Sodium carbonate and silicon dioxide react when molten to form sodium silicate and carbon dioxide.

Sodium silicate is a white solid that is soluble in water, producing an alkaline solution. There are many kinds of this compound, including sodium orthosilicate, Na₄SiO₄; sodium metasilicate, Na₂SiO₃; sodium polysilicate, (Na₂SiO₃)n; sodium pyrosilicate, Na6Si2O7, and others. All are glassy, colourless and dissolve in water.

Sodium silicate is stable in neutral and alkaline solutions. In acidic solutions, the silicate ion reacts with hydrogen ions to form silicic acid, which when heated and roasted forms silica gel, a hard, glassy substance