What are Physical Separation Methods Definition Types and Examples
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
Filtration
Centrifugation
Magnetism
Evaporation
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.
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.
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.
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.
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.
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
FAQs on Physical Separation Methods in Chemistry
1. What are physical separation methods in chemistry?
Physical separation methods are techniques used to separate components of a mixture without changing their chemical identity. These methods rely on differences in physical properties such as size, density, solubility, boiling point, or magnetism.
- No new substances are formed during separation.
- The components retain their original chemical composition.
- Common examples include filtration, distillation, evaporation, and chromatography.
Physical separation is widely used in laboratories, industries, and everyday processes like purifying water or separating sand from water.
2. What is the difference between physical and chemical separation methods?
The main difference is that physical separation methods do not change chemical composition, while chemical separation methods involve chemical reactions that form new substances.
- Physical separation: Based on properties like boiling point, solubility, or density (e.g., distillation of water from salt solution).
- Chemical separation: Involves chemical reactions (e.g., extracting a metal from its ore by reduction).
- Physical methods are reversible in most cases; chemical methods are usually not easily reversible.
For example, separating NaCl from water by evaporation is physical, but decomposing water by electrolysis (2H2O(l) → 2H2(g) + O2(g)) is a chemical process.
3. What is filtration and how does it work?
Filtration is a physical separation method used to separate an insoluble solid from a liquid using a porous barrier.
- The mixture is poured through filter paper.
- The solid remains as the residue.
- The liquid that passes through is called the filtrate.
For example, sand can be separated from water because sand is insoluble in H2O. Filtration is commonly used in laboratories and water purification systems.
4. What is distillation in chemistry?
Distillation is a physical separation technique that separates liquids based on differences in their boiling points.
- The mixture is heated until the lower boiling liquid vaporizes.
- The vapor is cooled in a condenser.
- The condensed liquid is collected as the distillate.
For example, pure water can be obtained from salt water because water boils at 100°C (at 1 atm), while dissolved salt does not vaporize. Distillation is widely used in petroleum refining and alcohol purification.
5. What is the difference between simple distillation and fractional distillation?
Simple distillation is used when liquids have widely different boiling points, while fractional distillation is used when boiling points are close.
- Simple distillation: Suitable when boiling point difference is large (e.g., water and salt).
- Fractional distillation: Uses a fractionating column to separate liquids with close boiling points (e.g., ethanol at 78°C and water at 100°C).
- Fractional distillation allows repeated vaporization and condensation for better separation.
Fractional distillation is essential in separating crude oil into useful fractions like petrol, kerosene, and diesel.
6. What is evaporation as a separation method?
Evaporation is a physical method used to separate a dissolved solid from a liquid by heating the solution until the solvent vaporizes.
- The solvent (usually water) changes from liquid to vapor.
- The dissolved solid remains behind as residue.
- No chemical change occurs.
For example, heating a solution of NaCl(aq) leaves solid NaCl(s) after the water evaporates. This method is commonly used in salt production from seawater.
7. What is chromatography and what is it used for?
Chromatography is a physical separation technique used to separate components of a mixture based on differences in their movement through a stationary phase.
- It involves a stationary phase (e.g., paper) and a mobile phase (e.g., solvent).
- Components travel at different speeds depending on solubility and adsorption.
- Common types include paper chromatography and thin-layer chromatography (TLC).
Chromatography is widely used to separate dyes, analyze drugs, and identify compounds in forensic and biochemical analysis.
8. What is centrifugation in chemistry?
Centrifugation is a physical separation method that uses rapid spinning to separate substances of different densities.
- The mixture is placed in a centrifuge tube.
- It is spun at high speed.
- Denser particles settle at the bottom as sediment, while lighter liquid remains as supernatant.
Centrifugation is commonly used to separate blood components, precipitates from solutions, and solid particles from liquids.
9. What is decantation and when is it used?
Decantation is a physical separation method used to separate a liquid from a settled solid or from another immiscible liquid by carefully pouring off the top layer.
- Used after sedimentation of an insoluble solid.
- Can separate immiscible liquids like oil and water.
- Relies on differences in density.
For example, after sand settles in water, the clear water can be gently poured off without disturbing the sediment.
10. What are the main types of physical separation methods?
The main types of physical separation methods include filtration, distillation, evaporation, chromatography, centrifugation, decantation, and magnetic separation.
- Filtration – separates insoluble solids from liquids.
- Distillation – separates liquids based on boiling point.
- Evaporation – recovers dissolved solids.
- Chromatography – separates based on differential movement.
- Centrifugation – separates by density using rotation.
- Magnetic separation – removes magnetic materials like iron from mixtures.
Each method depends on specific physical properties and is chosen according to the nature of the mixture being separated.
