Existence of either acid, or main properties is characteristic of the majority of substances, however in the nature the connections capable to show also those, and other signs meet. Similar connections are called amphoteric. How to prove that substance belongs to this class?
Instruction
1. It is possible to prove amphoteric character of connection if to be based on the theory of electrolytic dissociation. According to it, electrolytes which are ionized at the same time both on acid, and on the basic to types will be amphoteric. For example, nitrogenous acid which is amphoteric connection during electrolytic dissociation will break up to a cation of hydrogen and hydroxide-anion.
2. As it appears from definition, the amphoteric character is an ability of substances to interact both with acids, and with the bases. To prove amphoteric character of connection, it is necessary to make experiment on its interaction with one and other class of substances. For example, if to dissolve oxide or hydroxide of chrome in hydrochloric acid, solution of violet or green color is as a result formed. If to connect chrome hydroxide to sodium hydroxide, complex Na salt [Cr(OH)4(H2O)2] is as a result formed that confirms acid properties of connection.
3. The amphoteric character of any oxide can be proved, having connected it serially to acid and to alkali. As a result of reactions with acid salt of this acid is formed. As a result of reaction with alkali complex salt is formed if reaction proceeds in solution, or average salt (with amphoteric elements in anion) if reaction proceeds in fusion.
4. According to the protolytic theory of Brensteda-Louri, sign of amphoteric character ability of protolitas will act at the same time as the donor and an acceptor of a proton. For example, the amphoteric character of water can be confirmed with the following equation: H2O + H2O ↔ H3O + + OH-
5. For many connections important, though indirect sign of amphoteric character is the ability of an amphoteric element to formation of two rows of salts, cationic and anion type. For example, for zinc it will be ZnCl2 and Na2ZnO2 salts.