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|Section2= |Section3= |Section7= |Section8= }} Hexafluorosilicic acid (systematically named oxonium hexafluorosilanediuide and oxonium hexafluoridosilicate(2−)) is an inorganic compound with the chemical formula (also written as or ). In aqueous solution, the oxonium cation is traditionally equated with a solvated proton, and as such, the formula is often written as . Extending that metaphor, the pure compound is then written as . It is a colorless liquid rarely encountered undiluted. Hexafluorosilicic acid has a distinctive sour taste and pungent smell. It is mainly produced as a precursor to aluminum trifluoride and synthetic cryolite. It is commonly used as a source of fluoride for water fluoridation.〔The New Zealand Institute of Chemistry (NZIC) - Hydrofluorosilic acid and water fluoridation (hydrofluorosilic acid ).〕 Concentrated hexafluorosilicic acid is corrosive and can attack the skin. == Structure == In solid hexafluorosilicic acid, the component ions form a network, being connected by ionic bonds. In the liquid phase, the oxonium ions react reversibly with the hexafluoridosilicate(1−) ions, producing water and various protonated silicon complexes. These complexes undergo decomposition reversibly, producing a small concentration of hydrogen fluoride. The result is a complex mixture containing water, hydrogen fluoride, tetrafluorosilane, and other related species, all in dynamic equilibrium. Therefore, unless the liquid phase is kept in a sealed container, the differing volatilities will cause the hexafluorosilicic acid to degrade rapidly. Hexafluorosilicic acid is only available commercially as an equilibrium mixture in an aqueous solution or other solvents that contain strong proton donors at low pH (acids described similarly include chloroplatinic acid, fluoroboric acid, and hexafluorophosphoric acid, and, more commonly, carbonic acid). Purifying hexafluorosilicic acid by using distillation has not proven possible, all reported attempts has only yielded the decomposition products, which are HF, , and water. In this octahedral anion, the Si-F bond distances are 1.71 Å.〔Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Hexafluorosilicic acid」の詳細全文を読む スポンサード リンク
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