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 Na
2HPO
4. 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 ...
:
:HPO
42− + H
2O H
2PO
4− + 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 ...
:
:H
3PO
4 + 2 NaOH → Na
2HPO
4 + 2 H
2O
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. ]
:CaHPO
4 + NaHSO
4 → NaH
2PO
4 + CaSO
4
In the second step, the resulting solution of monosodium phosphate is partially neutralized:
:NaH
2PO
4 + NaOH → Na
2HPO
4 + H
2O
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