Silicic Acid
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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)
SiO2·xH2O (anhydrous) 60.08 CAS RN®: 1343-98-2.-White, amorphous powder. Insoluble in water and in acids; soluble in hot solutions of strong alkalies.
1 RESIDUE ON IGNITION (Reagent test)
Not less than 80.0%.
2 NONVOLATILE WITH HYDROFLUORIC ACID
Heat 500 mg with 1 mL of sulfuric acid and 10 mL of hydrofluoric acid in a platinum crucible to dryness, and ignite to constant weight: the weight of the residue does not exceed 1.0 mg (0.2%).
3 CHLORIDE (Reagent test)
One g shows not more than 0.05 mg of Cl (0.005%).
4 SULFATE (Reagent test)
Boil 2 g with 20 mL of dilute hydrochloric acid (1 in 40), filter, neutralize the filtrate with ammonia TS, and dilute with water to 20.0 mL. A 10-mL aliquot of the solution shows not more than 0.1 mg of SO4 (0.01%).
5 HEAVY METALS (Reagent test)
Boil 2.5 g with 50 mL of dilute hydrochloric acid (1 in 10) for 5 minutes, filter while hot, and evaporate the filtrate on a steam bath to dryness. Take up the residue in 20 mL of dilute hydrochloric acid (1 in 500), digest for 5 minutes, cool, add water to make 100 mL, and filter. To 40 mL of the filtrate add 10 mL of hydrogen sulfide TS: any color produced is not darker than that produced by adding 10 mL of hydrogen sulfide TS to a control containing 0.03 mg of Pb (0.003%).
6 IRON (241), Procedures, Procedure 1 (CN 1-JUN-2023)
To 20 mL of the filtrate obtained in the test for Heavy Metals add 1 mL of hydrochloric acid, and dilute with water to 47 mL: the solution shows not more than 0.015 mg of Fe (0.003%).
