Kalpana Kalpana (Editor)

Disodium phosphate

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Formula
  
Na2HPO4

Molar mass
  
141.96 g/mol

Density
  
500 kg/m³

Appearance
  
White crystalline solid

IUPAC ID
  
Sodium hydrogen phosphate

Melting point
  
250 °C

Soluble in
  
Water

Disodium phosphate 2imimgcomdata2JLDIMY2356184disodiumphosph

Related compounds
  
Monosodium phosphate Trisodium phosphate

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.

Contents

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 ⇌ 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 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. 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.

References

Disodium phosphate Wikipedia