Aluminium is very light (nearly three times less dense than iron) yet possesses high tensile strength. These properties make up its substantial usage in the transportation industries, in the construction of aircraft, ships as well as cars.
It is extremely reactive, though the metal is secured by a surface layer of inert transparent oxide (Al2O3) that creates quickly in the air, providing excellent rust resistance. A few of its important reactions are discussed in this article.
Reaction with Air
When a piece of aluminium sheet is exposed to moist air it obtains a thin, continual layer of aluminium oxide, which prevents more attacks on the metal by atmospheric oxygen and water under normal conditions.
Because of this aluminium sheets are stated to be corrosion-free. However, if the aluminium powder is heated to 800 ° C or above, the metal will react with air to form aluminium oxide, Al2O3, and aluminium nitride, AIN.
The reaction is accompanied by the development of heat and intense white light. This characteristic of aluminium is utilized in flashlight photography.
4 Al (s) + 3 O2 (g) à 2 Al2O3 (s)
2 Al (s) + N2 (g) à 2Al N (s)
As a result of its capability to incorporate both oxygen and also nitrogen, the metal is often used to remove air bubbles from liquified or molten metals. Salt solutions corrode aluminium severely so aluminium and aluminium alloys are not suitable for marine usage.
Reaction with Non-Metals
Heated aluminium integrates with the halogens, sulphur, nitrogen, phosphorus and carbon, accompanied by the formation of heat.
2 Al (s) + 3 Cl2 (g) à 2Al Cl3 (s)
Aluminium on heating with hydrogen forms aluminium hydride.
2 Al (s) + 3 H2 (g) à 2 Al H3 (s)
Reaction with Acids and Alkalies
Aluminium is amphoteric. It dissolves in both acids as well as bases with the liberation of hydrogen gas. Aluminium reacts slowly with weakened acid and more quickly with concentrated hydrochloric acid to release hydrogen.
2 Al (s) + 6 HCl (aq) à 2 Al Cl3 (aq) + 3 H2 (g)
Aluminium does not react with dilute sulphuric acid. However, it is oxidized by hot concentrated sulphuric acid to liberate sulphur dioxide gas.
2 Al (s) + 6 H2 SO4 (aq) à Al2 (SO4)3 (aq) + 6 H2O (l) + 3 SO2 (g)
Aluminium does not react with nitric acid at any type of concentration, most likely due to the development of a protective layer of aluminium oxide. The acid is said to render the aluminium passive.
Nitric acid is, therefore, frequently delivered in aluminium containers. Aluminium dissolves in both sodium as well as potassium hydroxides to develop a soluble aluminate, with the formation of hydrogen.
2 Al (s) + 2 Na OH (aq) + 6 H2O (l) à 2 Na Al (OH)4 (aq) + 3 H2 (g)