AimL 

To perform and observe the action of heat on ferrous sulphate crystals and also to identify the type of reaction involved.

Apparatus and Chemical

• Hard glass test tubes
• Test tube holder
• Test tube stand
• Asbestos sheet
• Bunsen burner
• Fresh ferrous sulphate crystals (light green coloured)

Principle

Chemical composition of ferrous sulphate crystals is FeSO₄. 7H₂O i.e., ferrous sulphate exist as its heptahydrate in crystalline form. It is also known as green vitrol. When strongly heated it decompose into ferric oxide, steam, sulphur dioxide and sulphur trioxide.
2( FeSO₄.7H₂O) → Fe₂O₃ + SO₂ ↑ + SO₃ ↑ + 14 H₂O ↑

It is an example of decomposition reaction.

Procedure

• In a clean and dry test tube, take a nearly 10 g of fresh light green coloured powered crystals of ferrous sulphate.
• Heat the test tube over a burner by using a test tube holder.
• Note the colour and smell of gases of vapours evolved.
• continue heating till the colour of the residue in the test tube changes.
• Place the hot test tube on an asbestos sheet to cool down.
• Note the colour of the residue when it has cooled down.
• Record your observation in the notebook.

Observations and Inference

S.No.	Observation	Experiment	Inference
1.	Note the colour of from ferrous sulphate crystals.	pale green	Ferrous sulphate crystals are light green in colour.
2.	Note the colour and smell of gas/ vapour evolved on heating ferrous sulphate crystals.	Pungent smelling colourless gas with a smell of burning sulphur.	Sulphur dioxide is a colourless gas with a smell of burning sulphur.
3.	Note the colour of the residue after cooling	It is red in colour.	Iron (III) oxide is red in colour.

Light green coloured crystals of ferrous sulphate on heating decomposes to give a mixture of gasses (SO₂ and SO₃) and a red coloured residue (Fe₂O₃). It is an example of decomposition reaction.

Precautions

• Test tube used for the experiment should be clean and dry.
• Carry out the experiment in an open and well ventilated place or in fume cupboard.
• Continue heating the test tube strongly till a red coloured residue is obtained.
• Use only fresh light green coloured crystals of ferrous sulphate for the experiment.
• Use only hard glass or borosil test tube for the experiment.