Metaboric acid is the name for a family of inorganic compounds with the same empirical formula HBO2[2] that differ in their molecular structure. They are colourless water-soluble solids formed by the dehydration or decomposition of boric acid.
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Names | |||
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IUPAC name
Oxoborinic acid
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Other names
Metaboric acid
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Identifiers | |||
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3D model (JSmol)
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ChemSpider |
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ECHA InfoCard | 100.033.313 | ||
EC Number |
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121829 | |||
PubChem CID
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CompTox Dashboard (EPA)
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Properties | |||
B3H3O6 | |||
Molar mass | 131.45 g·mol−1 | ||
Appearance | white solid | ||
Density | 1.784 g/cm3 | ||
Melting point | 176 °C (349 °F; 449 K) | ||
Acidity (pKa) | 9.236 | ||
Conjugate base | Metaborate | ||
Structure | |||
trigonal at B | |||
Hazards | |||
GHS labelling:[1] | |||
Warning | |||
H315, H319, H335 | |||
P261, P305+P351+P338 | |||
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references
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Metaboric acid is formally the parent acid of the metaborate anions.
The main forms of metaboric acid are:
When heated above about 170 °C, metaboric acid dehydrates, forming tetraboric acid, also called pyroboric acid (H2B4O7):[6][7]
Metaborates are derivatives of BO2−. Like metaboric acid, the metaborates exist with disparate structures. Examples are sodium and potassium metaborates, salts formed by deprotonation of orthorhombic metaboric acid containing the cyclic B3O63− ion and calcium metaborate, Ca(BO2)2, which contains the chain polymeric ion (BO2−)n.[2]