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Topic 1 Planet Earth

Part A Unit-based exercise

Unit 1 Introducing chemistry

Fill in the blanks

1 safety glasses

2 hazard

3 rack

4 spatula

5 Bunsen

6 electronic

7 measuring cylinder

8 dropper

9 mortar; pestle

10 desiccator

True or false

11 F Solid chemicals should be transferred by a spatula.

12 T

13 F Returning excess chemicals to reagent bottles may lead to contamination.

14 F When the air hole of a Bunsen burner is closed, very little air mixes with the gas. The gas does not burn well. The temperature of the flame is not high.

15 F During heating, fill the test tube with liquid to about 13

of its capacity.

16 T Hydrogen is less dense than air and thus can be collected by upward delivery.

17 T Concentrated nitric acid tends to decompose. The decomposition is speeded up by light so the acid is stored in brown bottles.

18 F Yellow phosphorus is stored in water.

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19 F During weighing, put the chemical in a weighing bottle or on a piece of filter paper.

20 T Fuel, oxidant (usually oxygen in the air) and heat are needed to start a fire and keep it going. The three conditions form a fire triangle.

Using sand to cover the burning sodium keeps the air out. Thus the fire will go out.

Multiple choice questions

21 B Option A — Solid substances should be put into appropriate waste bottles after use.

Option C — Use a blue flame when a higher temperature is required.

Option D — If any chemicals get onto the clothing, wash the affected area with plenty of water.

22 C

23 A Option Hazard warning label Hazardous nature indicated

A toxic

B carcinogenic

C corrosive

D oxidizing

24 D

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25 D Option Hazard warning label Hazardous nature indicated

A explosive

B irritant

C flammable

D corrosive

Concentrated sulphuric acid is corrosive.

26 B Option Hazard warning label Hazardous nature indicated

A explosive

B irritant

C flammable

D carcinogenic

Dilute hydrochloric acid is irritant.

27 B Option A — Lead is toxic.

Option C — Both yellow phosphorus and red phosphorus are flammable and toxic.

Option D — Sodium is flammable and corrosive.

28 C Option A — Alcohol is flammable. Thus it should be stored in a cool place.

Option B — In the laboratory, concentrated nitric acid is commonly stored in brown bottles.

Option C — Magnesium shows very little reaction with water. Hence it should NOT be stored in water.

Option D — Sodium is a reactive metal. It is stored in paraffin oil to prevent it from reacting with the air.

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29 A (3) Sodium is flammable and corrosive.

30 B (1) Carbon dioxide gas is NOT flammable. It can be used to put out fires.

(3) Oxygen supports combustion, but it is NOT flammable.

31 D (1) Students should NOT remove anything from the laboratory without the teacher’s permission.

32 C Carbon dioxide is denser than air. It can be collected by downward delivery (I).

Gas syringe (III) can be used to collect any gas.

33 A (3) The end of the delivery tube for the incoming gas should be put under the drying agent. This ensures that all the incoming gas can pass through the drying agent.

34 D (1) Calcium reacts with water. Thus it should NOT be stored in water.

(2) Silver nitrate solution tends to decompose when exposed to light. Thus the solution is stored in brown bottles.

(3) Town gas (containing hydrogen gas and carbon monoxide gas) is flammable. Thus it should be stored in a cool place.

35 C (1) The oil will float on the water and the fire will spread. Therefore water should NOT be used to put out the fire.

(2) Fuel, oxidant (usually oxygen in the air) and heat are needed to start a fire and keep it going. The three conditions form a fire triangle.

Using the lid to cover the pan keeps the air out. The fire will go out.

(3) Carbon dioxide extinguishers contain carbon dioxide gas under high pressure. When the trigger is pressed, the gas rushes out. Carbon dioxide gas is denser than air and does not burn. The gas forms an invisible layer over the fire and keeps out the air. The fire will go out.

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Unit 2 The atmosphere

Fill in the blanks

1 matter

2 pure substance

3 mixture

4 water; carbon dioxide

5 elements

6 compounds

7 carbon; oxygen

8 hydrogen; oxygen

9 mixture

10 oxygen; nitrogen; carbon dioxide; noble gases; water vapour

11 fractional distillation

12 physical

13 chemical

14 chemical

15 glowing

True or false

16 F Pure substances can be classified into elements and compounds.

17 T

18 F Altogether 111 different elements are known.

19 F Water is a compound composed of hydrogen and oxygen.

20 T Sugar is a compound composed of carbon, hydrogen and oxygen.

21 F Ammonia is a compound composed of hydrogen and nitrogen.

22 T

23 T Petroleum is a mixture of many hydrocarbons. Hydrocarbons are compounds composed of carbon and hydrogen.

24 F Iron(II) sulphide gives hydrogen sulphide when reacts with dilute hydrochloric acid.

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25 T

26 F Red wine is a mixture of water, ethanol and many other substances. It does NOT have a sharp boiling point.

27 T

28 F Air contains 0.9% of noble gases (by volume).

29 T Oxygen and nitrogen in the air can be separated by fractional distillation of liquid air because they have different boiling points.

30 T The colour of water can be determined without changing the chemical composition of water. Hence the colour of water is a physical property.

Multiple choice questions

31 A Option A — Carat gold is a mixture of gold, silver and copper.

Options B and D — Common salt and water are compounds.

Option C — Copper is an element.

32 C Option A — Air is a mixture of gases.

Option B — Coffee is a mixture of water, caffeine and other substances.

Option D — Toothpaste contains active ingredient(s) (compound(s) containing fluorine) and other substances.

33 D Option A — Cola drink is a mixture of water, carbon dioxide, sugar and many other substances.

Option B — Concrete is made by mixing cement, aggregate (a mixture of stone chips and sand) and water.

Option C — Red wine is a mixture of water, ethanol and many other substances.

34 A Option A — Ammonia is a compound composed of hydrogen and nitrogen.

Option B — Carbon is an element.

Options C and D — Milk and sand are mixtures.

35 B

36 B Calcium carbonate consists of calcium, carbon and oxygen.

37 A Ammonia consists of hydrogen and nitrogen.

38 C Many compounds occur naturally.

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39 C Option A — This diagram represents pure carbon dioxide gas.

Option B — This diagram represents pure oxygen gas.

Option C — This diagram represents a mixture of carbon monoxide gas and oxygen gas.

Option D — This diagram represents pure carbon monoxide gas.

40 B Options A, C and D — Cola drink, sugar solution and white wine are mixtures. They do NOT have sharp boiling points.

41 A

42 D

43 B Argon boils at –186 ºC. That means argon gas will condense to form liquid at –186 ºC. Argon exists as a liquid at –200 ºC.

Nitrogen and oxygen boil at –196 ºC and –183 ºC respectively. They also exist as a liquid at –200 ºC.

Helium and neon boil at –269 °C and –246 °C respectively. They exist as a gas at –200 °C.

44 C In fractional distillation, a component with a lower boiling point is distilled out first.

The boiling points of the components are in the order of neon < argon < krypton. Hence neon is distilled out first, followed by argon and krypton.

45 D Option A — Nitrogen does NOT support burning.

Option C — Nitrogen is odourless.

46 C A new substance (carbon dioxide) forms upon burning of the liquid. The statement describes an ability to form new substance(s), i.e. a chemical property.

47 B Option A — Aluminium burns to give aluminium oxide, a new substance. The statement describes an ability to form new substance(s), i.e. a chemical property.

Option B — The colour of common salt can be determined without changing the chemical composition of common salt. Hence the colour of common salt is a physical property.

Option C — A new substance (rust) forms during rusting. The statement describes an ability to form new substance(s), i.e. a chemical property.

Option D — Potassium reacts with water to give potassium hydroxide and hydrogen gas. The statement describes an ability to form new substance(s), i.e. a chemical property.

48 D Option A — Copper is still copper after hammered into thin sheets. This property can be measured without changing the chemical composition of copper, i.e. a physical property.

Option B — The density of water can be measured without changing the chemical composition of water. Hence the density of water is a physical property.

Option C — Silver is still silver after conducting heat. This property can be measured without changing the chemical composition of silver, i.e. a physical property.

Option D — A bottle of wine goes sour because a new substance (an acid) forms. The statement describes an ability to form new substance(s), i.e. a chemical property.

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49 A Option B — Oxygen is an element.

Option C — Oxygen supports combustion. Hence it will NOT extinguish a burning splint.

Option D — Oxygen is NOT flammable.

50 C Option C — Oxygen is NOT used to fill electric light bulbs as it will react with the tungsten filaments in light bulbs.

51 B (1) The dark brown substance (iron(II) sulphide) sinks in water.

(2) The dark brown substance (iron(II) sulphide) reacts with dilute hydrochloric acid to give hydrogen sulphide, a gas with a bad egg smell.

(3) The dark brown substance (iron(II) sulphide) is a compound. It can only be separated into its constituents by chemical methods.

52 B (2) The properties of a compound are very different from those of the elements in it.

53 D Air contains oxygen, nitrogen, carbon dioxide, water vapour and noble gases (including argon).

54 B (1) Air is cooled to –200 ºC during the process.

(3) Carbon dioxide in the air is removed before liquefaction of the air. Otherwise, carbon dioxide will freeze when the air is cooled, and block the pipes.

55 A (3) Air contains 21% of oxygen.

Unit 3 The ocean

Fill in the blanks

1 solution; solute; solvent

2 soluble; insoluble

3 dilute; concentrated

4 concentration

5 saturated

6 decantation; filtration

7 evaporation; crystallization

8 distillation

9 nitric; silver nitrate; precipitate

10 cobalt(II) chloride

11 chlorine; hydrogen; sodium hydroxide

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12 physical; chemical

13 sublimation

14 a) hydrogen; oxygen

b) hydrogen; chlorine; sodium hydroxide

c) sodium chloride

True or false

15 T

16 F Sand is insoluble in water.

17 T

18 F In filtration, the substance that passes through the filter paper is called the filtrate.

19 F Evaporating the solvent from a solution increases the concentration of the solution.

20 T

21 F The change of a liquid to a vapour is called evaporation (or boiling).

22 T

23 F Compounds of sodium give a golden yellow flame in flame test.

24 T Dry cobalt(II) chloride paper is blue in colour.

25 F During the electrolysis of sea water, chlorine gas is formed at the positive electrode. Hydrogen gas is formed at the negative electrode.

26 T

27 T Copper is still copper after hammered into sheets. No new substance is formed. Hence the process is a physical change.

28 F No new substance is formed when sugar dissolves in water. Hence the process is a physical change.

29 T Iodine sublimes when heated.

30 F Sea water contains chlorides. The chlorides react with silver nitrate solution to form a new substance (a white precipitate, i.e. silver chloride). Hence the process is a chemical change.

Multiple choice questions

31 B

32 C Option C — The common salt obtained by evaporation of sea water is impure.

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33 D When copper(II) sulphate solution is heated, the water changes to vapour and escapes. The water vapour condenses to form pure water when cooled.

34 C Option B — Upon evaporation of a saturated solution, the solvent cannot hold all the solutes. The extra solutes separate out as crystals.

Option C — If the solution is evaporated quickly, the crystals formed are usually small.

35 A Option A — When water is added to the mixture of common salt and sand, common salt dissolves while sand does not.

Filter to remove the sand.

Obtain pure common salt from the filtrate by crystallization.

36 B Option B — Filter to remove the copper powder from the salt solution.

Carry out distillation to obtain pure water and common salt.

37 A Option Flame colour Compound containing

A bluish green copper

B brick-red calcium

C golden yellow sodium

D lilac potassium

38 B

39 B A chloride gives a white precipitate (silver chloride) with silver nitrate solution.

40 D

41 C Option C — During the electrolysis of sea water, hydrogen is formed at the negative electrode while chlorine is formed at the positive electrode.

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42 D Manufacture of ammonia is a common use of hydrogen. Ammonia is a compound composed of nitrogen and hydrogen. It is formed by combining nitrogen and hydrogen.

43 C

44 B

45 A Option A — Adding ice cubes to soda water produces no new substance. Soda water is still soda water. The process is a physical change.

Option B — Burning petrol produces new substances, such as carbon dioxide and water. The process is a chemical change.

Option C — Making bread from flour produces a new substance (bread). The process is a chemical change.

Option D — Photosynthesis produces new substances (glucose and oxygen). The process is a chemical change.

46 B Option B — Electrolysis of sea water produces new substances (chlorine gas, hydrogen gas and sodium hydroxide solution). The process is a chemcial change.

47 C (1) Calcium carbonate is insoluble in water.

48 C distillation = evaporation + condensation

49 A (1) A sodium-containing compound gives a golden yellow flame in flame test.

(2) A solution containing chloride gives a white precipitate (silver chloride) in silver nitrate test.

50 D (1) Manufacture of soaps is a common use of sodium hydroxide.

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51 B (3) Chlorine can be obtained from sodium chloride.

52 D Electrolysis of sea water produces chlorine, hydrogen and sodium hydroxide.

(1) Hydrogen is used in the manufacture of ammonia.

(2) Chlorine and sodium hydroxide are used in the manufacture of bleaches.

(3) Sodium hydroxide is used in the manufacture of detergents.

53 D

54 A (1) A cut apple turns brown due to oxidation. The process involves a chemical change.

(2) A burning candle produces new substances, such as carbon, carbon dioxide and water. The process involves a chemical change.

(3) Making a cup of tea from tea bag produces no new substance. The process involves a physical change.

55 A (2) Liquid X (water) can turn dry cobalt(II) chloride paper from blue to pink.

(3) Copper(II) sulphate crystals give anhydrous copper(II) sulphate and water in the process. They undergo a chemical change.

Unit 4 Rocks and minerals

Fill in the blanks

1 compounds

2 minerals

3 ores

4 Bauxite

5 Haematite

6 heating

7 carbon; blast

8 electrolyzing

9 calcium hydroxide

10 limewater; calcium carbonate

11 calcium hydrogencarbonate

12 chalk; limestone; marble

13 weathering; erosion

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14 carbonic acid; calcium hydrogencarbonate

15 a) calcium oxide; carbon dioxide

b) calcium hydroxide

c) calcium carbonate; water

d) calcium hydrogencarbonate

e) calcium chloride; water; carbon dioxide

True or false

16 F Most metals exist as compounds in the Earth’s crust. Only a few metals, such as gold and silver, exist as free elements in the Earth’s crust.

17 T

18 F Bauxite is a common ore of aluminium.

19 T

20 T Aluminium is difficult to extract. It can only be extracted by electrolysis.

21 F Sodium is extracted by electrolyzing its molten ore.

22 F Iron is extracted by heating its ore with carbon.

23 F Magnesium is extracted by electrolyzing its molten ore.

24 F Limestone is composed primarily of the mineral calcite.

heat25 T calcium carbonate calcium oxide + carbon dioxide

26 F Calcium oxide is often called quicklime. Calcium hydroxide is often called slaked lime.

27 T

28 T This is due to the formation of insoluble white calcium carbonate.

29 T calcium carbonate + dilute hydrochloric acid calcium chloride + water + carbon dioxide

30 F Calcium carbonate is insoluble in water.

31 F Limestone is harder than chalk.

32 F Quicklime can be used to neutralize the acidity in soil.

33 F Limestone is required to make cement.

34 T

35 T Running water, gravity, waves, ice and wind are major causes of erosion.

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Multiple choice questions

36 D Metal Name of common ore

Aluminium bauxite

Copper copper pyrite

Lead galena

Iron haematite

37 B Options A, C and D — Aluminium, magnesium and sodium are extracted by electrolyzing their molten ores.

38 A

39 A Silver oxide decomposes to give silver and oxygen when heated. heat silver oxide silver + oxygen

The oxygen gas escapes. Hence the mass of the substance decreases with time.

40 D heat calcium carbonate calcium oxide + carbon dioxide

calcium oxide + water calcium hydroxide

41 C

42 B Option A — Calcium hydroxide is often called slaked lime.

Option C — Heating calcium carbonate gives calcium oxide. When water is added to calcium oxide, calcium hydroxide forms.

Option D — Calcium carbonate occurs naturally as marble.

43 A carbon dioxide + calcium hydroxide calcium carbonate + water

calcium carbonate + carbon dioxide + water calcium hydrogencarbonate

44 C Carbon dioxide turns limewater milky due to the formation of insoluble white calcium carbonate.

45 B The main chemical constituent of marble is calcium carbonate.

Compound containing Flame colour

Sodium golden yellow

Calcium brick-red

Copper bluish green

Potassium lilac

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46 A Option A — When water is added to the mixture, sodium chloride dissolves in the water while calcium carbonate does not. Calcium carbonate can be separated by filtration.

47 B

48 A (3) The common ore of sodium is rock salt.

49 C (1) Galena is a common ore of lead. The common ore of iron is haematite.

50 D Limestone (calcium carbonate) decomposes to give quicklime (calcium oxide) and carbon dioxide gas when heated.

heat calcium carbonate calcium oxide + carbon dioxide

51 A The main chemical constituent of limestone is calcium carbonate.

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

(1) Carbon dioxide gas evolves in the reaction.

(2) The limestone dissolves to form soluble calcium chloride.

(3) The acid would NOT turn milky.

52 C (1) A calcium-containing compound gives a brick-red flame in flame test.

(2) Silver nitrate test is used to test for the presence of chloride.

(3) A carbonate gives carbon dioxide gas (which turns limewater milky) when mixed with dilute hydrochloric acid.

53 C (1) Sea water contains chlorides. The chlorides give a white precipitate (silver chloride) with silver nitrate solution.

(2) calcium carbonate + dilute hydrochloric acid calcium chloride + water + carbon dioxide

Calcium chloride is soluble in water. Hence NO precipitate is produced in the reaction.

(3) Carbon dioxide gas reacts with calcium hydroxide solution to form a white precipitate (calcium carbonate).

54 A (3) Limestone is NOT a drying agent.

55 D Running water, gravity, waves, ice and wind are major causes of erosion.

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Part B Topic-based exercise

Multiple choice questions

1 C

2 A Option A — Limewater reacts with carbon dioxide in the air to give calcium carbonate.

calcium hydroxide + carbon dioxide calcium carbonate + water

3 A P floats on Q as its density is lower than that of Q.

4 D Option D — Alcohol (a flammable liquid) should be evaporated using a water bath.

Keep alcohol away from naked flames.

5 D Options A, B and C — These are physical properties of carbon dioxide.

Option D — Carbon dioxide turns limewater milky due to the formation of insoluble white calcium carbonate.

6 A Option A — This diagram represents a compound of X and Y.

Option B — This diagram represents a mixture of two compounds of X and Y.

Option C — This diagram represents a mixture of two elements, X and Y.

Option D — This diagram represents a mixture of a compound and an element.

7 D Option D — X is soluble in Y while Z is not. Hence Z can be separated from the mixture by filtration.

8 A Option A — boiling (or evaporation) liquid gas

9 B Option B — When the mixture is evaporated, water vapour escapes. Water can be obtained by condensing the vapour.

distillation = evaporation + condensation

10 A Option A — Iodine can sublime. Iodine solid changes to a vapour directly on heating. When in contact with a cool surface, the vapour changes to a solid directly.

11 A Option A — electricity sea water chlorine gas + hydrogen gas + sodium hydroxide solution

Option B — Iron is extracted from its ore by heating with carbon.

Option C — Nitrogen is obtained by fractional distillation of liquid air.

Option D — Silver is extracted from its ore by heating in air.

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12 C Option C — A sodium-containing compound gives a golden yellow flame in flame test.

Effervescence occurs when dilute hydrochloric acid is added to a carbonate.

13 B (1) and (3) Liquid air and soda water are mixtures. They do NOT have sharp boiling points.

14 A Chalk is the softest among the three. Limestone is harder than chalk while marble is the hardest.

15 D (1) Gas X can be collected over water as it is insoluble in water.

(2) Gases that are less dense than air can be collected by upward delivery.

(3) Gas syringe can be used to collect any gas.

16 B (1) The evolution of gas would slow down or stop when we turn off the burner. As the temperature drops, the gas inside the tube contracts. A partial vacuum is formed in the tube. Atmospheric pressure will push the test solution into the hot tube through the delivery tube if the test solution is not removed. This is called ‘sucking back’. The test solution may crack the hot tube.

17 B (2) Nitrogen is an element.

18 C Electrolysis of sea water produces chlorine, hydrogen and sodium hydroxide.

electricity

sea water chlorine gas + hydrogen gas + sodium hydroxide solution

(2) Sodium hydroxide is required in the manufacture of soaps.

(3) Hydrogen and chlorine are required in the manufacture of hydrochloric acid.

19 D (1) Magnesium tarnishes in air because it reacts with substances in the air to form a layer of oxide or sulphide. The process is a chemical change.

20 C (1) Sodium chloride does NOT undergo decomposition when heated.

(2) Calcium carbonate decomposes to give calcium oxide and carbon dioxide when heated. heat calcium carbonate calcium oxide + carbon dioxide

(3) Silver oxide decomposes to give silver and oxygen when heated. heat silver oxide silver + oxygen

21 C (1) Carbon dioxide is denser than air. It is NOT used in filling weather balloons.

(2) Carbon dioxide dissolves in water to give carbonic acid.

carbon dioxide + water carbonic acid

(3) Dry ice is solid carbon dioxide. Dry ice sublimes.

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22 B (1) Heating limestone (calcium carbonate) gives carbon dixoide. heat calcium carbonate calcium oxide + carbon dioxide

(2) Adding dilute hydrochloric acid to calcium hydroxide gives NO carbon dioxide.

calcium hydroxide + dilute hydrochloric acid calcium chloride + water

23 A (1) Sodium chloride gives a golden yellow flame in flame test. Calcium chloride gives a brick-red flame.

(2) Both sodium chloride and calcium chloride are white solids. They CANNOT be distinguished by observing their colours.

(3) There is NO observable change when dilute hydrochloric acid is added to sodium chloride and calcium chloride separately.

24 D (1) Carbon dioxide is denser than air. It should NOT be collected by upward delivery.

(2) Carbon dioxide is denser than air. It can be collected by downward delivery.

(3) Carbon dioxide is only slightly soluble in water. It can be collected over water.

25 D Calcium carbonate decomposes to give calcium oxide and carbon dioxide when heated. heat calcium carbonate calcium oxide + carbon dioxide

The carbon dioxide gas escapes. Hence the mass of the contents of the test tube decreases with time.

26 A

27 D Oxygen supports combustion, but it is NOT flammable.

28 C Hydrogen should be collected by upward delivery.

29 D Red wine is a mixture of water, ethanol and many other substances. It does NOT have a sharp boiling point.

30 C Iron(II) sulphide is a compound.

31 B Nitrogen boils before oxygen in the fractional distillation of liquid air because its boiling point (–196 ºC) is lower than that of oxygen (–183 ºC).

32 A

33 D Filtration CANNOT remove sodium chloride from sea water because both the water particles and those of sodium chloride can pass through the tiny holes on a piece of filter paper.

34 D The sodium chloride obtained by evaporation of sea water is impure.

35 B Common salt contains chloride (ions). Its solution gives a white precipitate (silver chloride) with silver nitrate solution.

36 B Sublimation of iodine is a physical change as no new substance is formed in the process.

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37 D Cinnabar is a main ore of mercury.

38 C The main chemical constituent of chalk is calcium carbonate. It gives a brick-red flame in flame test.

39 C There is NO need to store limewater in brown bottles.

40 A

Short questions

41 a) wash bottle (1)

b) dropper (1)

c) separating funnel (1)

d) watch glass (1)

e) desiccator (1)

f) crucible with lid (1)

g) pipe-clay triangle (1)

h) tripod (1)

42 a) Gas X is denser than air. (1)

b) Gas X is soluble in water. (1)

43 a) Chemical A — flammable (1)

Chemical B — toxic (1)

b) Chemical A — keep away from heat / naked flame. (1)

Chemical B — wear protective gloves and safety glasses. / perform the experiment inside a fume cupboard. / avoid breathing in its vapour. (1)

44 The green powder is a mixture. (1)

Its constituents can be separated by physical methods. (1)

45 a) decantation (1)

b) filtration (1)

c) evaporation (1)

d) crystallization (1)

e) distillation (1)

f) fractional distillation (1)

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46 a) deposition (1)

b) sublimation (1)

c) melting (1)

d) freezing (1)

e) boiling / evaporation (1)

f) evaporation / boiling (1)

g) condensation (1)

47 a) Physical change (1)

No new substance is formed in the process. (1)

b) Chemical change (1)

New substances (hydrogen and oxygen) are formed in the process. (1)

c) Physical change (1)

No new substance is formed in the process. (1)

d) Chemical change (1)

New substances (anhydrous copper(II) sulphate and water) are formed in the process. (1)

e) Chemical change (1)

Silver nitrate solution gives a white precipitate (a new substance) with the chlorides in sea water. (1)

48 a) Dissolve the solid samples in water, then add excess dilute nitric acid, followed by silver nitrate solution. (1)

Solution of sodium chloride gives a white precipitate. (1)

Solution of sodium sulphate does not give a white precipitate. (1)

b) Add water to the solid samples. (1)

Calcium hydrogencarbonate is soluble in water. (1)

Calcium carbonate is insoluble. (1)

c) Conduct a flame test. (1)

Potassium carbonate gives a lilac flame. (1)

Sodium carbonate gives a golden yellow flame. (1)

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Structured questions

49 a) Smell gases directly. (1)

Leave the reagent bottle open. (1)

b) Not wearing safety glasses. (1)

Point the mouth of the test tube towards classmate when holding the test tube for heating. (1)

c) Leave experiments unattended. (1)

Leave the bottle of alcohol near the naked flame. (1)

Put too much water in the beaker for heating. (1)

d) Not placing a fireproof mat under the Bunsen burner. (1)

Try to pick up the beaker of hot water using bare hands. (1)

The hair dangles. (1)

50 a) Sucking back of water. (1)

Take the delivery tube from the water before removing the flame. (1)

b) Alcohol is flammable and may catch fire. (1)

Heat alcohol using a water bath. (1)

c) Pressure builds up inside the set-up when the sea water is heated; an explosion may occur. (1)

Add a receiver adaptor between the condenser and the round-bottomed flask. (1)

51 a) i) Fractional distillation (1)

ii) The different gases in the air have different boiling points. (1)

b) To liquefy the air. (1)

c) Fractionating column (1)

d) A is nitrogen gas. (1)

B is argon gas. (1)

C is oxygen gas. (1)

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52 a) Substances in the sample of sea water are not chemically joined together. (1)

Therefore it is a mixture. (1)

b) i) Filtration (1)

ii)

(1 mark for correct set-up; 1 mark for labelling filter funnel and filter paper; 1 mark for labelling residue and filtrate; 0 mark if the set-up is not workable) (3)

c) i) Evaporation (1)

ii)

(1 mark for correct set-up; 1 mark for labelling evaporating dish; 0 mark if the set-up is not workable) (2)

iii) Dissolve the solid in water. (1)

Add dilute nitric acid, followed by silver nitrate solution to the solution. (1)

A white precipitate is formed. (1)

iv) As table salt / preservative / flavouring agent (1)

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53 a) When the sea water is heated, the water vapour escapes and passes through the condenser. (1)

The vapour is cooled by the cold water flowing around the condenser. (1)

The water vapour condenses to form liquid water. (1)

b) A — distillation flask (1)

B — condenser (1)

C — anti-bumping granules (1)

c) No stopper / screw-cap adaptor at the top of the distillation flask (1)

No outer jacket on the condenser (1)

The cooling water flows in a wrong direction. (1)

d) To ensure even boiling. (1)

e) Use dry cobalt(II) chloride paper. (1)

Water turns the paper from blue to pink. (1)

54 a) Y (1)

b) i) Hydrogen (1)

ii) Manufacture of ammonia / as rocket fuel / manufacture of hydrochloric acid (1)

c) i) Chlorine (1)

ii) Sterilizing drinking water / sterilizing swimming pool water / manufacture of bleach / manufacture of PVC / manufacture of organic solvents (1)

d) i) Sodium hydroxide solution (1)

ii) Manufacture of bleach / manufacture of soaps / manufacture of detergents (1)

e) Subsidence / cracks in buildings / destroys animal habitats (1)

55 a) i) To remove solids. (1)

ii) To kill germs / bacteria / microorganisms. (1)

b) B (1)

c) To help prevent tooth decay. (1)

d) To check for dissolved minerals. (1)

To check for microorganisms. (1)

e) The fuel cost is very high. (1)

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56 a) W — cement (1)

X — calcium oxide (1)

Y — carbon dioxide (1)

Z — calcium hydroxide (1)

b) The water was absorbed. (1)

Solid X fell apart / crumbled. (1)

c) Pass the gas into limewater. (1)

The limewater turns milky. (1)

d) Any two of the following:

Used in making steel from iron. (1) / To neutralize acidity in soil. (1) / As a drying agent in industry. (1)

e) i) Limestone dissolved in the acid. (1)

Effervescence occurred. (1)

ii) calcium carbonate + dilute hydrochloric acid calcium chloride + water + carbon dioxide (1)

57 a) i) Concentrated hydrochloric acid is highly corrosive. (1)

ii) Wash the acid off immediately with plenty of water. (1)

iii) Any two of the following:

Wear safety glasses and protective gloves. (1) / Carry out the experiment inside a fume cupboard. (1) / Do not add water to the acid directly when washing containers of concentrated hydrochloric acid. (1)

iv)

(1)

b) Based on the result of Test I, X probably contains calcium. (1)

Based on the result of Test II, X is a chloride. (1)

X is calcium chloride. (1)

58 a) It is more difficult to extract it than to make it. (1)

Lots of steps (energy) are (is) needed to purify the calcium carbonate from limestone. (1)

b) calcium carbonate + dilute hydrochloric acid calcium chloride + water + carbon dioxide (1)

c) Conduct a flame test. (1)

Calcium carbonate gives a brick-red flame. (1)

Magnesium carbonate does not give a characteristic flame colour. (1)

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d) To ensure that standards are comparable (across different tablets and the world). (2)

e) i) A mixture consists of two or more pure substances (1)

which have not been chemically joined together. (1)

ii) Vitamin pills / aspirin tablets / baking powder / washing powder (1)

59 a) calcium carbonate calcium oxide + carbon dioxide (1)

b) i) Limewater (1)

ii)

(1 mark for the set-up for testing the gas; 1 mark for the labels; 0 mark if the set-up is not workable) (2)

c) The skeletons and shells of sea animals are made up of calcium carbonate. (1)

When these animals die, their skeletons or shells sink into the mud at the bottom of the oceans. (1)

Pressure from the top layers changes the bottom layers into chalk. (1)

When the layers sink, higher pressure and heat cause the chalk to turn into limestone and marble. (1)

d) i) Any two of the following:

Dust from trucks (1) / noise from blasting and trucks (1) / eyesore (1) / destroys habitats (1) / increase traffic density (1)

ii) Any two of the following:

Limestone can be used in the extraction of iron (1) / limestone for constructing roads and buildings (1) / employment for the local people (1) / tax paid to the local government (1)

60 a) Gas Percentage by volume

Nitrogen 78% (0.5)

Oxygen 21% (0.5)

Carbon dioxide 0.03% – 0.04% (0.5)

Noble gases 0.9% (0.5)

b) A compound is a substance composed of two or more elements (1)

chemically joined together. (1)

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c) Set-up X (1)

The end of the delivery tube for the incoming gas should be put under the concentrated sulphuric acid. (1)

d) Anhydrous calcium chloride / calcium oxide (1)

e) i) Chemical change (1)

A new substance (an oxide) was formed in the process. (1)

ii) Physical change (1)

No new substance was formed in the process. (1)

f) Helium (1)

61 a) Carbon dioxide in the air dissolves in rainwater to form carbonic acid. (1)

water + carbon dioxide carbonic acid (1)

b) Acidification of water can harm water lives. / Acid rain can cause damage to plants, including crops and forests. (2)

c) The universal indicator turned red / orange (acidic colour). (1)

d) i) 0.3 million tonnes (1)

ii) Both peak in 2006. / Both decline steadily after 2006. (1)

e) i) Calcium carbonate (1)

ii) Chalk / limestone (1)

f) Taj Mahal is largely made of marble, i.e. calcium carbonate which can be attacked by acid rain. (1)

The introduction of cycle rickshaws will reduce the number of motor vehicles in the local area (1)

and thus reduce the acidic emissions. (1)

62 To show the presence of sodium in a solid sample, carry out a flame test.

First clean the end of a nichrome wire by dipping it into concentrated hydrochloric acid and then heat in a Bunsen flame. (1)

Dip the nichrome wire into concentrated hydrochloric acid and then into the solid sample. Put the end of the wire in the Bunsen flame again. (1)

The solid sample gives a golden yellow flame, indicating that it contains sodium. (1)

To show that a solid sample is a carbonate, add a little dilute hydrochloric acid to the sample. (1)

Gas bubbles are given off. (1)

The gas is carbon dioxide. It can turn limewater milky. (1)

(3 marks for organization and presentation)

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63 First prepare a saturated copper(II) sulphate solution. (1)

Place 50 cm3 of water in a beaker. Add copper(II) sulphate to the water until some solids remain in the beaker. (1)

Filter the saturated solution into another beaker. (1)

Suspend a well-shaped copper(II) sulphate crystal in the solution as a seed. (1)

Cover the beaker with a piece of paper. Leave the beaker in a warm place. (1)

As the water evaporates, the extra solutes separate out and the suspended copper(II) sulphate crystal grows. (1)

(3 marks for organization and presentation)