Aluminium hydroxide
From Wikipedia, the free encyclopedia
| Aluminium hydroxide | |
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| General | |
| Systematic name | Aluminium(III) hydroxide |
| Other names | Aluminium hydroxide, Hydrated alumina |
| Molecular formula | Al(OH)3 |
| Molar mass | 78.00344 g/mol |
| Appearance | White amorphous powder. |
| CAS number | [[]] |
| Properties | |
| Density and phase | 2.4 g/cm³, solid. |
| Solubility in water | Insoluble. |
| Melting point | 300°C |
| Boiling point | ?°C |
| Acidity (pKa) | N/A |
| Hazards | |
| MSDS | External MSDS |
| EU classification | Irritant (I) |
| NFPA 704 | N/A |
| R-phrases | R36, R37, R38 |
| S-phrases | S26, S36 |
| Flash point | Non-flammable. |
| RTECS number | N/A |
| Supplementary data page | |
| Structure & properties | n, εr, etc. |
| Thermodynamic data | Phase behaviour Solid, liquid, gas |
| Spectral data | UV, IR, NMR, MS |
| Related compounds | |
| Other anions | None. |
| Related compounds | Sodium oxide, aluminium oxide hydroxide. |
| Except where noted otherwise, data are given for materials in their standard state (at 25°C, 100 kPa) Infobox disclaimer and references |
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Aluminium hydroxide, Al(OH)3, is the most stable form of aluminium in normal conditions. As found in nature it is known as the mineral gibbsite. Closely related are aluminium oxide hydroxide, AlO(OH), and aluminium oxide, Al2O3, differing only by loss of water. These compounds together are the major components of the aluminium ore, bauxite.
The character of 'aluminium hydroxide' has been controversial. It is safe to say that a simple scheme of Al3+ ions and OH- ions is oversimplified. More and less hydrated forms are very common. Some people write Al2O3.xH2O instead.
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[edit] Reactions
Aluminium hydroxide is amphoteric. In strongly acid conditions, Al(OH)2+ is formed; in strongly basic conditions, Al(OH)4- is formed. These are the main ions in dilute solutions; in concentrated solutions, polymeric ions are formed which can be quite complex.
Salts of the anion Al(OH)4- (or similar, such as AlO2-) are sometimes called aluminates.
Al(OH)3 has a molar mass of 78.01.
As a weak base, aluminum hydroxide can neutralize excess acid. For example, Al(OH)3 + 3HCl yields AlCl3 + 3H2O.
[edit] Pharmacology
Pharmacologically this compound, also known as Alu-Cap or Aludrox, is used as an antacid. The hydroxide reacts with excess acid in the stomach, reducing its acidity. This decrease of acidity of the contents of the stomach may in turn help to relieve the symptoms of ulcers, heartburn or dyspepsia. It can also cause constipation and is therefore often used with magnesium carbonate. This compound is also used to control phosphate levels in the blood for people suffering from kidney failure.
Aluminum hydroxide is included as an adjuvant in some vaccines, since it contributes to induction of a good antibody (Th2) response. However, it has little capacity to stimulate cellular (Th1) immune responses, important for protection against many pathogens (Petrovsky and Aguilar, 2004).
Because the brain lesions found in Alzheimer's disease contain aluminum, there is concern that consumption of excess aluminium compounds may cause or contribute to the development of this and other neurodegenerative diseases (Perl, 2006, Kawahara, 2005). In addition, elevated aluminum levels in blood, resulting from kidney dialysis with well water containing high aluminum, result in dementia that is similar to but probably different from that of Alzheimer's disease (Carpenter, 2001). However, this hypothesis is controversial.
[edit] References
Carpenter DO. Effects of metals on the nervous system of humans and animals. Int J Occup Med Environ Health. 2001;14(3):209-18.
Galbraith, A; Bullock, S; Manias, E. Hunt, B. & Richards, A. (1999). Fundamentals of pharmacology: a text for nurses and health professionals. Harlow: Pearson Education Ltd. p482.
Kawahara M. Effects of aluminum on the nervous system and its possible link with neurodegenerative diseases. J Alzheimers Dis. 2005 Nov;8(2):171-82; discussion 209-15.
Perl DP, Moalem S. Aluminum and Alzheimer's disease, a personal perspective after 25 years. J Alzheimers Dis. 2006;9(3 Suppl):291-300.
Petrovsky N, Aguilar JC. Vaccine adjuvants: current state and future trends. Immunol Cell Biol. 2004 Oct;82(5):488-96.
