anhydride, meaning that it forms by dehydration of carbonic acid H₂CO₃ (OC(OH)₂).

Silicic acid is the name given to a variety of compounds with a generic formula [SiO_x(OH)_4-2x]_n. Orthosilicic acid has been identified in very dilute aqueous solution. It is a weak acid with pK_a1 = 9.84, pK_a2 = 13.2 at 25 °C. It can be written as H₄SiO₄