List any two observations when ferrous sulphate is heated in a dry test tube?

When ferrous sulfate (FeSO4) is heated in a dry test tube, a couple of observations can be made:

• 1.Color Change: Ferrous sulfate crystals are typically green in color due to the presence of water of crystallization (FeSO4·7H2O). Upon heating, the crystals first lose their water of hydration, which results in a color change from green to white as the anhydrous ferrous sulfate (FeSO4) is formed. Further heating leads to the decomposition of ferrous sulfate, and the compound turns into a brownish color due to the formation of iron(III) oxide (Fe2O3).
• 2. Release of Gases: During the heating process, gases are evolved. Initially, water vapor is released as the hydrate loses its water of crystallization. As the decomposition proceeds, sulfur dioxide (SO2) and sulfur trioxide (SO3) gases are evolved, which have a characteristic pungent odor. These gases are products of the thermal decomposition of the sulfate ion (SO4^2−).

Dehydration reaction

FeSO₄ · 7H₂O(s) → FeSO₄(s) + 7H₂O(g)

Decomposition reaction

2FeSO₄(s) → Fe₂O₃(s) + SO₂(g) + SO₃(g)