NaH2PO4-H2O, 138.0, 10049-21-5
DEFINITION
Sodium Dihydrogen Phosphate Monohydrate contains not less than 98.0% and not more
than 100.5% of NaH2PO4, calculated with reference to the dried substance.
CHARACTERISTICS
Colourless crystals or a white powder.
Very soluble in water; very slightly soluble in ethanol (96%).
Dissolve 10.0 g in sufficient carbon dioxide-free water prepared from distilled
water to produce 100 ml (solution S).
IDENTIFICATION
A. Solution S is faintly acid.
B. Solution S yields the reactions characteristic of phosphates.
C. Solution S neutralized with a 10% w/v solution of potassium hydroxide yields
reaction A characteristic of sodium salts.
D. Complies with the test for Loss on drying.
TESTS
Acidity: pH of a mixture of 5 ml of solution S and 5 ml of carbon
dioxide-free water, 4.2 to 4.5.
Clarity and colour of solution: Solution S is clear and colourless.
Arsenic: 0.5 g complies with the limit test for arsenic - 2 ppm.
Heavy metals: 12 ml of solution S complies with limit test A for heavy
metals. Use lead standard solution (1 ppm Pb) to prepare the standard (10 ppm).
Iron: 10 ml of solution S complies with the limit test for - iron 10 ppm.
Chloride: Dilute 2.5 ml of solution S to 15 ml with water. The resulting
solution complies with the limit test for chlorides - 200 ppm.
Sulphate: To 5 ml of solution S add 0.5 ml of hydrochloric acid and dilute to
15 ml with distilled water. The resulting solution complies with the limit test for
sulphate - 300 ppm.
Reducing substances: To 5 ml of solution S add 0.25 ml of 0.02M potassium
permanganate and 5 ml of 1M sulphuric acid and heat in a water bath for 5 minutes.
The solution retains a slight red colour.
Loss on drying: When dried to constant weight at 130°, loses 11.5 to 14.5%
of its weight. Use 0.5 g.
NaH2PO4·xH2O
(anhydrous) 119.98
Phosphoric acid, monosodium salt, monohydrate.
Monosodium phosphate monohydrate 137.99 CAS 10049-21-5
Phosphoric acid, monosodium salt, dihydrate
Monosodium phosphate dihydrate 156.01 CAS 13472-35-0
Anhydrous CAS 7558-80-7
Monobasic Sodium Phosphate contains one or two molecules of water of hydration, or
is anhydrous. It contains not less than 98.0 percent and not more than 103.0 percent
of NaH2PO4, calculated on the anhydrous basis.
Identification: A solution (1 in 20) responds to the tests for Sodium 191 and
for Phosphate.
pH: between 4.1 and 4.5, in a solution containing the equivalent of 1.0 g of
NaH2PO4·H2O in 20 mL of water.
Water: less than 2.0% (anhydrous form); between 10.0% and 15.0%
(monohydrate); between 18.0% and 26.5% (dihydrate).
Insoluble substances: Dissolve a portion equivalent to 10.0 g of NaH2PO4-H2O
in 100 mL of hot water, filter through a tarred filtering crucible, wash the
insoluble residue with hot water, and dry at 105 for 2 hours: the weight of the
residue so obtained does not exceed 20 mg (0.2%).
Chloride: A portion equivalent to 1.0 g of NaH2PO4·H2O shows no more
chloride than corresponds to 0.20 mL of 0.020 N hydrochloric acid (0.014%).
Sulfate— A portion equivalent to 0.20 g of NaH2PO4·H2O shows no more
sulfate than corresponds to 0.30 mL of 0.020 N sulfuric acid (0.15%).
Aluminum, calcium, and related elements: A solution containing the equivalent
of 1.0 g of NaH2PO4·H2O in 10 mL of water does not become turbid when rendered
slightly alkaline to litmus paper with 6 N ammonium hydroxide.
Arsenic: the limit is 8 ppm.
Heavy metals: the limit is 0.002%.
Monosodium Phosphate; Sodium Biphosphate;
Monosodium Dihydrogen Phosphate
NaH2PO4 Formula weight, anhydrous 119.98
NaH2PO4·H2O Formula weight, monohydrate 137.99
INS: 339(i)
CAS anhydrous 7558-80-7
CAS monohydrate 10049-21-5
DESCRIPTION
Sodium Phosphate, Monobasic, is anhydrous or contains one or two molecules of water
of hydration and is slightly hygroscopic. The anhydrous form occurs as a white,
crystalline powder or granules. The hydrated forms occur as white or transparent
crystals or granules. All forms are freely soluble in water, but are insoluble in
alcohol. The pH of a 1:100 solution is between 4.1 and 4.7.
Function: Buffer; emulsifier; nutrient.
REQUIREMENTS
Identification: A 1:20 aqueous solution gives positive tests for Phosphate
and for Sodium.
Assay: Not less than 98.0% and not more than 103.0% of NaH2:PO4 after
drying.
Arsenic: Not more than 3 mg/kg.
Fluoride: Not more than 0.005%.
Insoluble Substances: Not more than 0.2%.
Lead: Not more than 4 mg/kg.
Loss on Drying Anhydrous: Not more than 2.0%; Monohydrate: Between 10.0% and
15.0%; Dihydrate: Between 20.0% and 25.0%.
