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Action of Heat on Ferrous Sulphate Crystals
A chemical reaction is a process that leads to the transformation of one set of chemical
substances to another. The substance (or substances) initially involved in a chemical reaction
are called reactants or reagents and the newly evolved chemical substance is called the product.
There are many different types of chemical reactions. Chemists have classified them into
combination reaction, decomposition reaction, displacement reaction and double displacement
reaction depending on the chemical changes taking place in the reaction.
In a combination reaction, two or more substances combine to form a new compound whereas in
a decomposition reaction, single compound undergoes a reaction that produces two or
more simpler substances. In a displacement reaction, one element replaces a similar element
in the compound where in a double-replacement reaction, the ions of two compounds exchange
places in an aqueous solution to form two new compounds.
The aim of this experiment is to find the action of heat on ferrous sulphate crystals
and classify it as combination reaction, decomposition reaction, displacement reaction or double
displacement reaction. Materials Required:
Ferrous sulphate crystals, Bunsen burner, boiling tubes, test-tube holder and spatula.
Procedure:
Take a small quantity of ferrous sulphate crystals and transfer it into a dry boiling
tube using a spatula. Hold the boiling test tube with a test tube
holder and note the color of ferrous sulphate crystals which may be light green in color.
Heat the boiling tube over the flame of a Bunsen burner.
On heating, the colour of the crystals changes from light green to white.
This is due to the formation of anhydrous ferrous sulphate that is produced on heating
ferrous sulphate crystals. Anhydrous ferrous sulphate is formed due to the loss of water
molecules on heating ferrous sulphate crystals. On further heating, the white substance changes
to dark brown solid. While heating, smell the fumes coming out
of the boiling tube, and note the odour. Here anhydrous ferrous sulphate decomposes
to form a dark brown solid i.e. ferric oxide and sulphur dioxide and sulphur trioxide which
are emitted out of the boiling tube as gases. Finally transfer the dark brown substance
in the boiling tube into a watch glass and label it as ferric oxide.
From the observation, it becomes clear that this is a decomposition reaction as the single
reactant, anhydrous ferrous sulphate breaks down to give simpler products like ferric
oxide, sulphur dioxide and sulphur trioxide.
Precautions:
Always use a test tube holder while heating the test tube.
Avoid inhalation of sulphur dioxide and sulphur trioxide as they may cause difficulty in breathing.