Amphoteric metals are simple substances that are similar in structure, chemical and physical properties to the metal group of elements. Metals themselves cannot exhibit amphoteric properties, unlike their compounds. For example, the oxides and hydroxides of some metals have a dual chemical nature - in some conditions they behave like acids, and in others they have the properties of alkalis.
The main amphoteric metals are aluminum, zinc, chromium, and iron. The same group of elements includes beryllium and strontium.
What is amphotericity?
This property was first discovered long ago. And the term "amphoteric elements" was introduced into science in 1814 by the famous chemists L. Tenard and J. Gay-Lussac. In those days, it was customary to divide chemical compounds into groups that corresponded to their basic properties during reactions.
However, the group of oxides and bases possessed dual abilities. In some conditions, such substances behaved like alkalis, in others, on the contrary, they acted as acids. That is how the term “amphotericity” arose. For such chemicals, the behavior during the acid-base reaction depends on its conditions, the nature of the reagents involved, and also on the properties of the solvent.
Interestingly, in vivo amphoteric metals can interact with both alkali and acid. For example, during the reaction of aluminum with sulfate acid , aluminum sulfate is formed. And when the same metal reacts with concentrated alkali, a complex salt is formed.
Amphoteric bases and their main properties
Under normal conditions, these are solids. They practically do not dissolve in water and are considered rather weak electrolytes.
The main method for obtaining such bases is the reaction of a metal salt with a small amount of alkali. The precipitation reaction must be carried out slowly and carefully. For example, when receiving zinc hydroxide in a test tube with zinc chloride, caustic soda is added dropwise. Each time you need to slightly shake the container to see a white precipitate of metal at the bottom of the dishes.
Amphoteric substances react with acids and acid oxides as bases. For example, the reaction of zinc hydroxide with hydrochloric acid produces zinc chloride.
But during reactions with bases, amphoteric bases behave like acids.
In addition, with strong heating, amphoteric hydroxides decompose to form the corresponding amphoteric oxide and water.
The most common amphoteric metals: a brief description
Zinc belongs to the group of amphoteric elements. And although the alloys of this substance were widely used in ancient civilizations, in its pure form they could be isolated only in 1746.
Pure metal is a rather fragile bluish substance. In air, zinc oxidizes quickly - its surface tarnishes and becomes covered with a thin film of oxide.
In nature, zinc exists primarily in the form of minerals - zincites, smitsonites, calamites. The most famous substance is zinc blende, which consists of zinc sulfide. The largest deposits of this mineral are in Bolivia and Australia.
Aluminum is today considered the most common metal on the planet. Its alloys have been used for many centuries, and in 1825 the substance was isolated in its pure form.
Pure aluminum is a light silver metal. It is easy to machine and cast. This element has a high electrical and thermal conductivity. In addition, this metal is resistant to corrosion. The fact is that its surface is covered with a thin, but very resistant oxide film.
Today, aluminum is widely used in industry.