Physical Separation Methods

Every home, every industry makes use of some of the other forms of the separation method. The separation method in simple terms is the process of segregation, where unwanted particles are separated from the essential parts. In this particular article, we shall be learning in detail about various physical separation methods. By the end of the discussion, students would be able to identify different methods and their significance.

Table of Content 

• Physical Separation Methods - An introduction

• What is a Mixture?

• Separation Methods

1. Filtration

2. Centrifugation

3. Magnetism

4. Evaporation

5. Distillation

• Key learnings 

• Frequently asked questions

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.

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.

2. 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 density of particles, viscosity (thickness) of the liquid medium, and 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. 

3. 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.              

4. 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. 

5. 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 vaporizes. The most volatile component vaporizes at the lowest temperature. The vapor 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 the lowest boiling point evaporates first, then it is condensed and isolated.

For example, Alcohol is a liquid that 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 vapors 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 vapors and cannot be collected.

Key Learnings from the Chapter:

• When two or more substances combine together they take the form of a mixture. 

• To separate the constituents of a mixture some form of physical methods of separation are to be used

• There are five major separation methods

• In the filtration method, the mixture is passed through a filter paper, the liquid gets strained to leave behind suspended particles

• The centrifugation method is used to strain the tiny suspended particles which could not be captured by the filtration method

• The evaporation method is used to separate the solid particle from the liquid by heating

• Distillation also make use of heat to separate the particles