Classification of solutions in chemistry
Solutions are called homogeneous mixtures consisting of at least two components. One of them is a solvent. It sets the aggregate state of the solution and, as a rule, makes up most of its mass. In this case, the system may contain several solvents and solutes simultaneously. The classification of solutions is quite extensive. Dividing them into species can be based on different characteristics.
Classification of solutions according to the nature of the solvent
In this case, the solutions are divided into aqueous and non-aqueous. Water is the most common and universal solvent on the planet, but it is not capable of dissolving all substances. The choice of solvent is often guided by the so-called similarity rule. It consists in the fact that substances of inorganic nature dissolve better in water. To dissolve organic compounds, it is necessary to use special organic solvents, such as benzene, chloroform or alcohols.
By particle size of solute
The most common classification principle. In this case, there are two types of systems: true and colloidal.
In the first case, the solute is in the form of individual atoms and molecules. The sizes of these particles are so small that they cannot be distinguished visually or with an optical microscope. True are, for example, aqueous solutions of salt, sugar or acetic acid. Their main distinguishing feature is the absence of clouding.
In colloidal systems, the solute is contained in the form of aggregates of sufficiently large size (from 1 to 1000 nm), which are noticeable to the naked eye. The light passing through such a solution is cone-shaped. This phenomenon is called the Tyndall effect.
Classification of colloidal systems
In turn, colloidal systems can be divided into types depending on the state of aggregation of the solvent and the solute. The table below shows their classification. The aggregate state of the solvent is indicated vertically, and the solute - horizontally.
|Solid||Alloy, ceramics, composite materials||Capillary systems (eg soil)||Porous bodies (pumice)|
|Liquid||Suspension (lime), gel||Emulsion (milk)||Foam|
|Gaseous||Aerosols (smoke)||Aerosols (fogs, clouds)||-|
Smoke is a solution of solid carbon particles in the air.
When water is mixed with oil, another type of dispersion systems is formed - emulsion. As a rule, they quickly exfoliate. If necessary, special substances-stabilizers are added to the emulsion.
Another rather unusual example of a solution is sea foam. Moreover, it can be viewed from two points of view: as a solution of air in water (this is the basis for foaming as such) and as a true aqueous solution of mineral salts.
Classification of true solutions
Examples of true are aqueous solutions of salt, soda, sugar, acetic acid, etc. They are usually classified according to the concentration of the solute. On this basis, there are three types of solutions in chemistry.
If under these conditions (temperature, pressure) it is possible to dissolve a larger amount of the substance than is already contained in the solution, it is called unsaturated.
Saturated solution contains the maximum possible in the conditions of the experiment the amount of solute.
If the solution contains more substance than the saturated one, such a system is called supersaturated. It can be obtained by very slowly and carefully cooling a saturated solution prepared at a higher temperature.
Supersaturated solutions are extremely unstable. In the event of an imbalance, the crystallization process of the excess solute begins immediately. A small crystal of substance, ingestion of a foreign body (for example, dust) or shaking of a solution can initiate precipitation.
Classification according to the degree of saturation
Another common principle is the separation of solutions into species. So, depending on the concentration of the solution, two types can be distinguished: diluted and concentrated. However, the boundary between them is very conditional.
Diluted solution is characterized by a low content of solute. However, it can not be identified with the unsaturated.
For example, a solution containing as little as 0.0000134 mol / l of silver chloride is diluted, since the concentration of the solute in it is very small.However, under normal conditions, it is impossible to dissolve a larger amount of the compound in it, and therefore such a solution will be simultaneously saturated.
By physical properties
Quite often, substances and their solutions are classified according to their ability to conduct electrical current. It has solutions of substances with an ionic bond in the molecules. Under the action of water molecules, these compounds are able to undergo electrolytic dissociation into ions. Such substances and their solutions are called electrolytes. Examples of electrolytes: solutions of sodium chloride, sulfuric acid, potassium bromide.
Organic substances, as a rule, are in solution in the form of neutral molecules or have little dissociation. Such systems are not able to conduct current and are called non-electrolytes.
Thus, the classification of solutions is extensive and diverse. Its type is selected depending on specific goals.