Probably everyone who is familiar with school chemistry and was even a little interested in it knows about the existence of complex compounds. These are very interesting compounds with wide 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 compound.
History
Complex s alts 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 a substance what properties it has.
This continued until 1893, until the Swiss chemist Alfred Werner proposed his theory, for which 20 years later he received the Nobel Prize in Chemistry. It is interesting that he conducted his studies only by interpreting various chemical reactions in which certain complex compounds entered. Research has been done beforethe discovery of the electron by Thompson in 1896, and after this event, dozens of years later, the theory was supplemented, in a much more modernized and complicated form has reached our days 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 the instability constant is, let's understand the theory we talked about above.
Theory of complex compounds
Werner in his original version of the coordination theory formulated a number of postulates that formed its basis:
- A central ion must be present in any coordination (complex) compound. This is, as a rule, an atom of a d-element, less often - some atoms of p-elements, and of the s-elements, only Li can act in this capacity.
- The central ion, together with its associated ligands (charged or neutral particles, such as water or chlorine anion) forms the inner sphere of the complex compound. It behaves in solution like one big ion.
- The outer sphere consists of ions opposite in sign to the charge of the inner sphere. That is, for example, for a negatively charged sphere [CrCl6]3- the outer sphere ion can be metal ions: Fe3 +, Ni3+ etc.
And now, if everything is clear with the theory, we can move on to the chemical properties of complex compounds and their differences with ordinary s alts.
Chemical properties
In a solution, complex compounds decompose into ions, or rather into inner and outer spheres. We can say that they behave like strong electrolytes.
In addition, the inner sphere can also decay into ions, but for this to happen, quite 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 form an insoluble compound, or if there is a cation in the solution, which will give an insoluble compound with chlorine, an outer sphere substitution reaction will occur.
And now, before proceeding to the definition of what an instability constant is, let's talk about a phenomenon that is directly related to this concept.
Electrolytic dissociation
You probably know this word from school. However, let's define 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, and others by the positive end to the anions. This is how hydrates are formed - ions surrounded by water molecules. Actually, this is the essence of the electrolyticdissociation.
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.
Instability constant of complex compounds
This indicator is actually the direct opposite of the stability constant of complexes. Therefore, let's start with it.
If you have heard about the equilibrium constant of a reaction, 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 the reaction products, raised to the power of their stoichiometric coefficients, to the initial substances, in which the coefficients in the reaction equation are taken into account in the same way. It shows in which direction the reaction will predominantly go at one or another concentration of starting substances 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 reactions of destruction and formation of the inner sphere of the complex. The connection between them is determined very simply: Kn=1/Kst.
To better understand the material, let's take an example. Let us take the complex anion [Ag(NO2)2]- and write the equation for its decay reaction:
[Ag(NO2)2]-=> Ag + + 2NO2-.
The instability constant of the complex ion of this compound is 1.310-3. This means that it is stable enough, but still not to such an extent as to be 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 concentrations of the starting and reacting substances:]2/[Ag(NO2)2] -].
Now that we have de alt with the basic concept, it is worth giving some data on various compounds. The names of chemicals are written in the left column, and the instability constant of complex compounds is written in the right column.
Table
| Substance | Instability constant |
| [Ag(NO2)2]- | 1.310-3 |
| [Ag(NH3)2]+ | 6.8×10-8 |
| [Ag(CN)2]- | 1×10-21 |
| [CuCl4]2- | 210-4 |
More detailed data on all known compounds are given in special tables in reference books. In any case, the instability constant of complex compounds, the table of which for several compounds is given above, is unlikely to be of much help to you without using the reference book.
Conclusion
After we figured out how to calculate the instability constant,only one question remains - about why all this is needed.
The main purpose of this quantity is to determine the stability of a complex ion. This means that we can predict the stability in a solution of a particular compound. This helps a lot in all areas, one way or another related to the use of complex substances. Happy learning chemistry!
