mixture separation methods



We explain what the methods to separate mixtures are and define each of these methods with some simple examples.

Filtration is one of the best known separation methods.

What are mixture separation methods?

It is known as methods of separation of mixtures orphase separation methodsto the different physical procedures that allow the separation of two or more components of a mixture. The components of the mixture they retain their identity and chemical properties after separation.

For these mechanisms to work, they must be mixtures in which the components retain their identity, and there have been no chemical reactions that permanently alter their properties or give rise to new substances.

In order for separation methods to be applied, properties such as theBoiling point, the density or the size should be conserved in the components of the mixture.

Instead, these methods work both in Homogeneous mixtures as in heterogeneous mixtures, since they do not involve any change in the identity of the components, which can thus be recovered more or less as they were before mixing. Depending on themethod applied, the original components with greater or lesser purity will be achieved.

See also:States of matter aggregation


Decantation is a method used to separate liquids that do not dissolve in each other (such as water and oil) orsolid insoluble in aliquid (like water and sand).

It consists of the use of an ampoule or a separatory funnel, where the mixture is allowed to settle until the densest ingredient settles and goes to the bottom. The valve is opened and it is let out, closing it in time for the less dense ingredient to remain inside. This method is often used as a first step towards obtaining purer substances.

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Filtration is a useful method of separating insoluble solids from liquids. It consists of the use of a filter (filter paper, filter stones, etc.) that allows the liquid to pass through a porous medium and retains the solid elements.

This is how the filters workWater of our houses, or the filter paper where we pour the solid coffee before adding the hot water. The water (which contains the finest coffee particles) passes through the paper, and the coarser coffee particles are retained in it.

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Magnetic separation

Magnetic separation consists of the separation of phases according to their magnetic potential. Some substances respond to magnetic fields and others not, and according to this difference a magnet or electromagnet to the mixture, which allows one component to be attracted and the other intact (for example, iron fragments in soil, mercury in water, pieces of metal in water).

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The sieving allows the passage of small fragments and retains the larger ones.

Sifting works in a similar way to filtering, but between solid substances of different sizes (such as gravel and sand, salt and popcorn, or rice and pebbles).

A net or sieve is used, the holes of which allow the passage of the smaller fragments and retain the larger ones. Depending on the material, it can be used as a first step in obtainingpure substances or as a final step.

Follow on:Sieving


Distillation allows soluble liquids to be separated from each other, but with different boiling points (such as water and alcohol). The difference between the boiling points of the components to be separated by this method should be approximately 80 ºC.

The procedure consists of pouring the mixture into a container and heating it by controlling the temperature so that only the lower-boiling component evaporates, and is carried through a conduit (called a distillation column) into another container, this time refrigerated. There it will condense and return to its original phase.

The liquids thus obtained are known as distillates (distilled water, distilled alcohol).

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Crystallization is an ideal method to separate dissolved solids from liquids (salt from water, sugar from water). It consists of evaporating the liquid until the crystals of the dissolved solid are obtained at the bottom of the container. For example, this is how you get sea salt. Depending on the speed of the evaporation, the crystals will be larger or smaller.

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Flotation allows the lower density solid phase to float in the liquid.

Flotation is the opposite of decantation and consists of allowing the solid phase of lower density to float in the liquid and then remove it manually or through a sieve. The perfect example of this is the swimming pool cleaning procedure.


Chromatography is a method used to separate complex mixtures that do not respond to any other separation method. It uses capillarity as a principle: a process that allows the advancement of a substance through a specific medium. The two phases of the mixture are thus identified as mobile phase (the one that advances) and stationary phase (on which it advances).

The operation of this separation depends on the affinity of the components of the mixture for both phases, and according to this affinity, the separation will be faster or slower. For example, when spilling coffee on a cloth, the coffee moves forward occupying a large amount of surface.

Currently there are different methods of chromatography:

  • Paper chromatography. The stationary phase is made up of a filter paper strip and the mobile phase is made up of a solvent that contains the sample to be separated. Place a few drops of the solvent containing the sample on one end of the paper and wait for the liquid to advance. Then it is allowed to dry, and if the different components of the sample have different colors, it will be possible to observe their different positions on the paper.
  • Thin layer chromatography. The stationary phase is composed of an absorbent material adhered to a plate that can be made of glass, aluminum or another material. The mobile phase is a liquid that will act as an eluent. The procedure consists of placing the sample on the plate and then immersing a part of it in the eluent. The components will be separated by difference in affinity between the eluent and the component adhered to the plate.
  • Column chromatography. The stationary phase consists of a solid absorbent material that is packed in a glass column (although there are now columns made of other materials, for example stainless steel). The mobile phase is made up of an eluent and the separation of the components of the sample depends on the affinity that its components have for both phases. Generally, the eluent passes through the column by gravity, although modern methods have been developed where it is driven by pumps that apply Pressure.
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