Monosodium phosphate

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.[1]

Monosodium phosphate
Ball-and-stick model of the dihydrogenphosphate anion
Names
IUPAC name
Sodium dihydrogen phosphate
Other names
monobasic sodium phosphate;
sodium dihydrogen phosphate;
sodium biphosphate
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.028.591
E number E339(i) (antioxidants, ...)
UNII
  • InChI=1S/Na.H3O4P/c;1-5(2,3)4/h;(H3,1,2,3,4)/q+1;/p-1 checkY
    Key: AJPJDKMHJJGVTQ-UHFFFAOYSA-M checkY
  • [Na+].[O-]P(=O)(O)O
Properties
NaH2PO4
Molar mass 119.98 g/mol
Appearance White powder or crystals
Density 2.36 g/cm3 (anhydrous)
59.90 g/100 mL (0°C)
Hazards
NFPA 704 (fire diamond)
NFPA 704 four-colored diamond
0
0
0
Flash point Non-flammable
Related compounds
Other cations
 Monopotassium phosphate
Monoammonium phosphate
Related compounds
 Disodium phosphate
Trisodium phosphate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Production and reactions

The salt is obtained by partial neutralization of phosphoric acid. The pKa of monosodium phosphate is 6.8-7.2 (depending on the physicochemical characteristics during pKa determination).[2]

Heating this salt above 169 °C gives the corresponding sodium acid pyrophosphate:

2 NaH2PO4 → Na2H2P2O7 + H2O

When heated at 550 °C, anhydrous trisodium trimetaphosphate results:[3]

3NaH2PO4 → Na3P3O9 + 3 H2O

Uses

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.[1] The sodium chloride equivalent value, or E-Value, is 0.49. It is soluble in 4.5 parts water.

Food additive

It is added in animal feed, toothpaste, and evaporated milk. It is used as a thickening agent and emulsifier.

Detection of magnesium

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.

Notes
  1. Schrödter, Klaus; Bettermann, Gerhard; Staffel, Thomas; Wahl, Friedrich; Klein, Thomas; Hofmann, Thomas (2008). "Phosphoric Acid and Phosphates". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a19_465.pub3.
  2. Salaun, F.: "Influence of mineral environment on the buffering capacity of casein micelles" Archived 2012-03-13 at the Wayback Machine, "Milchwissenschaft", 62(1):3
  3. Bell, R. N. (1950). "Sodium Metaphosphates". Inorganic Syntheses. Inorganic Syntheses. Vol. 3. pp. 103–106. doi:10.1002/9780470132340.ch26. ISBN 9780470132340.
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