NCERT Textbook - Is Matter Around Us Pure Class 9 Notes | EduRev

Science Class 9

Created by: Divey Sethi

Class 9 : NCERT Textbook - Is Matter Around Us Pure Class 9 Notes | EduRev

 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
particles.
As we look around, we can see that most
of the matter around us exist 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, known as a
substance. A substance cannot be separated
into other kinds of matter by any physical
process. We know that dissolved sodium
chloride can be separated from water by the
physical process of evaporation. However,
sodium chloride is itself a substance and
cannot be separated by physical process into
its chemical constituents. Similarly, sugar is
a substance because it contains only one kind
of pure matter and its composition is the same
throughout.
Soft drink and soil are not single
substances. Whatever the source of a
substance may be, it will always have the
same characteristic properties.
Therefore, we can say that a mixture
contains more than one 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
How do we judge whether milk, ghee, butter,
salt, spices, mineral water or juice that we
buy from the market are pure?
2 2
2 2 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
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
particles.
As we look around, we can see that most
of the matter around us exist 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, known as a
substance. A substance cannot be separated
into other kinds of matter by any physical
process. We know that dissolved sodium
chloride can be separated from water by the
physical process of evaporation. However,
sodium chloride is itself a substance and
cannot be separated by physical process into
its chemical constituents. Similarly, sugar is
a substance because it contains only one kind
of pure matter and its composition is the same
throughout.
Soft drink and soil are not single
substances. Whatever the source of a
substance may be, it will always have the
same characteristic properties.
Therefore, we can say that a mixture
contains more than one 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
How do we judge whether milk, ghee, butter,
salt, spices, mineral water or juice that we
buy from the market are pure?
2 2
2 2 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
More to  know
in water and (ii) sugar in water.
Compare the 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 pure
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 homogeneous
mixtures of metals 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
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
particles.
As we look around, we can see that most
of the matter around us exist 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, known as a
substance. A substance cannot be separated
into other kinds of matter by any physical
process. We know that dissolved sodium
chloride can be separated from water by the
physical process of evaporation. However,
sodium chloride is itself a substance and
cannot be separated by physical process into
its chemical constituents. Similarly, sugar is
a substance because it contains only one kind
of pure matter and its composition is the same
throughout.
Soft drink and soil are not single
substances. Whatever the source of a
substance may be, it will always have the
same characteristic properties.
Therefore, we can say that a mixture
contains more than one 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
How do we judge whether milk, ghee, butter,
salt, spices, mineral water or juice that we
buy from the market are pure?
2 2
2 2 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
More to  know
in water and (ii) sugar in water.
Compare the 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 pure
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 homogeneous
mixtures of metals 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 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 a dilute,
concentrated or a 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.
? 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 of solute present in a given amount
(mass or volume) of solution, or the amount
of solute dissolved in a given mass or volume
of solvent.
Concentration of solution = Amount of solute/
      Amount of solution
Or
Amount of solute/Amount of solvent
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
particles.
As we look around, we can see that most
of the matter around us exist 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, known as a
substance. A substance cannot be separated
into other kinds of matter by any physical
process. We know that dissolved sodium
chloride can be separated from water by the
physical process of evaporation. However,
sodium chloride is itself a substance and
cannot be separated by physical process into
its chemical constituents. Similarly, sugar is
a substance because it contains only one kind
of pure matter and its composition is the same
throughout.
Soft drink and soil are not single
substances. Whatever the source of a
substance may be, it will always have the
same characteristic properties.
Therefore, we can say that a mixture
contains more than one 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
How do we judge whether milk, ghee, butter,
salt, spices, mineral water or juice that we
buy from the market are pure?
2 2
2 2 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
More to  know
in water and (ii) sugar in water.
Compare the 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 pure
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 homogeneous
mixtures of metals 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 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 a dilute,
concentrated or a 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.
? 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 of solute present in a given amount
(mass or volume) of solution, or the amount
of solute dissolved in a given mass or volume
of solvent.
Concentration of solution = Amount of solute/
      Amount of solution
Or
Amount of solute/Amount of solvent
IS MATTER AROUND US PURE 17
There are various ways of expressing the
concentration of a solution, but here we will
learn only two methods.
(i) Mass by mass percentage of a solution
Mass of solute
= ×100
Mass of solution
(ii) Mass by volume percentage of a solution
Mass 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.
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)
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
particles.
As we look around, we can see that most
of the matter around us exist 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, known as a
substance. A substance cannot be separated
into other kinds of matter by any physical
process. We know that dissolved sodium
chloride can be separated from water by the
physical process of evaporation. However,
sodium chloride is itself a substance and
cannot be separated by physical process into
its chemical constituents. Similarly, sugar is
a substance because it contains only one kind
of pure matter and its composition is the same
throughout.
Soft drink and soil are not single
substances. Whatever the source of a
substance may be, it will always have the
same characteristic properties.
Therefore, we can say that a mixture
contains more than one 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
How do we judge whether milk, ghee, butter,
salt, spices, mineral water or juice that we
buy from the market are pure?
2 2
2 2 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
More to  know
in water and (ii) sugar in water.
Compare the 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 pure
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 homogeneous
mixtures of metals 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 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 a dilute,
concentrated or a 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.
? 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 of solute present in a given amount
(mass or volume) of solution, or the amount
of solute dissolved in a given mass or volume
of solvent.
Concentration of solution = Amount of solute/
      Amount of solution
Or
Amount of solute/Amount of solvent
IS MATTER AROUND US PURE 17
There are various ways of expressing the
concentration of a solution, but here we will
learn only two methods.
(i) Mass by mass percentage of a solution
Mass of solute
= ×100
Mass of solution
(ii) Mass by volume percentage of a solution
Mass 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.
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)
SCIENCE 18
Q
? They cannot be separated from the
mixture by the process of filtration. But,
a special technique of separation known
as centrifugation (perform activity 2.5),
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.
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.
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
Properties of a colloid
? A colloid is a heterogeneous mixture.
? The size of particles of a colloid is too
small to be individually seen by naked
eyes.
? 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.
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
Read More
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