Disodium phosphate

Disodium phosphate (DSP), or disodium hydrogen phosphate, or sodium phosphate dibasic, is an inorganic compound with the chemical formula Na₂HPO₄. It is one of several sodium phosphates. The salt is known in anhydrous form as well as hydrates Na₂HPO₄·nH₂O, where n is 2, 7, 8, and 12. All are water-soluble white powders. The anhydrous salt is hygroscopic.^[1]

Disodium phosphate

Sodium, Na   Phosphorus, P   Oxygen, O   Hydrogen, H
Names
IUPAC name Disodium hydrogen phosphate
Other names Acetest Dibasic sodium phosphate Disodium hydrogen orthophosphate Disodium hydrogen phosphate Disodium phosphate Sodium phosphate dibasic
Identifiers
CAS Number	7558-79-4 Y 10028-24-7 (dihydrate) Y 7782-85-6 (heptahydrate) Y 10039-32-4 (dodecahydrate) Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:34683 Y
ChEMBL	ChEMBL1060 Y
ChemSpider	22625 Y
ECHA InfoCard	100.028.590
EC Number	231-448-7
E number	E339(ii) (antioxidants, ...)
PubChem CID	24203
RTECS number	WC4500000
UNII	22ADO53M6F Y 94255I6E2T (dihydrate) Y 70WT22SF4B (heptahydrate) Y E1W4N241FO (dodecahydrate) Y
CompTox Dashboard (EPA)	DTXSID1026039
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
SMILES OP(=O)([O-])[O-].[Na+].[Na+]
Properties
Chemical formula	Na2HPO4
Molar mass	141.96 g/mol (anhydrous) 177.99 g/mol (dihydrate) 268.07 g/mol (heptahydrate)
Appearance	White crystalline solid
Odor	Odorless
Density	1.7 g/cm3
Melting point	250 °C (482 °F; 523 K) Decomposes
Solubility in water	7.7 g/(100 ml) (20 °C) 11.8 g/(100 ml) (25 °C, heptahydrate)
Solubility	Insoluble in ethanol
log P	−5.8
Acidity (pKa)	12.35
Magnetic susceptibility (χ)	−56.6·10−6 cm3/mol
Refractive index (nD)	1.35644 to 1.35717 at 20°C
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	Irritant
NFPA 704 (fire diamond)	1 0 0
Flash point	Non-flammable
Lethal dose or concentration (LD, LC):
LD50 (median dose)	17000 mg/kg (rat, oral)
Safety data sheet (SDS)	ICSC 1129
Related compounds
Other anions	sodium phosphite
Other cations	Dipotassium phosphate Diammonium phosphate
Related compounds	Monosodium 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

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

HPO2−4 + H₂O ⇌ H₂PO−4 + OH⁻

Production and reactions

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

H₃PO₄ + 2 NaOH → Na₂HPO₄ + 2 H₂O

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

CaHPO₄ + NaHSO₄ → NaH₂PO₄ + CaSO₄

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

NaH₂PO₄ + NaOH → Na₂HPO₄ + H₂O

Uses

It is used in conjunction with trisodium phosphate in foods and water softening 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.^{[citation needed]} It is also found in some detergents and cleaning agents.^[2]

Heating solid disodium phosphate gives the useful compound tetrasodium pyrophosphate:^{[citation needed]}

2 Na₂HPO₄ → Na₄P₂O₇ + H₂O

Laxative

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