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Silicic acid is a general name for a family of chemical compounds of silicon, hydrogen, and oxygen, with the general formula [SiO<sub>x</sub>(OH)<sub>4-2x</sub>]<sub>n</sub>. Some simple silicic acids have been identified in very dilute aqueous solution, such as metasilicic acid (H<sub>2</sub>SiO<sub>3</sub>), orthosilicic acid (H<sub>4</sub>SiO<sub>4</sub>, pK<sub>a1</sub>=9.84, pK<sub>a2</sub>=13.2 at 25° C), disilicic acid (H<sub>2</sub>Si<sub>2</sub>O<sub>5</sub>), and pyrosilicic acid (H<sub>6</sub>Si<sub>2</sub>O<sub>7</sub>); however in the solid state these probably condense to form polymeric silicic acids of complex structure.