Fluorides

Compounds such as sodium and calcium fluoride are usually found as white solids. Sodium fluoride dissolves easily in water while calcium fluoride does not. Hydrogen fluoride is a colourless, highly toxic and irritant gas. It readily dissolves in water, where it is also colourless at room temperature. Hydrofluoric acid is a water solution of hydrogen fluoride which is prepared by heating calcium fluoride in sulphuric acid, and is extremely corrosive. Hydrofluoric acid attacks glass and dissolves most minerals. Another compound is hydrofluosilicic acid which can combine with sodium and potassium to form salts called fluosilicates or silicofluorides.