SEPARATION TECHNIQUES
A mixture contains two or more different substances physically combined together.
Each constituent in a particular mixture still retains its individual properties, i.e, the properties of each substance in a particular mixture is still the same as when it wasn't mixed up with any other Substance.
Due to the physical properties of substances in a mixture,a mixture can be separated into its components by physical technques or methods,Using the physical properties of its constituents.
TYPES OF SEPARATION TECHNIQUES.
1) SIEVING:
Used to separate solid particles of different sizes.
A material called mesh,is used to separate the smaller particles from the bigger ones.Industries such as mining and garri industries,make use of this method.
2) MAGNETIC SEPARATION
This is used to separate magnetic substances from non-magnetic ones.
It is used in steel industry and to remove magnetic impurities from tin-ore.3) SUBLIMATION.
Some solids like ammonium chloride and iodine,when heated,sublimes, i.e,they change directly from solid to gaseous state, without Changing first to liquid.These types of solids can be separated from other solids of by sublimation because of their sublimation property and are purified industrially by the same method.
Sublimation
4. DECANTATION.
This is used to separate a mixture of a liquid and solid particles that cannot mix together (They seperate into two distinct layers on standing).
For example,garri and water. The liquid is poured out or decanted to separate it from the garri but this method is inaccurate in seperating mixtures.
Decantation
5) FILTRATION
This is used to separate insoluble particles ( particles that cannot dissolve in liquids) from liquids.
It is used in industries such as breweries and in purifying water.A pourous material is usually used.
Seperation by filtration.
CENTRIFUGATION.
This is used to separate the components of a suspension. A mach- ine called centrifuge is used to spin test tubes containing suspensions at high speeds which causes the heavier solid particles in the suspension to go to the buttom of the test tube, while the liquid in the test tubes seperates as an upper layer which can then be poured out.Centrifugation is used for only a small amount of mixture. For example, in hospitals,blood cells are seperated from the plasma by centrifugation.
A Centrifuge.
7) FLOATATION.
Used in seperating metals from their ores.
8) EVAPORATION TO DRYNESS.
This is used to recover a solid(the solute) from a solution. In this case,the solvent is lost. This is done using a heated water-bath.
( Solute + solvent =Solution.)
The process of obtaining Salt from its solution by evaporation.
Evaporation is the process by which liquid changes to vapour.
It takes place at all temperatures.
This process is used in salt-making industries.
9)CRYSTALLIZATION
This is used in seperating salts that decompose easily when heated,from their solutions.
The salt produced this way are pure and usually contain water of crystallization.It involves heating the salt solution first to make it saturated.When the saturated salt solution cools off,the salt crystals begin to form.
Crystallization.
10) Fractional crystallization.
When there are two or more solid solute particles in a solution in roughly equal amount,fractional crystallization is used to separate the needed substance (s) from the solution, using the solubility of the different solutes in the solvent.The solubility of these solutes must be different, i.e,the temperature at which a solute dissolves must be different from the one at which the other solutes dissolves in the given solvent.
At a particular temperature, crystals of the relevant solute comes out of the solution(after they had dissolved), leaving the others which are still within their limits of solubility.
11) Precipitation.
When we have a solid,which has different solubilities (rate at which it dissolves),in two different liquids that can mix together,such as water and ethanol.
Precipitation process is used to separate the solid from the liquids.The solid usually dissolve in one of the liquids.
Forexample,Iron(II)tetraoxosulphate(VI) is soluble (dissolves) in water but not in ethanol (which can mix with water).
If ethanol is added to a solution of iron(II) tetraoxosulphate (VI) in water,the solid will be precipitated out of the solution and can be seperated by filtering the liquids from it.
12) Distillation.
This is used to recover a solvent from a solution.
When we have two liquids in a solution,and they can mix together,and boils at widely different temperatures, distillation can also be used to recover the liquid needed or solvent from the solution.The solution is heated in a flask to vapourize the liquid or solvent (called
EVAPORATION). The vapour of the solvent or liquid that boils faster(using a thermometer to detect the boiling point) in order to vapourize travels alonga condenser called the liebig condenser, which is cooled by the circulating water in the outer jacket of the condenser.
This cooling effect changes the vapour back to liquid,called the distillate,which is then collected in a receiver.
The solute and other impurities are left behind in the flask.
Distillation.
Distillation is used in gin and water distilleries for the production of gin and distilled water respectively.13) Fractional Distillation.
This is used to separate a mixture of two or more miscible liquids that has little difference in their boiling points. i.e,the boiling point of one liquid is not far from that of the other in the mixture.
The fractions of liquids distil over in ascending order of their boiling points, starting with the liquid with the lowest boiling point and for this process to be efficient,the difference in boiling point must be more than 10°C.
The apparatus used are a fractionating column, liebig condenser,retort stand,tripod stand,round and flat buttom flasks,and thermometer.
Fractional Distillation.
Crude oil is seperated into it's fractions such as petrol,kerosine, Diesel,bitumen,etc,by fractional distillation.
14) seperating funnel method.
This is used to separate two or more liquids that cannot mix together.The liquids seperates into two or more distinct layers when added together.
A seperating funnel is used in which the denser liquid layer below is tapped off,while the less dense liquid layer below remains in the funnel.
Seperating funnel method
15) chromatography.
This is used to separate a mixture such as ink,dye,and amino-acids,etc, into its components through a porous,absorbent medium like paper .
There are various methods of chromatography such as:
a) Ascending Paper chromatograpy
b) Gas Chromatography
c)Thin-layer chromatography
Paper chromatography
It is also used to check the components of chemical products.
A substance can be purified using the appropriate seperation techniques.
TESTS FOR PURITY
The following are the criteria to determine the purity of a substance:1) The melting(for a solid) or boiling point (for a liquid) of a substance is always constant at a specific temperature,if impurities are present in the substance,the specific temperature is affected,it changes.
If the temperature wasn't affected,then the substance is probably pure.
Impurities increases the boiling point of a substance while it decreases the melting point of a substance. That is,if a liquid or solid is not pure,it will boil at a range of temperatures above or higher than the boiling point of the liquid or melt at a temperature below or lower than the melting point of the solid.
This is applied in countries with low temperature conditions below 0°C to melt the ice on their roads faster by sprinkling salt which serves as an impurity in the ice,hence lowering its melting point so it could melt faster.
2) On a paper chromatogram,a pure substance will give only one stop.
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