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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
3D model (JSmol)	Interactive image
ChEBI	CHEBI:34683
ChEMBL	ChEMBL1060
ChemSpider	22625
ECHA InfoCard	100.028.590
EC Number	231-448-7
E number	E339(ii) (antioxidants, ...)
PubChem CID	24203
RTECS number	WC4500000
UNII	22ADO53M6F
CompTox Dashboard (EPA)	DTXSID1026039
InChI InChI=1S/2Na.H3O4P/c;;1-5(2,3)4/h;;(H3,1,2,3,4)/q2*+1;/p-3Key: BNIILDVGGAEEIG-UHFFFAOYSA-K InChI=1/2Na.H3O4P/c;;1-5(2,3)4/h;;(H3,1,2,3,4)/q2*+1;/p-3Key: BNIILDVGGAEEIG-DFZHHIFOAK
SMILES ..P()()=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/cm
Melting point	250 ºC decomp.
Solubility in water	7.7 g/100 ml (20 ºC) 11.8 g/100 mL (25 °C, heptahydrate)
Acidity (pKa)	12.35
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	Irritant
NFPA 704 (fire diamond)	1 0 0
Flash point	Non-flammable
Related compounds
Other anions	sodium phosphite
Other cations	Dipotassium phosphate Diammonium phosphate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C , 100 kPa). N verify (what is  ?) Infobox references

Disodium hydrogen phosphate is the inorganic compound with the formula Na₂HPO₄. It is one of several sodium salts of phosphoric acid. 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.

Preparation and basic properties

It is prepared in a two-step process by treating dicalcium phosphate with phosphoric acid, 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

The pH of disodium hydrogen phosphate water solution is between 8.0 and 11.0, meaning it is basic. Heating solid disodium phosphate gives the useful compound tetrasodium pyrophosphate:

2 HNa₂PO₄ → Na₄P₂O₇ + H₂O

Uses

It is used as an in conjunction with trisodium phosphate in many steam-boiler applications. It retards calcium scale formation.anti-scale agent. It is also found in some detergents and cleaning agents.

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 deserts and puddings, e.g. Cream of Wheat to quicken cook time, and Jell-O Instant Pudding for thickening.

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

References

1. Physical data (pdf)
2. ^ Klaus Schrödter, Gerhard Bettermann, Thomas Staffel, Friedrich Wahl, Thomas Klein, Thomas Hofmann "Phosphoric Acid and Phosphates" in Ullmann’s Encyclopedia of Industrial Chemistry 2008, Wiley-VCH, Weinheim. doi:10.1002/14356007.a19_465.pub3
3. MSDS
4. [http://wishardhealth.kramesonline.com/Medications/26,1558

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