NSS Chemistry Chapter 2: Atmosphere
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HKDSE
S.4 Chemistry
Part I: Planet Earth
Chapter 2
Atmosphere
Name: __________________________________
Class: _____ No. ______
NSS Chemistry Chapter 2: Atmosphere
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2.1 Getting to know our planet Earth
A.
Structure of Earth (Just an introduction)
1.
Some data about our Earth. (no need to remember)
2.
The Earth has a layered structure.
Need to know the basic terms:
- inner core (mainly solid Fe and Ni)
- outer core (mainly liquid Fe and Ni)
- mantle (liquid, mainly SiO2)
- crust (solid, mainly SiO2)
3.
The Earth’s crust is made up of rocks and soils. Soils have been formed
mainly by the breakdown of rocks.
4.
The Earth’s crust, ocean and atmosphere are the major source of
chemicals.
NSS Chemistry Chapter 2: Atmosphere
B.
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Earth as a source of Chemicals
1.
Earth is the major sources of a variety of chemicals that we need.
2.
In atmosphere (remember)
~78% N2
~21 % O2
~ 0.9% Noble gases (Ar, Ne..etc)
~0.03% CO2
~ small amount of other gases (e.g. H2O, NO2, SO2..etc)
Class Exercises 2.2
1.
In our Earth, ______________% is covered by sea and __________% is covered
by sea.
2.
The following diagram shows the structure of Earth.
Label the four different parts:
NSS Chemistry Chapter 2: Atmosphere
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2.2 Classification of matter
A.
Pure substances and mixtures
1. A pure substance is a single substance that has no other substances mixed
with it. e.g. H2, O2, CO2.
A pure substance may be an element or a compound.
2.
A mixture consists of two or more pure substances which have not
chemically combined together.
e.g. air, sea water, steel(a mixture of C and Fe).
B.
Elements and Compounds
A pure substance can either be an element or a compound.
(a) An element is a substance that cannot be broken down into anything
simpler by chemical methods.
e.g. water is not an element as it can be decomposed by electricity to
hydrogen and oxygen.
(b) A compound is a pure substance made up of two or more elements
chemically combined together.
e.g. H2 , O2, CO2 and NaCl are all pure substances.
H2 and O2 are elements. CO2 and NaCl are compounds.
NSS Chemistry Chapter 2: Atmosphere
C.
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Differences between mixtures and compounds
1.
Consider iron, sulphur, iron + sulphur mixture, iron sulphide compound.
Their properties are tabled below:
2. The following table lists the differences between mixture and compounds.
NSS Chemistry Chapter 2: Atmosphere
D.
Summary Chart
E.
Properties of Substances
1. Physical Properties
2.
(a)
(b)
(c)
(d)
(e)
(f)
(g)
appearance
odour
taste
hardness
density
solubility
melting point
(h)
(i)
(j)
(k)
(l)
boiling point
malleability (can change shape)
ductility (draw into wire)
electrical conductivity
thermal conductivity
Chemical Properties
This means the chemical reactions with other substances.
New substances are formed.
e.g. Hydrogen can react with oxygen to form water.
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NSS Chemistry Chapter 2: Atmosphere
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Example:
Class Exercises 2.2
1.
In the following diagrams, o and  represent different atoms,
(a) A represents a mixture of two compounds.
B represents a pure compound.
C represents ____________________________________________.
D represents ____________________________________________.
(b) Suggest a chemical formula for
2.
(i)
________________________
(ii)
________________________
(iii)
________________________
(iv)
________________________
How can you separate a mixture of iron powder and sulphur powder?
_________________________________________________________________
_________________________________________________________________
NSS Chemistry Chapter 2: Atmosphere
3.
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Consider the boiling point table below:
Gas
Boiling point (°C)
Argon
–186
Nitrogen
–196
Neon
–246
Oxygen
–183
Xenon
–109
Carbon dioxide
–78
Helium
–269
Krypton
–153
Note:
Temp < m.p. = solid
m.p. < Temp < b.p. = liquid
b.p. < Temp = gas
(a) List the gases which would still be in gaseous state at
–200°C
_____________________________
(ii) -180 oC
_____________________________
(i)
(b) What are the electronic configuration of
(i) Neon
________________________
(ii) Argon
________________________
(c) Explain why the boiling points of argon is higher than neon.
NSS Chemistry Chapter 2: Atmosphere
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2.3 The atmosphere
1.
2.
3.
The atmosphere is a gaseous layer (about 80 km thick) surrounding the Earth.
The gases in the atmosphere are held around the Earth by gravity.
Air is a mixture of gas. The following diagram shows the composition of air:
4.
The noble gases include argon, helium, neon, krypton and xenon. Argon has the
highest percentage.
Other gases includes water vapour, waste gases from cars, industry, laboratory
e.g. SO2, CO…etc.
5.
2.4
Separation of nitrogen and oxygen from air
A.
Fractional distillation of liquid air (must remember how to write)
1.
The components of air can be separated according to their differences in
boiling points.
The air is first liquefied by repeated cooling and compression.
The liquid air is then warmed up bit by bit very slowly. Different gases in air boil
at different temperatures; we can collect them one by one.
2.
3.
4.
This process is called fractional distillation of liquid air. (Must remember this
method). It involves three stages:
Stage 1: Remove of impurities e.g. dust and CO2
Stage 2: Liquefaction of air
Stage 3: Fractional distillation of air.
Gases with lower boiling points will be collected at higher positions.(N2)
Gases with higher boiling points will be collected at higher positions. (O2)
NSS Chemistry Chapter 2: Atmosphere
B.
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Properties and uses of oxygen and nitrogen
1. Oxygen
(a) Properties of oxygen:
(i) Colourless, odourless gas,
(ii) Slightly soluble in water
(iii) It is very reactive. It reacts with many substances to form oxides.
(b) Testing for oxygen
Put a glowing splint into a test tube of oxygen. Glowing splint relights.
NSS Chemistry Chapter 2: Atmosphere
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(c) Uses of oxygen
(i)
Oxygen can keep us alive. We breathe in oxygen and breathe out
carbon dioxide.
(ii) Oxygen support combustion. It is used in welding of metals.
2.
Nitrogen
(a) Properties of nitrogen
(i) colourless and odourless
(iii) Nitrogen is very unreactive. It does not have much reactions.
(b) Uses of nitrogen
(i) Due to its unreactiveness, it is used in food packaging.
(ii) Due to its very low boiling point, it is used as a refrigerant.
NSS Chemistry Chapter 2: Atmosphere
3.
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Argon
(a) Properties of argon
(i) Colourless and odourless.
(ii) Argon is a noble gas, it has no reactions at all.
(b) Uses of argon
Due to its unreactiveness, it is used to fill light bulbs.
Class Exercises 2.3 and 2.4
1.
Oxygen is a very reactive gas. It can react with metals and non-metals on
heating. Write balanced word equations for the following:
a.
calcium + oxygen
calcium + oxygen  calcium oxide
b.
aluminium + oxygen
c.
iron + oxygen
d.
carbon + oxygen
f.
hydrogen + oxygen
g.
chlorine and oxygen
NSS Chemistry Chapter 2: Atmosphere
2.
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Test for oxygen：
Oxygen can __________________________________________________.
3.
Match the following uses with the following elements
oxygen, nitrogen, carbon dioxide, helium, neon and argon.
Uses
Element/Compound
To fill airships
As refrigerant
Fill in food package
To make advertising signs
Support combustion
To make ammonia
Fill in soft drinks
Keep us alive
To fill light bulbs
2.
Hydrogen is even lighter than helium. Why is hydrogen not used to fill airships
or party balloons?
NSS Chemistry Chapter 2: Atmosphere
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Some Past Papers
1. Nitrogen, instead of air, is used to fill the packets of potato chips. It is because
A.
B.
C.
D.
2.
air supports combustion but nitrogen does not.
the density of air is higher than that of nitrogen.
argon in air contaminates the chips but nitrogen does not.
oxygen in air makes the chips go bad but nitrogen does not.
2008 (8)
Ans: D
Which of the following components of air is NOT obtained industrially from
fractional distillation of liquid air?
A.
B.
C.
D.
Ar(g)
CO2(g)
N2(g)
O2(g)
Ans: D
1.
Argon and chlorine are elements in the same period of the Periodic Table.
(c) Complete the table below by stating the natural source and the method of
extraction from the source for each element. (4 marks)
Element
Natural source
Method of extraction
Argon
Chlorine
(HKDSE 2015 P1B Q1(c))
Element
Argon
Chlorine
Natural source
Method of extraction
The atmosphere/Air
Fractional distillation of liquid
air
Sea water
Electrolysis of sea water