NCERT Textbook: Is Matter Around Us Pure | Science & Technology for UPSC CSE PDF Download

 Page 1


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
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
How do we judge whether milk, ghee, butter,
salt, spices, mineral water or juice that we buy
from the market are pure?
2
I I I I IS S S S S M M M M MATTER ATTER ATTER ATTER ATTER A A A A AROUND ROUND ROUND ROUND ROUND U U U U US S S S S P P P P PURE URE URE URE URE? ? ? ? ?
Chapter
2024-25
Page 2


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
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
How do we judge whether milk, ghee, butter,
salt, spices, mineral water or juice that we buy
from the market are pure?
2
I I I I IS S S S S M M M M MATTER ATTER ATTER ATTER ATTER A A A A AROUND ROUND ROUND ROUND ROUND U U U U US S S S S P P P P PURE URE URE URE URE? ? ? ? ?
Chapter
2024-25
More to  know
colour of the solutions of the two
groups. Though both the groups have
obtained copper sulphate solution but
the intensity of colour of the solutions
is different. This shows that a
homogeneous mixture can have a
variable composition.
• Groups C and D have obtained
mixtures, which contain physically
distinct parts and have non-uniform
compositions. Such mixtures are called
heterogeneous mixtures. Mixtures of
sodium chloride and iron filings, salt
and sulphur, and oil and water are
examples of heterogeneous mixtures.
Activity ______________2.2
• Let us again divide the class into four
groups— A, B, C and D.
• Distribute the following samples to
each group:
- Few crystals of copper sulphate
to group A.
- One spatula full of copper
sulphate to group B.
- Chalk powder or wheat flour to
group C.
- Few drops of milk or ink to
group D.
• Each group should add the given
sample in water and stir properly
using a glass rod. Are the particles
in the mixture visible?
• Direct a beam of light from a torch
through the beaker containing the
mixture and observe from the front. Was
the path of the beam of light visible?
• Leave the mixtures undisturbed for
a few minutes (and set up the
filtration apparatus in the meantime).
Is the mixture stable or do the
particles begin to settle after some
time?
• Filter the mixture. Is there any
residue on the filter paper?
• 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.
Now, we shall learn about solutions,
suspensions and colloidal solutions in the
following sections.
uestions
1. What is meant by a substance?
2. List the points of differences
between homogeneous and
heterogeneous mixtures.
2.2 What is a Solution?
A solution is a homogeneous mixture of two
or more substances. You come across various
types of solutions in your daily life. Lemonade,
soda water, etc., are all examples of solutions.
Usually we think of a solution as a liquid that
contains either a solid, liquid or a gas dissolved
in it. But, we can also have solid solutions
(alloys) and gaseous solutions (air). In a
solution there is homogeneity at the particle
level. For example, lemonade tastes the same
throughout. This shows that particles of sugar
or salt are evenly distributed in
the solution.
Q
Fig. 2.2: Filtration
Alloys: Alloys are mixtures of two or
more metals or a metal and a non-metal
and cannot be separated into their
components by physical methods. But
still, an alloy is considered as a mixture
because it shows the properties of its
constituents and can have variable
composition. For example, brass is a
mixture of approximately 30% zinc and
70% copper.
IS MATTER AROUND US PURE? 15
2024-25
Page 3


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
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
How do we judge whether milk, ghee, butter,
salt, spices, mineral water or juice that we buy
from the market are pure?
2
I I I I IS S S S S M M M M MATTER ATTER ATTER ATTER ATTER A A A A AROUND ROUND ROUND ROUND ROUND U U U U US S S S S P P P P PURE URE URE URE URE? ? ? ? ?
Chapter
2024-25
More to  know
colour of the solutions of the two
groups. Though both the groups have
obtained copper sulphate solution but
the intensity of colour of the solutions
is different. This shows that a
homogeneous mixture can have a
variable composition.
• Groups C and D have obtained
mixtures, which contain physically
distinct parts and have non-uniform
compositions. Such mixtures are called
heterogeneous mixtures. Mixtures of
sodium chloride and iron filings, salt
and sulphur, and oil and water are
examples of heterogeneous mixtures.
Activity ______________2.2
• Let us again divide the class into four
groups— A, B, C and D.
• Distribute the following samples to
each group:
- Few crystals of copper sulphate
to group A.
- One spatula full of copper
sulphate to group B.
- Chalk powder or wheat flour to
group C.
- Few drops of milk or ink to
group D.
• Each group should add the given
sample in water and stir properly
using a glass rod. Are the particles
in the mixture visible?
• Direct a beam of light from a torch
through the beaker containing the
mixture and observe from the front. Was
the path of the beam of light visible?
• Leave the mixtures undisturbed for
a few minutes (and set up the
filtration apparatus in the meantime).
Is the mixture stable or do the
particles begin to settle after some
time?
• Filter the mixture. Is there any
residue on the filter paper?
• 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.
Now, we shall learn about solutions,
suspensions and colloidal solutions in the
following sections.
uestions
1. What is meant by a substance?
2. List the points of differences
between homogeneous and
heterogeneous mixtures.
2.2 What is a Solution?
A solution is a homogeneous mixture of two
or more substances. You come across various
types of solutions in your daily life. Lemonade,
soda water, etc., are all examples of solutions.
Usually we think of a solution as a liquid that
contains either a solid, liquid or a gas dissolved
in it. But, we can also have solid solutions
(alloys) and gaseous solutions (air). In a
solution there is homogeneity at the particle
level. For example, lemonade tastes the same
throughout. This shows that particles of sugar
or salt are evenly distributed in
the solution.
Q
Fig. 2.2: Filtration
Alloys: Alloys are mixtures of two or
more metals or a metal and a non-metal
and cannot be separated into their
components by physical methods. But
still, an alloy is considered as a mixture
because it shows the properties of its
constituents and can have variable
composition. For example, brass is a
mixture of approximately 30% zinc and
70% copper.
IS MATTER AROUND US PURE? 15
2024-25
SCIENCE 16
A solution has a solvent and a solute as its
components. The component of the solution
that dissolves the other component in it
(usually the component present in larger
amount) is called the solvent. The component
of the solution that is dissolved in the solvent
(usually present in lesser quantity) is called
the solute.
Examples:
(i) A solution of sugar in water is a solid
in liquid solution. In this solution,
sugar is the solute and water is
the solvent.
(ii) A solution of iodine in alcohol known
as ‘tincture of iodine’, has iodine (solid)
as the solute and alcohol (liquid) as the
solvent.
(iii) Aerated drinks like soda water, etc., are
gas in liquid solutions. These contain
carbon dioxide (gas) as solute and water
(liquid) as solvent.
(iv) Air is a mixture of gas in gas. Air is a
homogeneous mixture of a number of
gases. Its two main constituents are:
oxygen (21%) and nitrogen (78%). The
other gases are present in very
small quantities.
Properties of a Solution
• A solution is a homogeneous mixture.
• The particles of a solution are smaller
than 1 nm (10
-9 
metre) in diameter. So,
they cannot be seen by naked eyes.
• Because of very small particle size, they
do not scatter a beam of light passing
through the solution. So, the path of
light is not visible in a solution.
• The solute particles cannot be separated
from the mixture by the process of
filtration. The solute particles do not
settle down when left undisturbed, that
is, a solution is stable.
2.2.1 CONCENTRATION OF A SOLUTION
In activity 2.2, we observed that groups A and
B obtained different shades of solutions. So,
we understand that in a solution the relative
proportion of the solute and solvent can be
varied. Depending upon the amount of solute
present in a solution, it can be called  dilute,
concentrated or  saturated solution. Dilute
and concentrated are comparative terms. In
activity 2.2, the solution obtained by group
A is dilute as compared to that obtained by
group B.
Activity ______________2.3
• Take approximately 50 mL of water
each in two separate beakers.
• Add salt in one beaker and sugar or
barium chloride in the second beaker
with continuous stirring.
• When no more solute can be dissolved,
heat the contents of the beaker to raise
the temperature by about 5
o
C.°
• Start adding the solute again.
Is the amount of salt and sugar or barium
chloride, that can be dissolved in water at a
given temperature, the same?
At any particular temperature, a solution
that has dissolved as much solute as it is
capable of dissolving, is said to be a saturated
solution. In other words, when no more solute
can be dissolved in a solution at a given
temperature, it is called a saturated solution.
The amount of the solute present in the
saturated solution at this temperature is called
its solubility.
If the amount of solute contained in a
solution is less than the saturation level, it is
called an unsaturated solution.
What would happen if you were to take a
saturated solution at a certain temperature
and cool it slowly.
We can infer from the above activity that
different substances in a given solvent have
different solubilities at the same temperature.
The concentration of a solution is the amount
(mass or volume) of solute present in a given
amount (mass or volume) of solution.
There are various ways of expressing the
concentration of a solution, but here we will
learn only three methods.
(i) Mass by mass percentage of a solution
Mass of solute
= ×100
Mass of solution
2024-25
Page 4


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
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
How do we judge whether milk, ghee, butter,
salt, spices, mineral water or juice that we buy
from the market are pure?
2
I I I I IS S S S S M M M M MATTER ATTER ATTER ATTER ATTER A A A A AROUND ROUND ROUND ROUND ROUND U U U U US S S S S P P P P PURE URE URE URE URE? ? ? ? ?
Chapter
2024-25
More to  know
colour of the solutions of the two
groups. Though both the groups have
obtained copper sulphate solution but
the intensity of colour of the solutions
is different. This shows that a
homogeneous mixture can have a
variable composition.
• Groups C and D have obtained
mixtures, which contain physically
distinct parts and have non-uniform
compositions. Such mixtures are called
heterogeneous mixtures. Mixtures of
sodium chloride and iron filings, salt
and sulphur, and oil and water are
examples of heterogeneous mixtures.
Activity ______________2.2
• Let us again divide the class into four
groups— A, B, C and D.
• Distribute the following samples to
each group:
- Few crystals of copper sulphate
to group A.
- One spatula full of copper
sulphate to group B.
- Chalk powder or wheat flour to
group C.
- Few drops of milk or ink to
group D.
• Each group should add the given
sample in water and stir properly
using a glass rod. Are the particles
in the mixture visible?
• Direct a beam of light from a torch
through the beaker containing the
mixture and observe from the front. Was
the path of the beam of light visible?
• Leave the mixtures undisturbed for
a few minutes (and set up the
filtration apparatus in the meantime).
Is the mixture stable or do the
particles begin to settle after some
time?
• Filter the mixture. Is there any
residue on the filter paper?
• 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.
Now, we shall learn about solutions,
suspensions and colloidal solutions in the
following sections.
uestions
1. What is meant by a substance?
2. List the points of differences
between homogeneous and
heterogeneous mixtures.
2.2 What is a Solution?
A solution is a homogeneous mixture of two
or more substances. You come across various
types of solutions in your daily life. Lemonade,
soda water, etc., are all examples of solutions.
Usually we think of a solution as a liquid that
contains either a solid, liquid or a gas dissolved
in it. But, we can also have solid solutions
(alloys) and gaseous solutions (air). In a
solution there is homogeneity at the particle
level. For example, lemonade tastes the same
throughout. This shows that particles of sugar
or salt are evenly distributed in
the solution.
Q
Fig. 2.2: Filtration
Alloys: Alloys are mixtures of two or
more metals or a metal and a non-metal
and cannot be separated into their
components by physical methods. But
still, an alloy is considered as a mixture
because it shows the properties of its
constituents and can have variable
composition. For example, brass is a
mixture of approximately 30% zinc and
70% copper.
IS MATTER AROUND US PURE? 15
2024-25
SCIENCE 16
A solution has a solvent and a solute as its
components. The component of the solution
that dissolves the other component in it
(usually the component present in larger
amount) is called the solvent. The component
of the solution that is dissolved in the solvent
(usually present in lesser quantity) is called
the solute.
Examples:
(i) A solution of sugar in water is a solid
in liquid solution. In this solution,
sugar is the solute and water is
the solvent.
(ii) A solution of iodine in alcohol known
as ‘tincture of iodine’, has iodine (solid)
as the solute and alcohol (liquid) as the
solvent.
(iii) Aerated drinks like soda water, etc., are
gas in liquid solutions. These contain
carbon dioxide (gas) as solute and water
(liquid) as solvent.
(iv) Air is a mixture of gas in gas. Air is a
homogeneous mixture of a number of
gases. Its two main constituents are:
oxygen (21%) and nitrogen (78%). The
other gases are present in very
small quantities.
Properties of a Solution
• A solution is a homogeneous mixture.
• The particles of a solution are smaller
than 1 nm (10
-9 
metre) in diameter. So,
they cannot be seen by naked eyes.
• Because of very small particle size, they
do not scatter a beam of light passing
through the solution. So, the path of
light is not visible in a solution.
• The solute particles cannot be separated
from the mixture by the process of
filtration. The solute particles do not
settle down when left undisturbed, that
is, a solution is stable.
2.2.1 CONCENTRATION OF A SOLUTION
In activity 2.2, we observed that groups A and
B obtained different shades of solutions. So,
we understand that in a solution the relative
proportion of the solute and solvent can be
varied. Depending upon the amount of solute
present in a solution, it can be called  dilute,
concentrated or  saturated solution. Dilute
and concentrated are comparative terms. In
activity 2.2, the solution obtained by group
A is dilute as compared to that obtained by
group B.
Activity ______________2.3
• Take approximately 50 mL of water
each in two separate beakers.
• Add salt in one beaker and sugar or
barium chloride in the second beaker
with continuous stirring.
• When no more solute can be dissolved,
heat the contents of the beaker to raise
the temperature by about 5
o
C.°
• Start adding the solute again.
Is the amount of salt and sugar or barium
chloride, that can be dissolved in water at a
given temperature, the same?
At any particular temperature, a solution
that has dissolved as much solute as it is
capable of dissolving, is said to be a saturated
solution. In other words, when no more solute
can be dissolved in a solution at a given
temperature, it is called a saturated solution.
The amount of the solute present in the
saturated solution at this temperature is called
its solubility.
If the amount of solute contained in a
solution is less than the saturation level, it is
called an unsaturated solution.
What would happen if you were to take a
saturated solution at a certain temperature
and cool it slowly.
We can infer from the above activity that
different substances in a given solvent have
different solubilities at the same temperature.
The concentration of a solution is the amount
(mass or volume) of solute present in a given
amount (mass or volume) of solution.
There are various ways of expressing the
concentration of a solution, but here we will
learn only three methods.
(i) Mass by mass percentage of a solution
Mass of solute
= ×100
Mass of solution
2024-25
IS MATTER AROUND US PURE? 17
(ii) Mass by volume percentage of a solution
Mass of solute
= ×100
Volume of solution
(iii) Volume by volume percentage of a
solution
Volume of solute
= ×100
Volume of solution
Example 2.1 A solution contains 40 g of
common salt in 320 g of water. Calculate
the concentration in terms of mass by
mass percentage of the solution.
Solution:
Mass of solute (salt) = 40 g
Mass of solvent (water) = 320 g
We know,
Mass of solution = Mass of solute +
Mass of solvent
= 40 g + 320 g
= 360 g
Mass percentage of solution
Mass of solute
= ×100
Massof solution
                 
40
= ×100 =11.1%
360
2.2.2 WHAT IS A SUSPENSION?
Non-homogeneous systems, like those
obtained by group C in activity 2.2, in which
solids are dispersed in liquids, are called
suspensions. A suspension is a heterogeneous
mixture in which the solute particles do not
dissolve but remain suspended throughout
the bulk of the medium. Particles of a
suspension are visible to the naked eye.
Properties of a Suspension
• Suspension is a heterogeneous
mixture.
• The particles of a suspension can be seen
by the naked eye.
• The particles of a suspension scatter a
beam of light passing through it and
make its path visible.
• The solute particles settle down when a
suspension is left undisturbed, that is,
a suspension is unstable. They can be
separated from the mixture by the
process of filtration. When the particles
settle down, the suspension breaks and
it does not scatter light any more.
2.2.3 WHAT IS A COLLOIDAL SOLUTION?
The mixture obtained by group D in activity
2.2 is called a colloid or a colloidal solution.
The particles of a colloid are uniformly spread
throughout the solution. Due to the relatively
smaller size of particles, as compared to that of
a suspension, the mixture appears to be
homogeneous. But actually, a colloidal solution
is a heterogeneous mixture, for example, milk.
Because of the small size of colloidal
particles, we cannot see them with naked eyes.
But, these particles can easily scatter a beam
of visible light as observed in activity 2.2. This
scattering of a beam of light is called the
Tyndall effect after the name of the scientist
who discovered this effect.
Tyndall effect can also be observed when a
fine beam of light enters a room through a small
hole. This happens due to the scattering of light
by the particles of dust and smoke in the air.
Fig. 2.3: (a) Solution of copper sulphate does not
show Tyndall effect, (b) mixture of water
and milk shows Tyndall effect.
(a) (b)
2024-25
Page 5


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
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
How do we judge whether milk, ghee, butter,
salt, spices, mineral water or juice that we buy
from the market are pure?
2
I I I I IS S S S S M M M M MATTER ATTER ATTER ATTER ATTER A A A A AROUND ROUND ROUND ROUND ROUND U U U U US S S S S P P P P PURE URE URE URE URE? ? ? ? ?
Chapter
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More to  know
colour of the solutions of the two
groups. Though both the groups have
obtained copper sulphate solution but
the intensity of colour of the solutions
is different. This shows that a
homogeneous mixture can have a
variable composition.
• Groups C and D have obtained
mixtures, which contain physically
distinct parts and have non-uniform
compositions. Such mixtures are called
heterogeneous mixtures. Mixtures of
sodium chloride and iron filings, salt
and sulphur, and oil and water are
examples of heterogeneous mixtures.
Activity ______________2.2
• Let us again divide the class into four
groups— A, B, C and D.
• Distribute the following samples to
each group:
- Few crystals of copper sulphate
to group A.
- One spatula full of copper
sulphate to group B.
- Chalk powder or wheat flour to
group C.
- Few drops of milk or ink to
group D.
• Each group should add the given
sample in water and stir properly
using a glass rod. Are the particles
in the mixture visible?
• Direct a beam of light from a torch
through the beaker containing the
mixture and observe from the front. Was
the path of the beam of light visible?
• Leave the mixtures undisturbed for
a few minutes (and set up the
filtration apparatus in the meantime).
Is the mixture stable or do the
particles begin to settle after some
time?
• Filter the mixture. Is there any
residue on the filter paper?
• 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.
Now, we shall learn about solutions,
suspensions and colloidal solutions in the
following sections.
uestions
1. What is meant by a substance?
2. List the points of differences
between homogeneous and
heterogeneous mixtures.
2.2 What is a Solution?
A solution is a homogeneous mixture of two
or more substances. You come across various
types of solutions in your daily life. Lemonade,
soda water, etc., are all examples of solutions.
Usually we think of a solution as a liquid that
contains either a solid, liquid or a gas dissolved
in it. But, we can also have solid solutions
(alloys) and gaseous solutions (air). In a
solution there is homogeneity at the particle
level. For example, lemonade tastes the same
throughout. This shows that particles of sugar
or salt are evenly distributed in
the solution.
Q
Fig. 2.2: Filtration
Alloys: Alloys are mixtures of two or
more metals or a metal and a non-metal
and cannot be separated into their
components by physical methods. But
still, an alloy is considered as a mixture
because it shows the properties of its
constituents and can have variable
composition. For example, brass is a
mixture of approximately 30% zinc and
70% copper.
IS MATTER AROUND US PURE? 15
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SCIENCE 16
A solution has a solvent and a solute as its
components. The component of the solution
that dissolves the other component in it
(usually the component present in larger
amount) is called the solvent. The component
of the solution that is dissolved in the solvent
(usually present in lesser quantity) is called
the solute.
Examples:
(i) A solution of sugar in water is a solid
in liquid solution. In this solution,
sugar is the solute and water is
the solvent.
(ii) A solution of iodine in alcohol known
as ‘tincture of iodine’, has iodine (solid)
as the solute and alcohol (liquid) as the
solvent.
(iii) Aerated drinks like soda water, etc., are
gas in liquid solutions. These contain
carbon dioxide (gas) as solute and water
(liquid) as solvent.
(iv) Air is a mixture of gas in gas. Air is a
homogeneous mixture of a number of
gases. Its two main constituents are:
oxygen (21%) and nitrogen (78%). The
other gases are present in very
small quantities.
Properties of a Solution
• A solution is a homogeneous mixture.
• The particles of a solution are smaller
than 1 nm (10
-9 
metre) in diameter. So,
they cannot be seen by naked eyes.
• Because of very small particle size, they
do not scatter a beam of light passing
through the solution. So, the path of
light is not visible in a solution.
• The solute particles cannot be separated
from the mixture by the process of
filtration. The solute particles do not
settle down when left undisturbed, that
is, a solution is stable.
2.2.1 CONCENTRATION OF A SOLUTION
In activity 2.2, we observed that groups A and
B obtained different shades of solutions. So,
we understand that in a solution the relative
proportion of the solute and solvent can be
varied. Depending upon the amount of solute
present in a solution, it can be called  dilute,
concentrated or  saturated solution. Dilute
and concentrated are comparative terms. In
activity 2.2, the solution obtained by group
A is dilute as compared to that obtained by
group B.
Activity ______________2.3
• Take approximately 50 mL of water
each in two separate beakers.
• Add salt in one beaker and sugar or
barium chloride in the second beaker
with continuous stirring.
• When no more solute can be dissolved,
heat the contents of the beaker to raise
the temperature by about 5
o
C.°
• Start adding the solute again.
Is the amount of salt and sugar or barium
chloride, that can be dissolved in water at a
given temperature, the same?
At any particular temperature, a solution
that has dissolved as much solute as it is
capable of dissolving, is said to be a saturated
solution. In other words, when no more solute
can be dissolved in a solution at a given
temperature, it is called a saturated solution.
The amount of the solute present in the
saturated solution at this temperature is called
its solubility.
If the amount of solute contained in a
solution is less than the saturation level, it is
called an unsaturated solution.
What would happen if you were to take a
saturated solution at a certain temperature
and cool it slowly.
We can infer from the above activity that
different substances in a given solvent have
different solubilities at the same temperature.
The concentration of a solution is the amount
(mass or volume) of solute present in a given
amount (mass or volume) of solution.
There are various ways of expressing the
concentration of a solution, but here we will
learn only three methods.
(i) Mass by mass percentage of a solution
Mass of solute
= ×100
Mass of solution
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IS MATTER AROUND US PURE? 17
(ii) Mass by volume percentage of a solution
Mass of solute
= ×100
Volume of solution
(iii) Volume by volume percentage of a
solution
Volume of solute
= ×100
Volume of solution
Example 2.1 A solution contains 40 g of
common salt in 320 g of water. Calculate
the concentration in terms of mass by
mass percentage of the solution.
Solution:
Mass of solute (salt) = 40 g
Mass of solvent (water) = 320 g
We know,
Mass of solution = Mass of solute +
Mass of solvent
= 40 g + 320 g
= 360 g
Mass percentage of solution
Mass of solute
= ×100
Massof solution
                 
40
= ×100 =11.1%
360
2.2.2 WHAT IS A SUSPENSION?
Non-homogeneous systems, like those
obtained by group C in activity 2.2, in which
solids are dispersed in liquids, are called
suspensions. A suspension is a heterogeneous
mixture in which the solute particles do not
dissolve but remain suspended throughout
the bulk of the medium. Particles of a
suspension are visible to the naked eye.
Properties of a Suspension
• Suspension is a heterogeneous
mixture.
• The particles of a suspension can be seen
by the naked eye.
• The particles of a suspension scatter a
beam of light passing through it and
make its path visible.
• The solute particles settle down when a
suspension is left undisturbed, that is,
a suspension is unstable. They can be
separated from the mixture by the
process of filtration. When the particles
settle down, the suspension breaks and
it does not scatter light any more.
2.2.3 WHAT IS A COLLOIDAL SOLUTION?
The mixture obtained by group D in activity
2.2 is called a colloid or a colloidal solution.
The particles of a colloid are uniformly spread
throughout the solution. Due to the relatively
smaller size of particles, as compared to that of
a suspension, the mixture appears to be
homogeneous. But actually, a colloidal solution
is a heterogeneous mixture, for example, milk.
Because of the small size of colloidal
particles, we cannot see them with naked eyes.
But, these particles can easily scatter a beam
of visible light as observed in activity 2.2. This
scattering of a beam of light is called the
Tyndall effect after the name of the scientist
who discovered this effect.
Tyndall effect can also be observed when a
fine beam of light enters a room through a small
hole. This happens due to the scattering of light
by the particles of dust and smoke in the air.
Fig. 2.3: (a) Solution of copper sulphate does not
show Tyndall effect, (b) mixture of water
and milk shows Tyndall effect.
(a) (b)
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SCIENCE 18
Q
• Colloids are big enough to scatter a
beam of light passing through it and
make its path visible.
• They do not settle down when left
undisturbed, that is, a colloid is quite
stable.
• They cannot be separated from the
mixture by the process of filtration. But,
a special technique of separation known
as centrifugation can be used to
separate the colloidal particles.
The components of a colloidal solution are
the dispersed phase and the dispersion
medium. The solute-like component or the
dispersed particles in a colloid form the
dispersed phase, and the component in which
the dispersed phase is suspended is known
as the dispersing medium. Colloids are
classified according to the state (solid, liquid
or gas) of the dispersing medium and  the
dispersed phase. A few common examples are
given in Table 2.1. From this table you can
see that they are very common everyday life.
Tyndall effect can be observed when
sunlight passes through the canopy of a dense
forest. In the forest, mist contains tiny droplets
of water, which act as particles of colloid
dispersed in air.
Fig. 2.4: The Tyndall effect
uestions
1. Differentiate between homogen eous and heterogeneous mixtures with examples.
2. How are sol, solution and suspension different from each other?
3. To make a saturated solution,  36 g of sodium chloride is dissolved in 100 g of water
at 293 K. Find its concentration at this temperature.
Properties of a Colloid
• A colloid is a heterogeneous mixture.
• The size of particles of a colloid is too
small to be individually seen with
naked eyes.
Table 2.1:  Common examples of colloids
Dispersed Dispersing Type Example
phase Medium
Liquid Gas Aerosol Fog, clouds, mist
Solid Gas Aerosol Smoke, automobile exhaust
Gas Liquid Foam Shaving cream
Liquid Liquid Emulsion Milk, face cream
Solid Liquid Sol Milk of magnesia, mud
Gas Solid Foam Foam, rubber, sponge, pumice
Liquid Solid Gel Jelly, cheese, butter
Solid Solid Solid Sol Coloured gemstone, milky glass
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