2 g of ferrous sulphate crystals were heated in a hard glass test tube and observations recorded. i. What was the successive colour change? ii. Identify the liquid droplets collected on the cooler parts of the test tube. iii. What type of odour is observed on heating ferrous sulphate crystals? iv. Name the products obtained on heating ferrous sulphate crystals. v. What type of reaction is taking place?

Question

Philoid · Accepted Answer

When 2 g of ferrous sulphate crystals were heated in a hard glass test tube, the following observations take place:

i) Hydrated ferrous sulphate crystals are light green in colour. They contain two water molecules. The chemical formula is FeSO₄.2H₂O. 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 solid, while SO₂ and SO₃ are gases.

Thus, the colour changes from light green to brown.

ii) The liquid droplets on the cooler parts of the test tube are of water.

iii) Rotten type of odour is observed on heating ferrous sulphate crystals. This is due to the release of sulphur dioxide gas.

iv) When ferrous sulphate crystals are heated, give ferric oxide, sulphur dioxide and sulphur dioxide gas. The chemical reaction is given as:

2FeSO₄→ Fe₂O₃ + SO₂ + SO₃

v) In the reaction, we observe that a single reactant breaks down to give simpler products. This is a decomposition reaction.