(a) describe the volume composition of gases present in dry air as 78% nitrogen, 21% oxygen and the remainder being noble gases (with argon as the main constituent) and carbon dioxide
(b) describe the separation of oxygen, nitrogen and the noble gases from liquid air by fractional distillation
(c) state the uses of oxygen (e.g. in making steel; oxygen tents in hospitals; in welding)
(d) name some common atmospheric pollutants (e.g. carbon monoxide; methane; nitrogen oxides (NO and NO2); ozone; sulfur dioxide; unburned hydrocarbons)
(e) state the sources of these pollutants as
- (i) carbon monoxide from incomplete combustion of carbon-containing substances
- (ii) methane from bacterial decay of vegetable matter
- (iii) nitrogen oxides from lightning activity and internal combustion engines
- (iv) ozone from photochemical reactions responsible for the formation of photochemical smog
- (v) sulfur dioxide from volcanoes and combustion of fossil fuels
- (vi) unburned hydrocarbons from internal combustion engines
A presentation done by students of grade 11.
(f) describe the reactions used in possible solutions to the problems arising from some of the pollutants named in (d)
- (i) the redox reactions in catalytic converters to remove combustion pollutants
- (ii) the use of calcium carbonate to reduce the effect of ‘acid rain’ and in flue gas desulfurisation
Another presentation done by students of grade 11
(g) discuss some of the effects of these pollutants on health and on the environment
- (i) the poisonous nature of carbon monoxide
- (ii) the role of nitrogen dioxide and sulfur dioxide in the formation of ‘acid rain’ and its effects on respiration and buildings
(h) discuss the importance of the ozone layer and the problems involved with the depletion of ozone by reaction with chlorine-containing compounds, chlorofluorocarbons (CFCs)
(i) *describe the carbon cycle in simple terms, to include
- (i) the processes of combustion, respiration and photosynthesis
- (ii) how the carbon cycle regulates the amount of carbon dioxide in the atmosphere
Here is a presentation done by students of grade 11.
(j) state that carbon dioxide and methane are greenhouse gases and may contribute to global warming, give the sources of these gases and discuss the possible consequences of an increase in global warming
10.2 Water
(a) state that water from natural sources contains a variety of dissolved substances
- (i) naturally occurring (mineral salts; oxygen; organic matter)
- (ii) pollutant (metal compounds; sewage; nitrates from fertilisers; phosphates from fertilisers and detergents; harmful microbes)
(b) discuss the environmental effects of the dissolved substances named in (a)
- (i) beneficial, e.g. oxygen and mineral salts for aquatic life
- (ii) pollutant, e.g. hazards to health; eutrophication
Here is another presentation by grade 11 students.
(c) outline the purification of the water supply in terms of
- (i) filtration to remove solids
- (ii) use of carbon to remove tastes and odours
- (iii) chlorination to disinfect the water
(d) state that seawater can be converted into drinkable water by desalination
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