Page 15 - Curriculum Visions Dynamic Book

combustion: the special case of oxidisation of a substance where a considerable amount of heat and usually light are given out. Combustion is often referred to as “burning”.
 The sulphur is ignited in air and then introduced to the oxygen, where it burns with a bright blue flame.
Burning sulphur compounds
When sulphur or sulphur-containing compounds are burned, the reaction always produces sulphur dioxide gas as the example equation below shows. This can be a major problem for the iron and copper-refining industries as well as for power stations burning sulphur-rich coal or oil.
EQUATION: Burning sulphide ore
Iron sulphide + oxygen ➪ iron oxide + sulphur dioxide 4FeS(s) + 7O2(g) ➪ 2Fe2O3(s) + 4SO2(g)
Cubic crystals of pyrite
 Pyrite (iron sulphide) often occurs in brassy-coloured cubic crystals (see page 13). However, all sulphides form
in the absence of air. Sulphur reacts
so readily with oxygen that when it
is exposed to the air, especially damp
air, the crystals quickly oxidise to iron sulphate. The glass jar on the right, for example, once contained perfect cubic crystals, but these have now oxidised
to grey iron sulphate and therefore fallen apart. For this reason, if you want to keep samples of pyrite that you might have collected, they should be protected from contact with damp air.
EQUATION: Weathering of pyrite (iron sulphide) in damp air
Iron sulphide + water + oxygen ➪ iron sulphate + sulphuric acid 2FeS2(s) + 2H2O(l) + 7O2(g) ➪ 2FeSO4(s) + 2H2SO4(aq)
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