Chemistry is an interesting and quite complex science. Its terms and concepts come across to us in everyday life, and it is not always intuitively clear what they mean and what their meaning is. One of these concepts is solubility. This term is widely used in the theory of solutions, and in everyday life we encounter its use because we are surrounded by these same solutions. But it is not so much the use of this concept that is important, but the physical phenomena that it denotes. But before moving on to the main part of our story, let's fast forward to the nineteenth century, when Svante Arrhenius and Wilhelm Ostwald formulated the theory of electrolytic dissociation.
History
The study of solutions and solubility begins with the physical theory of dissociation. It is the easiest to understand, but too primitive and only in part of the moments coincides with reality. The essence of this theory is that the solute, getting into the solution, breaks up into charged particles called ions. It is these particles that determine the chemical properties of the solution and some of its physical characteristics, including conductivity and boiling point, melting point and crystallization point.
But there are morecomplex theories that consider a solution as a system in which the particles interact with each other and form the so-called solvates - ions surrounded by dipoles. A dipole is, in general, a neutral molecule, the poles of which are oppositely charged. The dipole is most often a solvent molecule. Getting into the solution, the dissolved substance decomposes into ions, and the dipoles are attracted to one ion by the oppositely charged end with respect to them, and to other ions by the other oppositely charged end, respectively. Thus, solvates are obtained - molecules with a shell of other neutral molecules.
Now let's talk a little about the essence of the theories themselves and take a closer look at them.
Solution theories
The formation of such particles can explain many phenomena that cannot be described using the classical theory of solutions. For example, the thermal effect of the dissolution reaction. From the standpoint of the Arrhenius theory, it is difficult to say why, when one substance is dissolved in another, heat can be absorbed and released. Yes, the crystal lattice is destroyed, and therefore energy is either expended and the solution cools, or released during decay due to the excess energy of chemical bonds. But it turns out to be impossible to explain this from the standpoint of the classical theory, since the destruction mechanism itself remains incomprehensible. And if we apply the chemical theory of solutions, it becomes clear that solvent molecules, wedged into the voids of the lattice, destroy it from the inside, as if "enclosing"ions from each other by a solvate shell.
In the next section, we will look at what solubility is and everything related to this seemingly simple and intuitive quantity.
The concept of solubility
It is purely intuitive that solubility indicates how well a substance dissolves in a given particular solvent. However, we usually know very little about the nature of the dissolution of substances. Why, for example, chalk does not dissolve in water, and table s alt - vice versa? It's all about the strength of the bonds within the molecule. If the bonds are strong, then because of this, these particles cannot dissociate into ions, thereby destroying the crystal. Therefore, it remains insoluble.
Solubility is a quantitative characteristic showing what proportion of a solute is in the form of solvated particles. Its value depends on the nature of the solute and solvent. Solubility in water for different substances is different, depending on the bonds between atoms in the molecule. Substances with covalent bonds have the lowest solubility, while those with ionic bonds have the highest.
But it is not always possible to understand which solubility is large and which is small. Therefore, in the next section, we will discuss what the solubility of various substances in water is.
Comparison
There are a lot of liquid solvents in nature. There are even more alternative substances that can serve as the last when certain conditions are reached, for example, a certainaggregate state. It becomes clear that if you collect data on the solubility in each other of each pair of "solute - solvent", it will not be enough for an eternity, because the combinations are huge. Therefore, it so happened that on our planet water is the universal solvent and standard. They did this because it is the most common on Earth.
Thus, a water solubility table was compiled for many hundreds and thousands of substances. We have all seen it, but in a shorter and more understandable version. The cells of the table contain letters denoting a soluble substance, insoluble or slightly soluble. But there are more highly specialized tables for those who are seriously versed in chemistry. It indicates the exact numerical value of the solubility in grams per liter of solution.
Now let's turn to the theory of such a thing as solubility.
Solubility Chemistry
How the dissolution process itself takes place, we have already analyzed in the previous sections. But how, for example, to write it all down as a reaction? Everything is not so simple here. For example, when an acid is dissolved, a hydrogen ion reacts with water to form a hydronium ion H3O+. Thus, for HCl, the reaction equation will look like this:
HCl + H2O =H3O+ + Cl-
The solubility of s alts, depending on their structure, is also determined by its chemical reaction. The type of the latter depends on the structure of the s alt andbonds within its molecules.
We figured out how to graphically record the solubility of s alts in water. Now it's time for practical application.
Application
If you list the cases when this value is needed, not even a century is enough. Indirectly, using it, you can calculate other quantities that are very important for the study of any solution. Without it, we would not be able to know the exact concentration of the substance, its activity, we would not be able to assess whether the medicine will cure a person or kill (after all, even water is life-threatening in large quantities).
In addition to the chemical industry and scientific purposes, understanding the essence of solubility is also necessary in everyday life. Indeed, sometimes it is required to prepare, say, a supersaturated solution of a substance. For example, this is necessary to obtain s alt crystals for a child's homework. Knowing the solubility of s alt in water, we can easily determine how much it needs to be poured into a vessel so that it begins to precipitate and form crystals from an excess.
Before we wrap up our brief excursion into chemistry, let's talk about a few concepts related to solubility.
What else is interesting?
In our opinion, if you have reached this section, you probably already understood that solubility is not just a strange chemical quantity. It is the basis for other quantities. And among them: concentration, activity, dissociation constant, pH. And this is not a complete list. You must have heard at least onefrom these words. Without this knowledge about the nature of solutions, the study of which began with solubility, we can no longer imagine modern chemistry and physics. What is the physics here? Sometimes physicists also deal with solutions, measure their conductivity, and use their other properties for their own needs.
Conclusion
In this article we got acquainted with such a chemical concept as solubility. This was probably quite useful information, since most of us hardly understand the deep essence of the theory of solutions without having the desire to dive into its study in detail. In any case, it is very useful to train your brain by learning something new. After all, a person must "study, study and study again" all his life.
