Aluminum and its reaction with water
What makes aluminum corrosion resistant
Aluminum was first obtained in the early 19th century, by the physicist Hans Christian Ørsted. He conducted his experiment with an potassium amalgam, aluminum chloride, and with the subsequent distillation of mercury.
Incidentally, the name of this silvery material came from the Latin word for alum (alumen), because this element is produced from them.
Alums are natural minerals on the basis of metals which combine a hydrated double sulfate salt in their composition.
Previously, aluminum was considered to be a precious metal and cost considerably more than gold. This was because the metal was rather difficult to separate from impurities. So only rich and influential people could afford jewelry made of aluminum.
But soon, in 1886, a method was developed by Charles Martin Hall and Paul Héroult for producing aluminum in industrial scale, which drastically reduced the cost of this metal, and allowed it to be used in the metallurgical industry. The industrial method involved the electrolysis of an alloy of cryolite, in which aluminum oxide was dissolved. It is difficult to appreciate the value of this metal in its present form, as many items made of aluminum are used by people in everyday life.
Application of aluminum
Thanks to its malleability and lightness, and also its corrosion resistance, aluminum is a valuable metal of great importance in modern industry, from which such household items are made as kitchenware, and in industry: for example, it is widely used in aircraft and automobile construction.
Aluminum is also one of the most inexpensive and economical materials, as it can be used endlessly, by melting down used aluminum cans and other objects.
Metallic aluminum is safe, but its compounds can have a toxic effect on humans and animals, particularly aluminum chloride, acetate, and sulfate.
The physical properties of aluminum
Aluminum is a silvery-white light metal, which can form alloys with the majority of metals, especially copper and magnesium, and also silicon. It is also very ductile, and can easily be turned into a thin sheet or foil. The melting point of aluminum is 660 °C, and its boiling temperature is 2470 °C.
The chemical properties of aluminum
If aluminum is left at room temperature, a durable protective layer of aluminum oxide Al₂O₃ forms on the metal, which protects it from corrosion.
Aluminum practically does not react with oxidizers because of the oxide film that protects it. But this film can be easily destroyed, so that the metal displays active reductive properties. The oxide film of aluminum can be destroyed by a solution or alloy of alkalis, or with acids, and also with mercury chloride or oxide. Thanks to its reducing properties, aluminum has found application in industry for obtaining other metals or non-metals, and this process is called aluminothermy. This feature of aluminum involves the interaction with oxides of other metals.
For example, let us examine the reaction with chromium oxide:
2Al + Cr₂O₃ = Al₂O₃ + 2Cr
Aluminum easily reacts with simple substances. For example, with halogens, fluorine is the exception, aluminum can form aluminum iodide, chloride or bromide:
2Al+3Cl₂ = 2AlCl₃
With other non-metals such as fluorine, sulfur, nitrogen, carbon etc. aluminum can only react when heated.
The silvery metal also reacts with complex chemical substances. For example, with alkalis it forms aluminates. i.e. complex compounds which are actively used in the paper and textile industry. It enters into the reaction as aluminum hydroxide
Al(ОН)₃ + NaOH = Na[Al(OH)₄],
and as metallic aluminum or aluminum oxide:
2Al + 2NaOH + 6Н₂О = 2Na[Al(OH)₄] + ЗН₂↑
Al₂O₃ + 2NaOH + 3H₂O = 2Na[Al(OH)₄]
With strong acids, for example, sulfuric and hydrochloric, aluminum reacts quite calmly, without ignition.
If a piece of the metal is put in hydrochloric acid, a slow reaction takes place, as initially the oxide film will be dissolved from its surface, but then the reaction speeds up. Aluminum reacts with hydrochloric acid with the release of hydrogen, and the result of the reaction is aluminum chloride:
Al₂O₃ + 6HCl = 2AlCl₃ + 3H₂O
The reaction of aluminum with water
If you take an aluminum filing and put it in water, nothing will happen, because aluminum is protected by an oxide film, which does not allow the metal to join into a reaction.
Only after the protective film is removed with mercury chloride can there be a result. The metal must be soaked for two minutes in a solution of mercury chloride, and then rinsed well. As a result, an amalgam forms, an alloy of mercury and aluminum:
3HgCI₂ + 2Al = 2AlCI₃ + 3Hg
The amalgam does not stay on the surface of the metal. Now, after putting the cleaned metal in water, you can observe a slow reaction, which is accompanied by the release of hydrogen and the formation of aluminum hydroxide:
2Al + 6H₂O = 2Al(OH)₃ + 3H₂↑