Monosodium phosphate

Monosodium phosphate
	; Phosphorus, P Oxygen, O Hydrogen, H Sodium, Na
Names
	IUPAC name Sodium dihydrogen phosphate
	Other names Monobasic sodium phosphate; Sodium biphosphate;
Identifiers
CAS Number	7558-80-7 ;
3D model (JSmol)	Interactive image;
ChEBI	CHEBI:37585 ;
ChEMBL	ChEMBL1368 ;
ChemSpider	22626 ;
ECHA InfoCard	100.028.591
E number	E339(i) (antioxidants, ...)
PubChem CID	24204;
UNII	KH7I04HPUU ;
CompTox Dashboard (EPA)	DTXSID7035222 ;
	InChI InChI=1S/Na.H3O4P/c;1-5(2,3)4/h;(H3,1,2,3,4)/q+1;/p-1 Key: AJPJDKMHJJGVTQ-UHFFFAOYSA-M ;
	SMILES [Na+].[O-]P(=O)(O)O;
Properties
Chemical formula	NaH2PO4
Molar mass	119.976 g·mol−1
Appearance	White powder or crystals
Density	2.36 g/cm3 (anhydrous)
Solubility in water	59.90 g/(100 mL) (0°C)
Hazards
NFPA 704 (fire 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). verify (what is ?) Infobox references

Monosodium phosphate (MSP), also known as monobasic sodium phosphate and sodium dihydrogen phosphate, is an inorganic compound with the chemical formula Na H₂P O₄. 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]

Production and reactions

The salt is obtained by partial neutralization of phosphoric acid. The pK_a of monosodium phosphate is 6.8-7.2 (depending on the physicochemical characteristics during pK_a 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

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

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

^ ^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. Vol. 3. pp. 103–106. doi:10.1002/9780470132340.ch26. ISBN 9780470132340.

[Ullmann-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. ISBN 978-3527306732.

[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. Vol. 3. pp. 103–106. doi:10.1002/9780470132340.ch26. ISBN 9780470132340.

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