Complex instability constant

Probably everyone who is familiar with school chemistry and was at least a little interested in it knows about the existence of complex compounds. These are very interesting compounds with a wide range of applications. If you have not heard of such a concept, then below we will explain everything to you. But let's start with the history of the discovery of this rather unusual and interesting type of chemical compounds.

History

Complex salts were known even before the discovery of the theory and mechanisms that allow them to exist. They were named after the chemist who discovered this or that compound, and there were no systematic names for them. And, therefore, it was impossible to understand by the formula of the substance what properties it possesses.

This continued until 1893, when the Swiss chemist Alfred Werner proposed his theory, for which, after 20 years, he received the Nobel Prize in chemistry. It is interesting that he conducted his research only with the help of interpreting various chemical reactions in which certain complex compounds entered. The research was done before the discovery of the electron by Thompson in 1896, and after this event, decades later, the theory was supplemented, in a much more modernized and complicated form, has survived to this day and is actively used in science to describe the phenomena that occur during chemical transformations involving complexes.

So, before proceeding to the description of what instability constant is, we will understand the theory that we talked about above.

Theory of Complex Compounds

Werner in his initial version of the coordination theory formulated a number of postulates that formed its basis:

1. In any coordination (complex) compound, a central ion must be present. This, as a rule, is an atom of a d-element, less often some atoms of p-elements, and only Li can act as s-elements in this capacity.
2. The central ion, together with the ligands associated with it (charged or neutral particles, for example water or a chlorine anion) forms the inner sphere of the compound. It behaves in solution as one large ion.
3. The outer sphere consists of ions opposite in sign of the charge of the inner sphere. That is, for example, for a negatively charged sphere [CrCl ₆ ] ^{3 - the} ion of the outer sphere can be metal ions: Fe ³⁺ , Ni ³⁺ , etc.

And now, if everything is clear with the theory, we can proceed to the chemical properties of complex compounds and their differences with ordinary salts.

Chemical properties

In solution, complex compounds decompose into ions, and more precisely into internal and external spheres. We can say that they behave like strong electrolytes.

In addition, the inner sphere can also decay into ions, but in order for this to happen, a lot of energy is required.

The outer sphere in complex compounds can be replaced by other ions. For example, if there was a chlorine ion in the outer sphere, and an ion is also present in the solution, which together with the inner sphere will give an insoluble compound, or if there is a cation in the solution that gives an insoluble compound with chlorine, the reaction of the outer sphere will take place .

And now, before moving on to determining what instability constant is, let's talk about a phenomenon that is directly related to this concept.

Electrolytic dissociation

You probably have known this word since school. But still we will give a definition to this concept. Dissociation is the disintegration of solute molecules into ions in a solvent medium. This is due to the formation of sufficiently strong bonds of solvent molecules with ions of the dissolved substance. For example, water has two oppositely charged ends, and some molecules are attracted by the negative end to the cations, while others are attracted by the positive end to the anions. Thus hydrates are formed - ions surrounded by water molecules. Actually, this is the essence of electrolytic dissociation.

Now, actually, back to the main topic of our article. What is the instability constant of complex compounds? Everything is quite simple, and in the next section we will analyze this concept in detail and in detail.

Complex instability constant

This indicator is actually the exact opposite of the stability constant of the complexes. Therefore, we will begin with it.

If you have heard about the equilibrium constant of the reaction, then you will easily understand the material below. But if not, now we will briefly talk about this indicator. The equilibrium constant is defined as the ratio of the concentration of reaction products raised to the degree of their stoichiometric coefficients to the starting materials, in which the coefficients in the reaction equation are also taken into account. It shows in which direction the reaction will predominantly go with one or another concentration of the starting materials and products.

But why did we suddenly start talking about the equilibrium constant? In fact, the instability constant and the stability constant are, in fact, the equilibrium constants, respectively, of the fracture reactions and the formation of the inner sphere of the complex. The relationship between them is determined very simply: K _n = 1 / K _mouth .

To better understand the material, we give an example. Take the complex anion [Ag (NO ₂ ) ₂ ] ^- and write the equation for the reaction of its decay:

[Ag (NO ₂ ) ₂ ] ^- => Ag ⁺ + 2NO ₂ ^- .

The instability constant of the complex ion of this compound is 1.3 * 10 ^-3 . It means that it is stable enough, but still not to such an extent that it is considered very stable. The greater the stability of the complex ion in the solvent medium, the lower the instability constant. Its formula can be expressed in terms of the concentration of the starting and reacting substances: K _n = [Ag +] * [2NO ₂ ^- ] ² / [[Ag (NO ₂ ) ₂ ] ^- ].

Now that we’ve figured out the basic concept, it’s worth giving some data on the various compounds. The names of chemicals are written in the left column, and the instability constant of complex compounds in the right column.

Table

More detailed data on all known compounds are given in special tables in the manuals. In any case, the instability constant of complex compounds, the table of which for several compounds is given above, is unlikely to seriously help you without using the directory.

Conclusion

After we figured out how to calculate the instability constant, there remains only one question - why this is necessary.

The main purpose of this quantity is to determine the stability of a complex ion. So, we can predict the stability in solution of a particular compound. This helps a lot in all areas, one way or another connected with the use of complex substances. Have a nice study of chemistry!