Techniques of separation

INTRODUCTIONMost of the natural substances are not

chemically pure. They are either mixed with impurities of other substances or are mixtures of some substances. In order to study the properties of individual substances, we need each component of the mixture in the pure state. Different methods have been used to separate the individual components of a mixture.

Pure SubstancesA pure substance is made up of only

one substance and is not mixed with any other substance .

Purity of a substance can be determined by its melting and boiling points or chromatography .

Impure substances: Mixtures

A mixture is a substance which consists of two or more elements or compounds which are not chemically combined together.

Examples -: milk, air, soil, glass.Mixture are not pure as it contains many particles in it that are

not chemically combined .Two types of mixtures:- Homogeneous and Heterogeneous.It does not have a definite melting or boiling point….

Separation Of MixturesThe method to be used for separating a mixture depends on

the nature of its Constituents.The various processes used to separate constituent of

mixture are : Filtration, Evaporation , Sublimation,Centrifugation

chromatography, Distillation, Fractional distillation, Crystallization…….

By these we can separate the non-volatile component (solute) from

its volatile solvent …

Separation Methods

Magnetic Attraction Magnetic substances from non-magnetic ones

Crystallization Dissolved solids in a solution

Simple Distillation Liquids in a solution

Fractional Distillation Mixture of miscible (dissolved) liquids

Separating Funnel Immiscible (undissolved) liquids

Sublimation Substances that sublime from two substances

Evaporation Solids that cannot decompose when heated in a solution

Separation method

What it separates

Chromatography Compounds in a solution with same properties

Filtration Solids or group of solids and liquids in a mixture

Difference in Properties that enable the Separation Methods to Work

Evaporation State of object (solid and liquid)

Crystallisation State of object (solid and liquid)

Simple Distillation Boiling points Fractional Distillation

Boiling points

Separating Funnel Both are immiscible Sublimation Ability to sublime Magnetic Attraction Magnetism

Separation methods

Differences between objects

Chromatography Solubility with ethanol Filtration Size of particles

FILTRATIONUsed to separate heterogeneous mixtures

composed of solids and liquidsUses a porous barrier to separate the solid from

the liquidLiquid passes through leaving the solid in the

filter paperFiltration differs from adsorption, where it is not

the physical size of particles that causes separation but the effects of surface charge. Some adsorption devices containing activated charcoal and ion exchange resin are commercially called filters, although filtration is not their principal function.

Filtration can be used to separate an insoluble substance from a soluble substance

Evaporation

Evaporation is a type of vaporization of a liquid that occurs only on the surface of a liquid.

The other type of vaporization is boiling, which, instead, occurs on the entire mass of the liquid.

With sufficient heat, the liquid would turn into vapor quickly.

APPLICATIONS:-When clothes are hung on a laundry line, even though the ambient temperature is below the boiling point of water, water evaporates. This is accelerated by factors such as low humidity, heat, and wind..

Separation of mixtures by Evaporation Activity-:

Aim : To obtain coloured component(dye) from its volatile solvent by the method of evaporation.

Materials : A beaker, a watch glass, a burner, water and some blue ink.

Procedure : 1. Fill half a beaker with water.o 2. Cover it with a watch glass, put a few drops of ink on it and heat it.o 3. Evaporation starts from the watch glass. o 4.Continue to heat till you see that there are no further changes on thewatch glass. Observation: The water gets evaporated from the watch glass and residue is left . Therefore it is not a single substance but a mixture of dye in water.

Evaporation of sea water to produce salt

SEPERATING FUNNELA separating funnel can be used to

separate two liquids which are immiscible

The Separation of two immiscible liquids by a separating funnel is based on the difference in their densities…..

PRINCIPLE INVOLVED :- When a mixture of two

immiscible liquids is allowed to stand they separate out in two separate layers depending upon their densities.

APPLICATIONThe mixture is put into a separating funnel, shaken and allowed to settle. The oil and water from two separate layer. The liquid with higher density, in this case water forms the lower layer. Remove the stopper and open the tap after standing. The water runs out through the tap. The oil remains in the funnel and can be run out into another beaker.

Separation of mixtures by separating funnelActivity:- Aim: To separate kerosene oil from water using a

separating funnel… Procedure: 1. Pour the mixture of oil and water in a separating

funnel. Do not disturb it till layer of oil and water is formed. Opening the stop clock of the funnel, pour the lower level of water

carefully. Close the stop clock as the soil reaches the it and is left behind in

the separating funnel. Conclusion: We conclude that immiscible liquids can be separated

with the help of separating funnel…

Sublimation Most of the solids substances when heated changes into

liquid and finally into Vapours (or gas).This vapour on cooling ,first forms liquid and finally the

solids.On the other hand there are some solid substances like

ammonium chloride which directly changes into vapours on heating and the vapours gives back solid substance on cooling.

The change of a solid directly into a vapour on heating and of the vapuor into solids on cooling is known as Sublimation ….

Principle Involved in SUBLIMATION On heating some solid substances

change from solid to the vapor state directly without passing through the liquid state. Such substances are known as sublimate. Sublimation is used to separate sublimable volatile compounds from non-sublimable impurities/compounds.

Separation of mixtures by Sublimation ACT IV ITY: - Aim:-To separate a mixture of salt and ammonium chloride.. Procedure:- 1 The mixture of ammonium chloride and salt is

taken in a china dish and covered with an inverted funnel. A loose cotton plug is put in the stem of the funnel to

prevent the ammonium chloride vapours from escaping in the atmosphere.

On heating ammonium chloride changes into vapours. These vapours condense on the cold inner side of the funnel to

give back solid ammonium chloride.. Sodium Chloride does not vaporise on heating so it remains behind in the china dish…. CONCLUSION : Solids directly changes into vapor state without going through liquid state due to SUBLIMATION

CENTRIFUGATIONCentrifuges rotate containers of liquids to separate suspended materials with different densities.

Centrifuges separate different components of human blood or milk and to clarify solutions. A high speed separator can rotate at great speed to separate fat (cream) from milk.

The spin drier in washing machines is a type of centrifuge that throws out the liquid by the "centrifugal force" of the rotation.

Centrifugation

Distillation Distillation is the process of heating a liquid to form vapour and

then cooling the vapour to get back the liquid… Liquids

The liquid obtained by condensing the vapours is called distillate. Process in which the components of a substance or liquid mixture are separated by heating it to a certain temperature and condensing the Resulting Vapors…..

Vapours(or gas)Heating

Cooling

FRACTIONAL

DISTILLATION The process by which a mixture of two or more miscible liquids are separated is called fractional distillation PRINCIPLE

INVOLVED :- If the difference in boiling points of liquids is not much simple distillation cannot be used. In fractional distillation vapours of liquid with lower boiling point condense first, the vapour rising up become richer in more volatile component and can be separated from less volatile component.

Separation of mixtures by Distillation Activity:-

Aim: To separate alcohol and water from their solution.Procedure: 1 Take the solution in a distillational flask fitted

with fractionating column. Fit it with a thermometer.Arrange it like the that done in the picture..Heat the mixture slowly keeping a close watch at the

thermometer reading.The alcohol evaporates, condenses in the condenser and can be collected from the condenser outlet.Water is left behind in the distillation flask…..Observation: By this method alcohol and water are separated…

PROCEDURE Take a mixture of two liquids chloroform and benzene of which

chloroform is more volatile than benzene. When such a liquid mixture is heated, the temperature rises slowly and the mixture starts boiling. The vapors formed mainly consist of the more volatile liquid, i.e., chloroform with little of the less volatile liquid, .i.e., benzene. As these vapors travel up in fractionating column , the vapours of less volatile liquid condense more readily than those of the more volatile liquid. Therefore, the vapours rising above become richer in chloroform and the liquid flowing down becomes richer in benzene. This process of distillation is repeated in every point of fractionating column. As a result of series of successive distillation, by the time vapours reach the top of the column and escape into the condenser, they consist entirely of the more volatile component. It is collected in a flask When the more volatile component has completely distilled over, the temperature will again start rising and when the boiling point of less volatile is reached, benzene starts distilling which is collected in another flask. In this way, separation of two miscible liquids whose boiling points differ by less than 25k can be achieved.

CONCLUSION Separation of two miscible liquids whose boiling points differ by less than 25K can be achieved by the process of fractional distillation.

DECANTATIONDecanting is done to

separate particulates from a liquid by allowing the solids to settle to the bottom of the mixture and pouring off the particle-free part of the liquid. Another method is to allow two immiscible liquids to separate and the lighter liquid is poured off.

A MAGNET Can be used to separate a magnetic

substance from a non-magnetic substanceMagnets are used in the re-cycling industry to

separate ferrous and non ferrous metals.

SIEVING a porous material is used to

separate particles of different sizes.

method is most commonly used to effect gross separations, as of liquids from suspended crystals or other solids.

to accelerate filtration, pressure usually is applied.

a series of sieves is stacked, with the screen of largest hole size at the top

ChromatographyThe process of separation of component of a mixture is known as

Chromatography .Chromatography is the technique used for the separation of those

solutes that dissolve in the same solvent…..Separates components of a mixture based on ability of each

component to be drawn across the surface of another materialMixture is usually liquid and is usually drawn across chromatography

paperSeparation occurs because various components travel at different

ratesComponents with strongest attraction for paper travel the slowest

The substances when present in well defined geometrical shapes Are called crystals. These are formed when a hot saturates solution of salt is allowed to cool slowly and undisturbed.

The process of preparation of crystals is termed as crystallization…..

Separation technique that results in the formation of pure solid particles from a solution containing the dissolved substance

As one substance evaporates, the dissolved substance comes out of solution and collects as crystals

Produces highly pure solids

Rocky candy is an example of this

MADE BY :-Yash – 43 Yash Lakra – 45Harsh Phogat – 15Tushar Chauhan - 40

CLASS – IXth - C

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