We explain what mixtures are and what their general characteristics are. Also, the types of mixtures that exist and examples.
What are mixtures?
We speak of mixing when two or more substances are combined without joining through chemical bonds . In everyday life, mixtures surround us, for example, many biological fluids , such as blood , are mixtures from a chemical point of view.
Mixture separation methods
A mixture can be defined as such only when the individual substances can be re-obtained by applying physical separation procedures. If the mixture generates some kind of chemical reaction, then physical separation mechanisms cannot be used. The most widely used physical methods for separating mixtures are filtration, decantation and distillation.
- Filtration . It is used to separate small particles of solids suspended in liquids. To separate the components a porous system is used, for example a sieve, thus the solid particles larger than the holes of the sieve are trapped in it, while the liquid flows through the holes.
- Decantation . It is used to separate suspended solids from liquids and also immiscible liquids (which do not dissolve in each other). The separation is based on the difference in densities of the components of the mixture. Usually a separatory funnel is used.
- Distillation . It is used to separate mixtures of liquids. The separation is achieved by differences in the boiling points: the liquid that has a lower boiling point passes into the vapor phase, is then condensed (using condensers) and is then collected in another container. The liquid that has a higher boiling point remains in the original container where the mixture was.
More in: Separation of mixtures
Characteristics of the mixtures
Certain mixtures can be separated using physical procedures.
- Its components can be separated . Mixtures are generated by the combination of substances under certain conditions (heat, pressure, etc.). For this reason, they can also be separated into their individual components and recovered by applying physical separation procedures, such as filtration or centrifugation (a method of separating solids mixed with liquids that uses rotary force).
- They have variable compositions . This is especially valid in the case of mixtures that occur in nature, such as air , soil or sea water , which at a certain moment may have a higher concentration of salts , nitrogen , suspended solids, etc. .
- They do not form chemical bonds . It should be clear that a mixture is not a chemical substance, which means that it does not originate as a result of chemical reactions. That is why there is no net energy change in the mixing process, although in some solutions heat is released, which can be very intense (such as when trying to make a solution of sulfuric acid or sodium hydroxide). .
- They can be radioactive . Some mixtures can be reactive under certain conditions. For example, in an internal combustion engine, gasoline or diesel mix with air and this starts the engine ignition.
- They have no chemical formula . They cannot be represented by a chemical formula. As they are not composed of defined proportions of the elements that make it up, mixtures cannot be expressed by means of a formula, as can be the case with substances of known composition.
- They can have one or more phases . In many mixtures there are at least two phases that can be distinguished from each other, one is called the dispersed phase and the other, the dispersing phase. The dispersant is the predominant phase within which the dispersed phase is located. On the other hand, some mixtures, like solutions, have only one phase.
- Some physicochemical properties of the dispersant phase can vary . The substances that make up the mixture retain their chemical nature, but some physicochemical properties of the dispersing phase may vary due to the presence of the dispersed phase. For example, the boiling point of water increases and its freezing point decreases by adding a solute. This phenomenon is known as “cryoscopic descent” and it is important to take it into account in the manufacture of various products.
Types of mixtures
In homogeneous mixtures the components cannot be distinguished.
The two main types of mixes are:
- Homogeneous mixtures . Its components cannot be distinguished with the naked eye or using a magnifying glass or microscope , since they are integrated in a completely uniform way. They can be liquid, gaseous or solid, the final state generally depends on the solvent. The most common homogeneous mixtures are solutions of solids in liquids or solids in solids, such as alloys used in metallurgy.
- Heterogeneous mixtures . They present discontinuities and this often results in the formation of phases that are well distinguishable to the naked eye.
Examples of mixtures
Some homogeneous mixtures:
- Commercial bleach, which can have varying concentrations of sodium hypochlorite (NaClO).
- A coffee with milk
- A brine
- Tincture of iodine
- Some alloys of metal ( steel , alloy iron and carbon )
- Sugar in water
Some heterogeneous mixtures:
- the blood
- The ground
- Sand in water
- Oil and vinegar
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