E s s e n t i a l C h e m i s t r y f o r C a m b r i d g e I G C S E ® 2 nd E d i t i o n
Unit 15 Air and water
SUMMARY QUESTIONS:
1 Sulfur dioxide – acid rain
Nitrogen oxides – smog and acid rain
Methane – increased global warming
Lead compounds – damage to the nervous system
2 Add water to anhydrous / white copper sulfate; turns blue if water is present
3 Fifth; water; rust; oxidised; acid; fossil; sulfur; oxidised; trioxide; sulfuric
4 Rusting – corrosion of iron
Corrosion – ‘eating away’ of metal surfaces
Fossil fuels – burning these causes acid rain
Greenhouse gas – gases in atmosphere that absorb heat energy
Argon – gas forming 1% of air
Nitrogen – gas forming 80% of air
5 Coating with another metal / plastic etc. – prevents air and water getting to the iron
Greasing – prevents air and water getting to the iron
Galvanising – prevents air and water getting to the iron; zinc also protects by sacrificial
protection if its surface is broken; sacrificial protection (a more reactive metal in contact with a
less reactive metal corrodes in preference to the less reactive metal).
6 (a) Nitrogen(II) oxide / nitrogen(IV) oxide
(b) Oxygen and nitrogen from the air combine under the high pressure and temperature in the
car’s engine.
(c) In the presence of a catalyst, nitrogen oxide is converted to nitrogen and carbon monoxide
is converted to carbon dioxide. Carbon monoxide also reacts catalytically with nitrogen
oxides to form nitrogen and carbon dioxide.
7 B → F →D → C → E → A
PRACTICE QUESTIONS:
1 C Both air and water are needed for rusting
2 D The amount of carbon dioxide put into the atmosphere by respiration is roughly the same
as carbon dioxide removed by photosynthesis
3 (a) (i) O2 ; CO2 ; Ar or other noble gas
(ii) Any one of:
CO2 = 0.03% or 0.04% / argon = 1% / oxygen = 21% (ALLOW: 20%)
(b) (i) Burning hydrocarbons / burning fossil fuels / burning coal or named fossil fuel;
incomplete combustion / combustion in limited oxygen. NOT: in lack of oxygen.
(ii) Poisonous NOT: harmful / combines with haemoglobin / stops blood carrying oxygen.
(c) (i) E.g. bacterial action in waste heaps / decomposition of vegetation / rice paddy fields /
termites / cow or sheep flatulence.
(ii) Absorbs infrared radiation; traps heat in atmosphere / warms up the atmosphere.
(iii) Any suitable effect, e.g. glaciers melt / ice caps melt / rise in sea levels / desertification /
extremes of weather.
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E s s e n t i a l C h e m i s t r y f o r C a m b r i d g e I G C S E ® 2 nd E d i t i o n
4
(a) (i) Any suitable use, e.g. coolant / solvent / as a reactant
(ii) Any suitable use, e.g. cooking / washing / cleaning
(b) Anhydrous / white copper sulfate; turns blue
(c) (i) Filtration; through (layers of) sand / gravel
(ii) To kill bacteria
(d) (i) Rain with pH below about pH 5 / lower pH than normal rain
(ii) Any three of:
Burning fossil fuels containing sulfur / volcanoes / roasting sulfide ores; sulfur dioxide
formed; sulfur dioxide oxidised to sulfur trioxide; to form sulfuric acid / acidic solution.
5 (a) Carbon dioxide and water combine; in the presence of light and chlorophyll; to form
oxygen and glucose. ALLOW: oxygen and starch
(b) 6CO2 + 6H2O → C6H12O6 + 6O2
(c) (i) Dissolving of CO2 in oceans / reacting of CO2 in water
(ii) Burning fossil fuels / bacterial decay / warming of water in the oceans
(d) Glucose + oxygen → carbon dioxide + water
(e) (i) Gas which absorbs infrared radiation; warms the Earth / leads to increased global
warming.
(ii) Industrial revolution / more cars / increase in population / more industry etc.
NOT: cars / people unqualified
6 (a) Any source, e.g. lightning / bacteria in the soil (denitrifying)
(b) Nitrogen and oxygen combine under high temperature and pressure in car’s engine; carbon
monoxide formed by incomplete combustion of hydrocarbons.
(c) Nitrogen oxides converted to nitrogen; carbon monoxide converted to carbon dioxide; with
the help of catalysts / platinum / palladium / rhodium
(d) Reductant = C6H14 ; because carbon oxidised to carbon dioxide / hydrogen removed.
Oxidant = NO2 ; because NO2 loses oxygen.
4
1
nitrogen; 20% or oxygen; 0.03 to 0.5% carbon dioxide; 1% argon
5
5
Lowering the temperature of the air / liquefying the air; fractional distillation.
Boiling point
Any type of coating, e.g. plastic / zinc / tin / grease / paint
Strip of more reactive metal placed on less reactive metal; more reactive metal loses
electrons more easily than less reactive metal; so more reactive metal corrodes rather
than less reactive metal.
7 (a) 80% or
(b) (i)
(ii)
(c) (i)
(ii)
© OUP 2015: this may be reproduced for class use solely for the purchaser’s institute