Monosodium phosphate

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]

Monosodium phosphate

Ball-and-stick model of the dihydrogenphosphate anion   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 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:37585 Y
ChEMBL	ChEMBL1368 Y
ChemSpider	22626 Y
ECHA InfoCard	100.028.591
E number	E339(i) (antioxidants, ...)
PubChem CID	24204
UNII	KH7I04HPUU N
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 Y Key: AJPJDKMHJJGVTQ-UHFFFAOYSA-M Y
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). N verify (what is YN ?) Infobox references

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 adjusted by mixtures of various sodium phosphates, such as this salt.^[1] It is added in animal feed for its nutritional value.^[1]