0.07 N Ferrous Ammonium Sulfate VS
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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)
(USP 1-May-2021)
In a 1000-mL volumetric flask, dissolve 27.5 g of ferrous ammonium sulfate in 500 mL of water. Add 20 mL of sulfuric acid. Cool and dilute with water to volume.
Standardization
See Volumetric Solutions, 1. Introduction.
See Titrimetry (541).
Standardize by one of the following procedures. [NOTE-Other standardization procedures may be used. See Volumetric Solutions, 2. Preparation and Standardization, 2.3 Standardization.]
Standardization with visual endpoint: (USP 1-May-2021) Standardize this solution on the day of use.
Dilute 25 mL of 0.025 N potassium dichromate VS with water to 100 mL. Add 30 mL of sulfuric acid and cool to room temperature. Add 3 drops of ferroin TS and titrate with the ferrous ammonium sulfate solution. The color change is sharp, going from blue-green to reddish brown.
N = [mL K2Cr2O7 × N K2Cr2O7] / mL Fe((NH4)2SO4)2
Standardization with potentiometric endpoint: Standardize this solution on the day of use.
Dilute 25 mL of 0.025 N potassium dichromate VS with water to 100 mL. Add 30 mL of sulfuric acid and cool to room temperature. Titrate potentiometrically with the ferrous ammonium sulfate solution using a combined platinum (Pt) electrode.
N = [mL K2Cr2O7 × N K2Cr2O7] / mL Fe((NH4)2SO4)2
[NOTE-If this volumetric solution is used in a qualitative application such as pH adjustment, dissoluton medium, or diluent, its standardization is not required.] (USP 1-MAY-2021)
