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7.1 A Composition of air I
i Concept
Checking
Decide whether the following statements are true or false,
and try to rewrite the true statements. (10
marks)
1 Air contains oxygen, nitrogen, carbon dioxide and water vapour only. True
/ False
Air
contains oxygen, nitrogen, carbon dioxide, water vapour, noble gases and other
gases.
2 The
composition of air is constant. True
/ False
The
composition of air is variable / not constant.
3 The
percentage of water vapour in air is affected by the weather. True / False
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4 One
difference between nitrogen and noble gases is that nitrogen is reactive while
noble True / False
gases are unreactive.
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5 The
lights in commercial signs contain noble gases. True / False
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i Short
Questions
1 *(a) Why
are noble gases also called inert gases
(惰性氣體)? (1 mark)
Noble
gases are unreactive. / Noble gases do not react with other chemicals easily.
(b) Name
TWO noble gases and state ONE use for each of them. (4 marks)
Any
TWO of the followings:
Helium.
It is used to fill balloons.
Neon.
It is used to fill neon light.
Argon.
It is used to fill light bulbs.
2 (a) What
is the gas with the highest percentage in air? (1 mark) Nitrogen
(b) State
ONE use of this gas. (1 mark)
Nitrogen
is used to fill food package so as to extend the shelf life of food. / Liquid
nitrogen is used to store living cells./ Nitrogen is used to make fertilizers肥料.
i Long
Questions
1 The photo shows a light bulb. It is filled with gas X and there
is a tungsten wire (鎢絲) inside. When electricity passes through
the wire, the wire gives out light and heat.
Vivian and Kenny are arguing what gas X is. Vivian thinks
that it is
oxygen but Kenny thinks that it is a noble gas.
*(a) Suggest
why Kenny’s idea is more reasonable. (2 marks)
It is because noble gases are
unreactive (1) and do not react with the tungsten wire (1), so that the wire
can have a longer life.
(b) Name the noble gas that is used to fill
light bulbs. (1 mark) Argon.
(c) Name
ONE other noble gas and state its use. (2 marks)
Neon; it is used to fill neon
light. / Helium; it is used to fill balloons that float in air.
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