Is matter around us pure

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How do we judge whether milk, ghee, butter,

salt, spices, mineral water or juice that we buy

from the market are pure?

Fig. 2.1: Some consumable items

Have you ever noticed the word ‘pure’

written on the packs of these consumables?

For a common person pure means having no

adulteration. But, for a scientist all these things

are actually mixtures of different substances

and hence not pure. For example, milk is

actually a mixture of water, fat, proteins, etc.

When a scientist says that something is pure,

it means that all the constituent particles of

that substance are the same in their chemical

nature. A pure substance consists of a single

type of particle. In other words, a substance is

a pure single form of matter.

As we look around, we can see that most

of the matter around us exists as mixtures of

two or more pure components, for example,

sea water, minerals, soil, etc., are all mixtures.

2.1 What is a Mixture?

Mixtures are constituted by more than one

kind of pure form of matter. We know that

dissolved sodium chloride can be separated

from water by the physical process of

evaporation. However, sodium chloride is itself

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a pure substance and cannot be separated by

physical process into its chemical constituents.

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

Depending upon the nature of the components

that form a mixture, we can have different

types of mixtures.

Activity 2.1

• Let us divide the class into groups A,

B, C and D.

• Group A takes a beaker containing

50 mL of water and one spatula full

of copper sulphate powder. Group B

takes 50 mL of water and two spatula

full of copper sulphate powder in a

beaker.

• Groups C and D can take different

amounts of copper sulphate and

potassium permanganate or common

salt (sodium chloride) and mix the

given components to form a mixture.

• Report the observations on the

uniformity in colour and texture.

• Groups A and B have obtained a

mixture which has a uniform

composition throughout. Such

mixtures are called homogeneous

mixtures or solutions. Some other

examples of such mixtures are: (i) salt

dissolved in water and (ii) sugar

dissolved in water. Compare the

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IS MATTER AROUND US PURE?

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• Discuss the results and form an

opinion.

Groups A and B have got a solution.

Group C has got a suspension.

Group D has got a colloidal solution.

• Filter the mixture. Is there any

residue on the filter paper?

• Leave the mixtures undisturbed for

a few minutes (and set up the

filtration apparatus in the meantime).

Is the mixture stable or do the