Solutions are a homogeneous mass consisting of two or more substances or a mixture in which one substance acts as a solvent and the other as a soluble particle.
There are two theories of the interpretation of the origin of solutions: chemical, the founder of which is Mendeleev D.I., and physical, proposed by the German and Swiss physicists Ostwald and Arrhenius. According to Mendeleev’s interpretation, the components of the solvent and the solute become participants in the chemical reaction with the formation of unstable compounds of these same components or particles.
The physical theory, however, denies the chemical interaction between the molecules of the solvent and the soluble substance, explaining the process of formation of solutions as a uniform distribution of particles (molecules, ions) of the solvent between the particles of the soluble substance due to a physical phenomenon called diffusion.
Classification of solutions according to various criteria
Today there is no unified system for classifying solutions, however, conditionally, the types of solutions can be grouped according to the most significant criteria, namely:
I) According to the state of aggregation emit: solid, gaseous and liquid solutions.
II) By the particle size of the dissolved substance: colloidal and true.
III) According to the degree of concentration of the particles of the dissolved substance in the solution: saturated, unsaturated, concentrated, diluted.
IV) By the ability to conduct electric current: electrolytes and non-electrolytes.
V) By purpose and scope: chemical, medical, construction, special solutions, etc.
Types of solutions according to the state of aggregation
The classification of solutions according to the state of aggregation of the solvent is given in the broad sense of the meaning of this term. It is customary to consider liquid substances as solutions (moreover, both liquid and solid elements can act as a soluble substance), however, given the fact that a solution is a homogeneous system of two or more substances, it is quite logical to recognize solid solutions as well, and gaseous. Solid solutions are considered mixtures, for example, of several metals, more commonly known as alloys. Gaseous types of solutions are mixtures of several gases, an example is the air surrounding us, which is presented as a combination of oxygen, nitrogen and carbon dioxide.
Solutions by size of dissolved particles
Types of solutions according to the size of dissolved particles include true (ordinary) solutions and colloidal systems. In true solutions, the soluble substance breaks up into small molecules or atoms, similar in size to the molecules of the solvent. In this case, the true types of solutions retain the initial properties of the solvent, only slightly transforming it under the influence of the physicochemical properties of the element added to it. For example: when dissolving table salt or sugar in water, the water remains in the same state of aggregation and the same consistency, almost the same color, only its taste changes.
Colloidal solutions differ from ordinary ones in that the added component does not completely decompose, preserving complex molecules and compounds whose sizes significantly exceed solvent particles, exceeding a value of 1 nanometer.
Types of concentration of solutions
Different amounts of the element to be dissolved can be added to the same amount of solvent; we will have solutions with different concentrations at the output. We list the main ones:
- Saturated solutions are characterized by the degree of solubility of the substance, in which the soluble component, under the influence of a constant value of temperature and pressure, no longer decomposes into atoms and molecules and the solution reaches phase equilibrium. Saturated solutions can also be conditionally divided into concentrated, in which the mass fraction of the dissolved component is comparable to the solvent, and diluted, where the dissolved substance is several times smaller than the solvent.
- Unsaturated - these are those solutions in which the soluble substance can still decompose into small particles.
- Supersaturated solutions are obtained when the parameters of the influencing factors (temperature, pressure) change, as a result of which the process of “crushing” of the dissolved substance continues, it becomes more than it was under normal (ordinary) conditions.
Electrolytes and Non-Electrolytes
Some substances in solutions decay into ions that can conduct an electric current. Such homogeneous systems are called electrolytes. This group includes acids, most salts. And solutions that do not conduct electric current are commonly called non-electrolytes (almost all organic compounds).
Groups of solutions for the intended purpose
Solutions are indispensable in all sectors of the economy, the specificity of which has created such types of special solutions as medical, construction, chemical and others.
Medical solutions are a combination of preparations in the form of ointments, suspensions, mixtures, solutions for infusion and injection and other dosage forms used for medical purposes for the treatment and prevention of various diseases.
Types of chemical solutions include a huge variety of homogeneous compounds used in chemical reactions: acids, salts. These solutions can be of organic or inorganic origin, aqueous (seawater) or anhydrous (based on benzene, acetone, etc.), liquid (vodka) or solid (brass). They found their application in various sectors of the national economy: chemical, food, textile industry.
Types of mortars differ in viscous and thick consistency, which is why the name of the mixture is more suitable for them.
Due to their ability to quickly harden, they are successfully used as a
binding material for masonry walls, ceilings, load-bearing structures, as well as for finishing work. They are aqueous solutions, most often three-component ones (solvent, cement of various markings, aggregate), where sand, clay, gravel, lime, gypsum and other construction materials are used as filler.