Sodium metasilicate is the chemical substance with formula, which is the main component of commercial sodium silicate solutions. It is an ionic compound consisting of sodium cations and the polymeric metasilicate anions [––]n. It is a colorless crystalline hygroscopic and deliquescent solid, soluble in water (giving an alkaline solution) but not in alcohols.

Preparation and properties

The anhydrous compound can be prepared by fusing silicon dioxide (silica, quartz) with sodium oxide in 1:1 molar ratio. The compound crystallizes from solution as various hydrates, such as

Structure

In the anhydrous solid, the metasilicate anion is actually polymeric, consisting of corner-shared {SiO4} tetrahedra, and not a discrete SiO32− ion. In addition to the anhydrous form, there are hydrates with the formula Na2SiO3·nH2O (where n = 5, 6, 8, 9), which contain the discrete, approximately tetrahedral anion SiO2(OH)22− with water of hydration. For example, the commercially available sodium silicate pentahydrate Na2SiO3·5H2O is formulated as Na2SiO2(OH)2·4H2O, and the nonahydrate Na2SiO3·9H2O is formulated as Na2SiO2(OH)2·8H2O. The pentahydrate and nonahydrate forms have their own CAS Numbers, 10213-79-3 and 13517-24-3 respectively.

Uses

Sodium Metasilicate reacts with acids to produce silica gel.