Burning of Magnesium in Air (Chemical Reactions) Video Lecture | Science Class 9

Burning of magnesium in air
It is important to understand the difference
between physical and chemical changes. A physical
change does not produce a new substance and
it can mean a change in the size, shape or
in the state of matter of a substance. A chemical
change produces a new substance and it can
mean a change in colour or odour, the appearance
of bubbles, and release of energy or formation
of a precipitate.
Some examples of Chemical changes are the
burning of wood, dissolving salt in water,
mixing acids and bases and digesting food
.
Examples of Physical Changes are crumpling
a sheet of paper, melting an ice cube, casting
silver in a mould and breaking a bottle.
Our aim here is to carry out the reaction
of ‘Burning Magnesium in air’ and classifying
it as a physical or chemical change.
Materials Required:
Magnesium ribbon, Red Litmus Paper, a pair
of tongs, Bunsen burner.
Procedure:
Cut a piece of Magnesium ribbon and hold it
using a pair of tongs.
Flame this ribbon in the Bunsen burner, collect
the burnt ash in a watch glass and label it
as magnesium oxide.
This is a chemical reaction as oxygen and
magnesium come together to form magnesium
oxide.
i.e., 2 Mg(s ) + O2(g ) --> 2 MgO(s )
Now take red litmus paper and moisten it with
distilled water.
Place the moist red litmus paper over the
watch glass so that it is in contact with
magnesium oxide.
You can see that the red litmus turns blue.
From this, we can infer that magnesium oxide
is basic in nature.
This reaction shows a chemical change as the
reactants, oxygen and magnesium combine together
to form a new substance i.e. magnesium oxide.
The formed magnesium oxide has different chemical
composition which is different from both magnesium
and oxygen.
Precautions:
Make sure you hold the magnesium ribbon securely
with a pair of tongs while burning it.
It is better to use sunglasses to protect
eyes from the bright white light produced
by burning magnesium because it contains ultraviolet
light that can permanently damage the retina
of the eyes.