Book 1

Chemistry A Modern ViewExercise Book 1　Suggested answers

ContentsPART I INTRODUCING CHEMISTRYChapter 1 What is Chemistry? 2Chapter 2 The fundamentals of chemistry 4

PART II PLANET EARTHChapter 3 The atmosphere 6Chapter 4 Oceans 8Chapter 5 Rocks and minerals 9

PART III THE MICROSCOPIC WORLDChapter 6 Atomic structure 10Chapter 7 The Periodic Table 12Chapter 8 Chemical bonding: Ionic bonding 14Chapter 9 Chemical bonding: Covalent bonding 18Chapter 10 Structures and properties 20

PART IV METALSChapter 11 Occurrence and extraction of metals 23Chapter 12 Reactivity of metals 26Chapter 13 Reacting masses 29Chapter 14 Corrosion of metals and their protection 32

©Aristo Educational Press Ltd. 2003 - 1 -

CHAPTER 1What is Chemistry?

1. D

2. B

3. D

4. B

5. (a) Day and night alternate.

(b) There is full moon on the 15th day of every lunar month.

(c) In the Northern Hemisphere, it is hot during July and August but cold during December and

January.

(d) Grass is green.

(e) Water flows downhill.

(Other answers may be given.)

6. a. Volume of oxygen increases with increasing temperature.

b. Gas pressure also affects the volume of a gas. To study the effect of temperature on the volume of

a gas, we must keep other factors constant.

c. Repeat the experiment with other gases and see whether the pattern is still found.

7. a. (i) The light bulb is burnt out

(ii) The fuse is burnt out.

(iii) Someone else has switched off the light switch.

(iv) There is a breakdown of electricity supply in the area at that moment.

b. (i) Replace with a new light bulb.

(ii) Check the switch box turn on the circuit breaker or replace with a new fuse.

(iii) Check (or turn on) the light switch.

(iv) Look out from the window see whether there is also blackout in the nearby houses.

8. a. Observable change: perceived by eyes, hands, nose or ears;

Visible change: perceived by eyes only, thus it is only part of observable change

b. There is no visible change on mixing dilute hydrochloric acid and sodium hydroxide solution two

colourless solutions are mixed to give a colourless solution; but there is an observable change

the resulting solution becomes warm. (Other examples may be given)


9. a. Theory

b. Scientific fact

c. Scientific fact

d. Law

CHAPTER 2The fundamentals of chemistry


1. A

2. A

3. B

4. a. A, C

b. B, F

c. D, E

d. A, C

e. B, D, E, F

5. a. Mixture; Reason: water + salts

b. Mixture; Reason: nitrogen + oxygen + others

c. Element

d. Compound

e. Mixture; Reason: water + ethanol + others

f. Mixture; Reason: water + dyes

g. Compound

h. Mixture; Reason: water + sugar + carbon dioxide + others

6. a. E

b. A

c. F

d. C

e. D

f. B

7. a.

State Volume Shape

Gas Variable Variable

Liquid Fixed Variable

Solid Fixed Fixed

b. See textbook 1 p.30, fig 2.12


CHAPTER 3The atmosphere


1. B

2. C

3. A

4. C

5. A

6. E

7. G

8. F

9. A

10. D

11. B

12. C

13. a. The atmosphere is a gaseous layer surrounding the Earth.

b. 78% nitrogen, 21% oxygen, 1% argon, 0.03% carbon dioxide

c. Fractional distillation

14. a. Air expands on heating and this would affect the accuracy of the readings. Thus volumes should

be taken at the same temperature (room temperature).

b. No, because there was a further reduction in volume of air after the second heating and cooling.

c. Yes, because the same reading was obtained after third heating and cooling.

d. 20 cm3

e. Nitrogen

f. 20%

g. It changed to copper(II) oxide which is black in colour.

copper + oxygen copper(II) oxide


h. Heavier. Oxygen in air combined with copper to form copper(II) oxide thus made it heavier.

CHAPTER 4Oceans

1. C


2. B

3. A

4. A

5. C

6. D

7. C

8. a. Sea water is led into a special enclosure which can be exposed to direct sunlight. Water

evaporates, leaving common salt behind.

b. Pure common salt can be obtained from sea water by filtration followed by crystallization.

9. a. Sand and mud. Filtration.

b. Use chlorine to sterilize the water.

c. It is cheaper to buy water from the Guangdong Province.

CHAPTER 5Rocks and minerals

1. C

2. C


3. D

4. B

5. B

6. a. A : Calcium oxide (quicklime) B : Calcium hydroxide solution (limewater)

C : Calcium carbonate D : Calcium chloride

b. (i) When water is added to the white solid of calcium oxide, it turns into a white suspension of

calcium hydroxide (slaked lime), and gives out a lot of heat at the same time. After filtration,

a clear solution of calcium hydroxide (limewater) is formed.

calcium oxide + water calcium hydroxide

(ii) The clear colourless solution turns milky when carbon dioxide is passing through it.

calcium hydroxide + carbon dioxide calcium carbonate + water

(limewater)

(iii) Effervescence occurs. The solid calcium carbonate dissolves to give a colourless solution.

calcium carbonate + hydrochloric acid calcium chloride + carbon dioxide + water

(iv) No observable change.

calcium hydroxide + hydrochloric acid calcium chloride + water

7. (a) Ores

(b) Haematite

(c) After concentrating the haematite ore, the ore is heated with coke (carbon) to a high temperature

in a blast furnace.

iron(III) oxide + carbon iron + carbon dioxide

8. (a) Weathering of rocks is the slow process (usually over thousands of years) in which exposed rocks

are broken down into smaller pieces.

(b) See textbook 1, p. 94 95


CHAPTER 6Atomic structure

1. D

2. C

3. D

4. A

5. A

6. B

7. D

8. D

9. B

10. B

11. B

12. B

13. (a) O, C, H, N, Ca

(b) Ca

14. (a) 1540C.

(b) Bromine

(c) Phosphorus

(d) Helium

(e) 119 445C

(f) (i) Iron

(ii) Helium


(g) aluminium, copper, iron, lead, magnesium, mercury, potassium, sodium, zinc

bromine, chlorine, helium, nitrogen, oxygen, phosphorus, sulphur

(h) Mercury, potassium, sodium, lead, zinc, magnesium, aluminium, copper, iron

(i) (I) chlorine, helium, nitrogen, oxygen

(II) bromine, mercury

(III) aluminium, copper, iron, lead, magnesium, phosphorus, potassium, sodium, sulphur, zinc

15. 6 1013 g cm3

16. (a) B, D, F, G

A, C

E, H(b)

(b)

(c) B, D, F, G

(d) B, C, G

(e) D

(f) A : bromine, the only liquid non-metal; C : mercury, the only liquid metal

17. (a) P and R

(b) Carbon

(c) P : carbon-13, R : carbon-12

(d) P : C Q : B R : C S : N

18. 24.3

19. (a) 40, mass number

(b) Potassium

20. (a) 82

(b) Lead

CHAPTER 7


136

115

137

137

126

The Periodic Table

1. C

2. C

3. C

4. D

5.

ElementElectronic

arrangement

Atomic

number

Period

number

Group

number

A 2,6 8 2 VI

B 2,8,2 12 3 II

C 2,8,8,1 19 4 I

D 2,8 10 2 0

E 2,8,18,3 31 4 III

F 2,8,18,18,7 53 5 VII

6.

Group

I II III IV V VI VII 0

Period

2

3 A

4 B

5 E

6 C D

7 F

7. (a) P : 3, Q : 5, R : 11, S : 14, T : 16, U : 20

(b) P : 2, 1; Q : 2, 3; R : 2, 8, 1; S : 2, 8, 4; T : 2, 8, 6; U : 2, 8, 8, 2

(c) P : I, Q : III, R : I, S : IV, T : VI, U : II

(d) P : metal, Q : semi-metal, R : metal, S: semi-metal, T : non-metal, U : meta

8. (a) 2

(b) They have the same number of outer shell electrons.


(c) Increase

(d) (i) Beryllium does not react with cold water.

(ii) Barium reacts vigorously with cold water to give hydrogen gas.

(e) Stored under oil.

10. (a) magnesium

(b) fluorine

(c) chlorine

(d) sodium

11. (a) magnesium, silicon, chlorine. Period 3.

(b) lithium, rubidium, caesium. Group I.

(c) iron, copper

(d) caesium

(e) fluorine

(f) silicon

(g) helium

(h) fluorine, chlorine, helium

(i) fluorine, chlorine


CHAPTER 8Chemical bonding: Ionic bonding

1. B

2. C

3. D

4. C

5. D

6. A

7. B

8. B

9. D

10. sodium, calcium, platinum

magnesium sulphate, copper(II) chromate

iodine, oxygen, sugar, water

11. Orange colour migrates towards A.

12. No migration of colour.

13. Blue colour migrates towards B, yellow colour migrates towards A.

14.


ParticleAtomic

numberMass no.

Number of

protons neutrons electrons

(a) Na atom

(b) P atom

(c) U atom

(d) S2 ion

(e) Cs+ ion

(f) Os atom

(g) Ba2+ ion

(h) Br ion

11

15

92

16

55

76

56

35

23

31

238

32

133

192

138

79

11

15

92

16

55

76

56

35

12

16

146

16

78

116

82

44

11

15

92

18

54

76

54

36

15. (a) Ar, Cl, and K+

(b) Cl, Br

16. (a) E

(b) A, D

(c) A, D

(d) B

(e) C

17. (a) 2, 8, 18, 32, 18, 4

(b) 82

(c) Lead

18. (a) Group VI

(b) Semi-metal

(c) To gain 2 electrons

(d) 2

(e) Se2


19. (a)

Formulae Name

MnSO4 5H2O Manganese(II) sulphate-5-water

(NH4)2CO3 ammonium carbonate

AgNO3 silver nitrate

Fe(OH)3 iron(III) hydroxide

KMnO4 potassium permanganate

Na2SO3 sodium sulphite

CuSO4 5H2O copper(II) sulphate-5-water

FeCl3 6H2O iron(III) chloride-6-water

FeCl2 4H2O iron(II) chloride-4-water

Mg(HCO3)2 magnesium hydrogencarbonate

PbO lead(II) oxide

Na2SiO3 sodium silicate

(b)

Name Formulae

Potassium dichromate K2Cr2O7

Silver oxide Ag2O

Copper(I) oxide Cu2O

Mercury(II) chloride HgCl2

Lead(IV) oxide PbO2

Sodium nitrite NaNO2

Aluminium oxide Al2O3

Calcium phosphate Ca3(PO4)2

Zinc sulphide ZnS

Sodium hydrogensulphate NaHSO4

Chromium(III) chloride-6-water CrCl3 . 6H2O20

20. (a) 3+

(b) 2

(c) X : 2, 8, 3 Y : 2, 6

(d) X : aluminium, Y : oxygen; Al2O3


21. (a)

(b)

(c)

(d)


CHAPTER 9Chemical bonding: Covalent bonding

1. D

2. B

3. B

4. B

5. B

6. (ii) (a) (b)

(c) (d)

(e) (f)

7. (a) Cl, C, Ar, Na

(b) Cl2, C, S8, Ar, Na, NN

(c) Mg2+, Cl, S2

(d) HI, C2H6, CuSO4

(e) HI, NN

8. (a) molecules

(b) atoms

(c) molecules

(d) ions

(e) atoms

(f) molecules

(g) atoms

(h) ions

9. (a) (i); (v)


(ii); (iii), (iv)

(ii); (iii)

(iv); (v)

(b) A : chloride ion; B : sodium ion; C : oxygen atom; D : hydrogen atom; E : neon atom

10. (a) Cu, Hg

(b) NaCl, NH4Cl

(c) NaCl, NH4Cl, H2SO4

(d) N2, H2SO4, CO

(e) H2SO4, CO

(f) N2, NH4Cl, H2SO4, CO

11 (a) (b)

(c) (d)

(e) (f)

(g)

12. (a) 1, 4, 6, 7

(b) P

(c) (i) P2R

(ii) PS

(iii) QR2

(iv) QS4

(d) (i) (ii)

(iii) (iv)

CHAPTER 10


Structures and properties

1. D

2. B

3. D

4. B

5. C

6. B

7. A

8. C

9. (a) Sodium chloride consists of a giant ionic lattice of Na+ and Cl ions. Strong ionic bonds have to be

overcome for it to melt. It thus has a high melting point.

(b) Carbon dioxide is a covalent compound with a simple molecular structure. By overcoming the

weak intermolecular forces, the discrete molecules can be easily separated. This accounts for the

low melting point and boiling point. Silicon(IV) oxide, however, is a covalent compound with a

giant covalent structure. The atoms are held in a giant network by strong covalent bonds. To melt

the solid, very many strong covalent bonds have to be broken. This requires a lot of heat energy.

This accounts for the high melting point.

(c) There are only weak van der Waals' forces between N2 molecules. Thus nitrogen has low melting

point and boiling point. Within each N2 molecule, the two nitrogen atoms are joined by strong triple

covalent bond. Therefore it is very difficult to break the molecule into atoms.

10. (a) E. Electrical conductor when solid and liquid.

(b) B, D. Non-conductors of electricity when solid, conductors when liquid. (Note: Not all ionic

compounds are soluble in water. In this case, D is insoluble in water.)

(c) They are not solids at room conditions. (Ionic compounds are all solids at room conditions.)

(d) A, C

(e) F

(f) B, D, E, F

(g) A, C


11.

Elements in the

compound

Magnesium

and chlorine

Phosphorus

and hydrogen

Potassium

and fluorine

Formula of the

compoundMgCl2 PH3 KF

Type of

bondingionic covalent ionic

Type of

structuregiant ionic structure

simple molecular

structuregiant ionic structure

Electrical

conductivity

when

solidnon-conductor non-conductor non-conductor

when

liquidgood conductor non-conductor good conductor

12. (a) P and S do not react

(b) PR; ionic bond

(c) QR4; covalent bonds within molecule; van der Waals' forces between molecules

(d) Q and S do not react

13. (a) D

(b) E

(c) D

(d) E

(e) A

(f) A

(g) B

14. (a) D

(b) C

(c) A

(d) B

(e) B

(f) C D

15. (a) KCl; SnCl4

(b) Giant ionic structure; it is a high-melting solid formed from metal and non-metal.


(c) Simple molecular structure; low m.p.

(d) No; no ions present.

CHAPTER 11Occurrence and extraction of metals


1. B

2. D

3. A

4. C

5. A

6. C

7. B

8. C

9. A

10. B

11. A

12. C

13. D

14. B

15. D

16. D

17. B

18. D

19. B


20. A

21. D

22. (1) Overhead power cables: very good conductor of electricity, low density, ductile

(2) Saucepans: very good conductor of heat, non-poisonous, malleable, corrosion resistant

(3) Soft drink cans: non-poisonous, light, corrosion resistant, malleable

(4) Window frames: corrosion resistant, strong

(Other answers may be given)

23. (a) Strong, malleable, ductile, corrosion resistant, non-poisonous.

(b) (i) No. When used to transmit wave or digital signals, optical fibres can replace copper wires.

However, optical fibres are non-conductors of electricity. They therefore cannot replace

copper wires to transfer electric current.

(ii) Aluminium could be used as a cheap substitute for copper in making electrical wires.

However, electrical conductivity of aluminium is not as good as copper.

(c) The government may be reluctant to make more 'copper' coins. Besides, people may keep copper

coins instead of spending them.

24. (a)

(b) The black mixture first heated to red hot, and finally changed into a reddish-brown solid.

(c) 2CuO(s) + C(s) 2Cu(s) + CO2(g)

(d) Oxygen in air would react with hot copper to form copper(II) oxide again.


25. A metal will be recycled only if it is economical to do so. Gold is very expensive. On the other hand, the

cost of extracting iron from iron ore is low. In comparison, the cost of recycling iron from scrap iron may

be even higher in some cases.

26. (a) The factors to be considered in each case are:

(i) no wind-borne pollution B has advantages (ii) and (iii) only.

(ii) development area payment C has advantage (iii) only.

(iii) deep water port. D has advantages (ii) and (iii) only.

A has all the 3 advantages. E has none of the advantages.

(b) A is the best site.

(c) The aluminium refinery should be situated near electric power stations.

(d) A metal company will recycle used metal only if it is economical to do so. The company has to

work out the total cost of collecting the scrap, transporting it, sorting the metal out, melting it down,

getting rid of impurities, and cost of storage etc.

27. (a) (There is no specific answer for question 27.)

28. (a) 50 years

(b) (i) Reusing copper articles.

(ii) Recycling used copper.

(iii) Replacing copper by other materials.

(c) There are probably metal ores deep in the Earth's crust that we do not yet know about. With

advanced modern technology (e.g. satellite surveying), it is possible to detect and mine such ores.

(d) Aluminium

CHAPTER 12Reactivity of metals

1. D


2. A

3. C

4. C

5. C

6. C

7. C

8. A

9. D

10. B

11. B, D, C, A

12. (a) 4Al(s) + 3O2(g) 2Al2O3(s)

(b) 2C2H6(g) + 7O2(g) 4CO2(s) + 6H2O(l)

(c) 2Cu(NO3)2(s) 2CuO(s) + 4NO2(g) + O2(g)

(d) 2KClO3(s) 2KCl(s) + 3O2(g)

(e) 2C2H2(g) + 5O2(g) 4CO2(g) + 2H2O(l)

(f) 3CuO(s) + 2NH3(g) 3Cu(s) + N2(g) + 3H2O(l)

(g) 4FeS2(s) + 11O2(g) 2Fe2O3(s) + 8SO2(g)

(h) 4NH3(g) + 5O2(g) 4NO(g) + 6H2O(l)

(i) Mg3N2(s) + 3H2O(l) 3MgO(s) + 2NH3(g)

(j) 2Al(s) + 3Fe2+(aq) 2Al3+(aq) + 3Fe(s)

13. (a) Chromium(III) oxide + aluminium chromium + aluminium oxide

(b) Chromium is lower than aluminium in the reactivity series.

(c) Dip a piece of iron in a solution of chromium(III) salt.

(i) If displacement reaction occurs (as indicated by shiny deposit of chromium), it indicates iron

is higher than chromium in the reactivity series.

(ii) If there is no apparent change, it is probable that iron is lower than chromium in the series

confirm this by dipping chromium metal in a solution of iron(II) salt and check if


displacement reaction occurs.

14. (a) C

(b) E

(c) D

(d) B

(e) A

(f) E

15. (a) Fe(s) + Cu2+(aq) Fe2+(aq) + Cu(s)

(b) 2Br(aq) + Cl2(aq) 2Cl(aq) + Br2(aq)

16. (a) Al(s) + 3AgNO3(aq) Al(NO3)3(aq) + 3Ag(s)

(b) Al(s) + 3Ag+ (aq) Al3+(aq) + 3Ag(s)

17. (a) A

(b) C

(c) D

(d) E

(e) B

(f) C

(g) D

18. (a) C > A > D > B > E

(b) It would be too dangerous to attempt such an explosive reaction.

(c) C; it reacts with air readily; dull yellowish grey.

(d) E

(e) B, E

(f) Yes, B is above E in the reactivity series; no reaction.

(g) A (calcium); B (copper); C (potassium or sodium); D (aluminium, zinc or iron); E (mercury or

silver)

19. (a) Potassium or sodium.

(b) Silver or mercury.

(c) E. E reacts with cold water, while A does not.

(d) B

(e) C, E, A, B, D

(f) The more reactive metals tend to be first obtained at a later period. This is because they form

more stable compounds from which the metals are less easily extracted.


CHAPTER 13Reacting masses

1. D

2. B


3. D

4. B

5. D

6. C

7. D

8. C

9. (a) 24 g

(b) 39.6 g

(c) 702 g

(d) 163.5 g

(e) 858 g

10.

Substance or ionMolar mass

(g mol1)

No. of moles

(mol)Mass (g)

(a) Ar 39.9 2 79.8

(b)

(c)

N2 28 0.5 14

FeS 87.9 10 879

(d) CO32 60 0.25 15

(e) CuO 79.5 2.00 159

(f) Unknown 46 0.25 11.5

11.

FormulaMolar mass

(g mol1)Mass (g)

Number of

moles

(mol)

formula

units

(a) O 16.0 8.00 0.500 3.01 1023

(b) O2 32.0 16.0 0.500 3.01 1023

(c)

(d)

N2 14.0 1.40 0.100 6.02 1023

NO2 28.0 1.40 0.0500 3.01 1022


(e) NO2 46.0 2.30 0.0500 3.01 1022

(f) SO42 96.1 961 10.0 6.02 1024

(g) unknown 44.0 22.0 0.500 3.01 1023

12. (a) 0.100 mol

(b) 0.200 mol

(c) 0.100 mol

(d) 0.800 mol

(e) 4.82 3 1023

13. (a) 18.0 g mol1; yes

(b) 2.99 1023 g

(c) 2.99 105 g; no

14. (a) 0.20 mol

(b) 5.00 mol

(c) 8.00 mol

(d) (i) 0.0200 mol

(ii) 0.0600 mol

15. (a) Na: 14.28% S: 9.97% O: 69.54% H: 6.21%

(b) 36.0 g

(c) (i) 4.0 g

(ii) 59.5 g

(iii) 31 g

(d) 56

16. A. (3), (6), (7), (9)

B. (4), (10)

C. (1), (6), (8), (9) (Note: SiO2 is not a molecular formula, as there are no SiO2 molecules. Refer to

textbook 1 p.195.)

D. (2), (5)

17. (a) 1.00 g


(b) 4.80 g

(c) C2H5

18. (a) C: 1.44 g, H: 0.36 g, O: 1.92 g

(b) CH3O

19. MO

20. 8y

21. 64 g mol1

CHAPTER 14Corrosion of metals and their protection

1. B

2. D


3. C

4. D

5. D

6. C

7. C

8. A metal higher in the metal reactivity series corrodes faster (except when there is a protective layer

formed, e.g. Al, Zn)

9. (a) Oxygen (air), water

(b) (i) No or little oxygen

(ii) No oxygen, no water

(iii) Little water (very dry climate)

(c) Sea water; it contains a high concentration of salts (e.g. sodium chloride), thus more conducting.

10. (a) To provide a clean iron surface.

(b) A deeper blue colour indicates more Fe2+(aq) ions produced and a faster rate of rusting.

(c) Rusting in A the fastest (salt present, solution more conducting); B and C quite the same (no salt

present).

11. (a) Anodizing

(b) Oiling

(c) Chromium-plating

(d) Oiling

(e) Painting

(f) Use of stainless steel

(g) Use of gold electrical contacts

(h) Chromium-plating

(i) Chromium-plating

12. (a) Protective Al2O3 layer formed on surface by itself.

(b) Exposed iron still protected from rusting; zinc, being more reactive, loses electrons to iron,

preventing formation of Fe2+(aq) ions (sacrificial protection).

(c) Exposed iron is not protected and rusts even faster than no tin was plated. Iron, being more


reactive, loses electrons to tin, thus encouraging formation of Fe2+(aq) ions and speeding up

rusting.

(d) No, Zn2+ ions are poisonous.

(e) Stainless steel is too expensive for making large objects.

13. (a) D

(b) C

(c) C

(d) F

14. (a) (i) Water and air.

(ii) Water, air, sodium chloride and mud.

(iii) Yes.

(iv) Paint coatings exclude most of air and water from the iron surface.

(b) Car exhaust gases are very hot, consisting mainly of water vapour, carbon dioxide and nitrogen

dioxide. Thus high temperature and presence of acid solutions make the exhaust pipe rust more

rapidly.

(c) (i) Ceramic or plastic

(ii) Aluminium

15. (a) Slower. Fresh water contains much less salts than sea water. Salt solution speeds up rusting.

Zinc, magnesium.

(b) Zinc, magnesium.

(c) Zinc or magnesium, being more reactive than iron, protects the iron from rusting by sacrificial

protection.

(d) Connect the steel legs to the negative terminal of a d.c. source.

(e) No. Stainless steel is expensive and is usually only used for making small objects.

16. (a) Option 1: Another new bridge will need to be built after 12 years.

Minimum total cost

= ($ 8 000 000 + $ 800 000) 2

= $ 17 600 000

Option 2: Six times of painting will be required.

Total cost

= $ 8 000 000 + $ 800 000 x 6

= $ 12 800 000

Option 3: Total cost = $ 11 500 000 + $ 800 000


= $ 12 300 000

(b) Option 3, which is the cheapest one.


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