H2OsO4

H2OsO4, commonly known as orthosilicic acid, is a chemical compound with the formula H4SiO4. It is the simplest form of silicic acid, a group of compounds derived from silicic acid. Orthosilicic acid is a colorless, odorless, and highly soluble substance in water. It is a weak acid and its dissociation in water produces silicate ions. The concentration of orthosilicic acid in natural waters, such as oceans, rivers, and groundwater, is an important factor in aquatic ecosystems, as it is the primary form in which silicon is available for uptake by diatoms and other silica-utilizing organisms.

In geological contexts, orthosilicic acid is a product of the weathering of silicate minerals. Over time, these minerals break down, releasing silicon into the environment, which then forms orthosilicic acid in the presence of water. This process is crucial for the silicon cycle. In biology, orthosilicic acid is essential for the formation of silica structures in various organisms, including the frustules of diatoms, the cell walls of some plants, and the skeletal elements of some marine invertebrates. Its presence and concentration can influence the growth and health of these organisms. While generally stable in dilute aqueous solutions, orthosilicic acid can undergo polymerization to form more complex polysilicic acids and eventually amorphous silica gel under certain conditions, particularly at higher concentrations or with changes in pH.