Silicic aci is a general name for a family of chemical compounds of the element silicon, hydrogen, and oxygen, with the general formula [SiOx(OH)4-2x]n. Some simple silicic acids have been identified 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.