Decomposition Reaction Video Lecture | Science Class 10

Decomposition Reaction
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.