Q. 2 B4.2( 21 Votes )


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

Answer :


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

Chemical Compound: Ferrous sulphate crystals, blue litmus paper.


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.

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. SOand 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.


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.


The experimental procedure is described in the table:


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


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.

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