Download Ex. 02 Answer

21st Century Combined Science (Chemistry Part)
Suggested answers to in-text activities and unit-end exercises
Topic 1 Unit 2
In-text activities
Discussion (page 17)
Useful resources from the Earth:
• Coal, petroleum and natural gas
• Metals such as aluminium for making cooking utensils
• Sand and limestone for making glass and cement
• Silicon for making computer chips
• Nitrogen and oxygen from the atmosphere
Checkpoint (page 20)
a) Mushroom soup is a mixture of mushroom, water, flour and other substances.
b) Sea water is a mixture of salts and water.
c) Milk is a mixture of water and milk solids.
d) Distilled water is a pure substance.
e) Air is a mixture of gases.
Checkpoint (page 25)
1 a) An egg is a mixture of egg yolk, egg white and other substances.
b) Carbon dioxide is a compound.
c) Ice is water in the solid state, thus it is a compound.
d) Iron is an element.
e) Nitrogen is an element.
f) Concrete is a mixture of cement, stone chips, sand and water.
2 a) Sodium and chlorine are elements. Sodium chloride is a compound.
b) Sodium chloride and sand are not chemically joined together.
They can be separated by physical methods.
Checkpoint (page 29)
1 a) Physical property
The property can be measured without changing the chemical composition of the substance.
b) Physical property
The property can be measured without changing the chemical composition of the substance.
c) Chemical property
Milk turns sour because a new substance (an acid) forms. The statement describes the ability of
milk to form new substance(s), i.e. a chemical property of milk.
Suggested answers to in-text activities and unit-end exercises
Topic 1 Unit 2
1
© Jing Kung. All rights reserved.
21st Century Combined Science (Chemistry Part)
2 a) A compound
b) • At room temperature and pressure, carbon is a solid while carbon dioxide is a gas.
• Carbon is black in colour while carbon dioxide is colourless.
c) • Carbon burns in air to give carbon dioxide while carbon dioxide does not.
• Carbon dioxide turns limewater milky while carbon does not.
Everyday Chemistry (page 30)
1 • For patients during operations
• For patients with lung diseases
• For patients poisoned by carbon monoxide
• For premature babies
any one
any one
any three
• For babies with respiratory distress syndrome
2 • For use in ‘oxy-acetylene’ torches used for cutting and welding metals
• For use in steel industry
• Oxygen is used as an oxidizer in the fuel systems of large rockets. Oxygen reacts with
the fuel to supply the energy for launching and powering rockets.
any two
Unit-end exercises (pages 33-36)
1
Suggested answers to in-text activities and unit-end exercises
Topic 1 Unit 2
2
© Jing Kung. All rights reserved.
21st Century Combined Science (Chemistry Part)
2
3 a) Element
b) Compound
Magnesium oxide is a compound of magnesium 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 property
b) Chemical property
c) Physical property
d) Physical property
e) Physical property
5 a) False
Matter is anything which has mass and occupies space.
b) True
c) False
Ice melts at 0 °C is a physical property of ice.
d) False
Oxygen can relight a glowing splint.
Suggested answers to in-text activities and unit-end exercises
Topic 1 Unit 2
3
© Jing Kung. All rights reserved.
21st Century Combined Science (Chemistry Part)
6D
Soda water is a mixture of water and carbon dioxide.
7A
8D
Sugar is a compound composed of carbon, hydrogen and oxygen.
9B
10 C
11 The atmosphere on Earth contains
• less carbon dioxide;
• more nitrogen;
• more (or some) oxygen;
• some water vapour.
any three
12 a) Physical property
b) Chemical property
c) Physical property
d) Chemical property
Suggested answers to in-text activities and unit-end exercises
Topic 1 Unit 2
4
© Jing Kung. All rights reserved.