Silicic acid is a general name for a family of chemical compounds of silicon, hydrogen and oxygen, with the general formula [SiO_x(OH)_4-2x]_n. Some simple silicic acids have been identified in very dilute aqueous solution, such as metasilicic acid (H₂SiO₃), orthosilicic acid (H₄SiO₄), disilicic acid (H₂Si₂O₅), and pyrosilicic acid (H₆Si₂O₇); however in the solid state these probably condense to form polymeric silicic acids of complex structure.

Silicic acids may be formed by acidification of silicate salts (such as sodium silicate) in aqueous solution. When heated they lose water to form silica gel, an active form of silicon dioxide.

References

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.