AIM

To perform & observe the action of heat on ferrous sulphate crystals and classify the reaction.

MATERIALS REQUIRED

Apparatus: Test tubes, test tube holder, bunsen burner, tripod stand.

Chemical Compound: Ferrous sulphate crystals, blue litmus paper.

THEORY

1. The crystals of ferrous sulphate are green in colour, due to the presence of water of crystallisation.

2. When these crystals are heated, the colour of the crystal changes from light green to brown colour

3. The following reaction takes place

In this reaction, a single reactant breaks down to give simple products. Therefore, this is a decomposition reaction.

4. The ferrous sulphate on heating decomposes to ferric oxide (Fe₂O₃), sulphur dioxide (SO₂) and sulphur trioxide (SO₃). Ferric oxide is solid while SO₂ and SO₃ are gases.

5. SO₂ and SO₃ turn the moist blue litmus paper red since these gases are acidic in nature.

6. Sulphur dioxide evolved during the reaction can be used to reduce an acidified solution of potassium dichromate. This reaction can be utilized to confirm the presence of sulphur dioxide.

PROCEDURE

1. Take about 2 g crystals of ferrous sulphate in a dry test tube and note the colour of crystals.

2.  Using the bunsen burner, heat the test tube containing ferrous sulphate.

3. Bring a moist blue litmus paper in contact with the evolved gases from the test tube.

4. Soak a strip of filter paper in an acidified solution of potassium dichromate and place it above the mouth of the test tube.
5. Note the observation in the observation table.

OBSERVATION TABLE

The experimental procedure is described in the table:

S.No.	Observation	Inference
1.	The crystals are green in colour.	The colour of ferrous sulphate crystal is green. Due to the presence of water of crystallisation
2.	The colour of crystals changes to brown and colourless gas with a smell of burning sulphur is evolved.	New substances are formed by the heating of ferrous sulphate and the gas evolved is sulphur dioxide.
3.	When moist blue litmus paper is placed on the mouth of the test tube, it turns red.	The gas evolved during the reaction is acidic.
4.	The orange colour of strip of filter paper dipped in acidified potassium dichromate changes to green.	Sulphur dioxide gas is evolved during the chemical change.

RESULT

On heating, ferrous sulphate crystals, they decompose to give ferric oxide, sulphur dioxide, and sulphur trioxide. Hence, it is a decomposition reaction.

PRECAUTIONS

1. Use heating test tube for heating ferrous sulphate.

2. Always use the test-tube holder for holding the test tube during heating.

3. The gases SO₂ and SO₃ are very harmful, so do not take a deep breath of these gases.