Silicic acid

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Silicic acid
Metasilicic acid
IUPAC name
Silicic acid
Other names
Monosilicic acid
Orthosilicic acid
3D model (JSmol)
ECHA InfoCard 100.109.340
EC Number 233-477-0
Molar mass 96.11 g·mol−1
Acidity (pKa) 9.84, 13.2
−42.6·10−6 cm3/mol
Related compounds
Related compounds
Orthocarbonic acid
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 the general name for a family of chemical compounds containing the element silicon attached to oxide and hydroxyl groups. This family of compounds has the general formula [SiOx(OH)4-2x]n.[1][2] No simple silicic acids has been identified, these species being primarily of theoretical interest.


Silicic acid was invoked by Jöns Jacob Berzelius in the early 19th century. Silicic acid is thought to be produced by a non-biological process called hydration:

+ WaterH
Silicic acidH

Since no inorganic silicic acid has been purified, the reactivity of these species is inferred rather than observed. Generally silicic acids degrade to silicon dioxide and water. Like other silanols, silicic acids are a weak acid, the conjugate bases also are poorly defined. Examples have not been purified.


Examples, often only of theoretical interest, include: metasilicic acid (H2SiO3), i.e. the chain or cyclic [SiO(OH)2]n orthosilicic acid (H4SiO4, i.e. Si(OH)4 with calculated pKa1=9.84, pKa2=13.2 at 25 °C) disilicic acid (H2Si2O5), i.e. the polymer [SiO1.5(OH)]n pyrosilicic acid (H6Si2O7), i.e. O(Si(OH)3)2

Oceanic silicic acid[edit]

2009 silicic acid concentration in the upper pelagic zone.[3]

Dissolved silica (DSi) is a term used in the field of oceanography to describe the form of water-soluble silica, which is assumed to be Si(OH)4, and its conjugate base [Si(OH)3O]-, orthosilicic acid (H4SiO4).

The biogeochemical cycle of silica is regulated by the 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).[6]

In the uppermost water column the surface ocean is undersaturated with respect to DSi, except for the Antarctic Circumpolar Current south of 55°S. Levitus94-10m.gif

DSi is regenerated with increasing water depth, and DSi values increase along the conveyor belt from the Atlantic over the Indian into the Pacific Ocean.[7][8] Levitus94-1000m.gif Z-bar.gif

Biological research[edit]

Research of the correlation of aluminium and Alzheimer's disease has included the ability of silicic acid in beer to reduce aluminium uptake in the digestive system as well as to increase renal excretion of aluminium [9][10]

Choline-stabilized orthosilicic acid (ch-OSA) is a dietary supplement. It has been shown to prevent the loss of tensile strength in human hair;[11]to have a positive effect on the surface and mechanical properties of skin, and on the brittleness of hair and nails;[12] to abate brittle nail syndrome;[13] to partially prevent femoral bone loss in aged ovariectomized rats;[14] to increase the concentration of collagen in calves;[15] and to have a potentially beneficial effect on the formation of collagen in the bones of osteopenic women.[16]


  1. ^ N. N. Greenwood, A. Earnshaw, Chemistry of the Elements, 2nd ed., Butterworth-Heinemann, Oxford, UK, 1997.
  2. ^ R. K. Iler, The Chemistry of Silica, Wiley, New York, 1979.
  3. ^ Information, US Department of Commerce, NOAA National Centers for Environmental. "World Ocean Atlas 2009". Retrieved 17 April 2018. 
  4. ^ 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.
  5. ^ Treguer, P., Nelson, D. M., Van Bennekom, A. J., DeMaster, D. J., Leynaert, A. Queguiner, B. (1995). "The silica balance in the world ocean: A reestimate". Science. 268: 375–379. doi:10.1126/science.268.5209.375. 
  6. ^ Del Amo, Y., and M. A. Brzezinski. 1999. The chemical form of dissolved Si taken up by marine diatoms. J. Phycol. 35:1162-1170.
  7. ^ The figures here have been drawn using the interactive web site which feeds on annual DSi values from LEVITUS94: World Ocean Atlas 1994, an atlas of objectively analyzed fields of major ocean parameters at the annual, seasonal, and monthly time scales. Superseded by WOA98. Edited by Syd Levitus.
  8. ^ "World Ocean Atlas 1994". 
  9. ^ Exley C, Korchazhkina O, Job D, Strekopytov S, Polwart A, Crome P (2006). "Non-invasive therapy to reduce the body burden of aluminium in Alzheimer's disease". J. Alzheimers Dis. 10 (1): 17–24; discussion 29–31. doi:10.3233/jad-2006-10103. PMID 16988476. 
  10. ^ González-Muñoz MJ, Peña A, Meseguer I (2008). "Role of beer as a possible protective factor in preventing Alzheimer's disease". Food Chem. Toxicol. 46 (1): 49–56. doi:10.1016/j.fct.2007.06.036. PMID 17697731. 
  11. ^ Wickett RR, Kossmann E, Barel A, et al. (2007). "Effect of oral intake of choline-stabilized orthosilicic acid on hair tensile strength and morphology in women with fine hair". Arch. Dermatol. Res. 299 (10): 499–505. doi:10.1007/s00403-007-0796-z. PMID 17960402. 
  12. ^ Barel A, Calomme M, Timchenko A, et al. (2005). "Effect of oral intake of choline-stabilized orthosilicic acid on skin, nails and hair in women with photodamaged skin". Arch. Dermatol. Res. 297 (4): 147–53. doi:10.1007/s00403-005-0584-6. PMID 16205932. 
  13. ^ Scheinfeld N, Dahdah MJ, Scher R (2007). "Vitamins and minerals: their role in nail health and disease". J Drugs Dermatol. 6 (8): 782–7. PMID 17763607. 
  14. ^ Calomme M, Geusens P, Demeester N, et al. (2006). "Partial prevention of long-term femoral bone loss in aged ovariectomized rats supplemented with choline-stabilized orthosilicic acid". Calcif. Tissue Int. 78 (4): 227–32. doi:10.1007/s00223-005-0288-0. PMID 16604283. 
  15. ^ Calomme MR, Vanden Berghe DA (1997). "Supplementation of calves with stabilized orthosilicic acid. Effect on the Si, Ca, Mg, and P concentrations in serum and the collagen concentration in skin and cartilage". Biol Trace Elem Res. 56 (2): 153–65. doi:10.1007/BF02785389. PMID 9164661. 
  16. ^ Spector TD, Calomme MR, Anderson SH, et al. (2008). "Choline-stabilized orthosilicic acid supplementation as an adjunct to Calcium/Vitamin D3 stimulates markers of bone formation in osteopenic females: a randomized, placebo-controlled trial". BMC Musculoskelet Disord. 9: 85. doi:10.1186/1471-2474-9-85. PMC 2442067Freely accessible. PMID 18547426. 

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