Heating Effect on Sulphate Salts

  1. Most sulphate salts do not decompose by heat. For instance, sodium sulphate, potassium sulphate, and calcium sulphate are not decomposable by heat. 
  2. Only certain sulphate salts are decomposed by heat when heated strongly.
  3. For instance:
    1. Strong heating of green crystal iron (II) sulphate will release steam, sulphur dioxide, sulphur trioxide and leave behind a reddish solid iron (III) oxide residue. The steam released comes from the hydrated water of the crystallize salt.

      2FeSO4•7H2O → Fe2O3(p) + SO2(g) + SO3(g) + 14H2O(g) 

    2. Meanwhile, zinc sulphate, copper (II) sulphate, and iron (III) sulphate decompose when heated strongly to evolve sulphur trioxide gas and form a metal oxide.
      Example
      Zinc sulphate

      ZnSO4 → ZnO + SO3

      Copper (II) sulphate

      CuSO4 → CuO + SO3

      Iron (III) sulphate

      Fe2(SO4)3 Fe2O3  + 3SO3      

    3. When ammonium sulphate is heated strongly, this white solid sublimate and is decomposed to form ammonia gas and sulphuric acid. vapour

      (NH4)2SO4 → NH3 + H2SO4

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