Sulfur dioxide
Sulfur dioxide can be made by burning sulphur in air
This is the method used in the first stage of the manufacture of sulfuric acid
Sulfur dioxide is used as a bleach in the manufacture of wood pulp for paper, and as a preservative for foods and drinks by killing bacteria
Sulfites are often added to foods and these release sulfur dioxide in acidic conditions
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Sulfuric acid is synthesised by the Contact process which use sulfur and oxygen from air and is done in three distinct stages
The Contact Process
Stage 1
The first stage is the oxidation of sulfur:
Stage 2
The main stage is the oxidation of sulfur dioxide to sulfur trioxide using a V2O5 catalyst:
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Temperature 450°
Pressure: 2 atm
Once stage 2 is completed, the sulfur trioxide is absorbed into a solution of 98% sulphuric acid to produce a thick liquid called oleum:
It is not absorbed into water because a fine mist of sulfuric acid would be produced and this would be difficult to condense and is also highly dangerous
Oleum is added to water to form concentrated sulfuric acid:
Sulfuric acid is a strong dibasic acid as two of its hydrogen atoms can be replaced by a metal
It reacts in a similar way to other acids with metal carbonates, oxides, hydroxides (and ammonia) and metals, e.g:
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Concentrated sulphuric acid is corrosive and a powerful oxidising agent
Concentrated sulphuric acid is also a very powerful dehydrating agent and is very good at removing water from other substances
For example, if mixed with sugar (C6H12O6), concentrated H2SO4 will remove water molecules and leave behind carbon in a spectacular looking black tower
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In dilute solution it is used as a catalyst in many organic reactions and to clean the surface of metals
Concentrated sulfuric acid is used in car batteries, making fertilisers, soaps and detergents
It is also used to make acid drain cleaners and in the production of paints and dyes
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