ZIMSEC O Level Combined Science Notes: The production of sulphuric acid

  • Sulphuric acid is produced using the Contact process
  • In Zimbabwe there is a sulphuric acid production plant at Zimphos in Harare
  • Sulpher or iron pyrites (iron sulphide) is roasted to form sulphur dioxide
  • The word equation for roasting iron pyrites is:
  • \text{iron sulphide+oxygen}\rightarrow\text{iron oxide+sulpher dioxide}
  • The word equation for roasting sulpher is:
  • \text{sulphur+oxygen}\rightarrow\text{sulpher dioxide}
  • The sulphur dioxide is then mixed with excess air and then passed to a converter
  • In the converter the mixture is converted into sulphuric acid by the Contact Process
  • The sulphur dioxide is first converted into sulphur trioxide
  • The reaction is reversible and exothermic
  • \text{sulpher dioxide+oxygen}\xrightleftharpoons[catalyst]{450\degree C}\text{sulpher trioxide+heat}
The Contact Process

The Contact Process

  • Better yields are obtained at low temperatures
  • However the reaction would be slow at low temperatures thus a catalyst is used
  • Vanadium oxide is used as a catalyst
  • A yield of 95% is obtained at 450°C and 1 atm pressure
  • The sulpher trioxide is cooled and then absorbed into concerntrated sulphuric acid to oleum
  • The gas is not dissolved in water as this would merely produce a sulphuric acid  mist due to the heat of the reaction
  • The word equation for mixing sulphur trioxide and concerntrated sulphuric acid is:
  • \text{sulphur trioxide+sulphur trioxide}\rightarrow\text{ oleum}
  • The oleum is then mixed with either water or dilute sulphuric acid to form concentrated sulphuric acid
  • \text{oleum+water}\rightarrow\text{concentrated sulphuric acid}

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