Topic 1 Planet Earth Suggested Teaching Schemes

38

Topic 1 Planet Earth

Suggested teaching scheme for the Chemistry curriculumThe following suggested teaching schemes are for teachers’ reference only. Teachers may revise them based on the time-tabling arrangement of their own schools.

Scheme 1: Chemistry to be studied in Secondary 3, 4, 5 and 6In many schools, the Chemistry curriculum is studied in Secondary 3, 4, 5 and 6. Although the distribution of periods varies from school to school, the total number of periods for the curriculum is generally around 416. A possible distribution of periods is as follows:

A possible distribution of periods for S3, S4, S5 and S6

S3 S4 S5 S6

Number of teaching weeks per year 28 28 28 16

Number of periods per week 2 5 5 5

Total number of periods per year 56 140 140 80

Total number of periods for the curriculum 416

Suggested teaching scheme for the curriculum

Level ContentSuggested number

of period(s)

S3(56 periods)

Topic 1 Planet Earth 12

Topic 2 Microscopic World I 44

S4(140 periods)

Revision on laboratory safety 1

Topic 3 Metals 39

Topic 4 Acids and Bases 45

Topic 5 Redox Reactions, Chemical Cells and Electrolysis 41

Topic 6 Microscopic World II 14

S5(140 periods)


Topic 7 Fossil Fuels and Carbon Compounds 32

Topic 8 Chemistry of Carbon Compounds 45

Topic 9 Chemical Reactions and Energy 13

Topic 10 Rate of Reaction 16

Topic 11 Chemical Equilibrium 18

Topic 12 Patterns in the Chemical World 15

S6(80 periods)


Topic 13 Industrial Chemistry 39

Topic 14 Materials Chemistry 39

Topic 15 Analytical Chemistry 40

Schools taking investigative study need to allocate an extra of 30 periods for the curriculum.

Only 2 out of 3 Only 2 out of 3

Suggested Teaching Schemes

39


Scheme 2: Chemistry to be studied in Secondary 4, 5 and 6In some schools, the Chemistry curriculum is studied in Secondary 4, 5 and 6. The total number of periods for the curriculum is generally around 360. A possible distribution of periods is as follows:

A possible distribution of periods for S4, S5 and S6

S4 S5 S6

Number of teaching weeks per year 28 28 16

Number of periods per week 5 5 5

Total number of periods per year 140 140 80



Level ContentSuggested number

of period(s)

S4(140 periods)



Topic 3 Metals 32



S5(140 periods)


Topic 6 Microscopic World II 13

Topic 7 Fossil Fuels and Carbon Compounds 29

Topic 8 Chemistry of Carbon Compounds 41


Topic 10 Rate of Reaction 15

Topic 11 Chemical Equilibrium 16

Topic 12 Patterns in the Chemical World 13

S6(80 periods)


Topic 13 Industrial Chemistry 39

Topic 14 Materials Chemistry 39

Topic 15 Analytical Chemistry 40

Schools taking investigative study need to allocate an extra of 30 periods for the curriculum.

Only 2 out of 3 Only 2 out of 3

40


Suggested teaching scheme for the Combined Science (Chemistry Part) curriculumThe following suggested teaching schemes are for teachers’ reference only. Teachers may revise them based on the time-tabling arrangement of their own schools.

Scheme 1: Combined Science (Chemistry Part) to be studied in Secondary 3, 4, 5 and 6In many schools, the Chemistry Part of Combined Science is studied in Secondary 3, 4, 5 and 6. Although the distribution of periods varies from school to school, the total number of periods for the curriculum is generally around 228. A possible distribution of periods is as follows:

A possible distribution of periods for S3, S4, S5 and S6

S3 S4 S5 S6



Total number of periods per year 56 84 56 32



Level ContentSuggested number of

period(s)

S3(56 periods)



S4(84 periods)


Topic 3 Metals 37


S5(56 periods)



Topic 6 Fossil Fuels and Carbon Compounds (Units 24 & 25)

14

S6(32 periods)


Topic 6 Fossil Fuels and Carbon Compounds(Units 26–28)

18


41


Scheme 2: Combined Science (Chemistry Part) to be studied in Secondary 4, 5 and 6In some schools, the Chemistry Part of Combined Science is studied in Secondary 4, 5 and 6. The total number of periods for the curriculum is generally around 186. A possible distribution of periods is as follows:

A possible distribution of periods for S4, S5 and S6

S4S5

S61st term 2nd term



Total number of periods per year 84 70 32



Level ContentSuggested number of

period(s)

S4(84 periods)



Topic 3 Metals 32

Topic 4 Acids and Bases(Units 14 & 15)

13

S5(70 periods)


Topic 4 Acids and Bases(Units 16–18)

25


Topic 6 Fossil Fuels and Carbon Compounds(Units 24 & 25)

11

S6(32 periods)


Topic 6 Fossil Fuels and Carbon Compounds(Units 26–28)

19


42


Suggested number of periods for Topic 1

Chemistry / Combined Science

(Chemistry Part) for

Total number of periods

Suggested number of periods for each unit

S3–S6(Scheme 1)

12

Unit 1 Introducing chemistryUnit 2 The atmosphereUnit 3 The oceanUnit 4 Rocks and minerals

2433

S4–S6(Scheme 2)

8

Unit 1 Introducing chemistryUnit 2 The atmosphereUnit 3 The oceanUnit 4 Rocks and minerals

2222

43

Teaching Plan

The first unit of the topic gives a brief introduction of what chemistry is and its relationship with our daily lives. It also prepares students to work in the laboratory with a brief review of the laboratory safety rules.

The natural world is made up of chemicals. The atmosphere, the ocean and the Earth’s crust are major sources of chemicals. In the following units, students are going to study possible methods for isolating useful materials from these sources and analyzing the materials using various tests. They should also be able to use word equations to represent chemical changes, and suggest appropriate methods for separating mixtures and testing some chemical species.

Organization of the topic

Teaching Plan

Planet Earth

Unit 1Introducing chemistry

Unit 2The atmosphere

Unit 3The ocean

Unit 4Rocks and minerals

44


Unit 1 Introducing chemistry

Section Key point(s)Suggested task(s) for

studentsRemark

Total number of period = 1

1.1 What is chemistry? • Introducing chemistry

1.2 Why study chemistry?

• Roles that chemistry plays in our lives

• Discussion

• Greenhouse effect

1.3 Laboratory safety • Laboratory safety rules • Practice 1.1 • Resources on

Laboratory Safety and Management:

http://cd1.edb.hkedcity.net/cd/science/laboratory/content_activities.html

(accessed July 2014)• Students have studied

‘safety in the laboratory’ in Unit 1 of Science (secondary 1–3).


1.4 Hazard warning labels

• Common hazard warning labels for chemicals

• The hazardous nature of household chemicals

• Find & Share — Safety precautions for

handling household products

• Visit the following

website to learn more about the hazardous nature of chemicals around the house:

http://www.epa.gov/kidshometour/tour.htm

(accessed July 2014)

1.5 Common apparatus in the laboratory

• Common apparatus• Microscale apparatus

• Activity 1.1 — Introduction to practical work

• Practice 1.2

• Students have studied ‘common laboratory equipment’ in Unit 1 of Science (secondary 1–3).

45

Teaching Plan

Unit 2 The atmosphere


studentsRemark

Total number of periods = 2 (Scheme 1), Total number of period = 1 (Scheme 2)

2.1 The Earth • The Earth’s crust, the ocean and the atmosphere as major sources of chemicals

• List of useful resources from the Earth

2.2 Classification of matter: pure substances and mixtures

• Definitions• Some everyday mixtures

• Practice 2.1

2.3 Elements and compounds

• Definitions• Constituent elements

of some common compounds

• Practice 2.2 • Elements, compounds

and mixtures• Refer to an animation

showing elements and compounds:

http://studyjams.scholastic.com/studyjams/jams/science/mattert/elements-and-compounds.htm

(accessed July 2014)• Students have studied

‘compounds’ in Unit 13 of Science (secondary 1–3).

2.4 Differences between a mixture and a compound

• Differences between the properties of an iron-sulphur mixture and iron(II) sulphide

• Main differences between a mixture and a compound

• Activity 2.1 — Investigating the reaction between iron and sulphur

2.5 The atmosphere • Composition of gases in the air (percentage

by volume)

• Do you know — The story of our

atmosphere• Students have studied

‘what is air made up of’ in Unit 7 of Science (secondary 1–3).

46



studentsRemark

2.6 Separation of mixtures

• Names of common techniques for separating components of mixtures


2.7 Separating oxygen and nitrogen from the air

• Main stages in fractional distillation of liquid air

• Refer to the video clip

‘Gases from the Air’: http://www.

youtube.com/watch?v=vUybtRlaLLw


2.8 The particle theory of matter

• Dissolving crystal in water

• Spreading of bromine vapour

• Students have studied ‘particle theory’ in Unit 6 of Science (secondary 1–3).

2.9 Physical and chemical changes

• Definitions• Changing the state of

water • Sublimation• Words used to describe

the changes of states of a substance

• Discussion

• State control room• Refer to the following

website for the information on the physical states and properties of matters:

http://www.visionlearning.com/en/library/Chemistry/1/States-of-Matter/120

(accessed July 2014)• Sublimation of iodine• Students have studied

‘particle theory’ in Unit 6 of Science (secondary 1–3).

2.10 Physical and chemical properties

• Definitions• Examples

• Practice 2.3

2.11 Test for oxygen • Test for oxygen with a glowing splint

• Students have studied ‘test for oxygen’ in Unit 7 of Science (secondary 1–3).

47

Teaching Plan

Unit 3 The ocean


studentsRemark


3.1 Sea water: a vast solution

• Percentage by mass of salts in a typical sea water sample

• Solute and solvent• Dilute, concentrated

and saturated solutions

• Do you know — Why is sea water salty?• Students have studied

‘dissolving’ in Unit 5 of Science (secondary 1–3).

3.2 Obtaining common salt from sea water

• Decantation• Filtration• Evaporation• Crystallization

• Activity 3.1 — Obtaining common salt from muddy sea water

• Activity 3.2 — Growing crystals

• Filtration of muddy sea

water• Evaporating sea water

to obtain salt by direct heating

• Evaporating sea water

to obtain salt using a steam bath

• Do you know — Source of salt• Preparing copper(II)

sulphate crystals by crystallization

• Students have studied ‘common water purification methods’:

• sedimentation; • filtration; and • distillation in Unit 5 of Science

(secondary 1–3).

Continued on next page

48



studentsRemark


3.3 Obtaining pure water from sea water

• Distillation • Activity 3.3 — Obtaining pure water from sea water

• Problem Solving

• Obtaining pure water

from sea water —Distillation of sea water

3.4 Showing what species common salt contains

• Flame test• Test for chlorides —

silver nitrate test

• Activity 3.4 — Conducting flame tests on some metallic compounds

• Activity 3.5 — What does common salt contain?

• Flame test• Test for chloride ions

3.5 Test for the presence of water in a sample

• Test for the presence of water in a sample using blue cobalt(II) chloride paper

• Discussion

• Action of water, ethanol

and oil on dry cobalt(II) chloride paper

• Students have studied ‘test for water’ in Unit 7 of Science (secondary 1 – 3).

3.6 Electrolysis of sea water

• Electrolysis of sea water to obtain hydrogen, chlorine and sodium hydroxide

• Common uses of hydrogen, chlorine and sodium hydroxide

• Chemistry Magazine — Fresh water from sea

water

• Uses of chlorine• • Refer to the Salt

Institute for further information about salt:

http://www. saltinstitute.org/

(accessed July 2014) • Refer to the ETV

programme ‘Water treatment’:

http://resources. hkedcity.net/resource_ detail. php?rid=92063550


49

Teaching Plan

Unit 4 Rocks and minerals


studentsRemark


4.1 Metals in the Earth’s crust

• Minerals and ores • Students have studied ‘common metal ores’ in Unit 13 of Science (secondary 1–3).

4.2 Extracting metals from their ores

• Physical methods• Heating the ore alone• Heating the ore with

carbon• Electrolysis of the

molten ore

• Activity 4.1 — Extracting iron on a match head

• Students have studied ‘extraction of metals using carbon’ in Unit 13 of Science (secondary 1–3).

4.3 Investigating calcium carbonate

• Action of heat, dilute acid and water on calcium carbonate

• Word equations

• Activity 4.2 — Investigating the action of heat, water and dilute acid on calcium carbonate

• Activity 4.3 — Showing the presence of calcium carbonate in a variety of minerals and building materials

• Practice 4.1

• Students have studied ‘test for carbon dioxide’ in Unit 7 of Science (secondary 1–3).


4.4 Formation of chalk, limestone and marble

• The three main forms of calcium carbonate

• Their formation from sea animals

• Uses of limestone

• Discussion

• Formation of limestone

and limestone caves• Do you know —

Limelight

4.5 Formation of limestone caves

• Weathering and erosion• How limestone caves

form• Word equations

• Refer to animations

explaining physical and chemical weathering:

http://ees.as.uky.edu/sites/default/files/elearning/module07swf.swf


50


Teaching Notes


N1 page 9

Microscale chemistry is chemistry carried out on a reduced scale using small quantities of chemicals and often simple equipment.

Merits of microscale chemistry

Educational values

• By minimizing waste, microscale chemistry encourages students to use chemicals responsibly.

• Maximizing the opportunities for careful observation and interpretation as the processes of microscale experiments often take place very quickly.

• Providing opportunities for students to design their own experiments using the microscale kit and equipment.

Laboratory management

• Use of small quantities of chemicals and simple equipment leads to

— a reduction in materials cost;

— an improvement in laboratory safety;

— a reduction of waste;

— a shorter experiment time.

• Use of plastic apparatus leads to

— a reduction in glassware breakage;

— a reduction in the cost of breakage.

• The small scale equipment leads to a reduction in storage space.

51

Teaching Notes


page 24N2

We live in the troposphere with trips into the stratosphere. Only astronauts pass out of the atmosphere.

N6 page 32

Other examples of physical properties:

• lustre;

• hardness;

• strength;

• malleability;

• ductility;

• thermal conductivity; and

• solubility.

52



N2 page 69

The following substances can be used to distinguish between oxygen and carbon dioxide:

• limewater;

• burning splint;

• glowing splint.

Observations

Test with limewater Test with burning splint Test with glowing splint

Oxygen No observable changeBurning splint burns more brightly.

Glowing splint relights.

Carbon dioxide

Limewater turns milky. Burning splint extinguishes. Glowing splint extinguishes.

N6 page 75

There are two types of weathering:

• chemical weathering;

• physical weathering.

What we describe in the textbook is an example of chemical weathering.

In physical weathering, rock gets broken into fragments but it is not chemically changed. This can happen in several ways. For example, plant roots grow into cracks in rock and slowly prise the rock apart. In the winter, water in the cracks expands as it freezes, forcing the cracks wider. Eventually the rock breaks up.

In some places, the temperature drops below freezing point at night and rises during the day. So water in the cracks freezes and thaws cycle after cycle. The rock breaks up over time.

53

Suggested Answers

page 1

1 Micro-organisms

2 Filtration / sedimentation

3 Chlorine


Practice

P1.1 page 6

1 a) ❶ No eye protection when using a Bunsen burner.

❷ Not cleaning up chemical spillage immediately.

❸ Not stopping the reagent bottles immediately after use.

❹ Leaving the Bunsen flame unattended.

b) ❶ No eye protection when using a Bunsen burner.

❷ Pointing the mouth of the test tube towards someone when heating.

❸ Putting flammable alcohol near to a naked flame.

2 a) 1 or more.

b) Cover the thing that is on fire.

c) For extinguishing fire.

P1.2 page 10

1 W — evaporating dish

X — wire gauze

Y — tripod

Z — Bunsen burner

Suggested Answers

54


2 P — glass rod

Q — stand and clamp

R — filter paper

S — filter funnel

T — beaker

Discussion page 4

Good effect Bad effect

1 Explosive Used in building industry Used in wars

2 Insecticide Increase food production Poison our food

3 Aspirin A good painkiller Side effects

page 7Find & Share

Safety precautions for handling household products

Item number

ItemActive

ingredientSafety precautions

1glass

cleanserammonia

Any two of the following:• Can cause irritation to eyes and skin.• In case of eye contact, immediately flush eyes with plenty of water. Consult a doctor if irritation persists.• In case of skin contact, rinse with water.• If swallowed, drink a large amount of water. Call a doctor.

2chlorine bleach

sodiumhypochlorite

Any two of the following:• Wear eye protection.• Wear rubber household gloves.• Wear clothing that will cover your skin in case of spills.• Open the container and dilute the bleach out of rooms or in a very well- ventilated room to avoid a building up of vapour.• A toxic gas will be released if the bleach is mixed with acidic cleansing agents. An explosion can occur if sufficient quantities are mixed.

3oven

cleansersodium

hydroxide

Any two of the following:• Wear eye protection.• Wear rubber household gloves.• Wear clothing as protection against splashing.• Store at moderate temperatures in a dry, well-ventilated area.• Store away from oxidizing materials and acids.

55

Suggested Answers

pages 13–15Unit Exercise

1 a) A — flammable

B — toxic

C — corrosive

b) Chemical A — Keep away form heat / naked flames.

Chemical B — Any one of the following:

Avoid breathing in its vapour.

Wear protective gloves and safety glasses.

Perform the experiment inside a fume cupboard.

Chemical C — Wear protective gloves and safety glasses.

2 a) Test tube

b) Evaporating dish

c) Beaker

d) Tripod

e) Wire gauze

f) Stand and clamp

g) Filter funnel

h) Glass rod

i) Bunsen burner

j) Safety glasses

3 C

4 D Concentrated sulphuric acid is corrosive.

5 B Returning excess materials to the reagent bottle leads to contamination.

6 B

7 D

56


8 a) • No eye protection when using a Bunsen burner.

• The long hair tends to dangle.

• No fireproof mat under the Bunsen burner.

b) • Too much liquid in the test tube for heating.

• Placing the test tubes too near to the edge of the bench.

c) • Smelling a gas directly.

• Leaving the Bunsen flame unattended.

• Blocking the passage in the laboratory.

9 a) To measure the volume of a liquid.

b) To add a liquid drop by drop.

c) To grind a solid into a fine powder.

d) To transfer a small amount of solid.

10 a) Chlorine gas is toxic.

Carry out any activity involving chlorine inside a fume cupboard.

b) i)

ii) • Wear safety glasses and protective gloves when working with the alkali.

• If concentrated sodium hydroxide solution is spilt on the skin or clothes, wash it off immediately with plenty of water.


Practice

P2.1 page 19

Pure substances — (b) and (e)

57

Suggested Answers

P2.2 page 22

Substance Element Compound Mixture

Iron ✔

Sugar solution ✔

Carbon dioxide ✔

Nitrogen ✔

Petroleum ✔

P2.3 page 33

1 Physical property. The property can be observed without changing the chemical composition of the substance.

2 Physical property. The property can be measured without changing the chemical composition of the substance.

3 Chemical property. Milk turns sour because a new substance (an acid) forms. This property of milk can be observed when it undergoes a chemical change to form a new substance.

4 Physical property. The property can be observed without changing the chemical composition of the substance.

5 Chemical property. Magnesium reacts with hot air to form a new substance (magnesium oxide). This property of magnesium can be observed when it undergoes a chemical change to form a new substance.

Discussion page 32

1 a) Physical change. No new substance is formed in the process.

b) Physical change. No new substance is formed in the process.

c) Chemical change. New substances (hydrogen and oxygen) are formed in the process.

d) Chemical change. New substances (simple sugars) are formed in the process.

Sucrose (table sugar) is a disaccharide formed from two monosaccharides (glucose and fructose). Sucrose is spilt into the monosaccharides during digestion.

2 • Dry ice can produce a very low temperature (−78 °C).

• Dry ice sublimes and no messy liquid (as in the case of ice) is produced.

58



1) a) oxygen

b) nitrogen

c) carbon dioxide

d) noble gases

e) water vapour

f) glowing splint

g) fractional distillation

2 a) mixtures

b) coffee

c) hydrogen

d) compounds

e) water

f) melting point

g) chemical

h) reaction of magnesium with oxygen to form magnesium oxide

3 a) Element

b) Compound

Aluminum oxide is a compound of aluminum and oxygen.

c) Mixture

Paint is a mixture of solvent, pigment and other substances.

d) Compound

Iron(II) sulphide is a compound of iron and sulphur.

4 a) Physical change

b) Chemical change

Copper tarnishes because it reacts with air, moisture or other substances in the environment.

c) Chemical change

Candle burns to give carbon dioxide, water vapour, other substances, heat and light.

d) Physical change

59

Suggested Answers

5 a) Physical property

b) Chemical property

c) Physical property

d) Physical property

e) Physical property

6 a) sublimation

b) boiling / evaporation

c) condensation

d) melting

e) freezing

7 C Argon (a gas denser than nitrogen) is present in the nitrogen obtained from the air.

8 C The melting point of carbon dioxide is −78 °C. Carbon dioxide would solidify when cooled to −200 °C.

9 D Gas Boiling point (°C)

Nitrogen −196

Oxygen −183

Argon −186

Nitrogen has the lowest boiling point. Thus, it will boil off first.

Oxygen has the highest boiling point. Thus, it will boil off last.

10 B

11 B Ammonia is a compound composed of hydrogen and nitrogen.

12 B Calcium carbonate is a compound composed of calcium, carbon and oxygen.

13 C

14 D

15 A Oxygen supports burning, but it is NOT flammable.

60


16 C

17 D Carbon can burn in air is a chemical property of carbon.

18 A (1) Carat gold is a mixture of gold and other metals.

(2) Cola drink is a mixture of water, carbon dioxide and other substances.

19 B (1) The properties of a compound are different from those of its constituent elements.

(3) A compound can be separated into its constituent elements by chemical methods.

20 B (1) Sodium chloride is formed when hot sodium is put into a jar of chlorine. A chemical change occurs.

(3) Hydrogen and chlorine are formed in the electrolysis of sea water. A chemical change occurs.

21 a)Only in air Only in the Earth’s crust In both

metal elements ✔

non-metal elements ✔

b) Elements are substances which cannot be broken down into anything simpler by chemical methods.

Example — copper / sodium / carbon / aluminum / sulphur

Compounds are substances composed of two or more elements chemically joined together.

Example — sodium chloride / sugar / water

22 a) B

b) A

23 a) Any one of the following:

• Kills microbes.

• Improve taste / texture / flavour.

• Easier to digest.

b) New substance(s) is(are) formed.

24 a) The water vapour freezes.

b) The pipes would be blocked.

61

Suggested Answers

c) Oxygen and nitrogen liquefy.

Neon remains as a gas and can be removed.

Liquid nitrogen and liquid oxygen can be separated by fractional distillation.

The temperature of the liquids is raised slowly.

Nitrogen boils off at –196 °C.

Then oxygen boils off at –183 °C.

Unit 3 The ocean

Problem Solving page 50

Remove the oil using a dropper. Distil the common salt solution to obtain the common salt and water.

The oil and common salt solution can also be separated by using a separating funnel.

Discussion page 53

a) A — filtration

B — removing the kerosene by using a dropper (or separating the two liquids by using a separating funnel)

C — evaporation to dryness

b) Solid W — charcoal

Liquid X — kerosene

c) i) The brilliant golden yellow flame colour produced by the sodium compound masks the lilac flame colour produced by the potassium compound.

ii) Dissolve the solid in water. Add excess dilute nitric acid, followed by an aqueous solution of silver nitrate. A white precipitate appears.

Chemistry Magazine page 55

Fresh water from sea water

1 Any one of the following:

• To prevent death from water borne diseases.

• Dirty water contains harmful bacteria.

• Clean water reduces infections / diseases.

62


2 Pros

• It can continue to deliver drinking water for consumption even if there is no rain.

• It provides an alternative source of supply to make the overall supply more robust and less vulnerable to interruption.

• It provides a superior quality product regardless of the source water quality.

• It is accomplished by means of pumps, filters and other pieces of equipment. This feature results in smaller size facilities when compared with other conventional water supply alternatives, such as surface water reservoirs.

Cons

• The cost of plant construction is relative high.

• Water desalination consumes a lot of energy. Approximately one third of the operational costs of a water desalination facility is the power consumption.

• High-energy consumption also leads to increases in greenhouse gas emissions.


1 a) insoluble

b) soluble

c) solution

d) dilute solution

e) concentrated solution

f) saturated

g) crystals

2 a) hydrochloric acid

b) bleach

c) organic solvents

d) swimming pool water

3 a) Evaporation

b) Distillation

c) Fractional distillation

63

Suggested Answers

4 Compound of Flame colour

calcium brick-red

copper bluish green

potassium lilac

sodium golden yellow

5 A

6 D

7 A

8 B

9 C (1) Calcium sulphate is insoluble in water.

The following table shows the salt composition of sea water (percentage by mass):

Salt %

Sodium chloride 68

Magnesium chloride 14.6

Sodium sulphate 11.4

Calcium chloride 3.1

Other salts 2.9

10 D Compound Characteristic flame colour in flame test

Potassium chloride lilac

Copper(II) chloride bluish green

Calcium chloride brick-red

direct current11 C sea water chlorine gas + hydrogen gas + sodium hydroxide solution

64


12 B

13 a) Calcium

b) Oxygen

c) Water

d) Chlorine

14 a) A — thermometer

B — condenser

C — round-bottomed flask

D — Bunsen burner

E — tripod

b) Thermometer (A)

15 a)

65

Suggested Answers

b)

c)

16 Heat the solution to remove some of the water.

Allow the hot and concentrated solution to cool. Solid magnesium sulphate separates out.

17 a) Distillation

b) The boiling point of water is lower than those of the salts in sea water.

When the sea water is heated, the water boils.

The water vapour formed escapes and passes through the inner tube of the condenser.

The water vapour condenses to form a liquid.

c) Condenser

d) To ensure even boiling.

18 a) The colour of copper(II) sulphate crystals changes from blue to white upon heating.

b) Test the liquid obtained using dry cobalt(II) chloride paper.

The paper turns from blue to pink.

c) To prevent the condensed water from running back to the boiling tube and cracking the hot glass.

66


19 a) Dissolve some salt in water.

Add excess dilute nitric acid, followed by an aqueous solution of silver nitrate.

A white precipitate forms.

b) i) Dip a clean nichrome wire into concentrated hydrochloric acid.

Dip the nichrome wire into the salt.

Put the end of the wire in a Bunsen flame and observe the colour of the flame.

ii) The brilliant golden yellow flame colour produced by the sodium compound masks the lilac flame colour produced by the potassium compound.

20 a) A — mortar

B — glass rod

C — beaker

D — filter funnel

E — tripod

b) To speed up the dissolving of the salt.

c) Filtration

d) Clay and sand

e) Sodium chloride


Practice

P4.1 page 71

a) X — sodium

Y — calcium

b) X — carbonate ion

X reacts with dilute hydrochloric acid to produce carbon dioxide gas which turns limewater milky.

Y — chloride ion

Solution of Y gives a white precipitate (silver chloride) in the silver nitrate test.

c) X — sodium carbonate

Y — calcium chloride

67

Suggested Answers

Discussion page 74

Pros

• A new road is built for delivering the limestone. This also improves the transportation of the town.

• The company provides jobs for local people.

• The profit of the company can be taxed by the government of the town.

• There is a new village hall built by big donations from the company.

• The availability of limestone may lead to the development of other industries and hence the prosperity of the town.

Cons

• The rock dug from the ground becomes waste. This causes pollution problems.

• The blasting and the heavy traffic cause sound pollution.

• Consumption of energy may lead to greenhouse gas emissions.


1 a) ores

b) mercury

c) heating in air

d) haematite

e) heating with carbon

f) aluminium

g) electrolysis

2 a) limestone

b) marble

c) calcium carbonate

d) calcium oxide

e) carbon dioxide

f) calcium chloride

g) carbon dioxide

h) water

68


3 A — 4

B — 3

C — 1

D — 2

4 Across

① electrolysis

④ ore

⑦ limewater

⑧ minerals

⑩ compound

Down

② erosion

③ sodium

⑤ element

⑥ marble

⑨ iron

5 C

6 A Calcium carbonate is insoluble in water.

7 A Process 1

Process 2

8 B Photosynthesis consumes carbon dioxide.

9 A (1) Carbon dioxide extinguishes a burning splint while oxygen does not.

(2) Oxygen relights a glowing splint while carbon dioxide does not.

69

Suggested Answers

10 B Limestone is composed primarily of calcium carbonate.

(1) Limestone gives a brick-red flame in flame test.

(2) Limestone gives a colourless gas (carbon dioxide) when heated strongly.

11 A

12 C (1) Sea water contains sodium chloride. It gives a white precipitate (sliver chloride) with an aqueous solution of silver nitrate.

(2) Sodium chloride dissolves in water to give a colourless solution.

(3) Bubbling carbon dioxide gas into calcium hydroxide solution gives a white precipitate (calcium carbonate).

13 D

14 D

15 a) i) Effervescence occurs.

ii) calcium carbonate + dilute hydrochloric acid calcium chloride + water + carbon dioxide

b) The limewater turns milky.

16 a) The limewater turns milky due to the formation of insoluble white calcium carbonate.

When excess carbon dioxide is passed into the limewater, calcium carbonate dissolves to form soluble calcium hydrogencarbonate. Then the limewater becomes clear again.

b) carbon hydroxide + carbon dioxide calcium carbonate + water

calcium carbonate + carbon dioxide + water calcium hydrogencarbonate

c) Air contains a low percentage of carbon dioxide.

A similar observation would be made after a long period of time.

17 a) By filtration

b) i) Add the powder to water.

See if it dissolves.

ii) When the gas is added to limewater, the limewater turns milky.

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18 a) i) To avoid the interference of impurities

ii) Property ✔

Good electrical conductor

High density

High melting point ✔

Low boiling point

Unreactive ✔

iii) golden yellow

b) i) Effervescence occurs.

ii) milky

19 a) Process 1 — filtration

Process 2 — distillation

b) Process 1 Process 2

c) Calcium carbonate

20 a) Use flame test.

Potassium carbonate gives a lilac flame.

Calcium carbonate gives a brick-red flame.

b) Dissolve each solid in water.

Add excess dilute nitric acid followed by an aqueous solution of silver nitrate to each solution.

Only magnesium chloride solution gives white precipitate.

There is no observable change for magnesium sulphate solution.

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Suggested Answers

21 When sea animals die, their skeletons or shells sink into the mud at the bottom of the oceans. Over millions of years, layers build up. Pressure from the top layers changes the bottom layers into chalk.

When subject to higher pressure and heat, the chalk turns into limestone.

The limestone deposit may stay below the Earth for a long time. High temperature and pressure may turn the limestone into marble.

22 a) The carbon dioxide gas produced escapes.

b) Calcium oxide reacts with water or carbon dioxide.

c) A Wood

Advantage — screening of wood

Disadvantage — damage to habitat

B Town

Advantage — labour force near to site

Disadvantage — noise / visual / dust pollution / damage / subsidence

C Road / railway

Advantage — convenient transport for materials

Disadvantage — dust, noise carried to the town

D River

Advantage — convenient transport for materials

Disadvantage — polluting the river

Other factors

• Quality of limestone

– (Best) D > C > A > B (Worst)

– amount of waste

• Wind direction

– carries dust, noise, fumes etc. towards the town.

– only B and D are directly downwind of the town.

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pages 85–90Topic Exercise

1 C Liquefied petroleum gas is flammable.

2 C

3 A

From the above diagram, we can see that at −200 °C,

• helium is a gas;

• oxygen and nitrogen are liquids;

• argon is a solid.

4 B From the diagram in Question 3, we can see that oxygen stays liquid over the greatest temperature range.

5 B Nitrogen has the lowest boiling point. Thus, it will vaporize first.

Oxygen has the highest boiling point. Thus, it will vaporize last.

6 B

7 D Carbon dioxide is removed before the fractional distillation of liquid air.

8 C

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Suggested Answers

9 B Limestone sample B contains impurities that do not decompose when heated. Thus, the change in mass is smaller than when pure calcium carbonate is heated.

10 B (2) Fractional distillation of liquid air involves a physical change.

(3) Sea water contains sodium chloride. It gives a white precipitate with an aqueous solution of silver nitrate. A chemical change occurs.

11 A (2) Concrete is a mixture of cement, stone chips, sand and water.

(3) Ice is water in the solid state, thus it is a compound.

12 B Heating calcium carbonate strongly gives a gas (carbon dioxide).

13 C Oxygen supports burning, but it is NOT flammable.

14 B The correct explanation is oxygen and nitrogen have different boiling points.

15 A

16 a) i) C

ii) Wear safety glasses. / Wear protective gloves. / Perform the experiment inside a fume cupboard. / Wash affected areas with plenty of water if spilt on the skin or clothes.

b)

17 a) • Oxygen and nitrogen have different boiling points.

• The two gases can be seperated by fractional distillation.

• Liquefy the air. The temperature of the liquid is raised slowly.

• Nitrogen boils before oxygen.

b) Any two of the following:

helium / neon / argon / krypton / xenon

18 a) Filtration

b) Filter paper

c) Filter funnel

d) Filtrate

e) Residue

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f) The particles of sodium chloride in sea water are much smaller than mud particles in muddy water.

Hence particles of sodium chloride in sea water can pass through the tiny holes on the filter paper while mud particles cannot.

19 a) i) Evaporation

ii)

iii) Sodium chloride

iv) As table salt / preservative / flavouring agent

b) Electrolysis

c) i) Hydrogen

ii) Hydrogen gives a ‘pop’ sound with a burning splint.

d) Chlorine: sterilizing drinking water / sterilizing swimming pool water / manufacture of PVC and organic solvents / manufacture of hydrochloric acid / manufacture of bleach

Gas Y: manufacture of ammonia / as rocket fuel / manufacture of hydrochloric acid

20 Answers for the HKDSE question are not provided.

21 a) i) A white precipitate was observed.

ii) Chloride

b) i) Distillation

ii)

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Suggested Answers

22 a) i) Carbon dioxide

ii) Use limewater to test for the gaseous product.

The gas turns limewater milky.

b) i) Add water to calcium oxide.

ii) calcium oxide + water calcium hydroxide

c) i) Add dilute hydrochloric acid to calcium carbonate.

ii) Effervescence occurs. / Calcium carbonate dissolves in the dilute acid.

iii) calcium carbonate + dilute hydrochloric acid calcium chloride + water + carbon dioxide

23 a) Test Result Substance

Add dilute hydrochloric

acid

effervescence occurs

carbonate

Flame testbrick-red

flamecalcium

b) Calcium carbonate

c) Dip a clean nichrome wire into concentrated hydrochloric acid.

Dip the nichrome wire into the substance.

Put the end of the wire in a Bunsen flame and observe the colour of the flame.

d) Any one of the following:

• Use clean equipment.

• Ensure no contaminants in the reagents.

• Use distilled water.

24 a) 155 cm3

b) 71 cm3

c) Iron reacts with the oxygen.

d) (100 – 71) cm3

155 cm3 x 100 %

= 18.7%

Topic 1 Planet Earth Suggested Teaching Schemes

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