Silicic acid
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| Metasilicic acid | |
| Names | |
|---|---|
| IUPAC name
Silicic acid
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| Other names
Monosilicic acid
Orthosilicic acid |
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| Identifiers | |
10193-36-9  |
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| ChEBI | CHEBI:26675 |
| ChemSpider | 14236 |
| EC Number | 233-477-0 |
| 2009 | |
| Jmol 3D model | Interactive image |
| PubChem | 14942 |
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| Properties | |
| H4O4Si | |
| Molar mass | 96.11 g·mol−1 |
| Acidity (pKa) | 9.84, 13.2 |
| Related compounds | |
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Related compounds
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Orthocarbonic acid |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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| Infobox references | |
Silicic acid /sɪˈlɪsɪk ˌæsɪd/ is a chemical compound. It is a silanol. Silicic acid is the general name for a family of chemical compounds containing the element silicon attached to oxide and hydroxyl groups. This family of compounds have the general formula [SiOx(OH)4-2x]n.[1][2] Some simple silicic acids have been identified, but only in very dilute aqueous solution, such as metasilicic acid (H2SiO3), orthosilicic acid (H4SiO4, pKa1=9.84, pKa2=13.2 at 25 °C), disilicic acid (H2Si2O5), and pyrosilicic acid (H6Si2O7); however in the solid state these probably condense to form polymeric silicic acids of complex structure.
Contents
Chemical reactions
In general, silicic acid reactions are difficult to control. Partial dehydration to metasilicic acid, for example, is challenging because the reaction typically progresses all the way to silicon dioxide and water.
Acid-base reactions
Like other silanols, silicic acid is a weak acid. It can be deprotonated in solution, the conjugate base silicate is known.
Production
Silicic acid was discovered by Jöns Jacob Berzelius between 1810 and 1836 when studying silicon generated by his experiments. However, he failed to recognise it as distinct from silicon dioxide.
Hydration
Naturally occurring silicic acid is produced by a non-biological process called hydration involving water, and quartz, which is known to be common on Earth. The reaction producing silicic acid from quartz can be written as: Quartz + Water → Silicic acid, or (in balanced form): SiO
2 + 2 H
2O → H
4SiO
4.
Laboratory synthesis
Silicic acid can be produced by the acidification of sodium silicate in aqueous solution. The main problem in using silicic acids in chemical synthesis is that silicic acids readily lose water to form randomly polymeric silica gel, a form of silicon dioxide. Such conversion involve condensations.
Oceanic silicic acid
Silicic acid is created near the ocean's surface, by the process of hydration. It is carried into the abyssopelagic zone by falling water in the poles. Uncontrolled build-up of silicic acid in the ocean is naturally checked – although human influence can upset this natural regulation. It is primarily removed by conversion to silicon dioxide and water. In the oceans, silicon exists primarily as orthosilicic acid (H4SiO4), and its biogeochemical cycle is regulated by the group of algae known as the diatoms.[4][5] These algae polymerise the silicic acid to so-called biogenic silica, used to construct their cell walls (called frustules).
Silicic acid in health
Continuing research of the correlation of aluminium and Alzheimer's disease has in the last few years included the use of silicic acid in beverages,[6][7][8] due to its abilities to both reduce aluminium uptake in the digestive system as well as cause renal excretion of aluminium.
Study has shown that physiological concentration of orthosilicic acid stimulates collagen type 1 synthesis and osteoblastic differentiation in human osteoblast-like cells in vitro.[9]
Choline-stabilized orthosilicic acid is a bioavailable nutritional supplement. It has been shown to prevent the loss of hair tensile strength,[10] have positive effect on skin surface and skin mechanical properties, and on brittleness of hair and nails,[11] abate brittle nail syndrome,[12] partially prevent femoral bone loss in the aged ovariectomized rat model,[13] increase collagen concentration in calves ,[14] and have potential beneficial effect on bone collagen formation in osteopenic females.[15]
References
- ↑ N. N. Greenwood, A. Earnshaw, Chemistry of the Elements, 2nd ed., Butterworth-Heinemann, Oxford, UK, 1997.
- ↑ R. K. Iler, The Chemistry of Silica, Wiley, New York, 1979.
- ↑ http://www.nodc.noaa.gov/OC5/WOA09/pr_woa09.html
- ↑ Siever, R. (1991). Silica in the oceans: biological-geological interplay. In: Schneider, S. H., Boston, P. H. (eds.), Scientists On Gaia, The MIT Press, Cambridge MA, USA, pp. 287-295.
- ↑ Treguer, P., Nelson, D. M., Van Bennekom, A. J., DeMaster, D. J., Leynaert, A. and Queguiner, B. (1995). The silica balance in the world ocean: A reestimate. Science 268, 375-379.
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