Physical Separation Methods

What is A Mixture?

A mixture is a substance made by combining two or more different substances (elements or compounds), not necessarily in a definite ratio. In a mixture, the constituents do not combine chemically (no chemical reaction occurs). Since there is no chemical reaction involved, the constituents retain their original properties. In the formation of a mixture, there is no loss or gain of energy. We can easily separate the components of a mixture using physical methods. 

Separation of The Constituents of A  Mixture

A mixture is formed as a result of a physical change. Therefore, in order to separate the constituents of a mixture, certain physical methods or techniques can be employed by which a mixture can be separated back into its original components. These techniques are based on physical properties of the components such as densities, weight, size etc.

For example: Let us take a mixture of sand and water. Sand and water have different physical properties due to which we can separate sand and water by separation methods. When sand is added to water, it settles down at the bottom of the container because sand is heavier than water and insoluble in water(heterogeneous mixture). So, we can separate the sand from the mixture by filtration. A filter paper will allow the water to pass through as filtrate. We will discuss some physical separation methods here.

  1. Filtration

This is a very common separation technique, which is used for separating an insoluble solid from a liquid. In this process, the mixture is passed through a filter paper. The liquid which has passed through the filter is called filtrate and the solid which remains on the filter paper is called the residue.


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For example: In our daily life, the filtration method is used, while preparing tea.  We use a sieve at home to separate tea leaves from the water. Tea is obtained as the filtrate through the sieve pores.

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  1. Centrifugation

Sometimes, the solid particles in a liquid are minute enough to pass through a filter paper. In such cases,  filtration cannot be used for separation. Such mixtures are separated by centrifugation. So, centrifugation is the process in which insoluble substances are separated from a liquid, in situations where filtration does not yield the desired result. Centrifugation depends on the shape, size, and the density of particles, viscosity (thickness) of the liquid medium, and the speed at which the centrifuge is rotated. This method of separation is used when very tiny solid particles are suspended in a liquid medium. The principle on which a centrifuge works is that the denser particles remain at the bottom while the lighter particles collect at the top due to centrifugal force. 

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  1. Magnetism

In this technique of separation, a  magnet is used to separate the magnetic components from a mixture. 

This method can only be used when the given mixture contains a magnetic component like iron, nickel, cobalt etc. 

This process is widely used in waste management where the magnet is used to separate metal from discarded waste.              

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  1. Evaporation

This separation method is used to separate a soluble solid from a liquid. In this process, a mixture is heated until the solvent evaporates. The mixture should contain only one liquid component.

For example:

In many parts of the world, salt is obtained from seawater by evaporation. Water evaporates due to the heat coming from the Sun. 

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  1. Distillation

This is an effective method of separation of two or more liquids. This process is based upon the difference in boiling points of the different components in the mixture that are being separated. In this process, the mixture is heated and boiled until it reaches its boiling point. Then the temperature is maintained until the significant liquid completely vaporizers. The most volatile component vaporizes at the lowest temperature. The vapour passes through a cooled tube(condenser). This condensed liquid is collected in a container.

Simply, distillation is a process in which a mixture is heated. The component with lowest boiling point evaporates first, then it is condensed and isolated.

For example: Alcohol is liquid which is soluble in water. So, if we want to separate alcohol and water from a mixture, we will have to use the process of distillation. The mixture is kept in a distillation flask. As the heat is supplied, alcohol has a lower boiling point and will start forming vapours at 78°C. As these vapours will rise and enter the condenser, a supply of cold water cools the vapours to form alcohol droplets, which can then be collected in a container. The liquid left behind in the distillation flask will be water.

However, the method of distillation can also be used if we want to separate a soluble solid from a liquid and want to obtain both the liquid and the solid components. This is different from the case of evaporation because, in evaporation, we are able to obtain only the solid while the liquid component forms vapours and cannot be collected.


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FAQ (Frequently Asked Questions)

1. What is the need to separate different components of a mixture?

Solution:  We need to separate different components of a mixture because some components may not be useful, while others may be. Some unwanted components have to be removed from the mixture. Separating the components of a mixture also helps us to know more about their properties.

It is also used to remove the impurities which are present in a mixture.

For example: After preparing tea, we strain it to remove the used tea leaves from tea.

2. What are heterogeneous and homogeneous mixtures?

Solution: In a homogeneous mixture, the constituent particles are evenly distributed and uniformly mixed. Homogeneous mixtures also called as solutions. We can't judge a homogeneous mixture by seeing it, while heterogeneous mixtures have a non-uniform particles distribution, which can be easily identified by seeing the mixture.

For example: A mixture of sand and water is a heterogeneous mixture as we can see both the components individually and can separate them physically. On the other hand, a mixture of sugar and water is a homogeneous mixture. Sugar is soluble in water.