We already know that most natural substances are not chemically pure. In fact, they are a mixture of two or more pure substances which are not chemically combined but are physically mixed in any random proportion. Is it possible to separate the constituent components of a mixture? Yes�it is. A number of different methods are applied for separating the components of different kinds of mixtures.

 

The components of a heterogeneous mixture can be separated by simple physical methods such as:
� Hand-picking
� Sieving
� Filtration, and�
� Using Magnet etc

 

However, sometimes the components of a mixture cannot be separated by simple methods. In such cases, some special techniques are employed. Some important separating methods are:

 

• Evaporation
• Centrifugation
• Using Separating Funnel
• Sublimation
• Chromatography
• Distillation
• Crystallization

 

Distillation

 

We know that different methods are used for the separation of different kinds of mixtures. But do you know how a mixture of two miscible liquids is separated? Well�such a mixture can be separated by a method called Distillation. Distillation is the process of separating miscible components of a mixture that do not decompose upon boiling and have sufficient differences in their boiling points. The process involves heating the liquid until boiling and then capturing and cooling the resultant vapors.

 

The separation of liquids is usually achieved at their respective boiling points. The more volatile component vapourises at its boiling point and then condenses in the condenser while the other component is left behind in the distillation flask. Thus the separation of the mixture is achieved.

 

Can you separate a mixture of acetone and water? Yes�.it can be achieved by distillation. Let us have a look at the procedure of separation using the distillation method.

 

� Firstly, take the mixture in a distillation flask fitted with a thermometer.
� Now observe carefully how the apparatus is arranged.
� Then heat the mixture slowly keeping a close watch on the thermometer.
� See the acetone vaporizing and then condensing in the condenser. This acetone can now be collected from the condenser outlet.
� On the other hand, the water is left behind in the distillation flask.

 

Do you know there are several important applications of distillation? Let us discuss a few important ones.

 

� Distillation is employed in food processing to produce distilled beverages.
� Large-scale industrial distillation is widely used in petroleum refineries, petrochemical, and natural gas processing plants.
� Production of essential oils and herbal distillate is carried out by steam distillation.
� In addition to these applications, distillation is also used to separate the mixture of ether and toluene, and� the mixture of hexane and toluene.

 

Crystallization

 

We have learned many different types of methods for the separation of different types of mixtures. Can any of the methods which we have already learned be used to obtain pure copper sulfate from an impure sample?

No, In fact, to obtain pure copper sulfate from an impure sample, we use another method of separation known as Crystallization. Crystals are the purest form of a substance having a definite geometrical shape, and the process that separates a pure solid from a solution in the form of its crystals is known as crystallization.

It is one of the most commonly used techniques for the purification of inorganic and organic solids. In fact, when a crystal is formed it tends to exclude the impurities which remain in the solution.

 

Let us understand the process of crystallization by purifying an impure sample of copper sulfate.

 

� First of all, take approximately 5 grams of impure copper sulfate and dissolve it in the minimum amount of water.
� Then filter it to remove the insoluble impurities and transfer the filtrate to a china dish.
� Now heat the filtrate so that the water evaporates and a saturated solution is obtained.
� Finally cover the solution and leave it undisturbed, thus allowing it to cool for a few hours.
� Eventually, the crystals of pure copper sulfate separate out.

 

Do you find crystallization and evaporation similar in any way? Actually, crystallization is better and has several advantages over evaporation. Let us discuss these.

 

� Crystallization is a favored technique to purify substances like sugar that decompose or may get charred when heated to dryness.
� Also, some impurities may remain dissolved in the solution even after filtration. On evaporation, these may contaminate the solid.

 

After learning about crystallization and its procedure, let us discuss some of its important applications.

 

� Purification of salt obtained from seawater is carried out by the method of crystallization.
� This method is also employed for the separation of pure alum crystals from the impure sample.

 

Besides, crystallization has several other important applications and is also used for the purification of many organic and inorganic salts.

 

Chromatography

 

We have already learned about some techniques for the separation of components of a mixture. Let us now learn about another important separation technique- chromatography. Chromatography is used for the separation of a mixture where two or more substances are soluble in the same solvent, but exhibit different degrees of solubility in that solvent.

Can you tell if the dye in black ink is a single color or not? Well�.you can easily find this out by chromatography. Let us now understand the principle and the procedure of this technique one by one. Let�s move on to the principle of chromatography first.

 

When a solvent is allowed to pass over a mixture of substances soluble in the same solvent, the substance that is most soluble moves fastest and thus gets separated from the other components. Now, let�s see how separation can be achieved using chromatography.

On carefully observing the procedure you can also find out how chromatography can be used to determine whether the dye in black ink is a single color or not.

 

• First of all, take a thin strip of filter paper and then draw a line 3 cm above the lower edge of the paper using a pencil.
• Put a small drop of water-soluble ink from a fountain pen in the middle of this line.
• Then lower the filter paper into a glass jar containing water so that the drop of ink on the paper is just above the water level.
• Leave it undisturbed and watch carefully the water rising up on the filter paper.

 

So what do you observe? Do you see spots of different colors on the filter paper? Yes. This is because when the water rises on the filter paper, it takes along the dye particles with it. And depending on their solubility in water, the dye particles get separated. The dye in black ink is not a single color but a mixture of two or more colors.

 

Let us now discuss some useful applications of chromatography.

 

• Chromatography is used to separate colors in a dye.
• This technique is also useful to separate pigments from natural colors.
• Separating drugs from blood is another important application of this technique.

 

Centrifugation

 

We already know how evaporation is used for separating the components of a mixture. Let us learn some other techniques now. Centrifugation is another important technique for separating a mixture into its constituents.

Let us see an application for a better understanding of this technique. Do you know how the cream is separated from milk? Yes� by centrifugation. Do you know the principle on which this technique works? When a mixture is spun rapidly, the lighter particles stay on the surface while the heavier and denser particles settle down at the bottom.

This principle helps in the separation of particles using centrifugation. Though most liquid mixtures can be separated by the filtration method, yet there are some liquid mixtures in which the solid particles are very small and thus can easily pass through the filter paper. It is not possible to separate such particles by filtration technique. In such cases, centrifugation is a useful method.

 

Let�s have a look at the procedure of separation using centrifugation.

 

� To separate cream from milk, first take some full-cream milk in a test tube.
� Then, centrifuge the tube in a centrifuging machine for about two minutes. In the absence of a centrifuging machine, a mixer-grinder can also be used.

 

The lighter fat particles form cream at the surface while the heavier particles of the milk settle down at the bottom. This is how the cream is separated out from the milk.

Centrifugation has several other important applications:

 

� This technique is employed in diagnostic laboratories for blood and urine tests.
� In dairies and homes, centrifugation helps to separate butter from cream.
� This technique is also utilized in washing machines to squeeze out water from wet clothes.
� In laboratories and industries, centrifugation helps in separating suspended impurities from liquids.

 

Sublimation

 

We know that different methods are employed for separating different types of mixtures. Can you tell how a mixture of salt and ammonium chloride be separated? Yes� By sublimation. Let us learn about sublimation in this module. Let us see what principle lies behind this technique of separation of mixtures.

Some solids upon heating change directly into a gas without being converted into the liquid state first. Such solids are called Sublime Solids and the process is known as Sublimation. These solids can also be obtained back directly by cooling the gases so formed. Ammonium Chloride, Camphor, Naphthalene, Iodine, Anthracene, etc are some examples of sublime solids.

 

The process of sublimation is used to separate the components of a mixture that possesses one sublimable volatile component and a non- sublimable component often referred to as the impurity. Let us briefly understand the procedure of separation by Sublimation process:

 

� To separate the mixture of salt and ammonium chloride, take this mixture in a china dish.
� Then place an inverted funnel on the china dish with its end plugged with cotton so as to prevent the fumes of volatile components from escaping.
� Heat this mixture for some time.
� The sublime ammonium chloride vapourises and then cools and gets deposited back as solid on the inner walls of the funnel.

 

In this way, sublimation can be used for the separation of sublimable components from the non-sublimable component in a mixture.

 

Fractional Distillation

 

We have already learned about distillation and we also know that distillation is employed for the separation of miscible liquids with sufficient difference in their boiling points. But what if the difference in boiling points of the constituent liquids is very low? In such cases, we use another technique known as �Fractional Distillation�.

 

Fractional Distillation is, therefore, a process used for the separation of a mixture of two or more miscible liquids whose difference in boiling points is even less than 25 Kelvin. The process involves repeated distillations and condensations and is carried out using a fractionating column, fitted in between the distillation flask and the condenser.

The fractionating column is usually a long glass tube packed with glass beads or porcelain pieces. The beads provide a surface for the vapors to cool and condense repeatedly.

 

Now, can you tell how can we obtain different gases from the air? Yes�. Air is a homogeneous mixture of gases and can be separated into its components by fractional distillation.

 

Let us briefly understand how fractional distillation is used for the separation of the components of air.

 

� The air is first compressed by increasing the pressure and then is cooled by decreasing the temperature so as to obtain liquid air.
� The liquid air is then allowed to warm up slowly in a fractional distillation column where the gases get separated at different heights depending upon their boiling points.

 

In this way, air can be separated into its constituent gases by the fractional distillation method.

 

Evaporation

 

We already know that a mixture can be separated into its constituent components by various different techniques. Let us now discuss these techniques one by one and see how they can be employed for the separation of a mixture�s components. This process can be employed for separating the components of a mixture where one component is volatile and the other is non-volatile.

 

Let us see an example to understand this better. The colored component of the dye can be obtained from blue or black colored ink by the process of evaporation. This is because the ink is a homogeneous mixture of dye in water where water, the solvent, is a volatile component and dye, the solute, is a non-volatile component. But what actually is the procedure for separating the dye? Here it is:

 

� First, put a few drops of blue or black colored ink on a watch glass.
� Now, place this watch glass on the mouth of a beaker half-filled with water.
� And then, heat the water in the beaker. The steam thus formed will heat up the ink.
� The water present in the ink evaporates and ultimately a blue or black residue is left on the watch glass. This is the dye.

 

This technique of evaporation finds application in the separation of non-volatile components dissolved in volatile solvents. Therefore, common salt is also separated from the seawater using this method.

 

Separating Funnel

 

We already know about evaporation and centrifugation- the two important methods of separating the components of a mixture. There are several other important techniques employed for the separation of different types of mixtures.

Can you tell how a mixture of two immiscible liquids is separated? They can be separated by using a separating funnel. But what actually are immiscible liquids? Two or more liquids which when mixed together, form a heterogeneous mixture with separate layers of different densities are called immiscible liquids. A mixture of water and oil is an example of such a mixture.

 

The individual components of such a heterogeneous mixture can be separated by using a separating funnel. Let us now understand the principle behind separation using a separating funnel. When a mixture of two immiscible liquids is allowed to stand for some time, it forms separate layers depending upon the densities of the constituent liquids.

The heavier ones settle at the bottom while the lighter liquid stays at the surface, thus separating out in layers.

 

Let us now have a look at the procedure of separating a mixture of oil and water using a separating funnel.
� Firstly, take a separating funnel and pour the mixture of oil and water into it.
� Allow it to stand undisturbed for some time so that separate layers of oil and water are formed.
� Once the layers separate out, open the stopcock of the separating funnel to pour out the lower layer of water carefully.
� Close the stopcock of the separating funnel when the oil reaches the stopcock.
� And then the oil is taken out of the separating funnel, thus separating both the liquids.

 

Let us see some useful applications of separating funnel:

 

� It is used in separating the mixture of oil and water.
� This method of separation is also employed in the extraction of iron from its ore.

Read More: What is Mixture? Homogenous and Heterogeneous Mixture | Properties