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Worked solutions to textbook questions 1

Heinemann Chemistry 1 (4th edition)

Reed International Books Australia Pty Ltd

Chapter 5 Metals

Q1.

Where would you draw a line in Table 5.1 on page 79 to divide the metals from the

non-metals?

A1.

Between tungsten and carbon

Q2.

a Potassium is classed as a metal. In what properties is potassium similar to the

metal gold? In what ways is it different?

b Identify another element in Table 5.1 that has similar properties to potassium.

c Identify another metal in Table 5.1 that has similar properties to gold.

d Where are these four metals in the periodic table?

A2.

a Both potassium and gold have good thermal and electrical conductivity.

However, gold has a higher density, and higher melting and boiling temperatures

than potassium.

b sodium

c silver, copper

d Sodium and potassium are in group 1. Gold, silver and copper are transition

metals.

Q3.

a Which metals would you select if you wanted a good electrical conductor?

b What other factors not listed here might influence your choice?

A3.

a silver, copper, gold, aluminium

b Availability and cost need to be considered; also properties such as malleability

and ductility.

Q4.

Suggest some properties not included in Table 5.1 on page 79 that you would need to

consider before choosing between aluminium and iron for building a bridge.

A4.

tensile strength, cost, availability




Q5.

The properties of calcium mean that it is also classed as a metal.

a Draw a diagram to represent a calcium metal lattice.

b Describe the forces that hold this lattice together.

A5.

a

b Strong electrostatic forces of attraction between Ca2+ ions and the delocalised

valence electrons.

Q6.

Barium is an element in group 2 of the periodic table with a melting temperature of

850°C and conducts electricity in the solid state. Describe how the properties of

barium can be explained in terms of its bonding and structure.

A6.

Barium has a high melting temperature because there are strong attractive forces

between the positive ions and the delocalised electrons. Barium conducts electricity

because the delocalised electrons from the outer shell are free to move.

E1.

How many electrons are there in:

a an atom of cobalt?

b a cobalt ion with a charge of +2?

c a cobalt ion with a charge of +3?

AE1.

a 27

b 25

c 24

E2.

Write the electronic configuration of a Zn2+ ion.

AE2.

1s22s22p63s23p63d10




Q7.

Consider the following alloys: a 50-cent coin, carbon steel.

a List the elements present.

b Draw a diagram to show how the atoms of these elements are arranged in the

alloy.

A7.

a 50-cent coin: nickel and copper atoms; carbon steel: iron and carbon atoms

b

Q8.

Dentists fit partial dentures by means of small metal hooks, which attach the denture

to the remaining teeth. The hooks are easily bent at first to fit snugly in individual

mouths. If these hooks are bent backwards and forwards too often, however, they

become brittle and snap. Can you explain what happens?

A8.

The metal in the hooks becomes work-hardened and brittle.

Chapter review

Q9.

Look at groups 1–18 of the periodic table.

a Which groups contain metals only?

b Which groups contain a mixture of metals and non-metals?

A9.

a 1 and 2

b 13, 14, 15 and 16

Q10.

Which of the following metals would have similar properties to beryllium?

Ca, Cs, Cu, Pb, Mg, Zn, Sr, K

A10.

Mg, Ca, Sr

Q11.

Which of the following elements are metals?

boron, caesium, titanium, strontium, selenium, bismuth, tellurium, francium

A11.

caesium, titanium, strontium, bismuth, francium




Q12.

Look at the periodic table on page 408.

a Name a metal that would have similar properties to calcium.

b In which part of the periodic table are magnetic metals found?

A12.

a magnesium, strontium or barium

b transition series

Q13.

a What is the relative atomic mass of aluminium?

b Calculate the mass of 3.25 mol of aluminium.

c What mass of silver would contain the same number of silver atoms as there are

aluminium atoms in 500 g of aluminium?

A13.

a 27.0

b m = nM

m(Al) = 3.25 mol × 27.0 g mol–1

= 87.8 g

c n = M

m

n(Al atoms) = 0.27

500 = 18.5 mol

m = nM

m(Ag) = 18.5 mol × 107.9 g mol–1

= 2.00 × 103 g (2.00 kg)

Q14.

A bracelet is known to contain 22 g of gold.

a What is the relative atomic mass of gold?

b How many atoms of gold would be present in the bracelet?

A14.

a 197.0

b Use the formulas: N = n × NA, where NA = 6.02 1023, and n = M

m, where m is

the mass in grams, n the amount of substance in mol and M the molar mass.

n(Au) = 0.197

22 = 0.112 mol

Number of Au atoms = 0.112 × 6.02 1023 = 6.7 1022 atoms




Q15.

Use the data in Table 5.1 on page 79 to answer the following questions:

a Which metal is the best conductor of heat?

b Why is this metal not used in saucepans?

c What metals are used to make saucepans?

A15.

a silver

b It is too expensive and tarnishes readily.

c aluminium, copper (combined with stainless steel)

Q16.

Use Table 5.1 on page 79 to answer the following questions:

a Why is tungsten a suitable metal to use in the filament of an incandescent light

globe?

b Which metal would be the most suitable for building aircraft? Why?

c Which metal is a liquid at room temperature?

A16.

a Tungsten has a high melting temperature; its conductivity is not very high, that is,

it has a reasonably high resistance.

b aluminium, because of its relatively low density

c mercury

Q17.

Use the data in Table 5.1 on page 79 to answer the following questions:

a Which metal has the strongest forces of attraction between its metal ions and its

delocalised electrons?

b Why is that metal not used in place of aluminium in aircraft manufacture?

c Which metal has the lowest density?

d Why is the metal not used in making aircrafts?

A17.

a tungsten

b too dense or heavy

c potassium

d too reactive, especially in air and water

Q18.

What do you think is the most important property of each of the following metals that

has led to its widespread use?

a aluminium

b copper

c iron

A18.

a low density

b high electrical conductivity

c high tensile strength




Q19.

Metals have many uses in modern society.

a i Name one metal that is used in large quantities in the building industry.

ii What properties of the metal make it suitable for this use?

iii What properties limit its use in buildings?

b i Name one metal that is used in large quantities for making electrical wires.

ii What properties of this metal make it suitable for use in wires?

c i Name two metals that are used in large quantities in the jewellery trade.

ii What properties of these metals make them suitable for this use?

A19.

a i iron (steel) or aluminium

ii Iron and steel are strong. Aluminium has a low density (light) and can be

easily coloured.

iii Iron rusts easily. Aluminium is soft and lacks strength.

b i copper

ii good conductor of electricity and is ductile

c i gold, silver and platinum

ii non-reactive, malleable and ductile, lustrous

Q20.

Use the metallic bonding model to explain each of the following observations:

a Copper wire transmits electricity.

b A metal spoon used to stir a boiling mixture becomes too hot to hold.

c Iron has a high melting temperature, 1540°C.

d Lead has a density of 11.4 g mL–1, which is much higher than a non-metal such as

sulfur.

e Copper can be drawn out in the form of a wire.

A20.

a When a current is applied to the copper wire, the free-moving, delocalised

electrons move from one end to the other and so the copper wire conducts

electricity.

b The delocalised electrons in the metal spoon obtain energy from the boiling

mixture and move more quickly. These electrons move freely throughout the

spoon, colliding with other electrons and metal ions, transferring energy so that

the spoon becomes warmer and, eventually, too hot to hold.

c A lot of energy is required to overcome the strong forces of attraction between

the iron ions and the delocalised electrons in the metal lattice, so that the iron

changes from a solid to a liquid.

d Because of the strong forces of attraction between them, the lead ions and the

delocalised electrons form a closely packed three-dimensional structure. Also, the

lead atom itself has a higher mass-to-volume ratio than the sulfur atom. This

means that the density—the mass per volume—is high.

e As the copper is drawn out, the copper ions are forced apart and the delocalised

electrons rearrange themselves around these ions and re-establish strong forces of

attraction.




Q21.

Alloys are modified metals. In each example, state the metals used and one property

that is different from the original metals.

a an Australian 20-cent coin

b solder

c 9-carat gold

d stainless steel

e brass

f dental mercury amalgam

A21.

a copper and nickel; harder, more corrosion resistant and a silver colour

b tin and lead; lower melting temperature

c gold, silver and copper; harder

d iron, nickel and chromium; resists rusting, stronger

e copper and zinc; harder, stronger and resists corrosion

f mercury and zinc (sometimes a little silver is added); harder, non-toxic

Q22.

Draw your own concept map, using the following terms: metal, cation, delocalised

electron, lattice, electrostatic attraction.

A22.

A variety of answers is possible. An example of a possible answer is shown.




Q23.

Some metals are found as elements in nature; others are found as compounds,

combined with other elements, such as oxygen and sulphur, in ores. Australia has

natural reserves of many metals and ores, with mining producing large quantities of

metals, including aluminium, copper, gold, iron and silver.

a Give the chemical symbol for each of these metals.

b In which group, period and block of the periodic table are each of these metals

found?

c Which of these metals are found in nature as elements rather than compounds?

d Which of these metals are transition elements?

e Which of these elements is the rarest?

A23.

a aluminium Al, copper Cu, gold Au, iron Fe, silver Ag

b aluminium: period 3, group 13, p-block

copper: period 4, 1st transition series, d-block

gold: period 6, 3rd transition series, d-block

iron: period 4, 1st transition series, d-block

silver: period 5, 2nd transition series, d-block

c gold and silver

d copper, gold, iron and silver

e gold

Q24.

It has been shown using X-rays that metals occur as crystals.

a Explain, using the metallic bonding model, why metals form crystals.

b What problems can this crystalline structure of metals cause?

A24.

a The positive ions are arranged in a regular, three-dimensional lattice.

b Stress corrosion cracking can occur between the crystal grains.

Q25.

Do you think ‘Liquidmetal’ is an appropriate name for the material described on

page 89? Give reasons for your answer.

A25.

It is an appropriate name in terms of the lack of the regular, crystalline structure that is

generally associated with metals. However, there are other amorphous solids and they

are not classified as liquids because, overall, their properties do not fit the model of a

liquid.




Q26.

a Which metals are used in greatest quantities today?

b For what purposes are they used?

c How does the usage of metals today differ from that of 100 years ago?

A26.

Think about the metals you see around your house, your means of transport, your

town or suburb.

a iron, aluminium, copper

b buildings, bridges, transport

c Aluminium was not available 100 years ago. Many alloys are now available.

Q27.

Aluminium is the most abundant metal in the Earth’s crust. Why was aluminium not

available before 1886?

A27.

Aluminium is extracted from its ore by electrolysis. There was no source of electricity

available for this process until 1886.

Q28.

Titanium is a comparatively abundant metal in the Earth’s crust and Australia has

large reserves of this metal. It is used increasingly in our technological society. Find

out:

a where titanium is mined in Australia

b the main uses of titanium

c the properties of titanium that make it useful for those purposes

A28.

a Titanium is mined in the south-western coastal region of Western Australia and

the central eastern coast of Australia (Newcastle to Brisbane).

b Titanium is alloyed with aluminium in aircraft and spacecraft, and is also used in

spectacle frames for people with acidic skin, which stains regular frames green.

TiO2 is used as a white pigment in paints.

c Titanium is very strong and has a relatively low density.

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