|Molar mass||305.885 g/mol|
|Appearance||colorless or white crystals|
|Density||2.49 g/cm3 (anhydrous)
1.786 g/cm3 (hexahydrate)
|Melting point||53 °C (127 °F; 326 K) (hexahydrate, decomposes to anyhdrous)|
|22 g/100 mL|
|Solubility||insoluble in alcohol|
Refractive index (nD)
|Crystal structure||triclinic (hexahydrate)|
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
|what is: / ?)(|
Sodium trimetaphosphate (also STMP), with formula Na3P3O9, is a metaphosphate of sodium. It has the empirical formula NaPO3. It is the sodium salt of trimetaphosphoric acid. It is a colourless solid that finds specialised applications in food and construction industries. STMP is prepared by heating sodium polyphosphate at a few hundred degrees. 
Although drawn with a particular resonance structure, the trianion has D3d symmetry.
- Lide, David R. (1998). Handbook of Chemistry and Physics (87 ed.). Boca Raton, FL: CRC Press. pp. 4–86. ISBN 0-8493-0594-2.
- Klaus Schrödter, Gerhard Bettermann, Thomas Staffel, Friedrich Wahl, Thomas Klein, Thomas Hofmann "Phosphoric Acid and Phosphates" in Ullmann’s Encyclopedia of Industrial Chemistry 2008, Wiley-VCH, Weinheim. doi:10.1002/14356007.a19_465.pub3
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