Chemistry. Disperse systems - what is it?
In nature, it is quite difficult to find a pure substance. In different states, they can form mixtures, homogeneous and heterogeneous — dispersed systems and solutions. What are these connections? What types of them are they? Consider these questions in more detail.
First you need to understand what disperse systems are. By this definition, heterogeneous structures are understood, where one substance as the smallest particles is evenly distributed in the bulk of another. The component that is present in a smaller amount is called the dispersed phase. It may contain more than one substance. A component that is present in a larger volume is called a medium. Between the particles of the phase and it there is an interface. In this regard, dispersed systems are called heterogeneous - heterogeneous. Both the medium and the phase can be represented by substances in different aggregative states: liquid, gaseous or solid.
Dispersed systems and their classification
In accordance with the size of the particles entering the phase of substances, suspensions and colloidal structures are distinguished. In the former, the size of the elements is more than 100 nm, and in the latter, from 100 to 1 nm. When a substance is crushed to ions or molecules, whose value is less than 1 nm, a solution is formed - a homogeneous system. It is distinguished from others by its homogeneity and the absence of an interface between the medium and particles. Colloidal disperse systems are presented in the form of gels and sols. In turn, suspensions are divided into suspensions, emulsions, aerosols. Solutions are ionic, molecular-ionic and molecular.
These dispersed systems include substances with a particle size greater than 100 nm. These structures are opaque: their individual components can be seen with the naked eye. The medium and phase are easily separated on standing. What is a suspension? They can be liquid or gaseous. The first are subdivided into suspensions and emulsions. The latter are structures in which the medium and phase are liquids that are insoluble in each other. These include, for example, lymph, milk, water-based paint and others.A suspension is a structure where the medium is a liquid and the phase is a solid, insoluble substance. Such dispersed systems are well known to many. These include, in particular, “milk of lime”, sea or river sludge suspended in water, microscopic living organisms that are common in the ocean (plankton), and others.
These suspensions are distributed small particles of a liquid or a solid in a gas. There are fogs, smoke, dust. The first type is the distribution of small liquid droplets in a gas. Dust and smoke are suspended solids. In this case, the first particles are somewhat larger. To natural aerosols carry thunderclouds, actually fog. Above major industrial cities hangs smog, consisting of solid and liquid components, distributed in gas. It should be noted that aerosols, as dispersed systems, are of great practical importance and perform important tasks in production and household activities. Examples of a positive result from their use include treatment of the respiratory system (inhalation), chemical treatment of the fields, spraying of paint with a spray gun.
These are dispersed systems in which the phase consists of particles ranging in size from 100 to 1 nm. Such components are not visible to the naked eye. Phase and medium in these structures with the help of sedimentation are separated with difficulties. Sols (colloidal solutions) are found in the living cell and in the body as a whole. These fluids include nuclear sap, cytoplasm, lymph, blood, and others. These disperse systems form starch, adhesives, some polymers, proteins. These structures can be obtained through chemical reactions. For example, during the interaction of solutions of silicates of sodium or potassium with acidic compounds, silicic acid is formed. Externally, the colloidal structure is similar to the true one. However, the former differ from the latter by the presence of a "luminous path" - a cone when a beam of light passes through them. Sols contain larger particles than in true solutions. Their surface reflects light - and in the vessel the observer can see a luminous cone. In the true solution of this phenomenon is not. A similar effect can also be observed in the cinema. In this case, the light beam passes not through the liquid, but the aerosol colloid - the hall air.
In colloidal solutions, particles of the phase often do not settle even during prolonged storage, which is associated with continuous collisions with solvent molecules under the influence of thermal motion. When approaching each other, they do not stick together, since on their surfaces there are electric charges of the same name. However, under certain circumstances, a coagulation process may occur. It is an effect of sticking and precipitation of colloidal particles. This process is observed when charges are neutralized on the surface of microscopic elements when electrolyte is added. In this case, the solution turns into a gel or suspension. In some cases, the coagulation process is observed when heated or in the case of changes in acid-base balance.
These colloidal dispersion systems are gelatinous sediments. They are formed during coagulation of sols. These structures include numerous polymer gels, cosmetic, confectionery, medical substances (cake "Bird's milk", marmalade, jelly, jellied meat, gelatin). They also include natural structures: opal, jellyfish bodies, hair, tendons, nervous and muscle tissue, cartilage.The development of life on planet Earth can, in fact, be considered the history of the evolution of the colloidal system. Over time, there is a violation of the gel structure, and water begins to stand out from it. This phenomenon is called syneresis.
Solutions include two or more substances. They are always single-phase, that is, they are a solid, gaseous substance or liquid. But in any case, their structure is homogeneous. This effect is explained by the fact that in one substance another is distributed in the form of ions, atoms or molecules, the magnitude of which is less than 1 nm. In the case when it is necessary to emphasize the difference between the solution and the colloidal structure, it is called true. In the process of crystallization of a liquid alloy of gold and silver, solid mixed structures are obtained.
Ionic mixtures are structures with strong electrolytes (acids, salts, alkalis — NaOH, HC104, and others). Another type are molecular-ionic dispersed systems. They contain a strong electrolyte (hydrogen sulfide, nitrous acid, and others). The last type is molecular solutions.These structures include non-electrolytes - organic substances (sucrose, glucose, alcohol, etc.). The solvent is a component whose aggregative state does not change when a solution is formed. Such an element may, for example, be water. In the solution of salt, carbon dioxide, sugar, it acts as a solvent. In the case of mixing gases, liquids or solids, the component that will be greater in the compound will act as a solvent.