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Question
What is the colour of ferrous sulphate crystals? How does this colour change after heating?
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Solution
The colour of ferrous sulphate crystals is green. After heating, the ferrous sulphate crystal loses water molecules and forms anhydrous ferrous sulphate, which is white in colour.
\[\ce{\underset{(Green)}{FeSO4 * 7H2O} ->[\Delta] \underset{(White)}{FeSO4} + 7H2O}\]
Subsequently, it decomposes to give ferric oxide, which is brown in colour, sulphur dioxide and sulphur trioxide.
\[\ce{\underset{(White)}{2FeSO4} ->[\Delta] \underset{(Brown)}{Fe2O3} + \underset{(Gas)}{SO2} + \underset{(Gas)}{SO3}}\]
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