Disodium phosphate

Disodium phosphate
IUPAC name Sodium hydrogen phosphate
Other names Disodium hydrogen orthophosphate Sodium hydrogen phosphate Sodium phosphate dibasic disodium phosphate
Identifiers
CAS number	7558-79-4 Y,  10028-24-7 (dihydrate) 7782-85-6 (heptahydrate) 10039-32-4 (dodecahydrate)
PubChem	24203
ChemSpider	22625 Y
UNII	22ADO53M6F Y
EC number	231-448-7
ChEBI	CHEBI:34683 Y
ChEMBL	CHEMBL1060 Y
RTECS number	WC4500000
Jmol-3D images	{{#if:[Na+].[Na+].[O-]P([O-])([O-])=O|Image 1
SMILES [Na+].[Na+].[O-]P([O-])([O-])=O
InChI InChI=1S/2Na.H3O4P/c;;1-5(2,3)4/h;;(H3,1,2,3,4)/q2*+1;/p-3 N Key: BNIILDVGGAEEIG-UHFFFAOYSA-K N InChI=1/2Na.H3O4P/c;;1-5(2,3)4/h;;(H3,1,2,3,4)/q2*+1;/p-3 Key: BNIILDVGGAEEIG-DFZHHIFOAK
Properties
Molecular formula	Na2HPO4
Molar mass	141.96 g/mol (anhydrous) 268.07 g/mol (heptahydrate)
Appearance	White crystalline solid
Odor	odorless
Density	1.7 g/cm3
Melting point	250 °C decomp.
Solubility in water	7.7 g/100 ml (20 °C) 11.8 g/100 mL (25 °C, heptahydrate)
Acidity (pKa)	12.35
Hazards
MSDS	ICSC 1129
EU Index	Not listed
Main hazards	Irritant
NFPA 704	0 1 0
Flash point	Non-flammable
Related compounds
Other anions	sodium phosphite
Other cations	Dipotassium phosphate Diammonium phosphate
Related compounds	Monosodium phosphate Trisodium phosphate
N (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Infobox references

Disodium hydrogen phosphate is the inorganic compound with the formula Na₂HPO₄. It is one of several sodium phosphates. The salt is known in anhydrous form as well as forms with 2, 7, 8, and 12 hydrates. All are water-soluble white powders; the anhydrous salt being hygroscopic.^[1]

Acid-base properties

The pH of disodium hydrogen phosphate water solution is between 8.0 and 11.0, meaning it is basic:

HPO₄^2- + H₂O H₂PO₄^- + OH^-

Production and reactions

It can be generated by neutralization of phosphoric acid with sodium hydroxide:

H₃PO₄^2- + 2 NaOH → HNa₂PO₄ + 2 H₂O

Industrially It is prepared in a two-step process by treating dicalcium phosphate with phosphoric acid, which precipitates calcium sulfate:^[2]

CaHPO₄ + NaHSO₄ → NaH₂PO₄ + CaSO₄

In the second step, the resulting solution of monosodium phosphate is partially neutralized:

NaH₂PO₄ + NaOH → HNa₂PO₄ + H₂O

Uses

It is used as an in conjunction with trisodium phosphate in foods and water treatment. In foods, it is used to adjust pH. Its presence prevents coagulation in the preparation of condensed milk. Similarly, it is used as an anti-caking additive in powdered products.^[3] It is used in desserts and puddings, e.g. Cream of Wheat to quicken cook time, and Jell-O Instant Pudding for thickening. In water treatment, It retards calcium scale formation. It is also found in some detergents and cleaning agents.^[2]

Heating solid disodium phosphate gives the useful compound tetrasodium pyrophosphate:

2 HNa₂PO₄ → Na₄P₂O₇ + H₂O

Monobasic and dibasic sodium phosphate are used as a saline laxative to treat constipation or to clean the bowel before a colonoscopy.^[4]

References