Pure substances are almost never found in nature. Basically, they are presented in the form of mixtures that are able to form homogeneous or heterogeneous systems.
Features of true solutions
True solutions are a kind of dispersed systems that have greater strength between the dispersion medium and the dispersed phase.
Crystals of different sizes can be obtained from any chemical substance. In any case, they will have the same internal structure: ionic or molecular crystal lattice.
Dissolve
In the process of dissolving grains of sodium chloride and sugar in water, an ionic and molecular solution is formed. Depending on the degree of fragmentation, the substance can be in the form:
- visible macroscopic particles larger than 0.2mm;
- microscopic particles smaller than 0.2 mm can only be captured with a microscope.
True and colloidal solutions differ in the size of the particles of the solute. Crystals invisible under a microscope are called colloidal particles, and the resulting state is called a colloidal solution.
Solution phase
In many cases, true solutions are crushed (dispersed) systems of a homogeneous type. They contain a continuous continuous phase - a dispersion medium, and crushed particles of a certain shape and size (dispersed phase). How do colloidal solutions differ from true systems?
The main difference is the particle size. Colloidal-dispersed systems are considered heterogeneous, since it is impossible to detect the phase boundary in a light microscope.
True solutions - this is the option when in the environment a substance is presented in the form of ions or molecules. They refer to single-phase homogeneous solutions.
As a prerequisite for the formation of dispersed systems, mutual dissolution of the dispersion medium and the dispersed substance is considered. For example, sodium chloride and sucrose are insoluble in benzene and kerosene, so colloidal solutions will not form in such a solvent.
Classification of disperse systems
How are dispersed systems divided? True solutions, colloidal systems differ in several ways.
There is a division of dispersed systems according to the state of aggregation of the medium and the dispersed phase, the formation or absence of interaction between them.
Features
There are certain quantitative characteristics of the dispersity of a substance. First of all, the degree of dispersion is distinguished. This value is the reciprocal of the particle size. She ischaracterizes the number of particles that can be placed in a row at a distance of one centimeter.
In the case when all particles have the same size, a monodisperse system is formed. With unequal particles of the dispersed phase, a polydisperse system is formed.
With an increase in the dispersion of a substance, the processes that occur in the interfacial surface increase in it. For example, the specific surface of the dispersed phase increases, the physicochemical effect of the medium at the interface between two phases increases.
Variants of disperse systems
Depending on the phase in which the solute will be, different variants of dispersed systems are distinguished.
Aerosols are dispersed systems in which the dispersed medium is presented in gaseous form. Fogs are aerosols having a liquid dispersed phase. Smoke and dust are generated by the solid dispersed phase.
Foam is a dispersion in a liquid of a gaseous substance. Liquids in foams degenerate into films that separate gas bubbles.
Emulsions are dispersed systems, where one liquid is distributed over the volume of another without dissolving in it.
Suspensions or suspensions are low-dispersion systems in which solid particles are in a liquid. Colloidal solutions or sols in an aqueous dispersion system are called hydrosols.
Depending on the presence (absence) between the particles of the dispersed phase, free-dispersed or coherently dispersed systems are distinguished. To the first groupinclude lyosols, aerosols, emulsions, suspensions. In such systems, there are no contacts between the particles and the dispersed phase. They move freely in solution under the influence of gravity.
Cohesive-disperse systems arise in the case of contact of particles with a dispersed phase, as a result of which structures in the form of a grid or a framework are formed. Such colloidal systems are called gels.
The process of gelation (gelatinization) is the transformation of a sol into a gel, based on a decrease in the stability of the original sol. Examples of bonded disperse systems are suspensions, emulsions, powders, foams. They also include soil formed in the process of interaction of organic (humus) substances and soil minerals.
Capillary-dispersed systems are distinguished by a solid mass of substance penetrating capillaries and pores. They are considered fabrics, different membranes, wood, cardboard, paper.
True solutions are homogeneous systems consisting of two components. They can exist in solvents of different state of aggregation. A solvent is a substance taken in excess. A component that is taken in insufficient quantity is considered a solute.
Features of solutions
Hard alloys are also solutions in which various metals act as a dispersed medium and component. From a practical point of view, of particular interest are such liquid mixtures in which the liquid acts as a solvent.
From numerous inorganicsolvents of particular interest is water. Almost always, a true solution is formed when particles of a solute are mixed with water.
Among organic compounds, the following substances are excellent solvents: ethanol, methanol, benzene, carbon tetrachloride, acetone. Due to the chaotic movement of the molecules or ions of the dissolved component, they partially pass into the solution, forming a new homogeneous system.
Substances differ in their ability to form solutions. Some can be mixed with each other in unlimited quantities. An example is the dissolution of s alt crystals in water.
The essence of the dissolution process from the point of view of the molecular-kinetic theory is that after the introduction of sodium chloride crystals into the solvent, it dissociates into sodium cations and chlorine anions. Charged particles oscillate, collisions with the particles of the solvent itself lead to the transition of ions into the solvent (binding). Gradually, other particles are connected to the process, the surface layer is destroyed, the s alt crystal dissolves in water. Diffusion allows the distribution of particles of a substance throughout the volume of the solvent.
Types of true solutions
True solution is a system that is divided into several types. There is a classification of such systems into aqueous and non-aqueous according to the type of solvent. They are also classified according to the solute variant into alkalis, acids, s alts.
Eatdifferent types of true solutions in relation to electric current: non-electrolytes, electrolytes. Depending on the concentration of the solute, they can be diluted or concentrated.
True solutions of low-molecular substances from a thermodynamic point of view are divided into real and ideal.
Such solutions can be ion-dispersed, as well as molecular-dispersed systems.
Saturation of solutions
Depending on how many particles go into solution, there are supersaturated, unsaturated, saturated solutions. A solution is a liquid or solid homogeneous system, which consists of several components. In any such system, a solvent is necessarily present, as well as a solute. When some substances are dissolved, heat is released.
Such a process confirms the theory of solutions, according to which dissolution is considered as a physical and chemical process. There is a division of the solubility process into three groups. The first are those substances that are able to dissolve in an amount of 10 g in 100 g of a solvent, they are called highly soluble.
Substances are considered sparingly soluble if less than 10 g dissolves in 100 g of the component, the rest are called insoluble.
Conclusion
Systems consisting of particles of different state of aggregation, particle sizes, are necessary for normal human life. True, colloidal solutions, discussed above, are used todrug manufacturing, food production. Knowing the concentration of a solute, you can independently prepare the necessary solution, for example, ethyl alcohol or acetic acid, for various purposes in everyday life. Depending on the state of aggregation of the solute and solvent, the resulting systems have certain physical and chemical characteristics.
