There hydroxides which react with acids and bases, depending on the conditions.These compounds exhibit a dual nature, called amphoteric hydroxides.They are formed by a metal cation and a hydroxide ion as the reason.The ability to act as acid and base have only hydroxides, which contain in their composition, such metals: Be, Zn, Al, Pb, Sn, Ga, Cd, Fe, Cr (III), and others. As can be seen from the Periodic System D.I.Mendeleev, hydroxides to form the dual nature of the metals, which are closest to the non-metals.It is believed that such elements are transitional forms, and the division of metals and non-metals is rather arbitrary.
amphoteric hydroxides are solid powder fine-grained material, which often have a white color, do not dissolve in water and slightly conductive (weak electrolytes).Some of these bases may be soluble in acids and alkalis.Dissociation "dual connections" in aqueous solutions occurs by acids and bases.This is due to the fact that the strength of retention between the metal atoms and oxygen (Me- O) and between atoms of hydrogen and oxygen (O - H) is almost equal, ie,Me - O - N. Therefore, these relations will be broken off at the same time, as these substances -dissotsiirovat cations H + and OH- anions.
confirm the dual nature of these compounds will amphoteric hydroxide - Be (OH) 2.Consider the interaction of beryllium hydroxide with an acid and a base.
1. Be (OH) 2+ 2HCl -BeCl2 + 2H2O.
2. Be (OH) 2 + 2KOH - K2 [Be (OH) 4] - tetragidroksoberillat potassium.
In the first case, the neutralization reaction takes place, the result of which is the formation of salts and water.In the second case, the reaction product is a complex compound.The neutralization reaction is typical for all, without exception, hydroxides, but the interaction with their own kind is characteristic only for amphoteric.These dual properties will be other amphoteric compounds - oxides and the metals themselves, which they are formed.
Other chemical properties of such hydroxides are characteristic of all reasons:
1. Thermal decomposition, reaction products - corresponding oxide and water: Be (OH) 2 -VeO + N2O.
2. neutralization reaction with acids.
3. Responding to the acid oxides.
also need to remember that there are substances that do not interact with amphoteric hydroxides, ie,the chemical reaction is not it:
- non-metals;
- metals;
- insoluble base;
- amphoteric hydroxides.
- average salt.
Get these compounds by precipitation with alkali salt solutions appropriate:
BeCl2 + 2KOH - Be (OH) 2+ 2KCl.
salts of certain elements during this reaction to form a hydrate, the properties of which closely follows that of the dual nature of hydroxides.Themselves with the dual properties of the base part of the minerals in the form and which occur naturally (bauxite, goethite, etc.).
Thus, amphoteric hydroxides - are inorganic substances which, depending on the nature of the substance that enters them in the reaction, can act as bases or acids.Most often, they correspond amphoteric oxides containing the corresponding metal (ZnO-Zn (OH) 2; BeO - Be (OH) 2), etc.).
