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.