by Dilip Kumar Chandra PGT Biotechnology JNV Raipur CG

2.  A change in which a substance
undergoes a change in its physical
properties is called a physical change
ice water

3.  Iron rod changes its colour soon after
it looses its heat

4.  No new substances are formed in
physical change .
 These changes are reversible.

5.  A change in which one or more new
substances are formed is called a
chemical change

6.  Burning of Magnesium ribbon is a
Chemical change

7.  Take a small piece of magnesium ribbon.Take a small piece of magnesium ribbon.
 Clean its tip with sand paper.Clean its tip with sand paper.
 Bring the tip near a candle flame.Bring the tip near a candle flame.
 It burns with a brilliant white light.It burns with a brilliant white light.

8.  When the magnesium ribbon is
completely burnt it leaves behind a
powdery ash.
 Does the ash look like magnesium
ribbon?

9.  No, ash is a completely new substance
formed from the burning of magnesium
ribbon.
 The change can be represented by the
following equation:
 Magnesium (Mg) + Oxygen (O2 )
Magnesium oxide (MgO)

10.  Collect the ash and mix it with a
small amount of water.
 Stir the mixture well.
 Test the mixture with blue and red
litmus papers.

11.  Aqueous solution turns red litmus to
blue.
 So, it is a base.
 On dissolving ash in water it forms a
new substance, Magnesium hydroxide
Mg(OH)2

12.  Magnesium oxide is a new substance
formed on burning of magnesium
ribbon.
 Magnesium hydroxide is another new
substance formed by mixing
magnesium oxide with water.

13.  New substances are formed in
chemical change .
 These changes are irreversible.

14.  Physical changes are concerned with
energy and states of matter. A physical
change does not produce a new substance.
Changes in state or phase (melting,
freezing, vaporization, condensation,
sublimation) are physical changes.
Examples of physical changes include
crushing a can, melting an ice cube.

15.  A chemical change makes a
substance that wasn't there before.
There may be clues that a chemical
reaction took place, such as light,
heat, color change, gas production,
odor, or sound. The starting and
ending materials of a physical change
are the same, even though they may
look different.

16.  Definition: crystallization is the
slow precipitation of crystals from a
solution of a substance.
 Copper sulphate crystals can be
obtained from copper sulphate
solution