What are the steps involved in the contact process of manufacture of sulphuric acid

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What are the steps involved in the contact process of manufacture of sulphuric acid.

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Steps Involved in the Contact process

  1. Production of Sulphur Dioxide
    SO2 is produced by roasting metallic sulphides in air.
    4FeS2 +11O2 → 2Fe2O3+ 8SO2

  2. Purification of Gases
    To enhance the efficiency of a catalyst, various impurities present in the mixture of sulphur dioxide and air are first removed.

  3. Catalytic Oxidation of Sulphur Dioxide
    Oxidation of SO2 to SO3at 450°C in the presence of catalyst vanadium pentaoxide.
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  4. Absorption of Sulphur Trioxide in Sulphuric Acid
    Sulphur trioxide vapours are absorbed by a stream of conc. sulphuric acid.
    SO3 + H2SO4 → H2S2O7 (oleum or pyrosulphuric acid)

  5. Dilution of Oleum to Obtain Sulphuric Acid
    A calculated amount of water is added to obtain sulphuric acid of desired strength.
    H2S2O7 + H2O → 2H2SO4