2.is Matter Around Us Pure-Notes

Ch_2 Is Matter Around Us Pure
Class IX 2020-21 (Chap:2 Is Matter Around Us Pure) R.SEKAR, EMBASSY OF INDIA SCHOOL MOSCOW Page 1 of 20
Pure and Mixture:
For a common person pure means having no adulteration. But, for a scientist
mixtures of different substances are not pure.
For example, for a common person milk is pure but for a scientist it is not pure
since the milk is a mixture of water, fat, proteins etc.
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.
Pure substance:
*A pure substance consists of a single type of particles.
(or)
A substance contain only one kind of particles.
*Substance always have the same characteristic properties.
* Pure substances can be elements or compounds.
*A pure substances which can not be separated into other kinds of matter.
Example: Water, sugar, iron, common salt etc.,
Mixture:
A mixture contains more than one substance (element and/or compound) mixed in
any proportion.
Mixtures can be separated into pure substances using appropriate separation
techniques.
Pure substance Mixture
1. Pure substance consists of a single type Mixture consists of two or more
of substance. pure substances.
2. Pure substance cannot be separated into Mixture can be separated into its
other substances by physical methods. components by physical methods.
3. Pure substance has its own definite Mixture shows the properties of
properties. its components.
Note: Elements are made up of one kind of atoms only.

Compounds are made up of one kind of molecules only.
On the basis of their chemical composition, substances can be classified either
as elements or compounds.
An element as a basic form of matter that cannot be broken down into simpler
substances by chemical reactions.
Elements can be normally divided into metals, non-metals and metalloids.
Properties of Metals:
• They have a lustre (shine).
• They have silvery-grey or golden-yellow colour.
• They conduct heat and electricity.
• They are ductile (can be drawn into wires).
• They are malleable (can be hammered into thin sheets).
• They are sonorous (make a ringing sound when hit).
Example: Gold, Silver, Copper, Iron, Sodium, Potassium etc.
Exception: 1) Mercury is the only metal is liquid at room temperature.

2) Gallium and Cesium become liquid at a temperature slightly above
room temperature (303 K).
Properties of Non-Metals:
• They display a variety of colours.
• They are poor conductors of heat and electricity.
• They are not lustrous, sonorous or malleable.
Example: Hydrogen, oxygen, iodine, carbon (coal, coke), bromine, chlorine etc.
Exception: 1) Bromine is the only non-metal is liquid at room temperature.
Properties of Metalloids:
Elements have intermediate properties between metals and non-metals are called
Metalloids.
Example: Boron, Silicon, Germanium etc.
Give reasons to justify that water is a compound and not a mixture.

(i)Water cannot be separated into its constituentsm hydrogen and oxygen by
simple physical methods such as filtration, evaporation, distillation, etc.,
(ii)The composition of water is fixed. It has definite composition by mass.
(1:8 by mass ).
𝑀𝑎𝑠𝑠 𝑜𝑓 ℎ𝑦𝑑𝑟𝑜𝑔𝑒𝑛 2
= 16
𝑀𝑎𝑠𝑠 𝑜𝑓 𝑜𝑥𝑦𝑔𝑒𝑛
𝑀𝑎𝑠𝑠 𝑜𝑓 ℎ𝑦𝑑𝑟𝑜𝑔𝑒𝑛 1
=8
𝑀𝑎𝑠𝑠 𝑜𝑓 𝑜𝑥𝑦𝑔𝑒𝑛
(iii) Water has properties entirely different from those of its constituents,
hydrogen and oxygen.
For example,
Hydrogen is a gas and burns and oxygen is also gas and supports combustion
whereas
Water is a liquid, it does not burn, does not suppot combustion but it is
used to extinguish the fire.
Based on the above facts, we can say that water is a compound and not a
mixture.
Air is considered to be mixture and not a compound? Justify.

Air is a homogeneous mixture of different gases which can be separated by
suitable methods. Therefore, air is a mixture and not a compound.
Alloys:
Alloys are mixture of two more metals in variable composition.
( Some times Metal and Non-metal Example: Steel ).
Alloys cannot be separated into their components by physical methods.
Still, alloys are considered as mixture because these show the properties of its
constituents and can have variable composition.
Example: Brass is a mixture of approximately 30% zinc and 70% copper.
Copper alloys have excellent electrical and thermal performance, good
corrosion resistance, high ductility and relatively low cost.
Mixture of Iron filing and Sulphur:

A mixture shows the properties of all the components present in it.
For example: A mixture of iron filings and Sulphur shows the properties of
both iron and Sulphur.
1)If dilute sulphuric acid is added to the mixture, iron reacts with dilute
sulphuric acid and hydrogen gas is produced and Sulphur remains unchanged.
2)If carbon disulphide(CS2) is added to the mixture, Sulphur dissolves in
carbon disulphide leaving iron filings unchanged. On filtration, iron can be
separated from Sulphur. Also Sulphur can be recovered from the filtrate by
evaporating carbond disulphide.
3) The mixture of iron filings and Sulphur can be separated by moving
magnet in the mixture.
This means that the mixture of iron filings and Sulphur shows the
properties of iron and sulphur.
Compound of Iron filing and Sulphur:
Take 5g of iron filings and 3g of sulphur powder in a china dish and heat
strongly. On heating the two elements strongly we get a new substance called a compound.
This substance has totally different properties from its constituent elements of iron and
sulphur.
Fe(s) + S (s) ----------Heat---------→ FeS(s)
Iron Sulphur Ferrous Sulphide
(Yellow powder) (Brown Solid) ( A new substance is formed)
1)It will not be attracted by the magnet.
2)When we add carbon disulphide, sulphur will not dissolve in it.
3)The colour and texture of the compound are same throughout.
How to obtain gases from air?
Air is homogeneous mixture of many gases. The gases can be separated from air
by fractional distillation. In this method, the air is compressed by increasing the
pressure and then cooled by decreasing the temperature. Air will be compressed
to form liquid air called liquefied air. The liquefied air is subjected to fractional
distillation and different gases are collected at different temperatures. The
liquid air is allowed to warm up slowly in fractional distillation column, where gases
are separated at different heights depending upon their boiling points.
(i)the boiling point of liquid nitrogen(from air) is the lowest (-196°C).
Therefore, nitrogen gets distilled first of all.
(ii)Liquid argon(from air) has a slightly higher boiling point (-186°C). Therefore,
argon gets distilled after nitrogen.
(iii)Liquid oxygen(from air) has higher boiling point (-183°C). Therefore, after
argon, oxygen will be distilled and so on.
TYPES OF MIXTURES:
Mixtures are of two types (i) Homogeneous mixtures (ii) Heterogeneous mixtures
(i) Homogeneous mixtures:
A mixture which has uniform composition throughout is called homogeneous
mixture. Example: i) Mixture of Sugar in water ii) Mixture of Salt in water.
(ii) Heterogeneous mixtures:
A mixture which does not have uniform composition throughout is called
homogeneous mixture. Example: i)Mixture of Sulphur powder and Iron fillings.
ii) Mixture of oil and water.
iii) Mixture of salt and sulphur.
Difference between homogeneous and heterogeneous mixtures:
Sl.No Homogeneous Solution Heterogeneous Solution

1 It is made up of two or more In this mixture, the substance
substance when they are completely remain separated from each other
mixed together and do not react and one substance spreads
with each other. throughout the other as tiny
particles.
2 The composition remains uniform The composition does not remain
throughout. uniform throughout.
3 The component of the mixture The component of the mixture can be
cannot be separated by visible separated by visible boundaries.
boundaries.
4 Examples: Examples:
i) Mixture of Sugar in water i)Mixture of Sulphur powder and Iron fillings.
ii) Mixture of Salt in water. ii) Mixture of oil and water
iii) Mixture of salt and sulphur.
Solution:
A solution is a homogeneous mixture of two or more substances.
Solute + Solvent = Solution
Example: Salt + Water = Salt Solution
Solute:
The component of solution present in less quantity is known as solute.
Example: Salt(Solute) + Water(Solvent) = Salt Solution
Solvent:
The component of solution present in lager quantity is known as solvent.
Example: Salt(Solute) + Water(Solvent) = Salt Solution (Solution)
Aqueous Solution:
A solution in which water is used as a solvent is called Aqueous solution.
Alloys :
Alloys are solid in solid solutions.
Zinc (Solute - 30%) + Copper (Solvent- 70%) = Brass (Solution)
Note: Alloys 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.
Solubility:
The maximum amount solute which can be dissolved in a 100g of a solvent at a
specified temperature is known as the solubility of that solute in that solvent at
the specified temperature.
Solubility = Weight of solute in saturated solution X 100

Weight of solvent in saturated solution
Saturated Solution:
A solution in which no more solute can be dissolved at a given temperature is called
a saturated solution.
Unsaturated Solution:
A solution in which more solute can be dissolved at a given temperature is called a
unsaturated solution.
Note: A saturated solution at a particular temperature may become unsaturated when the
temperature is increased.
Concentration of a solution:
The concentration of a solution is the amount of solute present per unit volume or
per unit mass of the solution/solvent.
Dilute and concentrated solution:
Depending upon the amount of solute present in a solution, it can be called a dilute,
concentrated solution.
Dilute and concentrated are comparative terms.
Expressing the concentration of a solution: (we will learn only two methods)
Mass by mass percentage of a solution
Mass by volume percentage of a solution

True Solution:
A solution is a homogeneous mixture. 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.
Example: Salt solution.
Colloidal solution:
The particles of a colloid are uniformly spread throughout the solution. The solute
particles do not settle down when left undisturbed, that is, a Colloidal solution is
stable.
Due to the relatively smaller size of particles, the mixture appears to be
homogeneous. But actually, a colloidal solution is a heterogeneous mixture.
Example: Milk.
(Colloidal particles can be by separated by centrifugation)
Tyndall effect:
Due to small size of colloidal particles, we cannot see them with naked eyes. But,
these particles can easily scatter a beam of visible light. This scattering of a beam
of light is called the Tyndall effect.
Example:
(i) 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.)
(ii) 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.)
(a) Solution of copper sulphate does not show Tyndall effect, Canopy of a dense forest
(b) mixture of water and milk shows Tyndall effect. The Tyndall effect
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.
Example: Sand in water.
Separating the Components of a Mixture:
We have learnt that most of the natural substances are not chemically pure.
To separate different components of a mixture variety of physical techniques are

available.
All these separation techniques are based on difference in the physical properties
of the components present in the mixture.
(1) Evaporation :
Basic principle : Out of the two components of a mixture one can

evaporate [i.e., has less boiling point] and other has higher boiling point.
This method can be used to separate a solid substance from the solution in which
it is present.
Example : Mixture of dye [higher boiling point] and water. Out of water
and dye, water evaporates but dye is left behind in petri dish.
Note: In this case solvent is volatile and solute is non-volatile
Direct heating of the ink drops in this case is avoided because it may be
possible that the red dye present in the ink may decompose during direct heating.
2) Centrifugation Method:
Basic principle : When mixture is rotated very fast, then denser particles are
forced at the bottom and lighter particles stay above.
Example : Separating cream from milk.
(3) SEPARATION OF A MIXTURE OF TWO IMMISCIBLE LIQUIDS:
Basic principle : Two immiscible liquids (which do not dissolve in each other) can be
easily separated by using a separating funnel.
Immiscible liquids separate out in layers depending on their densities.
Example : Water from oil can be separated by first opening the stop cock
till water is removed in one beaker, then afterwards oil can be collected in a
separate beaker.
Pour the mixture of kerosene oil and water in a

separating funnel.
Let it stand undisturbed for sometime so that
separate layers of oil and water are formed.
Water forms the lower layer because its density
is high with respect to kerosene oil.
Open the stopcock of the separating funnel and
pour out the lower layer of water carefully.
Close the stopcock of the separating funnel as
the oil reaches the stop-cock.
Kerosene oil remains in the separating funnel.
Applications of above method:
1)To separate mixture of oil and water.
2)In the extraction of iron from its ore, the lighter slag is removed from the top
by this method to leave the molten iron at the bottom in the furnace.
(4) Sublimation:
Basic principle : Out of the two components, one will sublime (directly converts to
gas from solid) and other will not.
Example : NH4Cl (ammonium chloride) and NaCl common salt mixture can be easily
separated by heating so that NH4Cl sublimes but common salt remains behind.
Take a mixture of ammonium chloride and salt

in a China dish.
Cover the dish with an inverted funnel. Close
the stem of the funnel with a cotton plug.
Heat the china dish slowly.
On heating, solid NH4Cl sublimes (ie., changes
into vapour state).
These vapours get collected on the inner cold
surface of the funnel. This is known as
sublimate. The non-volatile salt remain on
the dish. The sublimate can be removed from
the funnel.
Some examples of solids which sublime are

Ammonium chloride, Camphor, Naphthalene and Anthracene.
5.Chromatography:
Basic principle : Coloured components of a mixture can be separated by using an
adsorbent on which they are adsorbed at different rates.
Chromatography is the technique used for separation of those solutes that dissolve
in the same solvent.
Take a thin strip of filter paper.
Draw a line on it using a pencil, approximately 3 cm above the lower edge.
Put a small drop of ink at the Centre of the line. Let it dry.
Lower the filter paper into a jar/glass/beaker/test tube containing water so that
the drop of ink on the paper is just above the water level and leave it undisturbed.
As the water rises up on the filter paper by capillary action, it takes along with it
dyes present.
The more soluble dissolves first, rises faster and produces a coloured spot on the
paper at a higher position. The less soluble dissolves a little later, rises slower
and forms a coloured spot at lower height.
SEPARATION A MIXTURE OF TWO MISCIBLE LIQUIDS
6.Simple Distillation:
Distillation is used for the separation of components of a mixture containing two
miscible liquids that boil without decomposition and have sufficient difference in
their boiling points more than 25 K.
Take the mixture in a distillation flask. Fit it with a thermometer.

Arrange the apparatus as shown in Figure.
Heat the mixture slowly keeping a close watch at the thermometer.
The acetone vaporises, condenses in the condenser and can be collected
from the condenser outlet.
Water is left behind in the distillation flask.
7.Fractional Distillation:
Fractional distillation process is used to separate a mixture of two or more

miscible liquids for which the difference in boiling points is less than 25 K.
This process is carried in a distillation flask which we have described earlier with
fractionating column.
Fractionating column is a long glass tube with different shapes ant designs. It is
packed with glass beads. The beads provide surface for the vapours to cool and
condense repeatedly. Sometimes, the glass tube is blown into a series of spherical
or pear-shaped bulbs.
Fractional column is to obstruct the upward movement of the vapours of the two
liquids. The vapour having high boiling point will get condensed and releasing
energy(latent heat of fusion) that will be taken up by the vapours of low boiling
liquid. This means that by using fractionating column, both evaporation and
condensation will occur simultaneously. The vapour of low boiling liquid will escape
from the flask and will collect in the receiver after condensation as described in
case of simple distillation. At the same time, the vapours of high boiling liquid will
fall back in the flask after getting condensed.
Examples: 1)Ethyl alcohol (B.P. is 78°C or 351K) and Water(B.P. is 100°C or 373K)
can be separated from the miscible liquid mixture.
2)Ethyl alcohol (B.P. is 78°C or 351K) and Acetone(B.P. is 56°C or 329K)
can be separated from the miscible liquid mixture.
3)Separation of various components of crude oil or petroleum.
4)Air can be separated by fractional distillation.
Some of the applications of fractional distillation :
(a) In petroleum refineries, petrochemical and chemical plants, natural gas
processing and cryogenic air separation plants.
(b) In oil refineries to separate crude oil into useful substances (or fractions).
(c) In the process of organic juice.
(d) In the separation of oxygen, liquid nitrogen and argon from air.
8.Crystallisation:
Basic principle : To remove impurities from a mixture by first dissolving
in a suitable solvent and then crystallising out one component.
For example :
Crystallisation is process that separates a pure solid in the form of its crystals
from a solution.
Take some (approximately 5 g) impure sample in a china dish.
Dissolve it in minimum amount of water.
Filter the impurities out.
Evaporate 1/3rd of water from the Sample solution and get a saturated solution.
Cover the solution with a filter paper and leave it undisturbed at room temperature
to cool slowly for a day.
You will obtain the crystals of pure sample in the china dish.
This process is called crystallisation.
Various steps in the preparation of Mohr salt
Applications :
(a) Purification of salt from sea water.
(b) Separation of crystals [e.g., alum (phitkari, copper sulphate)]
from their impure crystals.
Why is crystallisation better than evaporation ?

(i) Some solids decompose or get charred upon heating to dryness
during evaporation. E.g., sugar.
(ii) Some impurities remain dissolved in solution after filteration. On
evaporation, these impurities do not evaporate and remain with
the mixture.
Filtration
Physical properites:
The properties that can be observed are the physical properites.
Example: Colour, hardness, rigidity, fluidity, density, melting point, boiling point
etc.
Physical Change:
The changes is which the physical properties of the substances change but no
new substances are formed are called physical change.
Physical change is a temporary change in which only the physical properties of
the substances change. (Change in colour, volume, shape, state, etc.,)
It can be easily reversed by changing the conditions that is reversible in nature.
Example:
1)Conversion of water into steam or ice
2)Dissolution of salt in water (Salt can be recovered by evaporating water)
3)Breaking a piece of wood into smaller pieces.
4)Boiling of water
5)Melting of candle wax
Chemical Change:
The changes in which new substances are formed are called chemical changes.
In chemical change one or more kinds of matter are transformed into a new kind
of matter or several kinds of matter.
It is a permanent change and cannot be easily reversed.
A chemical change is also called a chemical reaction.
Example:
1) Rusting of iron
2) When magnesium ribbon is burnt in air, it forms Magnesium oxide.
3) Burning of candle to give CO2 and H2O
4) Formation of Iron sulphide(FeS) from iron and Sulphur.
5) Electrolysis of water
***********************
Home work:
How can you say that common salt (Sodium Chloride) is a substance, but air is
not a substance?.
We know that a substance can not be separated into other kinds of matter by
using any physical process.
Sodium chloride is a substance because it can not be separated into its chemical
constituents by any of the physical processes.
Air is not a substance because it can be separated into some other substances
such as Nitrogen, Oxygen, etc., by using simple processes.

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Ch_2 Is Matter Around Us Pure

Example: Water, sugar, iron, common salt etc.,

Note: Elements are made up of one kind of atoms only.

Elements can be normally divided into metals, non-metals and metalloids.

Exception: 1) Mercury is the only metal is liquid at room temperature.

Give reasons to justify that water is a compound and not a mixture.

Air is considered to be mixture and not a compound? Justify.

Mixture of Iron filing and Sulphur:

How to obtain gases from air?

Sl.No Homogeneous Solution Heterogeneous Solution

Solubility = Weight of solute in saturated solution X 100

Mass by mass percentage of a solution

Mass by volume percentage of a solution

To separate different components of a mixture variety of physical techniques are

Basic principle : Out of the two components of a mixture one can

(3) SEPARATION OF A MIXTURE OF TWO IMMISCIBLE LIQUIDS:

Pour the mixture of kerosene oil and water in a

Take a mixture of ammonium chloride and salt

Some examples of solids which sublime are

SEPARATION A MIXTURE OF TWO MISCIBLE LIQUIDS

Take the mixture in a distillation flask. Fit it with a thermometer.

Fractional distillation process is used to separate a mixture of two or more

Why is crystallisation better than evaporation ?

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