We know that the most of the natural substances are not chemically pure substances. They are mixtures that contain two or more kinds of substances. We use different methods of separation to get individual components from the mixture.
Separating or extracting different components from a mixture using some physical methods is called separation of mixtures. We often use it to remove unwanted or harmful components and to separate the individual components from the mixtures.
We can separate heterogeneous mixtures into their respective individual components by simple physical methods like hand picking, threshing, winnowing, sieving, filtration that we use in daily life. However, the choice of techniques to separate components of a mixture depends upon the type of mixture and the difference in the physical and chemical properties of the components of the mixture.
This is because the constituents of a mixture differ in many of their physical and chemical properties. The advantage of this difference in their physical properties is taken in the separation of a mixture. For example, every component keeps its own characteristic properties (like melting point, boiling point, solubility, etc.) even in the mixtures.
Based on the difference between its particular properties of different components of mixtures, we separate them into the mixtures. So, let’s understand the different ways of separating components of mixtures.
Various techniques or methods employed for the separation of mixtures are as follows:
Let us understand them in more detail one by one.
Sedimentation is the process or technique in which insoluble heavy particles in a liquid settle down in the lower part of the container. This simple technique applies to a mixture containing one liquid and another heavier, insoluble solid component. Let’s understand it with the help of an example.
Suppose you are making a tea. You have boiled the water in the saucepan and added some tea leaves into the water. Now keep the prepared tea with tea leaves, aside from some time. Then, you see that the tea leaves will settle down in the lower part of the saucepan. This settling down of particles in the lower part of the container is called sedimentation.
Another example of sedimentation is the settling down of mud particles in the water.
Decantation is the process of transferring the clean liquid getting after sedimentation into another container without disturbing settled particles. After settling down tea leaves, you can pour the clear tea (liquor) into a cup. This transfer of the clear tea is nothing but decantation.
Filtration is a technique of separating a liquid from an insoluble solid in the liquid. This common technique is useful when you want to filter solid particles from the liquid. You can do filtration with the help of various filtering agents, like filter-paper or other materials.
For example, common salt (water soluble) containing sand (insoluble solid) is separated by filtration. For separation, the mixture is shaken so as to dissolve common salt. The soluble components pass through the filter paper and the insoluble solid component sand remains on the filter paper, as shown in the below figure.
The sand collected on the filter-paper is taken in a basin and dried by heating. To obtain the soluble component salt from the water, the filtrate is taken into the evaporating dish and heated until the whole of the water is evaporated. Thus, solid common salt is obtained in the dish.
Another familiar example of separation of mixture by filtration is as:
(a) Sugar (soluble in water) and charcoal (insoluble in water) using water as solvent.
Evaporation is the process of separating a non-volatile soluble solid from its mixture in volatile liquid. This process is useful when solid particles do not break down on heating the solution up to the boiling point of the liquid component.
On heating, the volatile liquid evaporates, leaving behind the soluble solid as residue. For example, this method can separate a homogeneous mixture of sugar and water. Take the solution of sugar and water in the evaporating dish. Heat the dish carefully until the entire water in the dish gets evaporated. The whole crystals of sugar will remain as a residue after evaporation in the dish.
Similarly, we can separate salt from the solution of salt and water, sulphur from the solution of sulphur and carbon disulphide.
Sublimation is a process in which a solid substance directly converts into its vapours when heated and vapour reconverts into the solid on cooling. This process is useful when one component of the mixture undergoes sublimation and the other components are not broken down (or decomposed) by heating.
For example, iodine can be separated from the sand by sublimation. When the iodine is heated, it sublimes leaving behind the sand. The iodine vapours to be on cooling converts back to solid iodine.
Similarly, other mixtures that can be separated by sublimation are as:
| Mixture | Sublimate |
|---|---|
| 1. Ammonium chloride and Sodium chloride | Ammonium chloride |
| 2. Naphthalene and Common salt | Naphthalene |
This method is used when the solubility of one component of the mixture in a particular solvent (usually a low-boiling organic solvent) is more than other components. If will more, it forms a distinctly separate layer with the other liquid component if present in the mixture.
For example, a mixture of sulphur and sand can be separated with the help of this method. Since sulphur is soluble in carbon disulphide and sand is insoluble. Therefore, when a solution of carbon disulphide passes through the mixture of sand and sulphur, sulphur gets dissolved in it, as shown in the below figure.
Crystals are the purest substance, having a definite geometrical shape. The process by which an impure compound converts into its crystal form is called crystallisation. It is one of the most commonly used method for the purification of solid organic compounds. This method is based on the difference between the solubilities of pure compound and impure compound in a particular solvent.
When the impure compound dissolves in a suitable solvent, which is slightly soluble at room temperature but more soluble at higher temperature. On heating, the solution gets concentrated into nearly a saturated solution. When the saturated solution cools, crystals of pure substance will separate out, which are removed by the filtration method.
This method is used to separate a mixture which contains two solid components having different solubilities in the same solvent. For example, a mixture of potassium nitrate (KNO3) and sodium chloride (NaCl) can be separated out with the help of this method. When the aqueous solution of this mixture is heated and subsequently cooled, the more soluble potassium nitrate (KNO3) remains in the solution and the less soluble sodium chloride (NaCl) separate outs by leaving the more soluble and crystallizes out first, as shown in the below figure.
Another example of this separation method is a mixture of potassium chloride and sodium nitrate, in which potassium chloride is less soluble and crystallizes out first.
Distillation is a process in which a liquid converts into its vapour when heated and then condenses vapours again into the same liquid when cooled. Thus, distillation contains both vaporisation and condensation.
Distillation = Vaporisation + Condensation
This method is commonly used to the separation of that mixture, which contains pure liquid components having a large difference in boiling point. The component having lower boiling point vaporises first and its vapours is condensed using water condenser and then collected as shown in the below figure.
The component having higher boiling point remains behind in the distillation flask. Some examples of separation of mixtures by using this method are as:
You can also use this method of separation for separation and recovery of both components of a solid-liquid mixture. For example, this method can separate a homogeneous mixture of sodium chloride (NaCl) and water. On heating water evaporates and condenses back to the pure water on cooling, whereas sodium chloride (NaCl) left behind in the distillation flask.
Thus, sodium chloride is a soluble solid which recovered as a residue in the distillation flask and water is a liquid component that has recovered as the distillate from the mixture of sodium chloride and water.
We use this method of distillation for the separation of a mixture in which components have a small difference in boiling points. In this method, distillation flask is fitted with a large fractionating column having many bulbs as shown in the below figure.
When the flask heats, liquid vaporises and the vapours rise up from the column. The vapours of less volatile component condense back in the flask and the vapours of only more volatile component escape from the top of the fractionating column, condensed, and collected in a receiver.
For example, gasoline, diesel, kerosene, lubricating oil, etc. from crude petroleum can be separated by using fractional distillation method.
We mostly use the fractional distillation method when boiling point of two liquids of the mixture differ to one another by 10K.
Centrifugation is the process of separating suspended insoluble tiny solid particles from a liquid mixture. It is based on the shape, size, and density of the particles. This process is useful when the normal filtration does not work as well. In the centrifugation process, when we spun a liquid mixture, heavier particles move towards bottom and the lighter particles stay at the top and then get separated. For example, milk is a mixture of water, solid fat, and other components. When we churn milk rapidly, water which is heavier than fat, move towards bottom and the lighter particles stay at the top and then get drained out.
We use this process for the separation of a mixture having components of different densities. The powdered mixture undergoes with a stream of running water. The lighter components wash away with water, leaving the heavier ones. For example, a separation of gold particles from rocky substances occurs by gravity separation.
In this tutorial, you have known about various methods of separation of mixtures with examples. Hope that you will have understood the basic points of all techniques of separation of mixtures.
Thanks for reading.