Sodium Dihydrogen Phosphate

Sodium Dihydrogen Phosphate
Monosodium Phosphate
Sodium Phosphate, Monobasic
NaH2PO4nH2O (n = 2 or 0) Mol. Wt. dihydrate 156.01
anhydrous 119.98
monosodium dihydrogen monophosphate
anhydrous 7558-80-7
Definition Sodium Dihydrogen Phosphate occurs as two forms: the crystal form
(dihydrate) called Sodium Dihydrogen Phosphate (crystal) and anhydrous form called
Sodium Dihydrogen Phosphate (anhydrous).
Content Sodium Dihydrogen Phosphate, when dried, contains 98.0103.0% of
sodium dihydrogen phosphate (NaH2PO4).
Description Sodium Dihydrogen Phosphate (crystal) occurs as colorless to white
crystals or as a white crystalline powder. Sodium Dihydrogen Phosphate (anhydrous)
occurs as white powder or granules.
Identification Sodium Dihydrogen Phosphate solution (1 20) responds to all
tests for Sodium Salt and for Phosphate as described in the Qualitative Tests.
Purity For Sodium Dihydrogen Phosphate (crystal), dry the sample before the
tests.
(1) Clarity and color of solution Colorless, very slightly turbid (2.0 g, water 20
ml).
(2) pH 4.34.9 (1.0 g, water 100 ml).
(3) Chloride Not more than 0.11% as Cl (0.20 g, Control Solution 0.01 mol/l
hydrochloric acid 0.60 ml).
(4) Sulfate Not more than 0.048% as SO4 (0.5 g, Control Solution 0.005 mol/l
sulfuric acid 0.50 ml).
(5) Heavy metals Not more than 20µg/g as Pb.
Test Solution Weigh 1.0 g of Sodium Dihydrogen Phosphate, dissolve in 2 ml of
diluted acetic acid (1 20) and 30 ml of water, and add water to make 50 ml.
Control Solution Measure exactly 2 ml of Lead Standard Solution, add 2 ml of
diluted acetic acid (1 20) and water to make 50 ml.
(6) Arsenic Not more than 4.0µg/g as As2O3 (0.50 g, Method 1, Apparatus B).
Loss on Drying

Crystal: 22.024.0% (40, 16 hours, then 120, 4 hours).
Anhydrous: Not more than 2.0% (120, 4 hours).
Assay Weigh accurately about 3 g of Sodium Dihydrogen Phosphate, previously
dried, dissolve in 30 ml of water, add 5 g of sodium chloride, dissolve by shaking well,
keep at about 15, and titrate with 1 mol/l sodium hydroxide (indicator: 34 drops of
thymol blue TS).
1 ml of 1 mol/l sodium hydroxide = 119.98 mg of NaH2PO4