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Question
What would you observe when crystals of copper (II) sulphate and iron (II) sulphate are separately heated in two test tubes?
Solution
Action of heat on copper (II) sulphate crystals
When copper (II) sulphate crystals are heated in a hard glass test tube, the following observations are observed:
The crystals are converted to a powdery substance.
The crystals lose their blue coloration on further heating.
Steaming vapours are produced inside the tube which condense near the mouth of the tube to form a colourless liquid.
On further heating, steam escapes from the mouth of the tube and water gets collected in a beaker placed under the mouth of the tube.
On further heating, the residue changes to a white powder and steam stops coming out.
\[\ce{CuSO4.5H2O ->[\Delta] CuSO4 + 5H2O}\]
Action of heat on iron (II) sulphate
When iron (II) sulphate is heated in a test tube, the following is observed:
The crystals crumble to a white powder and a large amount of steam and gas are given out.
On strong heating, a brown residue of ferric oxide (Fe2O3) is produced and a mixture of SO2 and SO3 is given off.
\[\ce{FeSO4.7H2O ->[Heat] FeSO4 + 7H2O}\]
\[\ce{2FeSO4 ->[Ferric oxide][(Brown residue)] Fe2O3 + SO2 + SO3}\]
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