Science for Class 9

Topics: Gas, Temperature, Liquid Pages: 35 (5411 words) Published: August 30, 2012
C hapter 1



As we look at our surroundings, we see a large
variety of things with different shapes, sizes
and textures. Everything in this universe is
made up of material which scientists have
named “matter”. The air we breathe, the food
we eat, stones, clouds, stars, plants and
animals, even a small drop of water or a
particle of sand– each thing is matter. We can
also see as we look around that all the things
mentioned above occupy space, that is,
volume* and have mass.
Since early times, human beings have
been trying to understand their surroundings.
Early Indian philosophers classified matter in
the for m of five basic elements – the
“Panch Tatva”– air, earth, fire, sky and water.
According to them everything, living or nonliving, was made up of these five basic elements. Ancient Greek philosophers had
arrived at a similar classification of matter.
Modern day scientists have evolved two
types of classification of matter based on their
physical properties and chemical nature.
In this chapter we shall learn about
matter based on its physical properties.
Chemical aspects of matter will be taken up
in subsequent chapters.

1.1 Physical Nature of Matter
For a long time, two schools of thought
prevailed regarding the nature of matter. One
school believed matter to be continuous like
a block of wood, whereas, the other thought
that matter was made up of particles like
sand. Let us perform an activity to decide
about the nature of matter – is it continuous
or particulate?

Activity ______________ 1.1

Take a 100 mL beaker.
Fill half the beaker with water and
mark the level of water.
Dissolve some salt/ sugar with the help
of a glass rod.
Observe any change in water level.
What do you think has happened to
the salt?
Where does it disappear?
Does the level of water change?

In order to answer these questions we
need to use the idea that matter is made up
of particles. What was there in the spoon, salt
or sugar, has now spread throughout water.
This is illustrated in Fig. 1.1.

Fig. 1.1: When we dissolve salt in water, the particles
of salt get into the spaces between particles
of water.

1.1.2 HOW



Activity ______________ 1.2

Take 2-3 crystals of potassium
permanganate and dissolve them in
100 mL of water.

* The SI unit of volume is cubic metre (m3). The common unit of measuring volume is litre (L) such that 1L = 1 dm3, 1L = 1000 mL, 1 mL = 1 cm3.

Take out approximately 10 mL of this
solution and put it into 90 mL of clear
Take out 10 mL of this solution and
put it into another 90 mL of clear water.
Keep diluting the solution like this 5 to
8 times.
Is the water still coloured ?






Activity ______________ 1.3

Put an unlit incense stick in a corner
of your class. How close do you have to
go near it so as to get its smell?
Now light the incense stick. What
happens? Do you get the smell sitting
at a distance?
Record your observations.

Activity ______________ 1.4
Fig. 1.2: Estimating how small are the particles of
matter. With every dilution, though the colour
becomes light, it is still visible.

This experiment shows that just a few
crystals of potassium permanganate can
colour a large volume of water (about
1000 L). So we conclude that there must be
millions of tiny particles in just one crystal
of potassium permanganate, which keep on
dividing themselves into smaller and smaller
particles. Ultimately a stage is reached when
the particles cannot divide further into
smaller particles.
The same activity can be done using
2 mL of Dettol instead of potassium
permanganate. The smell can be detected
even on repeated dilution.
The particles of matter are very small –
they are small...
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