C hapter 2
IS MATTER AROUND US PURE
How do we judge whether milk, ghee, butter, physical process of evaporation. However,
d
salt, spices, mineral water or juice that we sodium chloride is itself a substance and
buy from the market are pure? cannot be separated by physical process into
he
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
is
substances. Whatever the source of a
substance may be, it will always have the
same characteristic properties.
bl
Therefore, we can say that a mixture
contains more than one substance.
Fig. 2.1: Some consumable items
pu
Have you ever noticed the word ‘pure’ 2.1.1 TYPES OF MIXTURES
written on the packs of these consumables?
Depending upon the nature of the
be T
For a common person pure means having no components that form a mixture, we can have
adulteration. But, for a scientist all these things
different types of mixtures.
re
are actually mixtures of different substances
o R
and hence not pure. For example, milk is Activity ______________ 2.1
actually a mixture of water, fat, proteins etc.
When a scientist says that something is pure, • Let us divide the class into groups A,
tt E
it means that all the constituent particles of B, C and D.
that substance are the same in their chemical • Group A takes a beaker containing
nature. A pure substance consists of a single 50 mL of water and one spatula full of
C
type of particles. In other words, a substance copper sulphate powder. Group B takes
50 mL of water and two spatula full of
is a pure single form of matter.
copper sulphate powder in a beaker.
no N
As we look around, we can see that most
• Groups C and D can take different
of the matter around us exist as mixtures of amounts of copper sulphate and
two or more pure components, for example, potassium permanganate or common
sea water, minerals, soil etc. are all mixtures. salt (sodium chloride) and mix the given
©
components to form a mixture.
2.1 What is a Mixture? • Report the observations on the
uniformity in colour and texture.
Mixtures are constituted by more than one • Groups A and B have obtained a
kind of pure form of matter, known as a mixture which has a uniform
substance. A substance cannot be separated composition throughout. Such
into other kinds of matter by any physical mixtures are called homogeneous
process. We know that dissolved sodium mixtures or solutions. Some other
chloride can be separated from water by the examples of such mixtures are: (i) salt
, 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
d
Fig. 2.2: Filtration
heterogeneous mixtures. Mixtures of
sodium chloride and iron filings, salt Now, we shall learn about solutions,
he
and sulphur, and oil and water are suspensions and colloidal solutions in the
examples of heterogeneous mixtures. following sections.
Q
Activity ______________ 2.2 uestions
is
• Let us again divide the class into four 1. What is meant by a substance?
groups – A, B, C and D. 2. List the points of differences
• Distribute the following samples to between homogeneous and
bl
each group: heterogeneous mixtures.
− Few crystals of copper sulphate to
group A.
pu
− One spatula full of copper
sulphate to group B. 2.2 What is a Solution?
− Chalk powder or wheat flour to
be T
group C. A solution is a homogeneous mixture of two
− Few drops of milk or ink to or more substances. You come across various
re
types of solutions in your daily life. Lemonade,
o R
group D.
• Each group should add the given soda water etc. are all examples of solutions.
sample in water and stir properly using Usually we think of a solution as a liquid that
contains either a solid, liquid or a gas
tt E
a glass rod. Are the particles in the
mixture visible? dissolved in it. But, we can also have solid
• Direct a beam of light from a torch solutions (alloys) and gaseous solutions (air).
In a solution there is homogeneity at the
C
through the beaker containing the
mixture and observe from the front. particle level. For example, lemonade tastes the
Was the path of the beam of light same throughout. This shows that particles of
sugar or salt are evenly distributed in the
no N
visible?
• Leave the mixtures undisturbed for a solution.
few minutes (and set up the filtration
apparatus in the meantime). Is the Alloys: Alloys are mixtures of two or
mixture stable or do the particles begin more metals or a metal and a non-metal
©
More to know
to settle after some time? and cannot be separated into their
• Filter the mixture. Is there any residue components by physical methods. But
on the filter paper? still, an alloy is considered as a mixture
Discuss the results and form an because it shows the properties of its
opinion. constituents and can have variable
• Groups A and B have got a solution. composition. For example, brass is a
• Group C has got a suspension. mixture of approximately 30% zinc and
• Group D has got a colloidal solution. 70% copper.
I S MATTER A ROUND U S P URE 15
, A solution has a solvent and a solute as proportion of the solute and solvent can be
its components. The component of the solution varied. Depending upon the amount of solute
that dissolves the other component in it present in a solution, it can be called a dilute,
(usually the component present in larger concentrated or a saturated solution. Dilute
amount) is called the solvent. The component and concentrated are comparative terms. In
of the solution that is dissolved in the solvent activity 2.2, the solution obtained by group
(usually present in lesser quantity) is called A is dilute as compared to that obtained by
the solute. group B.
Examples: Activity ______________ 2.3
d
(i)
A solution of sugar in water is a solid • Take approximately 50 mL of water
in liquid solution. In this solution, each in two separate beakers.
sugar is the solute and water is the
he
• Add salt in one beaker and sugar or
solvent. barium chloride in the second beaker
(ii) A solution of iodine in alcohol known with continuous stirring.
as ‘tincture of iodine’, has iodine (solid) • When no more solute can be dissolved,
as the solute and alcohol (liquid) as heat the contents of the beaker to
is
the solvent. raise the temperature by about 5°C.
(iii) Aerated drinks like soda water etc., are • Start adding the solute again.
gas in liquid solutions. These contain Is the amount of salt and sugar or barium
bl
carbon dioxide (gas) as solute and chloride, that can be dissolved in water at a
water (liquid) as solvent. given temperature, the same?
(iv) Air is a mixture of gas in gas. Air is a At any particular temperature, a solution
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homogeneous mixture of a number of that has dissolved as much solute as it is
gases. Its two main constituents are: capable of dissolving, is said to be a saturated
oxygen (21%) and nitrogen (78%). The
solution. In other words, when no more solute
be T
other gases are present in very small
can be dissolved in a solution at a given
quantities.
re
temperature, it is called a saturated solution.
o R
The amount of the solute present in the
Properties of a solution
saturated solution at this temperature is
• A solution is a homogeneous mixture. called its solubility.
tt E
• The particles of a solution are smaller If the amount of solute contained in a
than 1 nm (10-9 metre) in diameter. So, solution is less than the saturation level, it is
they cannot be seen by naked eyes.
C
called an unsaturated solution.
• Because of very small particle size, they What would happen if you were to take a
do not scatter a beam of light passing saturated solution at a certain temperature
through the solution. So, the path of
no N
and cool it slowly.
light is not visible in a solution. We can infer from the above activity that
• The solute particles cannot be different substances in a given solvent have
separated from the mixture by the different solubilities at the same temperature.
process of filtration. The solute particles
©
The concentration of a solution is the amount
do not settle down when left undisturbed, of solute present in a given amount (mass or
that is, a solution is stable. volume) of solution, or the amount of solute
dissolved in a given mass or volume of solvent.
2.2.1 CONCENTRATION OF A SOLUTION Concentration of solution = Amount of solute/
In activity 2.2, we observed that groups A and Amount of solution
B obtained different shades of solutions. So, Or
we understand that in a solution the relative Amount of solute/Amount of solvent
16 SCIENCE
IS MATTER AROUND US PURE
How do we judge whether milk, ghee, butter, physical process of evaporation. However,
d
salt, spices, mineral water or juice that we sodium chloride is itself a substance and
buy from the market are pure? cannot be separated by physical process into
he
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
is
substances. Whatever the source of a
substance may be, it will always have the
same characteristic properties.
bl
Therefore, we can say that a mixture
contains more than one substance.
Fig. 2.1: Some consumable items
pu
Have you ever noticed the word ‘pure’ 2.1.1 TYPES OF MIXTURES
written on the packs of these consumables?
Depending upon the nature of the
be T
For a common person pure means having no components that form a mixture, we can have
adulteration. But, for a scientist all these things
different types of mixtures.
re
are actually mixtures of different substances
o R
and hence not pure. For example, milk is Activity ______________ 2.1
actually a mixture of water, fat, proteins etc.
When a scientist says that something is pure, • Let us divide the class into groups A,
tt E
it means that all the constituent particles of B, C and D.
that substance are the same in their chemical • Group A takes a beaker containing
nature. A pure substance consists of a single 50 mL of water and one spatula full of
C
type of particles. In other words, a substance copper sulphate powder. Group B takes
50 mL of water and two spatula full of
is a pure single form of matter.
copper sulphate powder in a beaker.
no N
As we look around, we can see that most
• Groups C and D can take different
of the matter around us exist as mixtures of amounts of copper sulphate and
two or more pure components, for example, potassium permanganate or common
sea water, minerals, soil etc. are all mixtures. salt (sodium chloride) and mix the given
©
components to form a mixture.
2.1 What is a Mixture? • Report the observations on the
uniformity in colour and texture.
Mixtures are constituted by more than one • Groups A and B have obtained a
kind of pure form of matter, known as a mixture which has a uniform
substance. A substance cannot be separated composition throughout. Such
into other kinds of matter by any physical mixtures are called homogeneous
process. We know that dissolved sodium mixtures or solutions. Some other
chloride can be separated from water by the examples of such mixtures are: (i) salt
, 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
d
Fig. 2.2: Filtration
heterogeneous mixtures. Mixtures of
sodium chloride and iron filings, salt Now, we shall learn about solutions,
he
and sulphur, and oil and water are suspensions and colloidal solutions in the
examples of heterogeneous mixtures. following sections.
Q
Activity ______________ 2.2 uestions
is
• Let us again divide the class into four 1. What is meant by a substance?
groups – A, B, C and D. 2. List the points of differences
• Distribute the following samples to between homogeneous and
bl
each group: heterogeneous mixtures.
− Few crystals of copper sulphate to
group A.
pu
− One spatula full of copper
sulphate to group B. 2.2 What is a Solution?
− Chalk powder or wheat flour to
be T
group C. A solution is a homogeneous mixture of two
− Few drops of milk or ink to or more substances. You come across various
re
types of solutions in your daily life. Lemonade,
o R
group D.
• Each group should add the given soda water etc. are all examples of solutions.
sample in water and stir properly using Usually we think of a solution as a liquid that
contains either a solid, liquid or a gas
tt E
a glass rod. Are the particles in the
mixture visible? dissolved in it. But, we can also have solid
• Direct a beam of light from a torch solutions (alloys) and gaseous solutions (air).
In a solution there is homogeneity at the
C
through the beaker containing the
mixture and observe from the front. particle level. For example, lemonade tastes the
Was the path of the beam of light same throughout. This shows that particles of
sugar or salt are evenly distributed in the
no N
visible?
• Leave the mixtures undisturbed for a solution.
few minutes (and set up the filtration
apparatus in the meantime). Is the Alloys: Alloys are mixtures of two or
mixture stable or do the particles begin more metals or a metal and a non-metal
©
More to know
to settle after some time? and cannot be separated into their
• Filter the mixture. Is there any residue components by physical methods. But
on the filter paper? still, an alloy is considered as a mixture
Discuss the results and form an because it shows the properties of its
opinion. constituents and can have variable
• Groups A and B have got a solution. composition. For example, brass is a
• Group C has got a suspension. mixture of approximately 30% zinc and
• Group D has got a colloidal solution. 70% copper.
I S MATTER A ROUND U S P URE 15
, A solution has a solvent and a solute as proportion of the solute and solvent can be
its components. The component of the solution varied. Depending upon the amount of solute
that dissolves the other component in it present in a solution, it can be called a dilute,
(usually the component present in larger concentrated or a saturated solution. Dilute
amount) is called the solvent. The component and concentrated are comparative terms. In
of the solution that is dissolved in the solvent activity 2.2, the solution obtained by group
(usually present in lesser quantity) is called A is dilute as compared to that obtained by
the solute. group B.
Examples: Activity ______________ 2.3
d
(i)
A solution of sugar in water is a solid • Take approximately 50 mL of water
in liquid solution. In this solution, each in two separate beakers.
sugar is the solute and water is the
he
• Add salt in one beaker and sugar or
solvent. barium chloride in the second beaker
(ii) A solution of iodine in alcohol known with continuous stirring.
as ‘tincture of iodine’, has iodine (solid) • When no more solute can be dissolved,
as the solute and alcohol (liquid) as heat the contents of the beaker to
is
the solvent. raise the temperature by about 5°C.
(iii) Aerated drinks like soda water etc., are • Start adding the solute again.
gas in liquid solutions. These contain Is the amount of salt and sugar or barium
bl
carbon dioxide (gas) as solute and chloride, that can be dissolved in water at a
water (liquid) as solvent. given temperature, the same?
(iv) Air is a mixture of gas in gas. Air is a At any particular temperature, a solution
pu
homogeneous mixture of a number of that has dissolved as much solute as it is
gases. Its two main constituents are: capable of dissolving, is said to be a saturated
oxygen (21%) and nitrogen (78%). The
solution. In other words, when no more solute
be T
other gases are present in very small
can be dissolved in a solution at a given
quantities.
re
temperature, it is called a saturated solution.
o R
The amount of the solute present in the
Properties of a solution
saturated solution at this temperature is
• A solution is a homogeneous mixture. called its solubility.
tt E
• The particles of a solution are smaller If the amount of solute contained in a
than 1 nm (10-9 metre) in diameter. So, solution is less than the saturation level, it is
they cannot be seen by naked eyes.
C
called an unsaturated solution.
• Because of very small particle size, they What would happen if you were to take a
do not scatter a beam of light passing saturated solution at a certain temperature
through the solution. So, the path of
no N
and cool it slowly.
light is not visible in a solution. We can infer from the above activity that
• The solute particles cannot be different substances in a given solvent have
separated from the mixture by the different solubilities at the same temperature.
process of filtration. The solute particles
©
The concentration of a solution is the amount
do not settle down when left undisturbed, of solute present in a given amount (mass or
that is, a solution is stable. volume) of solution, or the amount of solute
dissolved in a given mass or volume of solvent.
2.2.1 CONCENTRATION OF A SOLUTION Concentration of solution = Amount of solute/
In activity 2.2, we observed that groups A and Amount of solution
B obtained different shades of solutions. So, Or
we understand that in a solution the relative Amount of solute/Amount of solvent
16 SCIENCE
