What are the Methods of Separating Mixtures?
All substances are not present in their pure form in nature. Most of the substances are present in the form of mixtures. We can separate useful components of the mixtures by using various methods of separation. You must have seen your mother separating stones or other impurities from rice by washing it before cooking it. You generally use different methods of separation in your daily life.
The Different Types of Separation Techniques
You must have studied many separating techniques in the chemistry of classes VI, VII, and IX. So, here in this article, we are going to discuss various separation techniques so that if you have any doubts, then you can clear through this article –
Handpicking
Threshing
Winnowing
Sieving
Sedimentation
Decantation
Filtration
Evaporation
Condensation
Sublimation
Distillation
Fractional distillation
Separating funnel
Magnetic separation
Now we will discuss all above-stated types of separation methods in detail –
Handpicking
If you want to separate black grapes from the mixture of black and green grapes, then you will simply pick black grapes using your hands from the mixture. So, the separation method in which components of a mixture can be separated by just picking them out by hands is called handpicking.
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Conditions for handpicking – The mixture should contain impurities of a little larger size and different colors.
Threshing
This method of separation is generally used by farmers in agriculture during the harvesting of crops as it is used in separating an edible part from a non-edible part of the grain. For example, the grain is separated from the stalks by beating it on the ground or a large stone.
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Winnowing
It is an agricultural technique, being used since ancient times. Nowadays, many machines are available for winnowing. Winnowing means the separation of grains from straw by the use of the current of air. The word winnow originated from the old English word ‘windwian,’ which means separation of the mixture through the wind. Winnowing can be defined as the separation of a heavier substance from a lighter substance of a mixture using the current of air or by blowing air. Corns are separated from straw by winnowing.
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Difference Between Winnowing and Threshing
If you also generally get confused between winnowing and threshing, then here we are providing you the difference between winnowing and threshing to clear your doubt.
Sieving
You must have either used this separation technique or seen someone using this at home. Generally, mothers use this technique in kitchens to separate stones or other larger impurities from Rava, rice, etc. We use this technique in making tea also.
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The separation technique in which we use a porous sieve to remove the impurities of the mixture is called sieving. It only removes those impurities which are larger in size than the pores in the sieve.
Sedimentation
Sedimentation is a separation technique in which heavier impurities present in water settle down at the bottom after some time if you keep the mixture still in one place. The heavier constituent which gets settled at the bottom is known as sediment, and the water above it is known as supernatant.
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Decantation
Decantation is the technique of removal of water after using the sedimentation technique.
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Filtration
Filtration is the method of separation in which impurities are removed from water by using filter paper.
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The solid impurity which we get on the filter paper is called a residue, and the water which passes through the filter paper and gets collected in a conical flask is called the filtrate.
Evaporation
It is used to separate those mixtures in which solvent is liquid and solute is soluble solid. As the name suggests, evaporation is the process of conversion of water into vapour. It is the method of separation in which liquid (solvent or organic solvent) evaporates and leaves the solid residue behind. For example, salt is obtained from seawater by evaporation.
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Condensation
Condensation is the process of conversion of vapours into a liquid state. This process is used in many separation techniques to collect the vapours of pure substance.
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Sublimation
Sublimation is the process in which a substance directly changes from a solid state to a liquid state. It is used as a separation technique for mixtures which contain sublimable volatile substances and non-sublimable volatile components. Some substances such as ammonium chloride, camphor, naphthalene, and anthracene are sublime substances.
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Mixtures of ammonium chloride and salt can be separated by the sublimation method of separation of mixtures.
Distillation
It is used for the separation of components of a mixture containing two miscible liquids that boil without decomposition and have sufficient differences in their boiling point. In this technique, liquid mixtures are boiled, vaporized, condensed, and isolated. A mixture of acetone and water is separated by distillation. The boiling point of acetone is 56°∁ , and water is 100℃.
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Fractional Distillation
It is the same technique as distillation, but its apparatus has fractionating column also. So that it can separate a mixture of miscible liquids which has a difference in their boiling point of less than 25K, separation of different gases from the air can be done by fractional distillation.
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Separating Funnel
It is used to separate two immiscible liquids such as oil and water. This method is used in the extraction of iron also. The principle is that immiscible liquids separate out in layers depending on their densities.
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Magnetic Separation
It is used in the separation of components of those mixtures in which one component shows magnetic properties and another one doesn’t. It is used in the extraction of metals to separate the metal from its impurity.
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FAQs on Methods of separation
1. What are the common methods used for separating the components of a mixture?
The choice of a separation method depends on the physical and chemical properties of the mixture's components. Some common methods include:
- Handpicking: Separating larger impurities by hand.
- Sieving: Using a sieve to separate components of different sizes.
- Filtration: Separating an insoluble solid from a liquid.
- Evaporation: Separating a soluble solid from a liquid by heating the liquid.
- Distillation: Separating two miscible liquids with different boiling points.
- Sublimation: Separating a substance that turns directly from solid to gas.
- Magnetic Separation: Separating magnetic components from non-magnetic ones.
2. What is the main difference between homogeneous and heterogeneous mixtures?
The main difference lies in their composition and appearance. A homogeneous mixture has a uniform composition throughout, and its components are not visibly distinct (e.g., saltwater). In contrast, a heterogeneous mixture has a non-uniform composition, and its components are visibly distinguishable (e.g., sand in water).
3. How do you decide which separation method is appropriate for a specific mixture?
The decision is based on the differing physical properties of the components you want to separate. For example:
- If components have different particle sizes, use sieving or filtration.
- If one component is soluble in a liquid and the other is not, use filtration followed by evaporation.
- If components are miscible liquids with different boiling points, use distillation.
- If one component is magnetic, use magnetic separation.
4. What is the step-by-step process to separate a mixture of sand, salt, and water?
To separate this mixture, you would use a combination of methods in the following order:
- Step 1 (Filtration): Pour the mixture through a filter paper. The sand, being insoluble, will be left on the filter paper as residue.
- Step 2 (Evaporation or Distillation): Heat the remaining saltwater solution. The water will evaporate, leaving the salt behind. If you need to collect the pure water, you would use distillation instead of evaporation.
5. Why can't simple filtration be used to separate salt dissolved in water?
Simple filtration cannot separate dissolved salt because when salt dissolves, its particles break down to an ionic or molecular level, becoming much smaller than the pores in standard filter paper. These dissolved particles pass through the filter along with the water molecules. A method that involves a phase change, like evaporation or distillation, is required to separate a dissolved solid from a liquid.
6. What is the purpose of using a separating funnel in a chemistry lab?
A separating funnel is specifically designed to separate a mixture of two or more immiscible liquids, which are liquids that do not mix, such as oil and water. The technique works because the liquids form distinct layers based on their differing densities. The denser liquid settles at the bottom and can be drained out through the stopcock.
7. What is the key difference between simple distillation and fractional distillation?
The key difference is their application based on the boiling points of the liquids being separated. Simple distillation is effective for separating miscible liquids with a large difference in boiling points (typically more than 25°C). Fractional distillation is used for liquids with very close boiling points, as it employs a fractionating column to provide multiple successive distillations for a more precise separation.
8. In what real-world industries are separation techniques most important?
Separation techniques are fundamental to many major industries. For instance:
- Petroleum Refining: Fractional distillation is used to separate crude oil into petrol, diesel, and kerosene.
- Water Purification: Filtration, sedimentation, and distillation are used to produce clean drinking water.
- Food Processing: Sieving, filtration, and centrifuging are used to process products like flour, juice, and dairy.
- Pharmaceuticals: Chromatography and crystallization are crucial for isolating and purifying medicinal compounds.
9. How does sublimation work as a method of purification?
Sublimation works as a purification method for mixtures where one of the solid components can change directly into a gas when heated, bypassing the liquid state. This is called a sublimable substance. When the mixture is heated, the sublimable component turns into vapour, which can then be cooled and collected as a pure solid, leaving the non-sublimable impurity behind. A classic example is separating ammonium chloride from sand.
