8659. Sodium Phosphate, Dibasic

Nomenclature

CAS number: 7558-79-4
Phosphoric acid sodium salt (1:2); dibasic sodium phosphate; disodium hydrogen phosphate; disodium orthophosphate; disodium phosphate; DSP; phosphate of soda; secondary sodium phosphate.
HNa2O4P; mol wt 141.96.
H 0.71%, Na 32.39%, O 45.08%, P 21.82%.
Na2HPO4.

Description and references

Industrial production: Faith, Keyes & Clark's Industrial Chemicals (John Wiley, New York, 4th ed., 1975) pp 746-754. Toxicity of heptahydrate: H. F. Smyth et al., Am. Ind. Hyg. Assoc. J. 30, 470 (1969).

Properties

Anhydr, exsiccated sodium phosphate. Hygroscopic powder. On exposure to air will absorb from 2 to 7 mols H2O, depending on the humidity and temp. Sol in ≈8 parts water, much more sol in hot water. Soly per 100 gal water increases from ≈14 lbs at slightly >0° to over 900 lbs at 95°. Insol in alc. pH of 1% aq soln at 25°: 9.1. Keep well closed.

Derivative

Dihydrate.

Nomenclature

CAS number: 10028-24-7
Sorensen's phosphate; Sorensen's sodium phosphate.
HNa2O4P.2H2O; mol wt 177.99.
H 2.83%, Na 25.83%, O 53.93%, P 17.40%.

Derivative

Heptahydrate.

Nomenclature

CAS number: 7782-85-6
HNa2O4P.7H2O; mol wt 268.07.
H 5.64%, Na 17.15%, O 65.65%, P 11.55%.

Properties

Crystals or granular powder. Stable in the air. d ≈1.7. Sol in 4 parts water, more sol in boiling water; practically insol in alcohol. The aq soln is alkaline, pH ≈9.5. LD50 orally in rats: 12.93 g/kg (Smyth).

Derivative

Dodecahydrate.

Nomenclature

CAS number: 10039-32-4
HNa2O4P.12H2O; mol wt 358.14.
H 7.04%, Na 12.84%, O 71.48%, P 8.65%.

Properties

Translucent crystals or granules; readily loses 5 mols of water on exposure to air at ordinary temp. mp 34-35° (when it contains the full 12 mols of H2O). d ≈1.5. Sol in 3 parts water; practically insol in alcohol. Aq soln is alkaline, pH ≈9.5. Keep well closed and in a cool place. Incompat: Alkaloids, antipyrine, chloral hydrate, lead acetate, pyrogallol, resorcinol.

Caution

Anhydr form may cause mild irritation to skin, mucous membranes; intern. causes purging.

Use

As sequestrant, emulsifier and buffer in foods. As mordant in dyeing; for weighting silk; in tanning; in manuf of enamels, ceramics, detergents, boiler compds; as fireproofing agent; in soldering and brazing instead of borax; as reagent and buffer in analytical chemistry.

Therapeutic Category

Cathartic.

Therapeutic Category (Veterinary)

Laxative.

Keywords

Laxative/Cathartic