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METAS ADVENTIST SCHOOL
CLASS - 7
CHEMISTRY
CHAPTER- 4 (SEPARATION TECHNIQUES)
INTRODUCTION:
We know that matter can be separated into its
components by various physical methods. We
usually separate the components of mixture to:
- Remove undesirable and unwanted
components.
- Get a pure sample of substance.
- Extract useful components from the mixture.
- Remove harmful components.
PRINCIPLE OF SEPARATION:
Each constituent of a mixture has some
property unique to itself and is shared by no
other component. This difference in property
is utilised to separate the various
components from the mixture.
METHODS OF SEPARATION:
Various methods are used to separate the
components of mixture. The choice of the
method to be used depends upon the
nature and composition of the mixture.
Sometimes we might use a combination of
various methods.
Various types of separation processes are:
--Evaporation
--Crystallization
--Sublimation
--Simple distillation
--Fractional distillation
--Separating funnel
--Chromatography.
Let’s discuss some of the separation
techniques
1. Evaporation
Evaporation is a technique used to separate out
homogenous mixtures where there is one or
more dissolved solids. This method drives off
the liquid components from the solid
components. The process typically involves
heating the mixture until no more liquid
remains, Prior to using this method, the mixture
should only contain one liquid component,
unless it is not important to isolate the liquid
components. This is because all liquid
components will evaporate over time. This
method is suitable to separate a soluble solid
from a liquid.
In many parts of the world, table salt is obtained
from the evaporation of sea water. The heat for
the process comes from the sun.
Salt is formed from evaporating saltwater
Once the sea water in these evaporation ponds
has evaporated, the salt can be harvested.
2. Crystallisation:
Crystallisation is a separation and purification
method which involves the precipitating of solid
crystals from its saturated solution on cooling.
In this process the impure sample is dissolved
in minimum amount of suitable solvent. The
formed solution is heated to get a saturated
solution. On cooling, this saturated solution
produce pure crystals of the sample.
Crystallisation is used for: Purification of salt
that we get from sea water and separation of
crystals of alum from impure samples.
3. Sublimation:
Sublimation is the transition from the solid phase to the gas phase without passing through an intermediate liquid phase. This endothermic phase transition occurs
at temperatures and pressures below the triple point.
The term "sublimation" only applies to physical changes of state and not to the transformation of a solid into a gas during a chemical reaction. For example, when candle wax undergoes combustion, the paraffin is vaporized and reacts with oxygen to produce carbon dioxide and water. This is not sublimation.
The opposite process of sublimation—where a gas undergoes a phase change into solid form—is called deposition or desublimation.
Examples
Dry ice is solid carbon dioxide. At room temperature and pressure, it sublimates into carbon dioxide vapor.
Freezer burn results from the sublimation of ice into water
4. Simple distillation:
Simple distillation is a method 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.
The distillation process involves heating a liquid
to its boiling points, and transferring the vapors
into the cold portion of the apparatus, then
condensing the vapors and collecting the
condensed liquid in a container. In this process,
when the temperature of a liquid rises, the
vapor pressure of the liquid increases. When
the vapor pressure of the liquid and the
atmospheric pressure reach the same level, the
liquid passes into its vapor state. The vapors
pass over the heated portion of the apparatus
until they come into contact with the cold
surface of the water-cooled condenser. When
the vapor cools, it condenses and passes down
the condenser and is collected into a receiver
through the vacuum adapter.
Applications:
--Separation of acetone and water.
--Distillation of alcohol.
Liebig Condenser:
The Liebig condenser or straight condenser is a piece of laboratory equipment, specifically a condenser consisting of a straight glass tube surrounded by a water jacket.
In typical laboratory operation, such as distillation, the condenser is clamped to a retort stands in
vertical or oblique orientation. The hot vapor of some liquid is introduced at the upper end of the inner tube, and condenses in contact with its colder walls. Water (or some other fluid) is constantly circulated in the jacket to carry away the heat of vaporization released by the condensing vavor, keeping the tube below the liquid's boiling point. The condensed liquid drips out of the lower end of the inner tube.
5. Fractional distillation:
Fractional distillation is used for the separation
of a mixture of two or more miscible liquids for
which the difference in boiling points is less
than 25K. The apparatus for fractional
distillation is similar to that of simple distillation,
except that a fractionating column is fitted in
between the distillation flask and the
condenser.
A simple fractionating column is a tube packed
with glass beads. The beads provide surface for
the vapors to cool and condense repeatedly.
When vapors of a mixture are passed through
the fractionating column, because of the
repeated condensation and evaporation, the
vapors of the liquid with the lower boiling point
first pass out of the fractionating column,
condense and are collected in the receiver
flask. The other liquid, with a slightly higher
boiling point, can be collected in similar fashion
in another receiver flask.
Applications:
--Separation of different fractions from
petroleum products.
--Separation of a mixture of methanol and
ethanol.
6. Using a separating funnel:
A separating funnel is used for the separation of
components of a mixture between two
immiscible liquid phases. One phase is the
aqueous phase and the other phase is an
organic solvent. This separation is based on the
differences in the densities of the liquids. The
liquid having more density forms the lower layer
and the liquid having less density forms the
upper layer.
Applications:
To separate a mixture of oil and water.
To separate a mixture of kerosene oil and
water.
7. Chromatography:
Chromatography is a separation technique
used to separate the different components in a
liquid mixture. It was introduced by a Russian
Scientist Michael Tswett. Chromatography
involves the sample being dissolved in a
particular solvent called mobile phase. The
mobile phase may be a gas or liquid. The
mobile phase is then passed through another
phase called stationary phase. The stationary
phase may be a solid packed in a glass plate or
a piece of chromatography paper.
The various components of the mixture travel at
different speeds, causing them to separate.
There are different types of chromatographic
techniques such as column chromatography,
TLC, paper chromatography, and gas
chromatography.
Paper chromatography
It is one of the important chromatographic
methods. Paper chromatography uses paper as
the stationary phase and a liquid solvent as the
mobile phase. In paper chromatography, the
sample is placed on a spot on the paper and
the paper is carefully dipped into a solvent. The
solvent rises up the paper due to capillary
action and the components of the mixture rise
up at different rates and thus are separated
from one another.
Applications:
To separate colors in a dye.
--To separate pigments from natural colors.
--To separate drugs from blood.
For more clarity click on the below given links:
https://youtu.be/bkYqqJa5P8w
https://youtu.be/XC1RxloV0Mo
WORKSHEET
Q-1 FILL IN THE BLANKS.
1. The process of cooling a hot, concentrated
solution of a substance to obtain crystals is
called crystallization.
2. Separating Funnel is the separation based
on the differences in the densities of the
liquids.
3. The solid obtained by cooling the vapour of
the solid is called sublimate.
4. Salt is obtained from seawater by the
process of evaporation.
5. The mixture of acetone-water can be
separated by fractional Distillation.
Q.2 ANSWER IN ONE WORD OR ONE
SENTENCE.
(a) Dyes in water soluble markers may be
separated by means of:
Ans. chromatography.
(b) Oil and water may be separated by using:
Ans. Separating funnel.
(c) Which method is used to separate a
mixture of naphthalene and common salt?
Ans. Sublimation.
(d) Which method is used to separate the
parts of a mixtureof either a gas or liquid
different chemicals?
Ans. Chromatography.
(e) Name the method to separate:
1. Sugar from sugar solution.
Ans. Evaporation.
2. Alcohol from mixture of alcohol and
water.
Ans. Fractional Distillation.
3. Water from salt solution.
Ans. Distillation.
4. Orange and blue dyes from a black ink.
Ans. Chromatography.
5. Sawdust from a mixture of sawdust and
salt.
Ans. Solvent Extraction.
6. Supended solids in liquids.
Ans. Filtration.
7. Insoluble solids, one having higher
density than that of water.
Ans. Sedimentation.
8. Immiscible liquids.
Ans. Separating funnel.
9. Miscible liquids.
Ans. Fractional Distillation.
10. Soluble solids from liquid.
Ans. Crystallisation.
Q-3 MATCH THE FOLLOWING
Colomn A Column B
1. Chromatography a. Naphthalene
2. Sublimation b. Ethanol and water
3. Evaporation c. Dyes and Pigments
4. Fractional Distillation d. Mercury and water
5. Separating Funnel e. Common Salt from
Sea water.
Ans) 1-c, 2-a, 3-e, 4-b, 5-d.
Q-4 PICK THE ODD ONE OUT. GIVE
SCIENTIFIC REASONS
1. Water-ether, water-kerosene oil, water-
common salt, water-benzene.
Ans. It is heterogeneous mixture rest are
homogenous mixtures.
2. Distillation flask, Funnel, thermometer,
Liebig Condenser.
Ans. It is not used in fractional distillation rest
are the apparatus used in fractional distillation
3. Surface area, Density, temperature,
humidity.
Ans. It is not the factor affectng rate of
evaporation whereas others are.
1. Could distillation be used to separate air
into nitrogen, oxygen, carbon dioxide,
argon and so forth? Explain.
Ans. No, distillation cannot be used.
Fractional Distillation is used to separate the
gases of air.
2. Describe how distillation is different from
evaporation.
Sr No
Evaporation Distillation
1. It is a process of transforming liquid into a gas under the influence of heat.
It involves obtaining gas from liquid by heating and condensing it to obtain liquid.
2. It is a slow process.
It is a fast process.
3. Write two applications of fractional
distillation.
Ans. a) Fractional Distillation is used to
separate mixtures of miscible liquids in the
laboratory.
b) Fractional Distillation is used to separate
gases of the air.
4. What are the advantages of
chromatography?
Ans. a) A very small amount of the substance
is sufficient.
b) Quantitative estimation of the constituents
is possible.
5. What are the factors that affect the rate of
evaporation?
Ans. Following are the factors that affect the
rate of evaporation:
a) Surface area.
b) Temperature.
c) Humidity.
d) Speed of wind.
6. Explain the method used to separate
coconut oil and water.
Ans. –Pour coconut oil and water in the
conical flask.
- Mix both liquids by shaking the conical flask
vigorously.
- Use a clamp to attach the separating funnel
to a retort stand.
- Ensure that the separating funnel is in the
closed position and pour in the mixture of
kerosene oil and water.
- Allow the mixture to settle for a few minutes.
We observe two layers as upper layer and
lower layer.
- Place a beaker under the mouth of the
separating funnel and open the stopcock.
Allow the lower layer of water to run off in
the beaker slowly and coconut oil in another
beaker.
7. What is Liebig condenser? Write the
functions of Liebig condenser.
Ans. Liebig condenser is a long glass tube
having an inlet and outlet for water. During
distillation, cold water from tap is circulated
through the outer tube of condenser. This water
takes away heat from the hot vapour passing
through the inner tube of condenser and causes
its condensation.