Hydroxides are chemical compounds in which a hydroxyl group is found in the molecule. They can be acidic, basic or amphoteric. The group of amphoteric compounds includes a compound with the molecular formula Al(OH)3, called aluminium hydroxide. What are the main uses and properties of aluminium hydroxide? Let us find out.
What is aluminium?
First, let us clarify the differences between aluminium as a chemical element, and aluminium as a technical grade material. The former is a substance commonly found in nature and one of the most important components forming the Earth’s crust. Technical grade aluminium is a popular raw material produced from an ore called bauxite, which is composed of aluminium hydroxides and metal oxides (iron, silicon, etc.).
Aluminium was discovered by a Danish chemist, Hans Christian Ørsted, who in 1825 decided to investigate what would happen if he reacted aluminium chloride with potassium amalgam. As a result of the experiment, he obtained a metallic powder. However, it was not until 50 years after his discovery that the mass production of aluminium began by means of an electrolytic method. Industrialists became interested in aluminium hydroxide as it turned out to be a very useful raw material, which is still true today.
How is aluminium hydroxide obtained?
Al(OH)3 is produced on a mass scale under laboratory conditions, while aluminium hydroxide can be obtained by reacting the aluminium salt solution with an ammonia solution or a sodium hydroxide solution.
Aluminium oxides are only formed when the aluminium salt is combined with substances stronger than them (they can be both hydroxides and other, stronger chemicals).
Aluminium hydroxide: physical and chemical properties
What are the distinguishing features of aluminium hydroxide? According to the safety data sheet of Al(OH)3, it is a white, odourless powder that is not soluble in water. When it is heated up, it transforms into alumina and shows amphoteric properties.
What does it mean that aluminium hydroxide is amphoteric? It means that when exposed to substances with different pH values, the compound may behave like an acid or a base. In other words, Al(OH)3 reacts with acids and with bases.
What else can be said about aluminium hydroxide? The properties of this compound largely depend on the production technologies used. For example, Al(OH)3 powder that has been stored and not used for too long is more difficult to process with acids or bases. Aluminium hydroxide in the form of a gel is easily dissolved in both acid and base environments. What is particularly noteworthy is that dissociation of aluminium hydroxide is not possible as it is one of the few Al(OH)3 hydroxides that do not dissolve in water and are not broken down into ions.
Application of aluminium hydroxide
How is aluminium hydroxide used in the industry today? The range of application of this compound is very broad – it is appreciated by manufacturers of the chemical, pharmaceutical, medical, electrical and paper industries. There are many products containing aluminium hydroxide. Where can aluminium hydroxide be found? It is used in cosmetic products, soaps and many other products that we reach for every day. Among other products, one should name here:
- medications and medicinal products used to treat gastric hyperacidity and ulcerative diseases;
- paper fillers.
Aluminium hydroxide: is it harmful? Facts and myths
Finally, let us answer the final important question. In recent years, there have been many negative opinions about aluminium hydroxide. Where do they come from, and are they true? Some claim that aluminium hydroxide used in vaccines, antiperspirants and soaps show a carcinogenic or irritating effect. However, it is worth knowing that this substance has not yet been confirmed as harmful. There are also no scientific studies that could prove the toxicity of aluminium hydroxide.