SEPARATION OF MIXTURES  
Many mixtures need to be separated in order to obtain the useful substances. This is  
because mixtures contain useful substances mixed with unwanted materials  
(impurities). The method used to separate mixture depends on the components of  
the mixture and their properties. Such properties are density, solubility, size,  
magnetic properties  
,
sublimation  
,
boiling and melting point.  
METHODS OF SEPARATING MIXTURE  
The following are methods used to separate mixtures  
(a) Decantation  
(d) Distillation  
(b) Filtration  
(c) Evaporation  
(f) Sublimation  
(i) Winnowing  
(k) Centrifugation  
(n) Sieving  
(e) Layer separation  
(h) Solvent extraction  
(g) Chromatography  
(j) Magnetic separation (Magnetization)  
(l) Crystallization (m) Hand picking  
Principle for separation of mixtures are applied in fields like mining, agriculture and  
other large-scale industries. For example, decantation, filtration and sedimentation  
are widely used in purification of water for public consumption.  
1. DECANTATION  
Decantation is the process of separating a heterogeneous mixture of a liquid and  
solid by pouring out the liquid only and leaving the solid at the bottom of the  
container.  
The process of some components of mixture settling at the bottom is called  
sedimentation.  
Note: Sedimentation works when the solid component is made up of large particles.  
If the particles are small, the process may not give a good separation.  
Decantation can be used to separate  
(i) Water from muddy water, water from mixture of water and sand.  
(ii) Rice and water, beans and water.  
Figure: Decantation of muddy water  
Separation application of decantation  
(i) Water treatment systems  
(ii) Separate of components of blood  
2. FILTRATION  
Filtration is the method used to separate a heterogeneous mixture of a solid and a  
liquid. During filtration, solids are separated from liquid by using porous filter such as  
filter paper.  
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Solid that remains on a filter is called residue  
Liquid that pass-through filter is called filtrate  
Separation application of filtration  
(i) Purification of water  
(ii) Extraction of juice from fruit  
(iii) Extraction of cream from milk  
3. EVAPORATION  
Evaporation is a method of separating a solute from a liquid solution through  
heating. During evaporation solvent is converted from liquid to gas and solute  
remains as residue. Example: Mixture of water (solvent) and salt (solute), when  
heated water evaporates leaving sand behind as residue.  
Other examples of mixtures which can be separated by evaporation are  
sea water and sugar solution.  
Separation application of evaporation  
Evaporation is used in extraction of common salt from sea water.  
4. DISTILLATION  
Distillation is a process of separating the components of a mixture by heating a  
liquid to a suitable temperature until it forms vapour (gas) and then cooling it back to  
liquid.  
In distillation process cooling process is done in the lie big condenser. The liquid  
from a cooled vapour is called distillate.  
Types of distillation  
There are two types of distillation: (i) Simple distillation (ii) Fractional distillation  
(i) Simple distillation  
Simple distillation is the process of obtaining single liquid from a suspension or a  
solution by boiling the mixture to form vapour and then condensing vapour back to a  
liquid.  
Simple distillation can be used to separate;  
(i) Distilling water from muddy water  
(ii) Distilling water from salt water  
Note: Simple distillation is used to purify water which is used in schools, hospitals,  
industries.  
Exercise  
1. What role does the Liebig condenser play in simple distillation?  
2. If you do not have a Liebig condenser, what will you use to carry out this simple  
distillation?  
(ii) Fractional distillation  
Fractional distillation is a method of separating homogeneous mixture of two or  
more liquids which have different boiling points by means of a fractionating column.  
A mixture of water and ethanol is a good example in which ethanol boils at 78 oC and  
water boils at 100 oC. Ethanol boils at 78 oC and is distilled first leaving behind water  
which will boil at 100 oC.  
The fractionating column separates the two liquids, the one with a lower boiling point  
moves to the upper part of the column and distils over.  
Note:  
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During distillation, the liquid with the lower boiling point is collected first as a  
distillate.  
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Each component collected is known as a fraction.  
Fractional distillation can be used in;  
(i) Separation and purification of ethanol from mixture of ethanol and water  
(ii) Separation of petroleum into its fractions such as petro, diesel, kerosene  
Application of distillation (All types of distillation)  
(i) Purification of water  
(ii) Manufacture of alcohol  
(iii) Separation of components of crude oil (petroleum) Example; petrol, diesel  
5. LAYER SEPARATION  
Layer separation is the process of separating immiscible liquids using a separating  
funnel.  
Immiscible liquids are liquids which do not mix up and form distinct layers when put  
together. Liquid with high density settles at the bottom while the liquid with low  
density remains at the top of the separating funnel.  
Examples of mixtures which can be separated by layer separation are:  
(i) Kerosene and water  
(ii) Cooking oil and water  
Figure: Separation of kerosene and water  
Separation application of layer separation  
Recovery of liquids from contaminations.  
6. SUBLIMATION  
Sublimation is a process by which solid changes directly to gas on heating without  
passing into liquid state.  
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Solid that forms after the vapour cools is called sublimate.  
Sublimation is used to separate mixture where one component sublimes.  
Iodine and ammonium chloride are few compounds can sublime.  
The reverse process of change from vapour to solid on cooling is called deposition.  
Sublimation can be used to  
(i) Separate iodine from mixture of sand and iodine  
(ii) Separate ammonium chloride from mixture of salt and ammonium chloride  
Separation application of sublimation is purification of substance.  
7. CHROMATOGRAPHY  
Chromatography is the process of separating mixtures using a moving solvent on a  
material that absorbs the solvent. It is a method which is used to separate coloured  
mixtures.  
In chromatography a mixture is firstly dissolved in a fluid called mobile phase. This  
fluid carries the mixture through a stationary phase.  
The moving solvent is called mobile phase and may be a gas or liquid  
The mobile phase flows through the stationary phase and caries the components of  
the mixture with it.  
The immobile substance is called stationary phase and is a material that absorbs  
solvent which can be either solid or liquid supported on a solid.  
Substance separated is called analyte.