Monosodium phosphate (MSP), also known as monobasic sodium phosphate and sodium dihydrogen phosphate, is an inorganic compound with the chemical formula NaH2PO4. It is a sodium salt of phosphoric acid. It consists of sodium cations (Na+) and dihydrogen phosphate anions (H2PO−4). One of many sodium phosphates, it is a common industrial chemical. The salt exists in an anhydrous form, as well as monohydrate and dihydrate (NaH2PO4·H2O and NaH2PO4·2H2O respectively).[1]
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 Phosphorus, P Oxygen, O Hydrogen, H Sodium, Na | |
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| Names | |
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| IUPAC name
Sodium dihydrogen phosphate
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Other names
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| Identifiers | |
3D model (JSmol)
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| ChemSpider | |
| ECHA InfoCard | 100.028.591 |
| E number | E339(i) (antioxidants, ...) |
PubChem CID
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| UNII | |
CompTox Dashboard (EPA)
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| Properties | |
| NaH2PO4 | |
| Molar mass | 119.976 g·mol−1 |
| Appearance | White powder or crystals |
| Density | 2.36 g/cm3 (anhydrous) |
| 59.90 g/(100 mL) (0°C) | |
| Hazards | |
| NFPA 704 (fire diamond) | |
| Flash point | Non-flammable |
| Related compounds | |
Other cations
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Related compounds
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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 reactions edit
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 disodium pyrophosphate:
- 2 NaH2PO4 → Na2H2P2O7 + H2O
When heated at 550 °C, anhydrous trisodium trimetaphosphate is formed:[3]
- 3 NaH2PO4 → Na3P3O9 + 3 H2O
Uses edit
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.[clarification needed] It is soluble in 4.5 parts water.[clarification needed]
Food additive edit
It is added in animal feed, toothpaste, and evaporated milk. It is used as a thickening agent and emulsifier.
Detection of magnesium edit
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 edit
- ^ a b 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. ISBN 978-3527306732.
- ^ 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
- ^ Bell, R. N. (1950). "Sodium Metaphosphates". Inorganic Syntheses. Inorganic Syntheses. Vol. 3. pp. 103–106. doi:10.1002/9780470132340.ch26. ISBN 9780470132340.