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 [âÂÂâÂÂ]<sub>n</sub>. It is a colorless crystalline hygroscopic and deliquescent solid, soluble in water (giving an alkaline solution) but not in alcohols.
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
In the anhydrous solid, the metasilicate anion is actually polymeric, consisting of corner-shared {SiO<sub>4</sub>} tetrahedra, and not a discrete SiO<sub>3</sub><sup>2â </sup> ion.
In addition to the anhydrous form, there are hydrates with the formula Na<sub>2</sub>SiO<sub>3</sub>÷nH<sub>2</sub>O (where n = 5, 6, 8, 9), which contain the discrete, approximately tetrahedral anion SiO<sub>2</sub>(OH)<sub>2</sub><sup>2âÂÂ</sup> with water of hydration. For example, the commercially available sodium silicate pentahydrate Na<sub>2</sub>SiO<sub>3</sub>÷5H<sub>2</sub>O is formulated as Na<sub>2</sub>SiO<sub>2</sub>(OH)<sub>2</sub>÷4H<sub>2</sub>O, and the nonahydrate Na<sub>2</sub>SiO<sub>3</sub>÷9H<sub>2</sub>O is formulated as Na<sub>2</sub>SiO<sub>2</sub>(OH)<sub>2</sub>÷8H<sub>2</sub>O. The pentahydrate and nonahydrate forms have their own CAS Numbers, 10213-79-3 and 13517-24-3 respectively.
Sodium metasilicate reacts with acids to produce silica gel.