NCERT Book Class 9 Science Chapter 2 Is matter around us pure?

C hapter 2
IS MATTER AROUND US PURE?
How do we judge whether milk, ghee, butter, a pure substance and cannot be separated by
salt, spices, mineral water or juice that we buy physical process into its chemical constituents.
from the market are pure? Similarly, sugar is a substance which contains
only one kind of pure matter and its
composition is the same throughout.
Soft drink and soil are not single pure
substances. Whatever the source of a
pure substance may be, it will always have
the same characteristic properties.
Therefore, we can say that a mixture
contains more than one pure substance.

2.1.1 TYPES OF MIXTURES
Fig. 2.1: Some consumable items
Depending upon the nature of the components
Have you ever noticed the word ‘pure’ that form a mixture, we can have different
written on the packs of these consumables? types of mixtures.
For a common person pure means having no
adulteration. But, for a scientist all these things
Activity ______________ 2.1
are actually mixtures of different substances • Let us divide the class into groups A,
and hence not pure. For example, milk is B, C and D.
actually a mixture of water, fat, proteins, etc. • Group A takes a beaker containing
When a scientist says that something is pure, 50 mL of water and one spatula full
of copper sulphate powder. Group B
it means that all the constituent particles of takes 50 mL of water and two spatula
that substance are the same in their chemical full of copper sulphate powder in a
nature. A pure substance consists of a single beaker.
type of particle. In other words, a substance is • Groups C and D can take different
a pure single form of matter. amounts of copper sulphate and
As we look around, we can see that most potassium permanganate or common
salt (sodium chloride) and mix the
of the matter around us exists as mixtures of given components to form a mixture.
two or more pure components, for example, • Report the observations on the
sea water, minerals, soil, etc., are all mixtures. uniformity in colour and texture.
• Groups A and B have obtained a
2.1 What is a Mixture? mixture which has a uniform
Mixtures are constituted by more than one composition throughout. Such
mixtures are called homogeneous
kind of pure form of matter. We know that
mixtures or solutions. Some other
dissolved sodium chloride can be separated examples of such mixtures are: (i) salt
from water by the physical process of dissolved in water and (ii) sugar
evaporation. However, sodium chloride is itself dissolved in water. Compare the