A mixture is a substance formed when two or more substances (element or compound) are mixed in any proportion. The mixture consists of different components. The different components of a mixture have their own physical properties. They have their own solubility, density, boiling point, melting point, size etc. These differences help to separate them from a mixture. There are various methods of separation of the mixture. Usually, in this lesson we discuss four methods of separation of the mixture. They are evaporation, sublimation, centrifugation, and crystallisation. Depending upon the physical properties of the components, we choose one of this method for separating components of a mixture. The four methods of separation of mixture are briefly described below,

Evaporation

It is defined as the process of vaporisation of the liquid. It is the process by which water changes from liquid state to gaseous state. It is used in the separation of components from the mixture of solid and liquid. It is based on the fact that liquids change easily into vapour on heating whereas solids do not change into vapour easily. Here, when we heat the mixture, the water or liquid is evaporated and the dissolved substance remains as a residue. Evaporation occurs every day in our environment. It occurs most often in the oceans around the world. The rate amount of evaporation depends on the temperature, and it also depends on the amount of water there is to evaporate. Evaporation occurs slowly at room temperature. But when the heat is supplied, evaporation occurs fast.
This method can be used to separate sugar from the mixture of sugar and water. At first, the solution of sugar and water is taken in a porcelain basin or a beaker and heat is supplied as shown in the figure. After sometimes, the water starts boiling and changes its state from liquid to gas. The sugar is left as a residue in a porcelain basin or a beaker as shown in the figure. This method is used in the separation of salt, sugar, copper sulphate, potassium nitrate. etc from their solutions in water.

Sublimation

When we heat the solid substances, it changes into a liquid state and when further heated, it changes into vapour. But there are some solid substances that change directly into vapour state when heated. And when these vapours are cooled down, they change directly into solid state instead of changing into the liquid state. Some of the examples of such substances are camphor, iodine, naphthalene, ammonium chloride etc. These substances are also known as sublimes. Therefore sublimation can be defined as the process of changing solid directly into vapour by the application of heat and of vapour into solid on cooling. Sublimation is the conversion between the solid and the gaseous phases of matter, with no intermediate liquid stage. This method is used in the separation of the sublime from the mixture of sublime and non- sublimes. For example, the mixture of iodine and common salt can be separated by using this method.

Experiment 1

Objective: To separate a mixture of sugar and iodine by the sublimation process.
Materials required: Iodine, Sugar, Porcelain basin, wire gauze, glass funnel, tripod stand, match box, moist filter paper, cotton and Bunsen burner.

Procedure

• At first, take a mixture of sugar and iodine in a porcelain basin.
• Now placed the basin in the wire gauge kept on a tripod stand.
• Cover the porcelain basin with an inverted glass funnel.
• Now cover the outer surface of the funnel with the help of moist filter paper. Close the top of the funnel with the help of cotton plug. Then, supply the heat with the help of burner.

Observation
When we heat the mixture of sugar and iodine, the iodine changes into vapour from solid state. The sugar does not change into vapour from solid state. The vapour of iodine comes in contact with the cold inner surface of the glass funnel and changes into the solid state. Like this, we can separate the iodine from the mixture of iodine and sugar.

Conclusion
By using sublimation method, we can separate the mixture of sugar and iodine.

Centrifugation

It is another method of separation of components of mixtures. It is used for the separation of heavy particles and light particles. It is done in a machine called centrifuge. Centrifugation is the process of separating the mixture of heavy particles and light particles or suspended particles of a substance by rotating the mixture at very high speed. In centrifugation at first, the mixture of suspended particles in a liquid is taken in test tubes. Then the test tubes are placed in the centrifuge and spin at a rapid speed for sometimes. Here, the heavier suspended particles settle down at the bottom of the test tubes and the lighter particles or liquid remains on top. Then after centrifugation, the mixture can be separated by decantation. Centrifugation method is used in the separation of cream from milk, chalk powder from water, blood cells from plasma, etc. When we rotate the mixture of light particles and heavy particles at a rapid speed, then more forces acts on heavy particles than in light particles. Therefore, the heavier particles are settled at the bottom of the container and light particles at the top of the container.

Activity 2
Prepare the solution of chalk powder and water. Put the solution in the plastic bottle and tie the neck of the bottle firmly with a strong string. Then spin it for some time. What do you observe in the solution when the bottle comes to rest? What do you conclude from this experiment?

Experiment 2

Objective: To separate the mixture of sand and water by centrifugation method.
Materials required: Test tubes, centrifuge and the mixture of sand and water.

Procedure

• Put the mixture of sand and water in four test tubes.
• Now, placed the test tubes in a centrifuge.
• Close the mouth of the centrifuge with the help of lid and rotate the centrifuge at high speed.
• After some time, allow the centrifuge to come to rest.
• Now, take out the test tubes and observe the mixture in the test tubes.

Observation
We can observe that the sand settles at the bottom and water remain over the sand. It is because more force acts on sand particles than on water.

Conclusion
The mixture of sand and water can be separated by the centrifugation method of separation.

Crystallisation

Crystallisation simply means the process of formation of crystals. When we cool hot and highly concentrated solution of a solid, then the crystals of the substance are formed. This method of separation is used to get pure crystals of a solid substance from its solution. Crystals are defined as the pure substances having fixed geometrical shape, sharp edges and smooth surfaces. It is used to separate the solid that has dissolved in a liquid and made a solution. It is used to purify an impure substance in the form of crystals. Crystallisation is done as follows,

Process of Crystallization

At first, the impure solid substance is dissolved in hot water in a required amount. Then, the mixture or solution of hot water and impure solid substance is filtered so as to remove the insoluble impurities that were present in the solid substance. Then the filtered hot concentrated solution is let for few days to cool down without disturbing it. After cooling for few days, pure crystals of the substance are obtained. These crystals are separated from the solution again by the process of filtration.

Experiment 3

Objective: To prepare crystals of sugar.
Materials required: Sugar, water, glass rod, wire gauze, porcelain basin, tripod stand. bunsen burner, match box.

Procedure

• At first, boil some water in a porcelain basin.
• Then dissolve as much as amount of sugar in it and stir it with the help of a glass rod.
• When the sugar gets completely dissolved, remove the basin from the flame and filter the mixture.
• Then leave the mixture for cooling without disturbing it.
• Then observe the mixture after 2- 3 days.

Observation
After 2- 3 days, we can see the crystals of sugar.

Conclusion
In this way, crystals of sugar can be obtained after crystallisation.

Uses of Mixture

• Various mixtures of colours are used in painting.
• A mixture of various chemicals is used in the preparation of medicines.
• During construction of houses, buildings etc. the mixture of cement, sand, water etc. are used.
• Plants absorb various minerals and salts in the form of a mixture.