Disodium phosphate (DSP), or disodium hydrogen phosphate, or sodium phosphate dibasic, is the

inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemist ...

with the formula Na₂HPO₄. It is one of several

sodium phosphates Sodium phosphate is a generic term for a variety of salts of sodium (Na+) and phosphate (PO43−). Phosphate also forms families or condensed anions including di-, tri-, tetra-, and polyphosphates. Most of these salts are known in both anhydrou ...

. The salt is known in anhydrous form as well as forms with 2, 7, 8, and 12

hydrates In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was understo ...

. All are water-soluble white powders; the anhydrous salt being

hygroscopic Hygroscopy is the phenomenon of attracting and holding water molecules via either absorption or adsorption from the surrounding environment, which is usually at normal or room temperature. If water molecules become suspended among the substance ...

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

basic BASIC (Beginners' All-purpose Symbolic Instruction Code) is a family of general-purpose, high-level programming languages designed for ease of use. The original version was created by John G. Kemeny and Thomas E. Kurtz at Dartmouth College ...

: :HPO₄²⁻ + H₂O H₂PO₄⁻ + OH⁻

Production and reactions

It can be generated by neutralization of

phosphoric acid Phosphoric acid (orthophosphoric acid, monophosphoric acid or phosphoric(V) acid) is a colorless, odorless phosphorus-containing solid, and inorganic compound with the chemical formula . It is commonly encountered as an 85% aqueous solution, w ...

with

sodium hydroxide Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations and hydroxide anions . Sodium hydroxide is a highly caustic base and alkali ...

: :H₃PO₄ + 2 NaOH → Na₂HPO₄ + 2 H₂O Industrially It is prepared in a two-step process by treating

dicalcium phosphate Dicalcium phosphate is the calcium phosphate with the formula CaHPO4 and its dihydrate. The "di" prefix in the common name arises because the formation of the HPO42– anion involves the removal of two protons from phosphoric acid, H3PO4. It is al ...

with

sodium bisulfate Sodium bisulfate, also known as sodium hydrogen sulfate, is the sodium salt of the bisulfate anion, with the molecular formula NaHSO4. Sodium bisulfate is an acid salt formed by partial neutralization of sulfuric acid by an equivalent of sodium ...

, which precipitates

calcium sulfate Calcium sulfate (or calcium sulphate) is the inorganic compound with the formula CaSO4 and related hydrates. In the form of γ-anhydrite (the anhydrous form), it is used as a desiccant. One particular hydrate is better known as plaster of Pari ...

: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. :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 Trisodium phosphate (TSP) is the inorganic compound with the chemical formula . It is a white, granular or crystalline solid, highly soluble in water, producing an alkaline solution. TSP is used as a cleaning agent, builder, lubricant, food a ...

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 Cream of Wheat is an American brand of farina, a type of breakfast porridge mix made from wheat middlings. It looks similar to grits, but is smoother in texture since it is made with ground wheat kernels instead of ground corn. It was first ma ...

to quicken cook time, and Jell-O

Instant Pudding Instant pudding is an instant food product that is manufactured in a powder form and used to create puddings and pie filling. It is produced using sugar, flavoring agents and thickeners as primary ingredients. Instant pudding can be used in som ...

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 Tetrasodium pyrophosphate, also called sodium pyrophosphate, tetrasodium phosphate or TSPP, is an inorganic compound with the chemical formula, formula Na4P2O7. As a salt, it is a white, water-soluble solid. It is composed of pyrophosphate anion an ...

: :2 Na₂HPO₄ → Na₄P₂O₇ + H₂O

Laxative

Monobasic and dibasic sodium phosphate are used as a saline laxative to treat

constipation Constipation is a bowel dysfunction that makes bowel movements infrequent or hard to pass. The stool is often hard and dry. Other symptoms may include abdominal pain, bloating, and feeling as if one has not completely passed the bowel movement ...

or to clean the bowel before a

colonoscopy Colonoscopy () or coloscopy () is the endoscopic examination of the large bowel and the distal part of the small bowel with a CCD camera or a fiber optic camera on a flexible tube passed through the anus. It can provide a visual diagnosis (''e. ...

References

External links

* solubility in Prophylaxis alcohol {{Sodium compounds Sodium compounds Phosphates Edible thickening agents