Chemical Reactions PDF

1.2.2 Decomposition Reaction Activity 1.5 n Take about 2 g ferrous sulphate crystals in a dry boiling tube....

1.2.2 Decomposition Reaction Activity 1.5 n Take about 2 g ferrous sulphate crystals in a dry boiling tube. n Note the colour of the ferrous sulphate crystals. n Heat the boiling tube over the flame of a burner or spirit lamp as shown in Fig. 1.4. n Observe the colour of the crystals after heating. Figure 1.4 Have you noticed that the green colour of the ferrous sulphate crystals Correct way of heating the boiling tube has changed? You can also smell the characteristic odour of burning containing crystals sulphur. of ferrous sulphate Heat 2FeSO4(s)  and of smelling the → Fe2O3(s) + SO2(g) + SO3(g) (1.19) odour (Ferrous sulphate) (Ferric oxide) In this reaction you can observe that a single reactant breaks down to give simpler products. This is a decomposition reaction. Ferrous sulphate crystals (FeSO4. 7H2O) lose water when heated and the colour of the crystals changes. It then decomposes to ferric oxide (Fe2O3), sulphur dioxide (SO2) and sulphur trioxide (SO3). Ferric oxide is a solid, while SO2 and SO3 are gases. Decomposition of calcium carbonate to calcium oxide and carbon dioxide on heating is an important decomposition reaction used in various industries. Calcium oxide is called lime or quick lime. It has many uses – one is in the manufacture of cement. When a decomposition reaction is carried out by heating, it is called thermal decomposition. Heat CaCO3(s)  → CaO(s) + CO2(g) (1.20) (Limestone) (Quick lime) Another example of a thermal decomposition reaction is given in Activity 1.6. Activity 1.6 n Take about 2 g lead nitrate powder in a boiling tube. n Hold the boiling tube with a pair of tongs and heat it over a flame, as shown in Fig. 1.5. n What do you observe? Note down the change, if any. Figure 1.5 You will observe the emission of brown fumes. Heating of lead nitrate and These fumes are of nitrogen dioxide (NO2). The emission of nitrogen dioxide reaction that takes place is – 8 Science 2024-25