Monosodium phosphate (MSP), also known as monobasic sodium phosphate and sodium dihydrogen phosphate, is an inorganic compound of sodium with a dihydrogen phosphate (H2PO4−) anion. One of many sodium phosphates, it is a common industrial chemical. The salt exists in an anhydrous form, as well as mono- and dihydrates.
Sodium dihydrogen phosphate
monobasic sodium phosphate;
sodium dihydrogen phosphate;
3D model (JSmol)
|E number||E339(i) (antioxidants, ...)|
CompTox Dashboard (EPA)
|Molar mass||119.98 g/mol|
|Appearance||White powder or crystals|
|Density||2.36 g/cm3 (anhydrous)|
|59.90 g/100 mL (0°C)|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Production and reactionsEdit
Heating this salt above 169 °C gives the corresponding sodium acid pyrophosphate:
- 2 NaH2PO4 → Na2H2P2O7 + H2O
Phosphates are often used in foods and in water treatment. The pH of such formulations is generally adjusted by mixtures of various sodium phosphates, such as this salt. The sodium chloride equivalent value, or E-Value, is 0.49. It is soluble in 4.5 parts water.
Detection of magnesiumEdit
Monosodium phosphate is used to detect the presence of magnesium ions in salts. Formation of a white precipitate on the addition of ammonium chloride, ammonium hydroxide and monosodium phosphate to an aqueous or dilute HCl solution of the salt indicates presence of magnesium ions.
- 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
- Salaun, F.: "Influence of mineral environment on the buffering capacity of casein micelles", "Milchwissenschaft", 62(1):3