Disodium phosphate

Disodium phosphate

Names
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) N 7782-85-6 (heptahydrate) N 10039-32-4 (dodecahydrate) N
ChEBI	CHEBI:34683 Y
ChEMBL	ChEMBL1060 Y
ChemSpider	22625 Y
EC Number	231-448-7
Jmol 3D model	Interactive image
PubChem	24203
RTECS number	WC4500000
UNII	22ADO53M6F Y
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 [Na+].[Na+].[O-]P([O-])([O-])=O
Properties
Chemical 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 (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 alcohol
log P	-5.8
Acidity (pKa)	12.35
Refractive index (nD)	1.35644..1.35717 at 20°C
Vapor pressure	{{{value}}}
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

Disodium phosphate (DSP), or sodium 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.

Acid-base properties

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

HPO₄²⁻ + H₂O $\overrightarrow{\leftarrow}$ H₂PO₄⁻ + OH⁻

Production and reactions

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

H₃PO₄ + 2 NaOH → HNa₂PO₄ + 2 H₂O

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

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 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. 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.

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.