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Questions 4.5.5

  1. In many cases, the first product of thermal decomposition of sulphates (and other salts) is steam. Explain why steam is a common product when salts are heated.
  2. On further heating, sulphates decompose into metal oxide, Sulphur (IV) oxide and Sulphur (VI) oxide. Write the equation for thermal decomposition of zinc (II) sulphate (ZnSO4.7H2O), iron (II) sulphate (FeSO4.7H2O), and copper (II) sulphate (CuSO4.5H2O). For iron (II) sulphate, the residue is iron (III) oxide.


Answers to Questions 4.5.5

  1. Many salts form crystals by combining with water of crystallization. Water of crystallization is released or breaks off readily as the salt is heated.

  2. 2FeSO4.7H2O(s)   ⟶   Fe2O3(s)   +   14H2O(g)   +   SO3(g)   +  SO2(g)

    2CuSO4.5H2O(s)   ⟶   2CuO(s)   +   10H2O(g)   +   SO3(g)

    2ZnSO4.7H2O(s)   ⟶   2ZnO(s)   +   14H2O(g)   +   SO3(g)