Introduction
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
1. What are the common physical methods used for separating mixtures?
Physical separation methods exploit differences in the physical properties of components to separate them. Common methods include:
- Filtration: Separating an insoluble solid from a liquid using a filter medium (e.g., separating sand from water).
- Evaporation: Separating a soluble solid from a liquid by heating the liquid until it evaporates, leaving the solid behind (e.g., obtaining salt from seawater).
- Distillation: Separating liquids with different boiling points by heating the mixture, vaporising the more volatile liquid, and then condensing it back into a liquid (e.g., separating alcohol from water).
- Centrifugation: Separating very fine, suspended particles from a liquid using high-speed rotation (e.g., separating cream from milk).
- Magnetic Separation: Separating magnetic components from a non-magnetic mixture using a magnet (e.g., separating iron filings from sulphur).
- Sublimation: Separating a substance that sublimes (turns directly from solid to gas) from a non-sublimable one (e.g., separating camphor from salt).
2. What is the fundamental principle that makes the physical separation of mixtures possible?
The fundamental principle behind all physical separation methods is the difference in the physical properties of the individual components in a mixture. Since no chemical reaction occurs when a mixture is formed, each substance retains its unique properties. Separation techniques are designed to exploit these differences, such as variations in:
- Boiling point (used in distillation)
- Particle size and solubility (used in filtration)
- Density (used in centrifugation)
- Magnetic attraction (used in magnetic separation)
- The ability to sublime
3. How do you decide which physical separation method to use for a particular mixture?
The choice of separation method depends entirely on the nature of the mixture and its components. Key factors to consider are:
- The physical state of the components: For example, separating two solids would require a different method (like magnetic separation or handpicking) than separating a solid from a liquid (like filtration or evaporation).
- The type of mixture: For a heterogeneous mixture with an insoluble solid in a liquid (like sand in water), filtration is suitable. For a homogeneous mixture with a soluble solid in a liquid (like salt in water), evaporation or distillation is used.
- The specific properties of the components: If you need to separate two miscible liquids, you must check their boiling points. If the boiling points are significantly different, distillation is the ideal method.
4. What is the main difference between evaporation and distillation?
While both evaporation and distillation are used to separate a soluble solid from a liquid, they have a key difference in their objective and outcome:
- Objective: In evaporation, the primary goal is to recover only the solid component; the liquid solvent is lost to the atmosphere as vapour. In distillation, the goal is often to recover both the liquid solvent and the solid solute.
- Process: Distillation involves an extra step. After the liquid turns into vapour, it is channelled through a condenser that cools it back into a pure liquid, which is then collected separately. Evaporation simply involves heating until the liquid is gone.
5. In what situation is centrifugation preferred over simple filtration?
Centrifugation is preferred over filtration when the solid particles suspended in a liquid are extremely small or colloidal in nature. These fine particles are tiny enough to pass through the pores of a standard filter paper, making filtration ineffective. The high-speed rotation in a centrifuge generates a strong force that pushes the denser, fine particles to the bottom of the container, allowing for effective separation. A common example is separating blood cells from plasma.
6. What is sublimation and when is it used as a separation technique?
Sublimation is the process where a substance transitions directly from a solid state to a gaseous state upon heating, without passing through the liquid phase. This unique property is used as a separation technique when one component of a solid mixture can sublime while the others cannot. For example, in a mixture of iodine and sand, heating the mixture will cause the iodine to turn into a vapour, which can then be collected and cooled to recover the pure solid iodine, leaving the sand behind.
7. Why is separating mixtures an important process in daily life and industry?
Separating mixtures is a crucial process for several practical reasons:
- To remove impurities: It is essential for purifying substances. For instance, filtration is used to purify drinking water by removing suspended solids and impurities.
- To isolate a useful component: Many valuable substances are found in mixtures in nature. Evaporation is used to obtain common salt from seawater, and fractional distillation is used to separate crude oil into useful products like petrol, diesel, and kerosene.
- For analysis and research: In scientific laboratories, components of a mixture are separated to study their individual properties and composition.
