Question

What would you observe when crystals of copper (II) sulphate and iron (II) sulphate are separately heated in two test tubes?

Answer 1

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.

\[\ce{FeSO4.7H2O ->[Heat] FeSO4 + 7H2O}\]

\[\ce{2FeSO4 ->[Ferric oxide][(Brown residue)] Fe2O3 + SO2 + SO3}\]