Are there many chemically pure substances in nature ? What is seawater, milk, steel wire - individual substances, or do they consist of several components? In our article, we will get acquainted with the properties of solutions - the most common physicochemical systems with a variable composition. They may contain several components. So, milk is an organic solution containing water, drops of fat, protein molecules and mineral salts. What is a solution and how can I get it? We will answer this and other questions in our article.
The use of solutions and their role in nature
Metabolism in biogeocenoses is carried out in the form of the interaction of compounds dissolved in water. For example, the absorption of a soil solution by plant roots, the accumulation of starch as a result of photosynthesis in plants, the digestive processes of animals and humans - all of them are reactions that occur in chemical solutions. It is impossible to imagine modern industries: space and aircraft industry, military industry, nuclear energy without the use of alloys - solid solutions with unique technical characteristics. Several gases can also form mixtures, which we can call solutions. For example, air is a physicochemical system that contains components such as nitrogen, oxygen, carbon dioxide, etc.
What is a solution?
Mixing sulfate acid and water together, we get its aqueous solution. Consider what it consists of. We will find a solvent - water, a dissolved substance - sulfuric acid and the products of their interaction. These include hydrogen cations, hydrosulfate - and sulfate ions. The composition of the physico-chemical system, consisting of a solvent and components, will depend not only on which substance is the solvent.
The most common and important solvent is water. Of great importance is the nature of the soluble components. They can be divided into three groups. These are practically insoluble compounds, sparingly soluble and highly soluble. The last group is the most important. It includes most salts, acids, alkalis, alcohols, monosaccharides. Sparingly soluble compounds are also found in nature quite often. These are gypsum, nitrogen, methane, oxygen. Metals, noble gases: argon, helium, etc., kerosene, oils will be practically insoluble in water.
How to quantify the solubility of a compound
The concentration of a saturated solution is the most important value indicating the solubility of a substance. It is expressed by a value numerically equal to the mass of the compound in 100 g of solution. For example, a disinfecting medical product - salicylic alcohol is sold in pharmacies in the form of a 1% alcohol solution. This means that 100 grams of the solution contains 1 gram of the active substance. What is the largest mass of sodium chloride that can be dissolved in 100 g of solvent at a certain temperature? You can find the answer to this question using a special table of solubility curves of solid compounds. So, at a temperature of 10 ⁰, 38 g of table salt can be dissolved in 100 g of water, at 80 ⁰ - 40 g of substance. How to make the solution diluted? It is necessary to add a certain amount of water to it. You can increase the concentration of the physico-chemical system by evaporating the solution, or by adding to it a certain portion of the dissolved compound.
Types of Solutions
At a certain temperature, the system may be in equilibrium with the soluble compound in the form of its precipitate. In this case, they speak of a saturated solution. How to make the solution saturated? To do this, refer to the solubility table of solids. For example, sodium chloride weighing 31 g is introduced into water at a temperature of 20 º and normal pressure, then it is well mixed. With additional heating and the introduction of an additional portion of salt, its excess provides the formation of a supersaturated solution. Cooling the system will result in the precipitation of crystals of sodium chloride. Diluted will be called such solutions in which the concentration of the compounds in comparison with the volume of the solvent will be sufficiently small. For example, physiological saline, which is part of the blood plasma and used in medicine after surgery, is a 0.9% sodium chloride solution.
Substance dissolution mechanism
Having examined the question of what a solution is, we determine what processes underlie its formation. At the heart of the phenomenon of dissolution of substances we see the interaction of both physical and chemical transformations. The main role in them is played by the phenomenon of the destruction of chemical bonds: covalent polar or ionic, in the molecules of the soluble compound. The physical aspect of bond breaking is expressed in energy absorption. Solvent particles also interact with solute molecules, called solvation, and in the case of aqueous solutions, hydration. It is accompanied not only by the emergence of new bonds, but also by the release of energy.
In our article, we examined the question of what a solution is, and also found out the mechanism of formation of solutions and their significance.