Many of the material around us are mixtures. These mixtures have two or more than two substances (or constituents) mixed in them. It may not be possible to use a mixture as such in homes and in industries. We may require only one or two separate constituents of a mixture for our use. So, it is necessary separating the components of a mixture to make them useful in our daily life.
The various constituents of a mixture have different physical properties such as density, solubility, size of particles, behaviour towards a magnet, volatility, boiling points etc. This difference in physical properties of constituents is used to separate them from a mixture. The method to be used for separating a mixture depends on the nature of its constituents. Different mixtures are separated by using different physical processes.
The various physical processes which are commonly used to separate the constituents of mixtures are: Sublimation, Magnet, Solvents, Filtration, Centrifugation, Evaporation, Crystallisation, Chromatography, Distillation, Fractional Distillation and separating funnel.
There are following three cases of mixtures which we need to learn to separate:-
- Mixture of two solids
- Mixture of a solid and a liquid
- Mixture of two liquids
Separation of a mixture of two solids
All the mixtures containing two solid substances can be separated by one of the following methods:
- By using a suitable solvent
- By process of sublimation
- By using a magnet
Separation using a suitable solvent –
In some cases, one constituent of a mixture is soluble in a particular liquid solvent whereas the other constituent is insoluble in it. This difference in solubilities of constituents of a mixture can be used to separate them. For example – a mixture of sugar and sand can be separated by using water as solvent, a mixture of sulphur and sand can be separated by using carbon disulphide as a solvent.
Separation by sublimation –
Changing of a solid directly into vapours on heating, and of vapours into solid on cooling is called sublimation. The process of sublimation is used to separate those substances from mixture which sublime on heating. Some substances that undergo sublimation are – ammonium chloride, iodine, camphor, naphthalene and anthracene can be separated from a mixture by sublimation.
Separation by using a magnet –
Iron is attracted by a magnet. This property of iron is used to separate it from a mixture. So, if a mixture contains iron as one of the constituents, it can be separated by using a magnet. For example – to separate a mixture of iron filings and sulphur powder, a horse-shoe type magnet is moved on the surface of the mixture. In factories, scrap iron is separated from the heap of waste materials by using big electromagnets fitted to a crane.
Separation of a mixture of a solid and a liquid
All the mixtures containing a solid and a liquid can be separated by one of the following methods:-
- By filtration
- By centrifugation
- By evaporation
- By crystallisation
- By chromatography
- By distillation
Separation by filtration –
Filtration is used to separate insoluble substances from a liquid. The mixture of insoluble solid and the liquid is passed through the filter paper cone fitted inside a funnel. The liquid passes through the filter paper and collects in the beaker kept below the funnel. The solid does not pass through filter paper and is left behind as the residue.It is used to separate mixture of chalk and water, sand and water, tea leaves from tea
Separation by centrifugation –
Centrifugation is a method to separate the suspended particles of a substance from a liquid in which the mixture is rotated at a high speed in a centrifuge. In this process the mixture is taken in a test tube which is placed in a centrifuge machine and rotated rapidly for some time. As they rotate the force acting on heavy particles bring them down, the liquid remains at the top. It is used to separate clay particles suspended in water, cream from milk.
Separation by evaporation –
Evaporation is used to separate a solid substance that has dissolved in water (or any other liquid). The use of process of evaporation for separating a mixture is based on the fact that liquids vaporise easily whereas solids do not vaporise easily. The common salt dissolved in water can be separated by evaporation. The coloured component in ink used in fountain pens can be obtained from evaporation.
Separation by crystallisation –
The process of cooling a hot, concentrated solution of a substance to obtain crystals is called crystallisation. This is done as follows: the impure solid substance is dissolved in minimum amount of water to make a solution and filtered. It is heated gently on a water bath till a concentrated solution is obtained. We stop heating and allow it to cool slowly. The crystals of pure solid are formed, impurities remain dissolved in solution. Separate the crystals of pure solid by filtration. Pure copper sulphate can be obtained from impure sample by crystallisation.
Separation by chromatography –
Chromatography is a technique used to separate two or more dissolved solids that are present in a solution in very small quantities. Simplest form of chromatography is paper chromatography. It is based on the fact that though two or more substances are soluble in the same solvent but their solubilities may be different. It can be used to separate the dyes present in black ink.
Separation by distillation –
Distillation is the process of heating a liquid to form vapour, and then cooling the vapour to get back the liquid. We can obtain salt from salt-water mixture by evaporation but water cannot be recovered, it is lost in the air. In order to recover both, salt as well as water, from a salt-water mixture.
Separation of a mixture of two or more liquids
All the mixtures containing two or more liquids can be separated by one of the following methods:
- By the process of fractional distillation
- By using a separating funnel
Before discussing these, we need to know about miscible and immiscible liquids. Those liquids which mix together in all proportions and form a single layer when put in container are called miscible liquids. Those liquids which do not mix together and form separate layers when put in container are called immiscible liquids.
Separation by fractional distillation –
Fractional distillation is the process of separating two or more miscible liquids by distillation, the distillate being collected in fractions boiling at different temperatures. The separation of two liquids by fractional distillation depends on the difference in their boiling points. It is carried out in a fractionating column. It is used to separate a mixture of alcohol and water.
Separation by separating funnel –
A mixture of two immiscible liquids can be separated by using a separating funnel. The separation of two immiscible liquids by a separating funnel depends on the difference in their densities. A separating funnel is a special type of funnel which has a stop cock in its stem to allow the flow of liquid from it, or to stop the flow of liquid from it. A mixture of water and kerosene can be separated by using a separating funnel.
Questions related to Separating the Components of a Mixture from NCERT textbook –Page 24
How will you separate a mixture containing kerosene and petrol (difference in their boiling points is more than 25˚C), which are miscible with each other?
If the difference in the boiling points of two miscible liquids is 25˚C or more, their mixture can be separated by the process of simple distillation. In this case, the difference in the boiling points of two miscible liquids, kerosene and petrol, is 25˚C, therefore, a mixture containing kerosene and petrol can be separated by simple distillation.
This can be done as follows:
- The mixture of kerosene and petrol is taken in a distillation flask fitted with a thermometer and a water condenser.
- On heating the distillation flask with a burner, the petrol having lower boiling point distils over first and collected in a suitable container.
- Kerosene having higher boiling point distils over later and collected in another container.
Name the technique to separate:
- Butter from curd
- Salt from sea-water
- Camphor from salt
What type of mixtures are separated by the technique of crystallisation?
The mixtures containing solids in which impurities may be either ‘less soluble’ in the solvent or ‘more soluble’ in the solvent than the solids, are separated by the technique of crystallisation. For example – the impurities present in impure copper sulphate, common salt and alum etc. can be separated by the technique of crystallisation to obtain the respective pure substances.
Questions related to Separating the Components of a Mixture from NCERT textbook – Page 28, 29 and 30
Which separation technique will you apply for the separation of the following?
- Sodium chloride from its solution in water
- Ammonium chloride from a mixture containing sodium chloride and ammonium chloride
- Small pieces of metal in the engine oil of a car
- Different pigments from an extract of flower petals
- Butter from curd
- Oil from water
- Tea leaves from tea
- Iron pins from sand
- Wheat grains from husk
- Fine mud particles suspended in water
- Separating funnel
- Magnetic separation (by using a magnet)
- Loading (by using alum)
There may be many substances present around us and we need to separate them to use them individually or to remove harmful substances from it. Separating the components of a mixture can be carried out in a variety of different ways – filtration, distillation, using magnet, using separating funnel, chromatography etc.