2 SEPARATION OF MIXTURES
Rice is the staple diet of the people of Take a teaspoon each of iron powder
Kerala. What is pictured above is a and sulphur powder in a china dish.
common sight in the courtyards of Mix them thoroughly. Look at the
farmers in the harvesting season. Why mixture through a lens. Can you see
is the paddy winnowed after the the black grains of iron and the yellow
reaped stalk bundles are threshed? powder of sulphur?
When the bundles are threshed there
Some of the properties of iron and
will be plenty of chaff mixed with
sulphur are given in the table below
paddy. What happens when it is
When paddy is de-husked what we get Density More Less
is rice mixed with bran. How are these
Magnetism Magnetic Non-magnetic
In water Insoluble Insoluble
Many of the substances which we use
in our daily life are found in the form
of mixtures. What might be the most practical
method of separating this mixture?
What are the characteristic features of
mixtures? Let us conduct an Find out on the basis of the properties
experiment to find out. of the components.
Physical Sciences 17
Can you suggest other methods? Saline water is a mixture formed from
a solid and a liquid. Can mixtures be
If the proportion of iron powder and
formed from substances in any
sulphur powder in the mixture is
physical state? Find more examples
changed, can the same methods be
and add to the table.
used to separate the components?
Why is this possible? Type of mixture Examples
Now, with the help of the teacher, Solid and solid Soil, ......, ......
conduct the following experiments
also, and record the observations. Solid and liquid Saline water,
Take a small portion of the iron and Liquid and liquid ......, ......, ......
sulphur mixture in a test tube and
Gas and gas ......, ......, ......
add dilute hydrochloric acid (HCl).
Which is the gas produced? What
do you see at the bottom of the test Table. 2.2
tube? Which component has
Many mixtures like these are handled
reacted with the acid? Write down
by us in our everyday life. On many
occasions we have to separate their
Take another portion of this mixture components.
in a test tube and add a little carbon
Consider some examples.
disulphide. Shake the test tube
gently. What do you observe? • Removing the sediment from tea.
Explain. • Removing stones and paddy from
On the basis of the above experimental rice.
observations discuss the following.
What is the minimum number of
substances necessary to form a
What is the required proportionate
quantity of each substance?
Is there any change in the
chemical/physical properties of the
substances when they are mixed?
Is the formation of a mixture a Fig. 2.1
chemical change or a physical change?
List more instances after discussion.
Note down the conclusions in the Tabulate the method of separation in
science diary. each instance and also the property on
Aren't the components of the mixture the basis of which the separation is
used in the above experiment solids? effected (table 2.3). Enter in the science
18 Physical Sciences
Instance Method Property basis
Tea Filtration Difference in the size of
Stones and paddy in rice Picking up by hand Colour, size
Saline water Vaporisation Tendency to evaporate
Muddy water - -
Iron + sand - -
Sugar + sand -, -, - -
Now it is clear that mixtures are Arrange the equipment as shown in the
separated into components based on illustration, and try to separate by
the properties of those components. Let filtration clear water from water in
us familiarise ourselves with some which soil is mixed and water in which
other methods used to separate chalk powder is mixed.
Why was it possible to separate the
How to separate clear water water using filter paper?
from muddy water Why does one component remain
Is it possible to filter clear water in the filter paper after filtration?
from muddy water by using the Think in terms of particle size. Write
same type of strainer used for down your conclusion in the science
filtering tea? diary.
If a filter paper is used instead of Can this method be adopted to
the strainer? separate water and salt from saline
water? Explain your answer.
Separation of components of
muddy water saline water
rod How can the salt and water in saline
water be separated?
filter You know that common salt is obtained
by the vaporisation of sea water using
What happens to the water when
saline water is heated?
clear Why is the salt left behind? Is there
any method for collecting the
Physical Sciences 19
See the illustration showing the Separation of a mixture of
equipment for separating such completely miscible liquids
mixtures (fig 2.3) Acetone and water are two liquids that
mix with each other, in all proportions.
thermo meter The boiling point of water is 100°C and
that of acetone is 56°C. Let us see a
method of separating the components
of this mixture based on the large
condenser difference in their boiling points. See
fig 2.4. Have you noticed the
flask saline thermometer fitted on the top of the
water flask? When the mixture is heated
which component boils and evaporates
first? Why? How can this substance be
condensed recovered from the vapour? Discuss
and note down the conclusions in the
The mixture (saline water) is boiled in thermometer
a round bottomed flask
Which component evaporates, salt
or water? condenser
When the vapour passes through the acetone
condenser, it condenses and flows into flask
the collecting flask as a liquid.
What is the substance that remains
in the round bottomed flask?
This process is known as distillation. acetone
Ordinary drinking water contains
many salts dissolved in it. These salts Fig. 2.4
are removed by distillation in order to This method is possible only when
produce distilled water used for there is a substantial difference
injecting medicines and in storage between the boiling points of the two
batteries. component liquids. Also they should
This process is used in separating not decompose on boiling. This type
of separation is also called distillation.
mixtures where one component is
volatile and the other is not. Find out How can the component liquids be
other examples. separated if there is only a small
difference in their boiling points?
20 Physical Sciences
Ethanol and methanol are two can also be separated on the basis of
completely miscible liquids with only the increasing order of their boiling
a small difference in their boiling points. This method is called fractional
points. The equipment shown in fig. distillation.
2.5 is used to separate this mixture.
Crude oil is a mixture of liquid hydro
carbons which have only small
water difference in their boiling points. The
components of this mixture such as
petrol, diesel, kerosene etc. are
condenser separated by the above mentioned
fractionating method of fractional distillation.
How to separate the different
components of air?
+ Ammonia is an important raw material
ethanol in the manufacture of chemical
fertilizers. Ammonia is manufactured
methanol by combining nitrogen and hydrogen.
Nitrogen is obtained by separating it
Fig. 2.5 Some details about the components of
When the vapours of the mixture pass air are given in table 2.4.
through the fractionating column, due Oxygen Argon Nitrogen
to the repeated condensation and Boiling point -1830C -1860C -1960C
evaporation the vapours of methanol, Quantity (%) 20.9 0.9 78.1
with a lower boiling point first passes
out of the fractionating column,
condense and get collected in the What is the physical state of oxygen
conical flask. After this, ethanol which at - 1820C?
has a slightly higher boiling point can And at _1840C ?
be collected in similar fashion in
Which component has the highest
another flask. If there are more than
two components in the mixture, they
cooled at Liquefied evaporate
Air air Argon _ 1860C
high pressure slowly in a
Flow Diagram 2.1
Physical Sciences 21
Which one has the lowest?
See the flow diagram showing the
process of separation of these gases.
(flow diagram 2.1)
Which gas will condense first into separating
From the liquid mixture which
component will evaporate first?
Which component is obtained first
from the fractionating column?
What will be its state - solid, liquid
Which will be the last component
obtained? In which physical state?
Note down your conclusions in the
Can the components of black
ink be separated?
Thus we have become familiar with
The ink we use is a dye which
some of the processes of industrial
dissolves in water.
Carry out the following experiment.
How to separate a mixture of Take some black ink in a china dish
two immiscible liquids and heat it. (It is enough to keep the
Suppose kerosene gets mixed with dish on hot sand bath.) Can you see
water. How can they be separated? the vapours? Once the evaporation
Take some kerosene and some water stops, remove the dish from the heat
in a bottle. Shake the bottle well. Keep source.
the bottle motionless for a while. What
Which could be the substance that
do you see? Why does this happen?
The arrangement for separation of the
Is there anything left behind in the
components of such a mixture is shown
in the figure. See fig 2.6.
Is ink a single substance? Or is it a
Which liquid gets collected at the
mixture? What is your conclusion?
Why does kerosene remain above In black ink is there just one
water? colour or is it a combination
of many colours?
How can the water underneath be
removed? Take a filter paper strip 1 inch wide
and 6 inches long. Put one drop of
What if these two liquids were
black ink (from a sketch pen or a
fountain pen) at about 1 inch from one
22 Physical Sciences
end of the filter paper. Allow it to dry greater extent whereas some other
for one minute. Take water in a jar. components are not adsorbed to that
Immerse the filter paper (as shown in extent.
the figure) into the water in the jar so
that the ink spot is just above the water The dyes present in ink are usually a
level (fig 2.7). mixture of two or more coloured
Observe carefully as the water rises up substances. The water rises through the
through the filter paper. Write down filter paper by capillary action. The
your observations in the science diary. weakly adsorbed component rises
glass rod faster through the paper. Those which
paper clip are strongly adsorbed rise slowly. In
glass jar this way the colours are separated. As
filter this method was first used for
paper separating coloured substances it was
paper termed chromatography. Chromato-
graphy is the process used for
separation of solutes soluble in the
Fig. 2.7 same solvent. See the uses of this
Do different colours appear in the process.
filter paper? • separation of components from
What could be the reason for the dyes
colours rising through the paper? • separation and identification of
chemicals mixed in blood
Adsorption Look at a situation in every day life
where separation of mixtures happens.
Some substances like cotton, sponge etc.
absorb liquids into them. But some other Butter from curd
substances hold particles of certain other You would have seen curd being
substances on their surface alone. This churned to obtain butter. During
phenomenon is called adsorption. In this churning, particles of butter are
way, the carbon particles in gas masks separated. Being less dense, these
remove poisonous gases from the air and particles float on top of the curd.
the charcoal in water filters removes An instrument called centrifuge (fig
coloured and foul smelling substances 2.8-a) is used to separate components
from water. So also, dust particles stick from a mixture using the difference in
to walls because of adsorption. The rate densities of the components.
at which adsorption occurs on a
Examine some situations where this
substance depends on the nature of the
process is used.
substance. During adsorption of mixtures
some of the components are adsorbed to a
Physical Sciences 23
Can the constituent elements
of a compound be separated?
As already understood, formation of
mixtures is a physical change. But the
formation of compounds is a chemical
change. Compounds are formed by
chemical combination of elements in
fixed proportions. Therefore, the
elements in a compound can be
Fig. 2.8 (a)
separated only by suitable chemical
See the compounds and their formulae
Mercuric oxide - HgO
Calcium oxide - CaO
Both are metal oxides.
If HgO is heated it decomposes into Hg
Fig. 2.8 (b) and O 2 . But if CaO is heated the
elements do not separate.
In order to separate the elements in
• Separation of cream from milk
compounds different methods suited
• Separation of blood plasma in a to the nature of the compounds are
clinical lab adopted.
• Separation of precipitates in a You can familiarise yourselves with
laboratory these methods when you study more
You have now gone through some of of chemical processes in higher classes.
the methods of separating mixtures.
24 Physical Sciences