 b i iii 1b The table below gives some information about three metals A, B and C : Metal Rate of corrosion of moist air Electrical conductivity Strength of metal A fast very good moderate B fast good good C slow very good moderate i Based on the information given above, explain which metal is most suitable for making (1) electrical cable. (2) window frames. (1) A , because – of its very good electrical conductivity – of its low cost – it can be protected from corrosion by the plastic coating [Accept rusting in place of corrosion.]

1

Cost per tonne $ 13400 $ 13800 $ 37000 5

1 mark 1 mark 1 mark

I. Uses of common metals or C , because – of its very good electrical conductivity – its slow rate of corrosion – it can last longer despite its high cost [Award 0 mark for choosing B and the explanations.] (2) B , because – of its good metallic strength – of its low cost / fast rate of corrosion overcome by painting etc.

C

C

Page 6 (1 mark) (1 mark) (1 mark)

1 mark 1 mark

or C, because – of its slow rate of corrosion (1 mark) – it can last longer despite it is more expensive (1 mark) [Award 0 mark for choosing A and the explanations.] This is an open ended question. Candidates were expected to choose a metal for making (1)electric cables and (2) window frames. In each case they should support their choice with explanations based on relevant information from the given table, e.g. Metal A was considered suitable for making electric cables because of its very good electrical conductivity and its low cost. Credit was also given to candidates who could offer an alternative choice with valid reasons, e.g. Metal C was considered equally acceptable for the said purpose because of its very good conductivity and slow rate of corrosion in air, despite its high cost. Many candidates did not score full marks because they indiscriminately copied information from the given table without first considering the relevance of each piece of information, or comparing the given data before making a choice. iii Why can metals conduct electricity ? 1 Metals have mobile (free / delocalized) electrons to conduct electricity. 1 mark [Do NOT accept metallic bond.] Some candidates thought that the conductivity of metals was due to mobile metal ions rather than free electrons.

93 I 2 b ii 2b Physical properties of substances depend mainly on the types of binding force between their constituent particles. ii In their solid states, sodium conducts electricity but sodium chloride does not. Explain. There are mobile electrons in solid sodium 1 mark but the ions in solid sodium chloride are not free to move / solid sodium chloride has no mobile ion. 1 mark C Many candidates could not distinguish between 'ions' and 'electrons'. Thus incorrect answers such as 'sodium is a conductor because it has free ions' and 'solid sodium chloride does not conduct electricity because it has no free electrons' were commonly found.

2

94 I 7 b ii 7b The table below lists some physical properties of lead, bromine and lead(II) bromide. Lead Bromine Lead(II) bromide Melting point 328 ºC -7 ºC 370 ºC Electrical conductivity in the solid state Conducting Non-conducting Non-conducting Electrical conductivity in the liquid state Conducting Non-conducting — ii Explain the difference in electrical conductivity between lead and lead(II) bromide in the solid state. 2 Lead is a metal / the bonding between lead atoms in solid is metallic bond. There exists mobile / delocalized (freely-moving) electrons in lead ∴ it conducts electricity. 1 mark In solid lead(II) bromide, the ions are not mobile ∴ it does not conduct electricity. 1 mark C The electrical conductivity of metals was often explained in terms of the presence of 'free electrons' in metals. As the term 'free electrons' might carry other meanings, it is recommended that 'free electrons' should be replaced by more proper terms such as 'delocalized electrons'. 95 I 6 b i ii iv 6b The table below gives some information about five metals. Metal Abundance in the Price per kg ($) Relative resistance of corrosion earth’s crust (%) (1 = least, 4 = most resistant) Al 8.1 170 3 Cu 0.005 140 3 Au 0.0000004 1100000 4 Fe 5.0 20 1 Zn 0.007 160 2

Relative strength of metal (1 = lowest, 3 = highest) 1 3 2 3 2

I. Uses of common metals Page 7 i Although gold has a very low abundance in the earth's crust, gold was discovered by man a long time ago. Why ? 1 Gold is very unreactive / inert / does not combine with other elements easily / can be found free in nature. 1 mark C Many candidates thought that it was the price or the appearance (colour) of gold that caused it to be discovered by men a long time ago. ii Which of the metals in the above table is the most suitable to make pipes for hot water ? Explain your answer. 3 Copper / Cu 1 mark because it does not corrode easily and has a high metallic strength / is relatively cheap. 2 marks (Award mark for explanation only if Cu is chosen.) iv (1) Based on the information given in the table, suggest ONE factor that affects the price of a metal. 2 (2) Suggest ONE other factor (not indicated in the table) that can also affect the price of a metal. (1) The price depends on its abundance in the earth's crust. 1 mark (2) Cost of extraction / cost in mining / supply / demand of the metal. 1 mark 98 I 8 b ii iv 8b The photograph below shows a can of fruit juice. The body of the can is made of iron coated with another metal. The top of the can and the ring-pull are made of aluminium.

ii iv

92 45 C 97 41 A

99 46 A

Suggest ONE reason why aluminium, rather than iron, is used for making the top of the can and the ring-pull. There is an increasing tendency for manufacturers to use cans made entirely of aluminium for the storage of fruit juice. Suggest ONE advantage and ONE disadvantage of using aluminium cans for the storage of fruit juice.

45 Both zinc and molten sodium chloride conduct electricity.

1 2

Both zinc and molten sodium chloride contain mobile ions.

41 Aluminium is used to make window frames because (1) it is strong. (2) it can resist corrosion. (3) it is the most abundant metallic element in the earth crust. Which of the above statements are correct ? A. (1) and (2) only B. (1) and (3) only C. (2) and (3) only D. (1), (2) and (3)

46 Metals have good thermal conductivity.

Metals are composed of giant lattices of positive ions surrounded by valence electrons which are free to move throughout the lattices.