Mixture separation methods are physical techniques used to separate the components of a mixture. A mixture can be homogeneous, when its components cannot be distinguished with the naked eye, or heterogeneous, when the differences between its components are evident.
The importance of these methods is that they allow us to obtain pure substances from their mixtures, without altering their chemical structure. For example, to obtain sea salt, evaporation is used to remove water from the mixture.
Method of
separation
Definition
Kind of
mix
Example Filtration Separation of components
solids of a liquid mixture Heterogeneous Filtering of ground coffee from coffee Sieving Separation of particles according to their size through a sieve Heterogeneous Sifting of flour for desserts Sedimentation Deposit of suspended particles in a mixture by action of gravity Heterogeneous Wastewater treatment Decanting Transfer a liquid from a
container to another Heterogeneous Separation of sediments from wine Distillation Separation of components with
different boiling points Homogeneous Distillation of water to remove impurities Evaporation Elimination of solvents
of a Homogeneous mixture Obtaining organic extracts dissolved in alcohol Magnetization Separation of components by
its magnetic property Heterogeneous Obtaining iron filings in a mixture with sand Chromatography Separation of components by their affinity for a mobile phase and a fixed phase Homogeneous
Heterogeneous Separation of plant pigments on paper Centrifugation Separation based on centrifugal force Heterogeneous Separation of red blood cells from blood plasma Crystallization Promote crystal formation Homogeneous Formation of sugar crystals from a sugar-water mixture Electrophoresis Separation based on the difference in electric charge Homogeneous Separation of proteins Sublimation Turn a solid into a gas without going through a liquid Heterogeneous Separation of iodine from sand
1. Filtration
Through a paper or cloth filter, the liquid coffee is separated from the ground when it is boiled with water.
Filtration consists of passing a liquid-solid heterogeneous mixture through a material that retains the solid and allows the liquid to pass. For example, we use a filter to separate the mixture of ground coffee and liquid coffee.
The filters can be of different materials, whose main characteristic is that it must be porous. For example, a coagulated milk mixture is passed through a fine cloth, separating the whey from the milk solid, which is how cheese is made.
2. Screening
Sieving is the method of separating mixtures with solid components with different sizes, which pass through a strainer or sieve.
Sifting is used to remove lumps of flour and use the finest flour for pastry. It is also used in construction, separating the fine sand from the pebbles.
3. Sedimentation
Sedimentation is the method that separates the solid components of a liquid mixture by the effect of gravity.
This method is used in sewage or sewage treatment plants, leaving the solid waste to settle, that is, to fall to the bottom.
4. Decantation
The decanter is a wide-bottomed jug with a narrow neck used to decant sediment from wine.
This method consists of transferring a liquid from one container to another. It is applied to separate heterogeneous solid-liquid mixtures, such as water and sand, or liquid-liquid that do not mix with each other, such as water and oil or water and gasoline.
In the chemistry laboratory, a separatory funnel is used, which facilitates the separation of liquids, because it has a stopcock at the bottom.
For example, decanting is used to separate red wine from the sediments that settle to the bottom of the bottle.
5. Distillation
Laboratory equipment for distillation.
Distillation is the process that separates the components of a liquid mixture, based on the difference in temperature that each one passes into the gaseous state. The distillation equipment allows the gas to be obtained again in a liquid state, through condensers.
For example, water boils at 100ºC while alcohol boils at 78.37ºC. When a mixture of alcohol and water is heated above 78ºC, the alcohol turns to a gas and rises, passing through the condenser and ultimately dripping into a collection vessel.
Distilleries are factories where large-scale distillations are carried out, generally to concentrate the alcohol level of the fermented fruit, to produce liquors, spirits, rums, among others. In the past, this process was carried out in copper stills.
Gasoline and other petroleum derivatives are obtained through fractional distillation. This process is done in oil refineries.
6. Evaporation
Evaporation equipment used in chemical laboratories.
Evaporation is a physical separation method that is based on evaporating the liquid where the substances are dissolved. It is mainly used in chemistry, when organic substances are extracted by means of solvents such as acetone, ethanol or hexane. These are liquids with low boiling points, so they evaporate at low temperatures.
7. Magnetization
In mixtures where there is a magnetic substance, it can be separated using a magnet.
Magnetization is the method of separating heterogeneous mixtures that is based on trapping components that are attracted by a magnet.
Some laboratories have designed proteins attached to magnetic particles, which serves to separate them using magnets.
8. Chromatography
Chromatography is a method of separating homogeneous or heterogeneous mixtures. It is based on the difference in speed of a substance between two phases: a mobile and a fixed phase. The mobile phase moves dragging the different components of the mixture, which separate as they collide with the fixed phase.
The fixed phase can be solid like paper, a gel like agar, or a liquid like acetonitrile. The mobile phase can be liquid or gas. Depending on this, we have thin layer chromatography, liquid chromatography, and gas chromatography.
9. Centrifugation
In the clinical laboratory, centrifuges are used to separate the components of blood.
Centrifugation is a method of separating liquid heterogeneous mixtures based on centrifugal force. This force originates when a body rotates and tends to move away from the axis of rotation. In this way, the more dense components of a mixture are separated from the less dense ones. For example, blood cells are separated from plasma using centrifugation.
Centrifuges are devices that rotate at high speed, where the samples to be separated are placed. They are widely used in clinical laboratories and in research.
10. Crystallization
Crystallization is a method of separating homogeneous mixtures of a solid from a liquid. It consists of promoting the formation of crystals with ordered structures. This can be accomplished in a number of ways: by cooling a solution, by evaporating the solvent, or by adding a different solvent.
Crystallization is observed when a solution is saturated with salt in boiling water and then allowed to cool.
11. Electrophoresis
Nucleic acid samples can be separated by electrophoresis using an agarose gel.
Electrophoresis is the separation technique based on the electrical charge of the substances present in a mixture. It consists of placing the mixture and passing an electric current, in such a way that the positively charged substances move towards the negative pole, while the negatively charged substances move to the positive pole.
This technique is fundamental in the analysis of biological samples and is used to separate proteins and nucleic acids, among other compounds. For example, lipoproteins in blood plasma can be separated by electrophoresis, and then their cholesterol content can be measured to assess the risk of cardiovascular disease.
12. Sublimation
Sublimation is the change from a solid to a gas without going through the liquid state. Sublimation is used to separate mixtures of organic compounds, where some of the compounds may sublime.
For example, in a mixture of sand and iodine, the iodine can be separated by heating it. This goes to the gaseous state rising and when it passes through a cold surface it solidifies again.
See also: