We explain what mixture separation is and the methods it uses. We also explain its general characteristics and the types of mixtures.
What is mixture separation?
Separation of mixtures or phase separation is a physical process by which components can be separated of a mixture. These components do not change during the separation process, but remain the same, except that after the separation the components have been separated.
The separation of mixtures is a physical, not chemical, process. This means that new substances are not formed after the separation of the mixtures, as happens in chemical processes, where two or more substances are chemically combined (chemical bonds are broken and formed) to form new ones.
There are different methods, including filtration, decantation, distillation, evaporation, centrifugation, levigation, magnetization, selective leaching, flotation and crystallization, among others. The choice of method for separation will depend on the type of mixture that you want to separate since there are homogeneous mixtures and heterogeneous mixtures.
See also: Fluids
Purposes of mixture separation
The separations of the mixtures have different purposes or objectives:
- Use the components of a mixture (homogeneous or heterogeneous) individually in other processes.
- Separately quantify the substances that compose them.
- Perform combinations of different separation methods to improve or facilitate the separation of complex or difficult-to-separate mixtures.
Phases of a mixture
There are at least two phases that make up the mixtures:
- Dispersed phase. It is the phase that is found in the smallest proportion in the mixture. It can be composed of one or more substances that are dispersed or dissolved in another (dispersant phase). For example, in a solution of salt in water, the salt is the dispersed or dissolved phase, while the water is the dispersing phase.
- Dispersing phase. It is the phase that is found in the greatest proportion in the mixture. One or more phases may be dispersed or dissolved in it (dispersed phase). In the previous example, the dispersing phase would be water, because it is in greater proportion and contains the dispersed phase (salt).
Types of mixtures
There are two types of mixtures:
- Homogeneous mixturesThey are characterized by the fact that it is not possible to distinguish their phases with the naked eye (even with a microscope). The most common are mixtures of solids with solids or liquids in liquids. For example: bleach (which can contain different amounts of chlorine), coffee with milk, sugar in water, lemonade, iodine tincture, among others. They are known as solutions.
- heterogeneous mixtures. These mixtures present discontinuities, that is, their different phases can be distinguished. Some examples of heterogeneous mixtures are cement, seawater, sand in water, water and oil, oil and vinegar. In turn, they can be divided into:
- Simple or coarse mixes. The components can be distinguished or differentiated with the naked eye. For example, a lettuce and tomato salad.
- SuspensionsThe particles of solid substances are tiny and cannot be recognized with the naked eye, but when the mixture is at rest for a certain time, it is possible to distinguish them at the bottom of the container, as they descend through the liquid. For example, a mixture of water and talc.
Examples of mixtures in everyday life
In our lives we are constantly in contact with different mixtures, whether homogeneous or heterogeneous. For example:
- Seawater is a mixture of sodium chloride (NaCl), water and other components.
- Concrete or concrete, used in construction, is a mixture of cement, water, sand and gravel.
- A latte, the staple of most people’s breakfast, is a mix.
- Bronze is a mixture of copper and tin called an alloy.
Difference between mixture and chemical reaction
A mixture is the combination of two or more substancesbut this combination does not imply the formation of one or more new substances, as occurs in a chemical reaction. In a mixture, the mixed substances maintain their chemical properties and their chemical composition without any change.
On the other hand, in a chemical reaction, reacting substances can break their chemical bonds to recombine in another way with other substances (which also broke their bonds) and thus form new bonds, which implies the formation of new chemical compounds.
Difference between mixture and chemical compound
The components of a mixture can be separated using physical separation methods.while the elements that form a chemical compound cannot be separated by these methods: for this, chemical separation methods are necessary.
The reason for this is that in mixtures the components do not form chemical bonds, while the elements do form chemical bonds to form a certain chemical compound. Furthermore, in chemical compounds these elements are linked in defined proportions, which allows them to be represented by chemical formulas, while mixtures cannot be represented in this way.
Physical properties of mixtures
The physical properties of mixtures, such as the boiling point or the freezing pointmay be different from those of its separate components.
For example, When table salt is added to water (when it contains this dissolved substance), the boiling point of the mixture increases and the freezing point decreases, compared to those of pure water. The first is called ebullioscopic increase and the second, cryoscopic decrease.
Some methods of separating mixtures
Methods of separating mixtures are Physical methods that are based on some physical property of the components of the mixture that you want to separate, such as the melting point, the boiling point, the state of aggregation, the magnetism, among others.
- Filtration. It is used to separate a solid from a liquid, as long as the solid is insoluble in the liquid. A filter is used through which the mixture is passed, the solid is retained in the filter and the liquid passes through it.
- Decantation. It is used to separate mixtures of two liquids that are insoluble in each other or mixtures of a solid and a liquid, which are also insoluble in each other. To achieve the separation, the mixture is left to rest in a separating funnel; the densest substance will descend, while the less dense substance will remain on the surface. The funnel valve is then opened and the densest substance is allowed to pass through.
- DistillationThis method is used to separate mixtures of liquids that are soluble in each other. It is based on the differences in the boiling points of the various liquids. To separate the mixture, heat is first applied until the liquid with the lower boiling point passes into the vapor phase and condenses in another container. In this way, it is separated from the liquid with the higher boiling point, which remains alone in the container where the mixture was originally.
- Centrifugation. It is generally used to separate an insoluble solid from a liquid. The mixture is spun in a centrifuge (a rotating container), causing the centrifugal force to send the solid to the bottom of the container and leaving the liquid on top. They can then be separated using decantation.
- Levigation. It is used to separate mixtures of solids. The solids are crushed and a solvent is added. This new mixture can then be separated according to the different densities of its components.
- MagnetizationIt consists of separating a mixture of substances in which at least one of them has magnetic properties and can be attracted by a magnet.
- Selective leachingIt is a method that uses different solvents to separate a mixture. Each component of the mixture will have more affinity for a specific solvent, so when each solvent is put in contact with the mixture, the component with the most affinity will be separated. This process is widely used in mining to extract gold.
It may be useful for you: Colloids
References
- Mixture separation methods. metodosdeseparaciondemexclas.win
- Chemistry I. Introduction to the study of the subject. Ana Beatriz Picado and Milton Alvarez. Editorial State Distance University. 2008. ISBN: 978-9968-31-626-2
- Practice Manual. General chemistry. María Rocio villa Gerley. 2007. ISBN: 958-98129-2-1
- “Mixture” in Wikipedia.
- “Phase separation methods” on Wikipedia.