1(a) no. of moles of moles of oxygen = 100/24
no. of moles of potassium superoxide required = 4/3 × 100/24
Thus, mass of potassium superoxide required = 4/3 × 100/24 × [39 + 2(16)]
= 394 g (to 3 sig. fig.)
(b) (i) potassium carbonate
(ii) 2KOH + CO2 → K2CO3 + H2O
(c) The relative atomic mass of lithium is smaller than that of potassium. So a smaller
mass of lithium hydroxide is needed to absorb the same amount of carbon dioxide.
2(a) Oxygen is used in the industry for combustion. For example, in making steel, oxygen
gas is passed into molten iron to burn off impurities.
(b) C(s) + O2(g) → CO2(g)
(c) (i) The product is sulfur dioxide which is poisonous; it is an air pollutant and causes
the formation of acid rain.
(ii) calcium carbonate, CaCO3 [or calcium oxide, CaO; or calcium hydroxide,
(d) Air is first cooled and compress into liquid. Liquid air is then separated into its
constituents (or fraction) by fractional distillation, and oxygen is collected at its
boiling point of -183 °C.
3 (a) Ozone absorbs harmful ultraviolet radiation from the Sun, preventing it from
reaching the surface of the earth. If this radiation reaches the earth, it kills vegetation
and harms animals including humans. For example, it causes a drastic increase in the
number of cases of skin cancer, genetic mutations and eye damage.
(b) (i) From the cooling systems of old refrigerators [or from old polystyrene foam;
or from aerosol propellant.]
(ii) They are very stable and chemically unreactive. So they can remain in the
atmosphere for a very long time.
(iii) 2O3 → 3O2
(c) Nitrogen dioxide in the air reacts with unburnt hydrocarbons in sunlight to
produce ozone. Ozone is the main component of photochemical smog.
4 (a) carbon dioxide and water.
(b)(i) Carbon monoxide is formed because there is insufficient air to cause complete
combustion of all the petrol in motor car engines. Incomplete combustion of
the fuel in the car engine causes the production of carbon monoxide.
(ii) As the air/petrol ratio is increased in the engine, the concentration of carbon
(iii) There is more oxygen in more air to cause complete combustion of all the
(c) (i) The high temperature in motorcar engine causes the nitrogen and oxygen in
the air to react to form nitrogen monoxide. The nitrogen monoxide then reacts
with more oxygen to form nitrogen dioxide.
(ii) The maximum amount of heat energy us produced at a ratio of 15, so the
temperature is highest and so more nitrogen dioxide is produced.
(d) unburnt hydrocarbons
(e) (i) Transition elements
(ii) Alloys are stronger and tougher than pure metals and so last longer.
(iii) The temperature is high, and the catalyst is in powdered form, so it has a
large surface area for reaction to take place.
(iv) nitrogen and carbon dioxide
(f) (i) Motorcar engines burn large amounts of hydrocarbon fuel and so put large
amounts of carbon dioxide into the atmosphere. Carbon dioxide traps heat
radiation from the Sun, and prevents much of it escaping into space.
(ii) Burn hydrogen in the engine in place of hydrocarbons (or use an electric
5 (a) Nitrogen: 79%; Oxygen : 20%
(b) Sulfur dioxde; it is produced from the combustion of fossil fuels such as coal.
(c) (i) The water will freeze to form solid ice. This will cause blockages to the pipes in
the fractionating column and prevent the distillation from taking place.
(ii) nitrogen, argon, oxygen and krypton
1. (a)(i) The carbon dioxide molecules in the air are continually being removed by green
plants in photosynthesis. Combustion of fossil fuels and other processes puts
large amounts of carbon dioxide into the atmosphere. This two-way process
has roughly been in balance over the past few millennia so that the amount of
carbon dioxide in the atmosphere has remained fairly constant.
(ii) Over the past century, global industrialization and increased number of motor
vehicles, increases the use of fossil fuels. The combustion of fossil fuels for
energy release carbon dioxide into the atmosphere.
(iii) The temperature of the sea will increase and sea levels will rise, causing
(b) Use hydrogen gas as a fuel in place of hydrocarbons or use electric vehicles.
2. (a) It is rain made more acidic than unpolluted rain due to acidic gases such as man-
made sulfur dioxide and oxides of nitrogen from air pollution.
(b) It is mainly caused by combustion of fossil fuels containing sulfur which
produces sulfur dioxide , and motor vehicle engines which produces oxides of
nitrogen. These gases are acidic and react with rain water to produce sulfuric
acid and nitric acid , which falls to the surface of the Earth as acid rain.
(c) (refer to page 9 and 10 of the notes.)
3 (a) (i) 2H2S + 3O2 → 2SO2 + 2H2O 
(ii) no. of moles of H2S = 6.8 / [2(1) + 32]
= 0.2 mol = no. of moles of SO2 
Mass of SO2 produced = 0.2 × [32 + 2(16)]
= 12.8 g  / 
(iii) acidified potassium dichromate(VI) / turns from orange to green 
(b) Sulfur dioxide produced is poisonous and can cause the production of acid rain.
4(a) no. of moles of CO2 = 1 000 000 / [12 + 2(16)]
= 22727.27 mol 
(b) The high temperature produced on burning coal caused the nitrogen and oxygen in
the air to react to form nitrogen monoxide . Nitrogen monoxide then reacts with
more oxygen in the air to form nitrogen dioxide .
(c) S + O2 → SO2 
(d) sulfur dioxide reacts with an aqueous suspension of calcium carbonate to form
calcium sulfite, CaSO3. 
CaCO3(s) + SO2(g) → CaSO3(s) + CO2(g)
The calcium sulfite is reacted with oxygen in the air to convert it into unreactive
calcium sulfate, CaSO4, and is then dumped. 
2CaSO3(s) + O2(g) → 2CaSO4(s)
(e) no. of moles of CaCO3 = 30 000 000 / 100
= 300 000 moles = no. of moles CaSO4 
Mass of CaSO4 = 300 000 × [40 + 32 + 4(16)]
= 408 00000 g  / 
5 Respiriation and combustion removes O2 from the air and produce CO2.
Photosynthesis removes CO2 from the air and produce O2.
This two-way process has roughly been in balance over the past few millennia so that
the composition of air has remained fairly constant..