Lead Monoxide
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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)
(Litharge), PbO 223.20 CAS RN®: 1317-36-8.-Heavy, yellowish or reddish-yellow powder. Insoluble in water and in alcohol; soluble in acetic acid, in diluted nitric acid, and in warm solutions of the fixed alkali hydroxides.
Assay: Accurately weigh about 300 mg, freshly ignited in a muffle furnace at 600 ± 50°, and dissolve it by warming with 10 mL of water and 1 mL of glacial acetic acid. Dilute with 75 mL of water, heat to boiling, add 50.0 mL of 0.1 N potassium dichromate VS, and boil for 2 to 3 minutes. Cool, transfer to a 200-mL volumetric flask with the aid of water, dilute with water to volume, mix, and allow to settle. Withdraw 100.0 mL of the clear liquid, and transfer to a glass-stoppered flask. Add 10 mL of diluted sulfuric acid and 1 g of potassium iodide, insert the stopper, mix gently, and allow to stand for 10 minutes. Then titrate the liberated iodine, representing the excess of dichromate, with 0.1 N sodium thiosulfate VS, adding 3 mL of starch TS as the endpoint is approached: each mL of 0.1 N potassium dichromate is equivalent to 7.440 mg of PbO. Not less than 98% is found.
Insoluble in Acetic Acid: Dissolve 2 g in 30 mL of dilute glacial acetic acid (1 in 2), boil gently for 5 minutes, filter, wash the residue with diluted acetic acid, and dry at 105° for 2 hours: the residue weighs not more than 10 mg (0.5%).
Substances Not Precipitated By Hydrogen Sulfide: Completely precipitate the lead from the filtrate obtained in the test for Insoluble in Acetic Acid by passing hydrogen sulfide into it, filter, and wash the precipitate with 20 mL of water. To one-half of the mixed filtrate and washings add 5 drops of sulfuric acid, evaporate to dryness, and ignite at 800 ± 25° for 15 minutes: the residue weighs not more than 5 mg (0.5%).
Volatile Substances: Accurately weigh about 5 g, and heat strongly in a covered porcelain crucible: it loses not more than 2.0% of its weight.
