SSS 2: SEPARATION TECHNIQUES
Separation techniques are physical methods used for the separation of the constituents of a mixture. A mixture contains two or more substances that are physically combined.
Types of Separation techniques
The types of separation techniques are:
1. Sieving
2. Magnetic Separation
3. Sublimation
4. Decantation
5. Filtration
6. Centrifugation
7. Evaporation
8. Crystallization
9. Fractional crystallization
10. Precipitation
11. Distillation
12. Fractional distillation
13. Separating funnel method
14. Chromatography
SIEVING
This is used to separate solid particles of different sizes. Particles smaller than the size of the sieve (mesh) pass through leaving behind particles of larger sizes. It is used in gold and diamond mines and garri industries.
MAGNETIC SEPARATION
Magnetic Separation involves the use of magnet to separate magnetic substance from non-magnetic particles. This method is used in the steel industry and to remove magnetic impurities from tin ore
SUBLIMATION
Sublimation is a process whereby solid changes directly to gas without passing through the liquid state. Sublimation is used to separate solids which sublime from other solids.
I. Iodine
II. Ammonium chloride
These substances can be separated from other solids by sublimation and can also be purified industrially by the same method.
SEPARATION OF INSOLUBLE SOLIDS FROM A SOLUTION
The methods for separating insoluble solids from a liquid are:
I. Decantation
II. Filtration
III. Centrifugation
DECANTATION
Decantation is a separation technique used to separate a mixture containing an insoluble solid from a liquid. This is done when the mixture is allowed to settle down with the upper clear liquid carefully poured or decanted into a clean container thereby leaving the lower solid in the container originally containing the mixture. This is a quick but inaccurate method of separating the components of a mixture.
FILTRATION
This method is used to separate insoluble solids from liquids using a filter. For example, a mixture of chalk particles in water can be separated using a filtration technique.
1. Filtration is used in the purification of pipe-borne water before being supplied to the consumers
2. Filtration is used in industries such as water purification plants and breweries to remove solid particles from liquid.
CENTRIFUGATION
Centrifugation is a machine which can spin test tubes containing suspension at high speed. The spinning causes heavier solid particles in the suspension to be thrown to the bottom of the test-tubes. They settle there while the clear liquid separate out as an upper layer which can easily be decanted. Centrifugation is often used when there is a small amount of material to be separated.
SEPARATION OF SOLUBLE SOLIDS FROM A SOLUTION
The methods for separating soluble solids from a solution are:
I. Evaporation to dryness
II. Crystallization
III. Fractional Crystallization
IV. Precipitation
EVAPORATION TO DRYNESS
Evaporation is used to recover soluble solute from its solution. In this process, the solvent is usually sacrificed. This method is not suitable for salts that are easily destroyed by heating.
Solution → Solute + Solvent
For example, salt can be separated from salt solution by evaporation.
CRYSTALLIZATION
Crystallization is used to separate salts which decompose easily on heating from their solution. The salt crystals obtained in this way are pure and usually contain water of crystallization. Examples of salt with water of crystallization are:
I. Copper (II) tetraoxosulphate (VI) pentahydrate, CuSO4.5H2O
II. Copper (II) trioxonitrate (V) trihydrate,
Cu(NO3)2.3H2O
3. Iron(II) tetraoxosulphate (VI) heptahydrate, FeSO4.7H2O
The salt solution is first heated to evaporate some of the Solvent. The solution becomes saturated. When the saturated solution is cooled, crystals of the Solute begin to form.
Crystallization is used in industries where purity of the product is important.
Uses of crystallization
I. Crystallization is used in manufacturing of drugs
II. It is used in manufacturing of sugar
FRACTIONAL CRYSTALLIZATION
Fractional Crystallization is used to separate two or more solid solutes which are present in the same solution in roughly equal amount. The solubilities of different solutes in the given solvent must differ at different temperature.
PRECIPITATION
Precipitation is a separation technique that uses the difference in solubility of a component in different solvents or under different conditions to form a solid, insoluble compound (the precipitate) from a solution. Iron(II) tetraoxosulphate,FeSO4, for example can dissolve in water but not in ethanol. If ethanol (which is miscible with water) is added to a solution of FeSO4, in water, the FeSO4 will be precipitated out of the solution and can then be separated by filtration.
DISTILLATION
Distillation is a separation technique that uses differences in boiling points to separate a liquid mixture. The process involves heating the liquid to vaporize the component with the lower boiling point, then cooling the vapor to condense it back into a separate liquid, called the distillate.
Uses of Distillation
Distillation is used in gin and water distilleries for the manufacturing of gin and water respectively. FRACTIONAL DISTILLATION
Fractional distillation is a separation technique that separates different components from a miscible liquid mixture based on their different boiling points. Fractionating column is used to achieve repeated vaporization and condensation. In the laboratory, the apparatus for fractional distillation is the same as the apparatus for simple Distillation except that a fractionating column is introduced between the distillation flask and the condenser.
1. Fractional distillation is used in separating crude oil (Petroleum)
2. It is used in the purification of reagents and products
SEPARATING FUNNEL METHOD
Separating funnel method is used to separate immiscible liquids e g. mixture of petrol and water or kerosene and water.
This method depends on the densities of the two liquids involved. The less dense will be on top and the denser below.
CHROMATOGRAPHY
Chromatography is a separation technique used for the separation of mixtures into their individual components based on their movement through a stationary phase and a mobile phase.
A mixture is dissolved in a mobile phase, which is a liquid or gas that flows through a stationary phase, which is a solid or liquid e.g. the chromatography separation of ink is based on the ability of the components to move at different speeds in the column.
In chromatography, there are two phases:
I. Stationary phase in which the solutes are ADSORBED,
II. Moving phase which dissolves the solutes and carries them.
Types of Chromatography
The different types of chromatography are:
1. Paper chromatography: It uses filter paper as stationary phase and a solvent as mobile phase.
2. Gas Chromatography: It uses gas as the mobile phase
3. Thin Layer Chromatography: It uses glass plates coated with silica or alumina.
4. Column Chromatography: It uses a column packed with adsorbent material.
5. Liquid Chromatography: It uses liquid as mobile phase through a solid stationary phase.
I. The ADSORPTION of the Solutes by the paper( a stationary phase)
II. The DISSOLUTION of the solutes in the solvent (a moving phase)
Applications or uses of Chromatography
Chromatography is used for:
1. Identifying substances in a mixture.
2. Purifying chemical compounds.
3. Testing for drugs and toxins in blood or urine.
4. Detecting pollutants in water or air.
5. Separating plant pigments and dyes.
6. Food analysis (e.g., detecting additives)
TEST FOR PURITY
The purity of a substance can be easily checked by determining their:
I. Melting point ( for solids)
II. Boiling points (for liquids)
III. A pure substance gives one spot on a paper chromatography.
Assignment
(a) What difference in physical properties enable the separation of mixtures by:
(i) simple distillation,
(ii) paper chromatography;
(iii) fractional distillation.
Comments
Post a Comment