Sodium Chromate
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This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition
Issued and maintained by the United States Pharmacopeial Convention (USP)
Na2CrO4 · 4H2O 234.03 CAS RN: 7775-11-3.-Lemon-yellow crystals. Soluble in water.
Assay: Accurately weigh about 300 mg, and dissolve in 10 mL of water contained in a 500-mL flask. Add 3 g of potassium iodide and 10 mL of diluted sulfuric acid, and dilute with 350 mL of oxygen-free and carbon dioxide-free water. Titrate the liberated iodine with 0.1 N sodium thiosulfate VS, adding 3 mL of starch TS as the endpoint is approached. Each mL of 0.1 N sodium thiosulfate consumed is equivalent to 7.802 mg of Na2CrO4 · 4H2O. Not less than 99% is found.
Insoluble Matter (Reagent test): not more than 1 mg, from 20 g dissolved in 150 mL of water (0.005%).
Aluminum: Dissolve 20 g in 140 mL of water, filter, and add 5 mL of glacial acetic acid to the filtrate. Add stronger ammonia water until alkaline, and digest for 2 hours on a steam bath. Pass through hardened filter paper, wash thoroughly, ignite, and weigh: the residue weighs not more than 0.8 mg (0.002%).
Calcium: Determine as directed in the test for calcium for ACS reagent grade Potassium Chromate (0.005%).
Chloride: Determine as directed in the test for chloride for ACS reagent grade Potassium Chromate (about 0.005%).
Sulfate: Determine as directed in the test for sulfate for ACS reagent grade Potassium Dichromate, but add 4.5 mL of hydrochloric acid to the water used to dissolve the test specimen: the residue weighs not more than 2.4 mg (0.01%).
