Potassium Bisulfate
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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)
KHSO4 136.17 CAS RN®: 7646-93-7.-Fused, white, deliquescent masses or granules. Very soluble in water. When ignited, it evolves SO3 and H2O, changing first to potassium pyrosulfate, then to sulfate.
Acidity: Dissolve 4 g, accurately weighed, in 50 mL of water, add phenolphthalein TS, and titrate with 1 N alkali: it contains between 34% and 36%, calculated as H2SO4.
Insoluble Matter and Ammonium Hydroxide Precipitate: Dissolve 10 g in 100 mL of water, add methyl red TS, render slightly alkaline with ammonia TS, boil for 1 minute, and digest on a steam bath for 1 hour. Pass through a tared filtering crucible, wash thoroughly, and dry at 105° for 2 hours: the precipitate weighs not more than 1 mg (0.01%).
For the following tests, prepare a Test solution as follows. Dissolve 6 g in 45 mL of water, add 2 mL of hydrochloric acid, boil gently for 10 minutes, cool, and dilute with water to 60 mL.
Heavy Metals (Reagent test): To 30 mL of Test solution add phenolphthalein TS, and neutralize with ammonia TS. Add 0.5 mL of glacial acetic acid, dilute with water to 40 mL, and add 10 mL of hydrogen sulfide TS: any brown color produced is not darker than that of a control containing 10 mL of Test solution and 0.02 mg of added Pb (0.001%).
IRON (241), Procedures, Procedure 1 (CN 1-Jun-2023): To 5 mL of Test solution add 2 mL of hydrochloric acid, and dilute with water to 47 mL: the solution shows not more than 0.01 mg of Fe (0.002%).
