Average, sour and main salts are products of full or incomplete replacement of atoms of hydrogen in molecules of acids atoms of metal or hydroxide ions in molecules of the bases the acid remains. But except average, sour and the main, there are also double and complex salts. What do they represent?
As double and complex salts are formed
Double and complex salts are formed by connection of neutral molecules of different substances with each other. These classes differ among themselves in the nature of dissociation in water solutions: if double salts dissociate odnostupenchato on cations of both metals (or an ammonium cation) and anions of the acid remains, then at dissociation of complex salts are formed the complex ions showing high stability in the water environment. Examples of dissociation of complexes:
K3 [Fe(CN)6] = 3K (+)+ [Fe(CN)6](3-).
Complex salts are weak electrolytes therefore dissociate in water solutions reversibly. There is both a direct, and return reaction.
Theory of complex connections
The theory of complex connections was created by the Swiss chemist A. Verner. According to this theory, in the center of a molecule there is an ion-kompleksoobrazovatel (metal ion) around which the ions of the opposite sign or neutral molecules called ligands, or addenda are oriented.
Most often as the central ions-kompleksoobrazovateley d-elements act.
Ligands of hydroksokomplex are OH-hydroxide ions, atsidokomplex – anions of the acid remains (NO 2-, CN-, Cl-, Br-, etc.), ammiakat and akvokomplex – neutral molecules of ammonia and water. For example: Na2 [Zn(OH)4], K4 [Fe(CN)6], [Ag(NH3)2] of Cl, [Al(H2O)6] of Cl3. Ion-kompleksoobrazovatel together with ligands forms the internal sphere of complex connection designated by square brackets. The number of ligands around the central ion is a coordination number. The charge of a complex ion consists of charges of an ion-kompleksoobrazovatelya and ligands.
The charge of a complex ion is equal to a charge of a kompleksoobrazovatel if neutral molecules act as ligands (for example, ammonia or water).
Ions behind square brackets form the external sphere of a complex. Depending on a charge of the internal sphere they can be cations or anina.
What role is played by complex connections in life of plants and animals
Complex connections perform specific exchange functions in living organisms. They are necessary for processes of photosynthesis, breath, oxidation and an enzymatic catalysis. So, a chlorophyll in cages of green plants are a complex compound of magnesium, hemoglobin of animals – an iron complex. B12 vitamin represents complex compound of cobalt.